The marine sediments were sampled from intertidal zone of Xiamen island on April 12, 2021 (11812′25′′E 2429′52′′N), the mangrove garden of Xia-Tan-Wei at the estuary of Xixi River of Xiamen on June 27, 2022 (11812′4′′E 2439′14′′N), and an abandoned pond nearby the mangrove conservation area at the estuary of Zhangjiang River, Zhangzhou on September 14, 2022 (11725′55′′E 2357′18′′N) ( Supplementary Figure S1 ). These samples are black and smell like rotten eggs, implying these sediments are enriched in sulfide. The samples were kept cool and returned to the laboratory. Each of 2 g (wet mass) was suspended with artificial seawater, and then 1 ml was transferred into 50 ml anaerobic bottles respectively containing 10 ml MMJHS medium supplied with 76% H₂/20% CO₂/4% O₂ (200kPa) with hydrogen and thiosulfate as energy sources, or 10 ml of MMJS medium, which contains 76% N₂/20% CO₂/4% O₂ (200 kPa) with thiosulfate as the sole energy source, or 10 ml MMJH medium which contains 76% H₂/20% CO₂/4% O₂ (200 kPa) with hydrogen as the energy source (See supplementary material for medium composition). All of them were incubated at 32°C according to a method described previously (Jiang et al., 2017). After 3-round enrichment, the cell growth in MMJH medium was observed. Subsequently, cells were purified three times with the dilution-to-extinction technique. The culture in the serum bottle showing growth at the highest dilution was designated as strains XGS-02, XTW-4, and zt1-1. The purity of these cultures was confirmed by microscopic examination and 16S rRNA gene sequencing.

Cultures were grown in MMJH medium at 30°C for 2 days, cell morphology was observed under transmission electron microscopy (HT7800, Hitachi, Japan). The physiological characterization of three strains was performed in MMJHS medium and growth was measured by direct cell counting using a phase contrast microscope (Eclipse 80i, Nikon) according to the method previously described (Jiang et al., 2017). The temperature range for growth was determined at 4, 10, 15, 20, 25, 28, 30,32, 35, 37, 40, 45, 50 and 60°C. The salinity range for growth was examined by adjusting the concentrations of NaCl between 0 and 9.0% (w/v) at 0.5 (w/v) intervals. Oxygen sensitivity was examined using MMJHS medium with different O₂ concentrations (0%, 1%, 2%, 4%, 6%, 8%, 10%, 15% and 20%) in the headspace gas. In the case of oxygen absence, 10 mM nitrate was added as a potential electron acceptor. The pH range was investigated from 3.5 to 9.0 with a 0.5 pH unit interval by altering pH with several buffers, including 30 mM acetate/acetic acid buffer (pH 3.0–5.0), MES (pH 5.5–6.0), PIPES (pH 6.5–7.0), HEPES (pH 7.5–8.0), Tris and CAPSO (pH 8.0 and above).

To determine the electron donors and acceptors, MMJ synthetic seawater containing 0.1% (w/v) NaHCO₃ was used as a basal medium, and H₂ was tested as the electron donor for the growth of three strains, nitrate (0.1%, w/v), nitrite (0.1 and 0.01%, w/v), thiosulfate (0.1%, w/v), sulfite (0.01%, w/v), elemental sulfur (1%, w/v), or molecular oxygen (1%), were tested as the only electron acceptor. The sulfur oxidation was tested with MMJS medium, using sodium thiosulfate (0.1%, w/v) or elemental sulfur (S) (1%, w/v) as sole electron donor, nitrate (0.1%, w/v), nitrite (0.1 and 0.01%, w/v), or molecular oxygen (0.1 and 1%, v/v) were tested as the only electron acceptor. Heterotrophic growth was tested in MMJ medium in the absence of NaHCO₃ and in a 94% N₂/6% O₂ (200 kPa) gas phase. The following potential organic carbon compounds were tested: 0.02% (w/v) glucose, galactose and fructose, 0.1% (w/v) peptone, starch and casein, 5 mM formate, acetate, citrate, fumarate and pyruvate.

For fatty acids analysis, cells grown on MMJHS medium at 30C for 24h were saponified, methylated, and extracted following the standard MIDI protocol (Sherlock Microbial Identification System, version 6.0B). The fatty acids were analyzed by gas chromatography (Agilent Technologies 6850), and then the result was identified using the TSBA6.0 database of the Microbial Identification System.

