4.1 Microbial diversity
Guizhou province has 264 hot springs and is considered one of the regions with the richest hot spring resources in China (The Central People's Government of the People's Republic of China, 2017). These hot springs contain more than 30 kinds of trace elements, including 14 mineral elements for the human body—such as strontium, selenium, zinc, fluorine, iron, manganese, chromium, and vanadium—making them high-quality natural “baths” (Xiao-qing et al., 2014). These hot springs have high medical value and are effective against rheumatism, chronic digestive tract disease, chronic liver disease, biliary tract disease, diabetes, gout, cardiovascular disease, and hypertension (Chen, 2021). Guizhou Baili Rhododendron Hot Spring (BLDJA, BLDJB, and BLDJC) contains two valuable trace elements: fluorine, which, in appropriate amounts, aids in the absorption of calcium and phosphorus in the human body, and lithium, which helps regulate central nervous system activity and has soothing and calming effects. Lithium rarely accumulates in groundwater, so lithium-rich springs are uncommon. However, the lithium content in Guizhou Baili Rhododendron Hot Spring water is 1.42 mg/L, reaching a medically significant concentration. Shiqian Hot Spring (SQ) is a magnesium sulfate and calcium bicarbonate hot spring that contains a variety of trace elements (Luan, 2016). The metasilicic acid content ranges from 35.57 to 48.72 mg/L, and the strontium content ranges from 2.91 to 4.26 mg/L, qualifying it to be classified as strontium–metasilicic acid compound natural mineral drinking water. Moderate intake of strontium has been shown to help prevent hypertension and cardiovascular diseases (Yong-kang and Gan-lu, 2020). The chemical type of Suiyang Crystal Hot Spring (SYSJ) is a carbonated, high-strontium, carbon dioxide radon spring. This spring contains high levels of selenium, strontium, metasilicic acid, fluorine, lithium, and other elements beneficial to the human body. Among them, the Sr2+ content in the hot spring water ranges from 5.26 to 11.17 mg/L, and the H2SiO3 content ranges from 30.16 to 44.72 mg/L, which can be classified as a strontium-metasilicic acid compound natural drinking mineral water (Xiao-qing et al., 2014). Clinical trials have shown that Suiyang Crystal drinking water has a beneficial treatment effect on gastrointestinal diseases, cardiovascular disease, blood uric acid and gout, neurodermatitis, urinary stones, diabetes, cancer, and postoperative rehabilitation (Xin et al., 2015). There are various types of hot springs in Guizhou, but in terms of the breadth and depth of research, they are far less extensive than those in Yellowstone National Park. In the early stage, Guizhou hot springs focused more on geological background and geochemical research, serving as a basis for the development of geothermal resources. In recent years, the development and utilization of hot spring biological resources have begun to attract attention, highlighting the many unanswered questions about hot spring microbial communities that remain worth investigating.
The microbial diversity of seven urban hot springs in Guizhou province was analyzed using 16S rRNA gene amplification and high-throughput sequencing techniques.
The microbial communities of the 11 hot springs share similar predominant bacterial groups, with Pseudomonadota and Bacillota as the predominant bacteria and Cyanobacteria and Actinobacteria as secondary but notable groups. Wang and Pecoraro (2021) reported that Pseudomonadota dominated the microbial communities in the alkaline sediments and water of Julong High-Altitude Hot Springs, Tianchi Volcano, Northeast China. Among the hot spring samples, Bacillota was identified as the most diverse phylum. Similarly, Samarasinghe et al. (2021) found Bacillota to be the primary microbial population in Sri Lankan hot springs. Mashzhan et al. (2021) discovered that Firmicutes dominated the microbial community in the Zharkent Geothermal Hot Spring.
Sahay et al. (2017) studied the two hot springs of Manikaran and Yumthang Hot Springs in the Indian Himalayas, demonstrating that Bacillota is the dominant group. Furthermore, Cloacimonetes, Poribacteria, Acetothermia, Balneolota, Woesearchaeota, and Nitrososphaerota are found only in separate hot springs. Bacteria account for a large proportion of this study's hot-source microbiome (>99%) compared to the abundance of archaea (< 1%). In summary, while the relative abundance of bacterial taxa in hot spring microbial communities may vary significantly across different environments, the dominant groups tend to be similar.
The species richness and evenness of Guizhou Baili Rhododendron Hot Spring No. 1 (BLDJA) and Xifeng Nanshan Tianmu Hot Spring (XFTM) were relatively high in the 11 hot springs, with the highest diversity and even distribution in Guizhou Baili Rhododendron Hot Spring No. 1 (BLDJA), which may be related to the lower pH (7.19) and the appropriate temperature (37°C). Many factors affect the microbial community of hot springs (Chan et al., 2017; Mathur et al., 2007; Tobler and Benning, 2011), such as temperature (Wang et al., 2013; Guo et al., 2020; Kumar, 2023; Kumar et al., 2023a,b), pH (Pagaling et al., 2012; Power et al., 2018; Loskutova et al., 2024), geographical location (Stout et al., 2009), and a variety of nutrients with chemical components (Uribe-Lorío et al., 2019) in hot springs. The effects of different factors on microbial communities are varied. However, temperature and pH are the most critical among the factors affecting microbial communities in hot spring environments (Loskutova et al., 2024). Many researchers have researched different types of hot springs. Guo et al. (2020) found that the microbial communities of alkaline hot springs were primarily affected by pH and temperature. In contrast, the microbial communities of acidic mesothermal springs were mainly impacted by sulfate concentration. In addition, the study by Kumar et al. (2024) suggests that the correlation between bacterial diversity and pH is weak, whereas temperature plays a dominant role in shaping microbial community structure. Several studies have investigated the relationship between microbial diversity and temperature (Kumar, 2023; Kumar et al., 2023a,b). Overall, microbial diversity was negatively correlated with temperature, a key factor in controlling hot spring microbial diversity. The similarity of microbial community composition among hot springs decayed with increasing temperature differences (Miller et al., 2009; Purcell et al., 2007; Yasir et al., 2021; Jiang et al., 2024; Negi et al., 2024). This finding explains why BLDJA hot springs have the highest microbial diversity. In addition, temperature is closely linked to the heat-tolerance mechanisms of hot spring microorganisms. High-temperature stress induces oxidative stress, DNA damage (Habibi et al., 2022), and protein dysfunction (Sinetova and Los, 2016), thereby impairing the physiological functions of thermophilic microorganisms. Thermophilic microorganisms resist these damages through their cell membranes, proteins, nucleic acids, and mechanisms that mitigate oxidative stress, thereby surviving in high-temperature environments. The cell membrane serves as the first line of defense for thermophilic organisms adapting to high-temperature conditions. The cell membrane structure of thermophilic bacteria is special. With the increased environmental temperature, the ratio of saturated fatty acids and cyclized fatty acids increases, effectively enhancing the cell membrane's thermal stability and preventing it from liquefying under high-temperature conditions (Zili et al., 2015). High-temperature environments will also accelerate the generation of reactive oxygen species in cells, and excessive reactive oxygen species will cause damage to proteins and DNA (Liu et al., 2020). To mitigate this oxidative damage, hot spring microorganisms stimulate the activity of antioxidant enzymes, such as superoxide dismutase (Barcyte et al., 2020) and catalase (Steimbrüch et al., 2022). Additionally, prolonged exposure to high-temperature environments may trigger genomic instability. Thermophilic microorganisms can produce heat-stable enzymes that maintain catalytic activity at high temperatures, ensuring normal metabolic processes within cells (Averhoff and Müller, 2010). Extreme thermophilic proteins exhibit enhanced DNA stability, protecting DNA molecules from degradation and damage caused by heat at high temperatures. For example, Taq polymerase retains its function at high temperatures, which is crucial for DNA replication (Stetter, 1999).