The total DNA of the three strains was extracted and the 16S rRNA gene was amplified as described previously (Jiang et al., 2009). The similarity of 16S rRNA gene sequences was determined using the EzBioCloud server (http://www.ezbiocloud.net/) and NCBI database, and sequences of close strains were downloaded for the phylogenetic analysis. Sequence comparison was performed using CLUSTAL_W (Larkin et al., 2007) and phylogenetic trees were constructed using MEGA X (Kumar et al., 2018) according to the Neighbor-Joining (Tamura et al., 2004), Maximum likelihood and Maximum Parsimony methods (Felsenstein, 1981). The online website TVBOT was used to embellish the phylogenetic tree (Xie et al., 2023). Genetic distance was calculated using Kimura two-parameter model. Bootstrap analysis was calculated based on 1000 replications. The complete genome of strain XGS-02 was sequenced by Tianjin Biochip Corporation (Tianjin, PR China) using the single molecule real-time (SMRT) technology on the Pacific Biosciences (PacBio) sequencing platform. De novo assembly was performed using the Hierarchical Genome Assembly Process (Version 4) workflow, and the complete circular genome was derived. Draft genome sequences of strains XTW-4 and zt1-1 were sequenced using Illumina Hiseq 2000 platform (Major Bio-Pharm Technology Co., Ltd, China). Raw reads were clipped and trimmed using Trimmomatic version 0.32 (Bolger et al., 2014). Trimmed reads were assembled using SOAPdenovo (Luo et al., 2015). The G+C content of the genomic DNA was determined from the whole genome sequence. Gene prediction and annotation were performed using NCBI Prokaryotic Genomes Annotation Pipeline (PGAP) (Tatusova et al., 2016) and the Rapid Annotation using Subsystem Technology (RAST) pipeline (Overbeek et al., 2014)

We downloaded all culturable Sulfurovum genomes available from NCBI database, including four strains Sulfurovum indicum ST-419^T, Sulfurovum riftiae 1812E^T, Sulfurovum lithotrophicum ATCC BAA-797^T, and Sulfurovum sp. NBC37-1 from deep-sea hydrothermal vent environments, four strains, Sulfurovum sp. TSL1, Sulfurovum sp. TSL6, Candidatus Sulfurovum sp. AR, and Sulfurovum sp. HSL1-3 from coastal sediments. A total of eleven genomic sequences, including three genomes from our newly isolated strains XGS-02, XTW-4, and zt1-1, were checked for completeness and contamination using CheckM (Parks et al., 2015). The phylogenomic tree was constructed based on an up-to-date 92 bacterial core gene sets by UBCG version 3.0 (Na et al., 2018), the ANI was compared using the pyani tool (Pritchard et al., 2016), Pan-genomic analysis was performed with BPGA software (Chaudhari et al., 2016). Protein sequences were identified using PowerBLAST (Zhang and Madden, 1997). Sequence comparison was performed using MEGA X (Kumar et al., 2018), and phylogenetic trees based on amino acid sequences were constructed using the Maximum Likelihood method with bootstrap values based on 1000 replicates.

The GenBank accession numbers for 16S rRNA gene sequence of strains XGS-02, XTW-4 and zt1-1 are OM960633, OP810811 and OP810810, respectively. The genome sequences have been deposited at GenBank under the accession numbers of CP093312, JAQIBC000000000 and JAQIBD000000000, respectively. The three Sulfurovum strains were deposited in the Marine Culture Collection of China (MCCC) under collection numbers MCCC 1A18820, MCCC 1A19406, MCCC 1A19490.

With enrichments with H₂ as the sole energy source, three strains of Sulfurovum were isolated from coastal sediments and designated as strains XGS-02, XTW-4, and zt1-1. In other enriched media, the isolates belonged to genus Thiomicrorhabdus and Sulfurimonas, which were not the focus of this study. The full-length 16S rRNA gene sequences of strains XGS-02 and zt1-1 retrieved from genomes were 1,503 bp and 1,513 bp, respectively. The 16S rRNA gene sequences of XTW-4 was 1,419 bp. BLAST analysis of the 16S rRNA gene sequences indicated that strains XGS-02, XTW-4, and zt1-1 shared the highest sequence similarity with S. aggregans Monchim33^T, which was isolated from a deep-sea hydrothermal vent chimney with similarities of 96.4%, 96.1%, and 95.9%, respectively. They were also closely related to S. indicum ST-419^T from the deep-sea hydrothermal plume with 95.6%, 94.6%, and 95.2% similarity, respectively. Furthermore, strains XGS-02 and XTW-4 shared 99.6% sequence similarity with each other and 95.9% and 96.0% similarity with strain zt1-1, respectively. The results indicate that strains XTW-4 and zt1-1 represent two novel species of the genus Sulfurovum.

Based on 16S rRNA gene sequences, the phylogenetic tree indicated that strains XGS-02 and XTW-4 clustered with Sulfurovum species from non-vent marine habitats, whereas those from vent environments formed separate clusters. Notably, strains zt1-1 and HSL1-3 represented a new branch located differently from other Sulfurovum species ( Figure 1 , Supplementary Figures S2, S3 ). The phylogeny was confirmed by whole-genome phylogenetic analysis based on 92 core gene sequences ( Figure 2 ), which was consistent with the phylogenetic tree based on the 16S rRNA gene sequences. Combining the phylogenetic tree based on 16S rRNA gene sequences and whole genomes, three different evolutionary branches of the genus Sulfurovum were revealed. Correspondingly, three groups were named: Group I, bacteria from intertidal sediments; Group II, bacteria from hydrothermal vent areas; and Group III, bacteria from intertidal sediments ( Figure 2 ).