At the genus level, the dominant bacteria in Longjing Hot Spring (LZLJ), Jiutian Hot Spring (YAS), Xifeng Hot Spring (XFLY), Xifeng Nanshan Tianmu Hot Spring (XFTM), and Jianhe Hot Spring (YAS) are Acinetobacter, which are widely distributed in nature and are mainly found in water and soil. The tolerant pH range is 3.0–9.0 (optimal pH range 6.0–7.0). Acinetobacter is an important degrader of petroleum hydrocarbons, playing a crucial role in mitigating the biological toxicity of these compounds, thereby facilitating their use in petroleum hydrocarbon restoration engineering (Yu-hua et al., 2016). The dominant bacterium of Guizhou Baili Rhododendron Hot Spring 2 (BLDJB) and Guizhou Baili Rhododendron Hot Spring No. 3 (BLDJC) is Thermodesulfitimonas, which also shows potential applications in the field of microbial electrosynthesis. Thermodesulfitimonas was proposed as one of the likely major producers in electrochemically active biofilms of a novel Knallgas bacterium, a technique that combines microbial metabolism with electrochemical processes for carbon dioxide conversion and fixation (Reiner et al., 2020). The dominant bacteria in Suiyang Crystal Hot Spring (SYSJ) is Nitrospira, which plays an important role in the nitrogen cycle. They can oxidize nitrite to nitrate, a process crucial for maintaining the health of aquatic ecosystems (van Kessel et al., 2015). Nitrospira is the primary nitrite-oxidizing bacterium in sewage treatment, closely related to the ammonia nitrogen, nitrate, and nitrite cycle system, and is crucial for aquatic plants. In addition, some bacteria of the genus Nitrospira possess the full ammonia oxidation capacity (comammox), which enables them to directly oxidize ammonia to nitrate and have significant ecological and environmental implications in the nitrogen cycle (Vijayan et al., 2021). The dominant bacteria in Yuncong Duohua Hot Spring (YCDH) were Meiothermus, and they grow optimally at 50–65°C and pH 7–8.5. Some strains of the genus Meiothermus exhibit specific functions. For example, Meiothermus ruber contains genes involved in the TPS/TPP trehalose synthesis pathway, which have been cloned, expressed, and functionally characterized (Zhu et al., 2010). Meiothermus sp. sk3-2 can convert maltose to trehalose, potentially serving as an alternative source for trehalose production (Goh et al., 2011).
4.2 Functional prediction diversity
Hot springs are considered valuable sources of bioactive compounds with significant potential for biotechnological applications in various fields. Many enzymes found in thermophilic microorganisms resist high temperatures, organic solvents, and decontaminants, providing unparalleled advantages in biometallurgy, wastewater treatment, food production, and papermaking (Cai-hong and Ye-jun, 2019). These microorganisms can produce valuable biotechnological products, such as antibiotics (Sahm et al., 2013), bioethanol (Bowen De León et al., 2013), and thermostable enzymes (Urbieta et al., 2015; Elleuche and Antranikian, 2013; Sharma et al., 2013). Exploring new sources of thermophilic microorganisms can enhance their research and utilization in various fields.
4.2.1 Prediction of major adaptation mechanisms
In the Kyoto Encyclopedia of Genes and Genomes (KEGG) level 3 function prediction, we found that primary functions, such as bacterial chemotaxis, base excision repair, and nucleotide excision repair, enable microorganisms to adapt to their environment and survive. Maintaining genome stability and the integrity of genetic information is essential for the accurate transmission of the genetic code. However, during DNA replication, it is constantly threatened by DNA-damaging reagents from within bacteria or in the environment, which produce multiple damages (Chatterjee and Walker, 2017) through oxidation, alkylation, deamination, or hydrolysis. If these DNA lesions are not properly repaired, the important cellular processes will be compromised, threatening the survival of the organism (Chatterjee and Walker, 2017; Terabayashi and Hanada, 2018; Kiwerska and Szyfter, 2019). Therefore, cells must repair these damages in a timely manner. In response to the potential harm caused by DNA damage, organisms have evolved a series of complete repair pathways to monitor and repair DNA damage. The most common mechanisms of DNA damage repair can be divided into five categories: base excision repair, nucleotide excision repair, mismatch repair, homologous recombination, and non-homologous end joining (Kim et al., 2018; Spampinato, 2017). Cells typically select one or more repair pathways to complete damage repair, depending on the type of damage, the cell cycle, and the biological species. Among them, base excision repair is a common class of DNA damage repair pathway in all organisms, which is often used to repair multiple DNA damages (Wallace, 2014; Dizdaroglu et al., 2017), including alkylation, deamination, and oxidation, and consists of multiple enzymes. Nucleotide excision repair is a repair mechanism that recognizes broad-spectrum DNA lesions and is particularly important for the repair of certain broad lesions, such as crosslinks, large adducts, and multibase lesions (Kemp, 2019).
Given the heterogeneous and complex natural environment, bacteria have evolved multiple patterns of chemotaxis behavior to accommodate changes in their surrounding microenvironment (Adler, 1969; Sampedro et al., 2015). Bacteria often actively utilize their movement ability to respond to the concentration gradient of chemicals in the environment, transforming their random movement into biased movement. This behavior is known as “chemotaxis” (Adler, 1969), a fundamental attribute of bacterial adaptation to their environment. The influence of bacterial chemotaxis on microbial communities is primarily reflected in the regulation of microbial community structure and the promotion of interactions with the environment. Motile bacteria play a very important role in nature. They can promote material metabolism, drug delivery, and nutrient circulation through chemotaxis (Karmakar, 2021), such as forming a symbiont with other organisms or facilitating directional movement and migration of non-motile bacteria, known as hitchhiking. This form of movement can enable non-motile bacteria in the community to move and migrate, driven by motile bacteria, thus affecting the microbial composition and metabolism of substances within the community (Fukui et al., 1999). This movement mechanism enables bacteria to find a suitable environment for survival, regulate temperature, maintain pH balance, and control nutrient uptake, thereby avoiding harmful substances and escaping adverse environments. It can also promote the circulation, transformation, and distribution of substances and is significant in regulating the structural diversity of microbial communities (Xiao-yan et al., 2019).
4.2.2 Biotechnological potential of the hot spring microbes
In 1831, the German Wachenreder was the first to isolate from the carrot root a carbohydrate pigment named “carotene” (Yong-hua and Shi-zhong, 2000). With the development and progress of society, domestic, and foreign scholars have continuously discovered and separated a series of other natural pigments through various technical methods, collectively known as “carotenoids” (Ke and Na, 2010). Natural pigments are primarily derived from plants and microorganisms, while plant-derived pigments have a relatively long growth cycle, which limits their large-scale applications. Microorganisms have broader application prospects than plant-source pigments due to their rapid growth, low nutritional requirements, minimal environmental impact, and low production costs. Several disadvantages of synthetic pigments have contributed to an increased demand for natural, organic, and eco-friendly pigments (Manikprabhu and Lingappa, 2013).
Carotenoids are a group of lipid-soluble pigments, also known as tetraterpenes, composed of eight 5-carbon isoprenoid molecules (Yong-hua and Shi-zhong, 2000), widely distributed in plants and microorganisms (Phadwal, 2005). Carotenoids are primarily produced by a wide range of phototrophic and non-phototrophic organisms, including bacteria, algae, fungi, and plants. Some bacteria and fungi, as non-photosynthetic species, also produce carotenoids to resist photooxidation, allowing them to survive in sufficient light and air. Carotene-producing bacteria encompass a diverse range of species, and all C45 and C50 carotenoids reported to date are synthesized by bacteria, with 107 bacterial species currently known to synthesize 307 carotenoids (Yabuzaki, 2017). The radiation energy captured and reflected by natural pigments serves a variety of biological functions, including harnessing solar energy for metabolism and shielding organisms from radiation damage.
Microbial pigments also exhibit potential biological activities, including antibacterial, anticancer, radiation resistance, and antioxidant properties, which promote the exploration of microbial pigments. Carotenoids have remarkable health benefits and play a significant role in regulating the body's immune function. In the early 1980s, carotenoids were discovered in Seifter and found to potentially enhance immune activity (Jun-hui, 2012). The presence of a certain number of highly active free radicals in the body can damage the cell membranes of normal cells, triggering a series of chain reactions that lead to a sharp decline in cell function and rapid aging of the body. Carotenoids, especially beta-carotene, have a notable effect on eliminating free radicals and delaying the aging process.
Additionally, they have positive preventive and therapeutic effects on coronary heart disease, thrombosis, and other diseases (Ling, 2008). It also plays a role in cancer prevention and anticancer effects (Giovannucci et al., 1995). The cancer prevention and treatment process not only inhibits the occurrence of a variety of cancers but also reduces the cancer mortality rate by 20–30% (Lan and Hao-ming, 1998). Carotenoids have been widely used in the healthcare, food, and cosmetics production industries for their antioxidant and anti-tumor properties (Borowitzka, 2013).
In 1918, betalain was isolated from red beetroot. It is a water-soluble, nitrogen-containing pigment belonging to quinone derivative pigment, soluble in water and polar solvents but insoluble in the majority of organic solvents (such as ethanol, methanol, acetone, ethyl acetate, and so on; Yan et al., 2021). Similar to many natural pigments, betalain has unstable structures and can be easily affected by temperature, light, pH, metal ions, and other environmental factors. Red beetroot has long been the sole source of betalain extraction. However, high levels of nitrates and earthy flavors in beetroot extract limit the development and utilization of beetroot pigments (Rodriguez-Amaya, 2019). Therefore, it is important to find other sources of betalain in nature. Currently, 75 types of betalain structures have been identified from 17 different plants (Khan and Giridhar, 2015). Betalain has high physiological activity, with antibacterial (Spórna-Kucab et al., 2018) and anti-fatigue (Rodriguez-Amaya, 2019) effects. As research continues to deepen, it has been found that betalain has an impact on cancer (Mancini et al., 2021; Lechner and Stoner, 2019), preventing coronary heart disease (Haswell et al., 2021), and lowering blood lipids (Rahimi et al., 2019), indicating that there is significant application potential in the field of betalain drug development. Moreover, due to the efficient coloring properties of betalain, it can also be used in the production of cosmetics. Betalain has a natural hue, can prevent UV rays, eliminate facial free radicals, and maintain facial moisture. It is easy to apply, wash off, and biodegradable, making it suitable for the development of blush products (Ping and Ming-zhe, 2021).
Microbial drugs play an indispensable role in the field of antimicrobial therapy. Currently, 70% of clinical antibiotics are derived from microbial natural products or their derivatives, which has saved hundreds of millions of lives. In addition to the two main groups of Actinomycetes and fungi, microorganisms that produce drugs also include Pseudomonas, Bacillus, Myxobacteria, Cyanobacteria, and others, as well as microbial communities from extreme environments. Among the 293 clinical drugs derived from microorganisms, 143 are from Actinomycetes, accounting for 49%; 121 are from fungi, accounting for 41%; and 29 are from bacteria, accounting for 10%. Among the 105 microbial drugs derived directly from natural products, 69 are from Actinomycetes, accounting for 66%; 17 are from fungi, accounting for 16%; and 19 are from bacteria, accounting for 18% (Jian-hua et al., 2021).
Antibiotics are a type of secondary metabolite or their artificial derivatives produced during the life activities of microorganisms or other biological organisms, which can inhibit or affect the life activities of other organisms at low concentrations (Qin-xiang, 2008). Antibiotics primarily act in the treatment of bacterial diseases. In general, antibiotics are drugs used to treat bacterial infections and infections caused by pathogenic microorganisms. Penicillin is the first known antibiotic found in the history of human development, but penicillin does not inhibit and kill all pathogens. Penicillin is mainly effective against Gram-positive bacteria (Qin-xiang, 2008). The mechanism of action of penicillin primarily targets the synthesis of cell walls in Gram-positive bacteria. In 1943, soil microbiologist Selman Waxman isolated a substance with strong inhibitory activity against Mycobacterium tuberculosis from a strain of Streptomyces griseus and named it “streptomycin.” Tuberculosis has been one of the most serious infectious diseases for thousands of years, and streptomycin, as the first effective drug used in tuberculosis treatment, opened a new era of tuberculosis treatment. The discovery of streptomycin has sparked great interest among scientists worldwide in conducting antibiotic screening research. By the end of the 1940s, several antibiotics, including kanamycin, tetracycline, chloramphenicol, and erythromycin, had been successfully developed, marking the emergence of the antibiotic family (Ju-lius et al., 1980). In the 1950s and 1960s, humans ushered in the golden age of antibiotic discovery. During this period, scientists almost found that the current clinical use of the vast majority of broad-spectrum antibacterial antibiotics (cephalosporins, macrolides, glycopeptides, cyclic serine, and so on), according to statistics, these antibiotics are mainly isolated from Streptomyces, accounting for around 70%–80% of all isolated compounds (Bérdy, 2005); they mainly have inhibitory activity against bacteria and fungi. Tetracycline antibiotics are named after their chemical structure, which features a naphthacene core (Hertweck et al., 2007; Fritzsche et al., 2008). They are a major class of broad-spectrum antibiotics that inhibit bacterial protein synthesis, including oxytetracycline, methacycline, doxycycline, and dimethylamino tetracycline. This class of antibiotics is widely used to treat infections caused by both Gram-positive and Gram-negative bacteria, as well as intracellular pathogens such as Mycoplasma, chlamydia, and Rickettsia. Its mechanism of action involves inhibiting the binding of aminoacyl-tRNA to the ribosome, thereby suppressing bacterial protein synthesis and achieving a bacteriostatic effect (Lei et al., 2021). In addition, in some countries, including the United States, tetracycline is widely used as a growth promoter in animal feed. On the other hand, vancomycin kills bacteria by blocking the synthesis of high-molecular-weight peptide polysaccharides that comprise the bacterial cell wall, resulting in cell wall defects. Additionally, it may alter the permeability of the bacterial cell membrane and selectively inhibit RNA synthesis, thereby exerting its bactericidal effect (Qiao-zhen, 2019).
Microorganisms account for approximately 60% of the total biomass on Earth (Singh and Macdonald, 2010), making them the most diverse and abundant group of species on the planet. In the face of complex and harsh natural environments, microorganisms have evolved structurally diverse and highly active natural products (secondary metabolites) as chemical weapons, using defense, attack, or signaling to kill competitors, thereby ensuring their survival and reproduction (Seipke et al., 2012; Klassen, 2014; Traxler and Kolter, 2015). The secondary metabolites produced by microorganisms exhibit a wide range of biological activities and can serve as anticancer drugs, antiparasitic drugs, anti-inflammatory agents, herbicides, feed additives, immunosuppressants, and more, playing a crucial role in human health, pest control, and food safety. Our findings suggest that the hot spring contains a wealth of uncharacterized new clusters and a large number of unknown sub-metabolites that remain to be explored.
4.2.3 Environmental potential
The rapid development of industrial and agricultural production has brought numerous conveniences to human production and life, but it has also led to the release of various pollutants into the environment. Due to their strong potential toxicity and characteristics such as bioaccumulation and biomagnification, the extensive use of environmental xenobiotics poses a serious threat to the global ecological environment and human health (Qing-ren et al., 2002). The treatment of xenobiotic pollution is urgent, and the primary methods for its remediation include physical, chemical, and biological methods. Bioremediation is the process of using the metabolic activities of specific functional microorganisms under suitable environmental conditions to reduce the activity of harmful substances in the soil or degrade them into harmless substances. Bioremediation is one of the most promising remediation methods, characterized by safety, cost-effectiveness, and minimal secondary pollution.
In recent decades, researchers have carried out a large number of fruitful studies on the chemotaxis of bacteria to environmental pollutants (Adadevoh et al., 2015, 2018) and found that the biodegradation efficiency of pollutants is not only related to the degradation ability of the degraded bacteria themselves but also depends on the bioavailability of pollutants. The bioavailability of soil pollutants is influenced by the soil media, the properties of the pollutants, and the mobility of soil microbes (Qi-shi et al., 2004). The majority of mobile bacteria can sense and search for pollutants (Lacal et al., 2013) through the chemotaxis process, and bacteria with motility and degradation abilities actively move to the adsorbed state of pollutants, which can improve pollutant bioavailability and biodegradation efficiency (Krell et al., 2013; Parales et al., 2015). The majority of organic pollutants in the environment can be degraded by microorganisms (Pieper and Reineke, 2000). Bacteria exhibit chemotaxis toward many compounds, with chemotactic substances mainly including naphthalene (Grimm and Harwood, 1997), toluene (Lacal et al., 2011), biphenyl (Gordillo et al., 2007; Tremaroli et al., 2011), polychlorinated biphenyls (Gordillo et al., 2007), benzoic acid (Gordillo et al., 2007), chlorobenzoic acid (Tremaroli et al., 2010), nitroaromatic compounds (Samanta et al., 2000), methyl parathion (Wen et al., 2007), atrazine (Liu and Parales, 2009), 2,4-D (Hawkins and Harwood, 2002), furofuran compounds (Nichols et al., 2012), and others.
Polycyclic aromatic hydrocarbons (PAHs) are organic pollutants that typically contain two or more fused benzene rings (Manousi and Zachariadis, 2020). They are highly toxic and semi-volatile (Zhao-xue and Xue-hua, 2018; Kun, 2023) and prone to long-term persistence and bioaccumulation. PAHs can migrate over long distances through various media—such as organisms, the atmosphere, water, and soil are widely distributed in the environment, making them difficult to degrade. In recent years, the pollution of PAHs in the atmosphere has become increasingly severe. The PAHs in the environment primarily originate from the incomplete combustion of oil, coal, wood, and urban waste. Additionally, the production process of petrochemical products, oil spills, leaks during oil development and transportation, volcanic eruptions, and vehicle exhaust emissions all generate PAHs. After entering the soil, it is easy to interact with soil particles and remain on their surface for a long time, making it difficult to degrade under natural conditions. Therefore, treating and repairing contaminated soil with polycyclic aromatic hydrocarbons is crucial.
Additionally, PAHs can enter the human body through the respiratory tract, digestive tract, and skin contact, exhibiting carcinogenic and mutagenic properties. Excessive exposure to PAHs often leads to lung cancer, which has the highest cancer mortality rate in the United States (Moorthy et al., 2015). Due to its severe impact on the ecological environment and human health, it has been included in the priority pollutant lists of the EU and the US Environmental Protection Agency. Although polycyclic aromatic hydrocarbon emissions are now regulated, they continue to have a significant impact on human health, so their various effects must be closely monitored.
Microbes are the most important decomposers in the ecosystem, and microbial degradation is the primary method for removing PAHs in the natural environment. Bacteria are one of the main groups of organisms belonging to the domain bacteria and are the most numerous and widely distributed type of microorganisms among all living organisms on Earth. Bacteria are widely used in the treatment of oily sludge, in situ remediation of oil-contaminated land, ex-situ remediation of oil-contaminated land, and the degradation of polycyclic aromatic hydrocarbons (PAHs) in oily sludge. Currently, it is known that many bacteria, such as Pseudomonas, Rhodococcus, Mycobacterium, Alcaligenes, Acinetobacter genus, Bacillus, and Micrococcus, have significant roles in the degradation of PAHs (Juhasz et al., 2010; Zhang et al., 2021). The degradation rate and efficiency of PAHs can be significantly improved by optimizing the conditions for microbial degradation, including temperature, pH, nutrient availability, and the selection of suitable microbial populations. Atrazine has become one of the most widely used herbicides due to its high efficiency, low toxicity, low cost, and broad range of applications. It is easily soluble in organic solvents such as methanol and acetone and has moderate persistence in the environment, with a half-life of 4–57 weeks in soil (Mandelbaum et al., 1993) and a half-life of up to 35 weeks in water environments (Bayati et al., 2020). The application of atrazine can lead to its spread beyond adjacent areas, contaminating soil, surface water, groundwater, and the atmosphere. Atrazine and its metabolites have been detected in various environmental media, including soil (Jablonowski et al., 2008), the atmosphere (Degrendele et al., 2022), and water (Dun-yu et al., 2022; Pan et al., 2023). Atrazine, as an endocrine disruptor, can have adverse effects on ecosystems and human health when used. In aquatic ecosystems, atrazine can alter biota and disrupt the food chains of many species, including benthic organisms (de Albuquerque et al., 2020; Xue-han et al., 2021). Degrendele and others (Degrendele et al., 2022) assessed the risk of human exposure to 30 pesticides, including atrazine. They found that infants' intake of pesticides is significantly higher than that of adults, emphasizing that infants are a vulnerable group to pesticide exposure.
To remediate environments contaminated by atrazine, researchers from various countries are dedicated to studying microorganisms that can efficiently degrade atrazine. Currently, microorganisms are isolated and have the ability to degrade atrazine, including bacteria and fungi. Bacteria play an important role in the degradation of atrazine. It has been reported that 14 genera of bacteria capable of degrading atrazine have been isolated from the environment, including Arthrobacter sp. (Wang and Xie, 2012), Citricoccus sp. (Yang et al., 2018), Acinetobacter (Tao et al., 2020), Agrobacterium (Liu et al., 2023), Shewanella (Ye et al., 2016), Pseudomonas (Fernandes et al., 2018), Achromobacter (Fernandes et al., 2018), Enterobacter (Dan-dan et al., 2017), Rhodococcus (Vancov et al., 2005), Paenarthrobacter (Zhao et al., 2025), Klebsiella (Zhang et al., 2019), Pseudaminobacter (Topp, 2001), Micrococcus (Sheng-wen et al., 2007), and Streptomyces (Mesquini et al., 2015). Five species of atrazine-degrading bacteria have been identified, namely Agrobacterium rhizogenes (Liu et al., 2023), Rhodococcus erythropolis (Vancov et al., 2005), Paenarthrobacter ureafaciens (Zhao et al., 2025), Klebsiella variicola (Zhang et al., 2019), and Micrococcus luteus (Topp, 2001).
Of the microbially active metabolites used today, 70% are obtained from Actinobacteria, the remaining 20% from fungi, 7% from Bacillus, and 1% from Pseudomonas. Bacilli and Fusobacteria are the primary components of Firmicutes, and the species contained within the Bacilli have have proven their significant application value in various fields, including agriculture, industry, environmental protection, health, medicine, and many other sectors. The thermophilic microbes from hot springs have been reported to degrade xenobiotic compounds in soil (Rong-ping et al., 2008), degrade crude oil (Shu-qian et al., 2006), fix air nitrogen (Zhang and Li, 2001), prevent plant pests (Chen et al., 2003), treat industrial wastewater, and so on. Additionally, microbes from hot springs are rich in vitamins, pigments, manganese compounds, polyunsaturated fatty acids, phosphorus, phenolic compounds, and numerous other compounds. They are a potential new type of bioactive compound “production plant” (Khalifa et al., 2021). Cyanobacteria exhibit significant metabolic multifunctionality, particularly in producing a wide range of structurally and functionally diverse metabolites with diverse biological activities, including antimicrobial, antifungal, antiviral, and antitumor properties. Recent research has detected a variety of compounds with anti-infectious and anti-cancer activities isolated from Cyanobacteria (Dixon et al., 2004). The multi-active substances produced by Cyanobacteria have great prospects for antimicrobial, insecticidal, antiviral, and anticancer applications (Singh et al., 2011).
The study of hot spring microorganisms not only helps us understand microbial genetic and functional diversity in high-temperature environments and their strategies for adapting to hostile habitats but also holds significant importance for screening strains with unique properties that have broad application prospects in industry, molecular biology, medicine, and other fields. This study found that the microbial resources in the hot springs of Guizhou Province are rich in species and have significant functional characteristics. There may be a substantial number of bioactive strains and related secondary metabolites with considerable biotechnological and industrial applications.