Morphological observation by TEM showed that strains XTW-4 and zt1-1 had no flagella. The result was confirmed by a genomic analysis, without genes encoding flagella in their genomes. The cells of strain XTW-4 was short rods, 0.2–0.4 µm wide and 0.4–1.2 µm long ( Supplementary Figure S4 ). The morphology of strain zt1-1 was short rod-shaped, 0.2–0.5 µm wide, and 0.4–1.2 µm long, which was similar to strain XTW-4 ( Supplementary Figure S4 ).

The growth experiment showed that strain XGS-02 could grow at a temperature range of 10–45°C, salinity range of 0.5–4.0% (w/v) NaCl, pH range of 5.5–8.5, and oxygen concentration range of 1–20%. Strain XTW-4 could grow at temperature (15–45°C), salinity (0.5–5.0% (w/v) NaCl), pH (5.0–8.5), and oxygen (1–15%) ranges. Strain zt1-1 could grow at 10–45°C, 0%–7.0% (w/v) NaCl, 4.5–8.5 pH, and 1%–20% O₂. The optimal temperature for the three newly isolated strains was approximately 30°C and the optimum pH was 6.0–6.5. The optimal salinity was 2.5% (w/v) NaCl for strains XGS-02 and XTW-4, and 1.5% (w/v) NaCl for strain zt1-1. The optimum oxygen concentrations were 8% for XGS-02 and XTW-4 and 15% for zt1-1. Chemoautotrophic growth showed that the three strains could utilize hydrogen and thiosulfate as electron donors but fail to oxidize elemental sulfur. They had the highest biomass with hydrogen as the electron donor. Thus, hydrogen may be the preferred energy source for these bacteria. All oxygen, thiosulfate and elemental sulfur can be used as electron acceptors. It is worth mentioning that the strains grew weakly when thiosulfate acted as the electron donor and oxygen acted as electron acceptor. All strains could not use nitrate and nitrite as electron acceptors.

We further compared the physiological characteristics of the three new non-vent strains with those of the vent-type strains, S. indicum ST-419^T (Xie et al., 2021), S. riftiae 1812E^T (Giovannelli et al., 2016), S. lithotrophicum ATCC BAA-797^T (Inagaki et al., 2004), S. denitrificans eps51^T (Mori et al., 2018), and S. aggregans Monchim33^T (Mino et al., 2014) ( Table 1 ). The results revealed an evident divergence between the vent and non-vent strains. The non-vent strains had an optimal oxygen range of 8–15%, showing higher oxygen adaptation than the vent strains. Moreover, the three non-vent strains could not use nitrate as an electron acceptor, whereas all the vent strains could. All the non-vent Sulfurovum-type strains could reduce thiosulfate, but all those of the vent species could not, except for S. aggregans. In the case of electron donor utilization, all non-vent strains can utilize hydrogen as an electron donor, while most (3/5) vent strains cannot. In contrast, none of the non-vent strains can grow with elemental sulfur as the sole energy source, whereas most (4/5) vent strains can grow.

The fatty acid profiles of strains XTW-4 and zt1-1 and related type strains are listed in Table 1 . Strain XTW-4 contained the predominant cellular fatty acids C_18:1ω7c (35.0%), C_16:1ω7c (24.5%), and C_16:0 (16.4%), and strain zt1-1 mainly contained C_16:1ω7c (35.9%), C_18:1ω7c (18.1%), and C_16:0 (17.6%). These profiles are similar to those of S. indicum ST-419^T, S. riftiae 1812^T, and S. denitrificans eps51^T.

The genome size of strain XTW-4 was 2.20 Mb with a GC content of 39.1%, and the genome size of zt1-1 was 2.18 Mb with a GC content of 39.3%. A total of 2,268 genes were predicted in the genome of strain XTW-4, including 2,203 protein-coding and 65 RNA genes. The genome of strain zt1-1 contains 2,267 genes, including 2,209 protein-coding genes and 58 RNA genes. The genomic similarity of strains XTW-4 and zt1-1 with other species of the genus Sulfurovum was determined using ANI values. The paired ANI values between strain XTW-4 and its close relatives, S. indicum and S. riftiae, were 86.0% and 85.7%, respectively. The paired ANI values between strain zt1-1 and its close relatives, S. indicum and S. riftiae, were 84.0% and 84.4%, respectively. These findings support the classification of strains XTW-4 and zt1-1 as two distinct species based on the cut-off threshold of ANI (95–96%) for the delineation of prokaryotic species. Strains XTW-4, zt1-1, and others of Sulfurovum species shared less than 40.0 % DDH values ( Table S2 ). The low DDH values (< 70%) confirmed that strains XTW-4 and zt1-1 represented two novel species within the genus Sulfurovum (Stackebrandt and Goebel, 1994; Auch et al., 2010; Meier-Kolthoff et al., 2014).

A total of 11 Sulfurovum genomes from hydrothermal vents and intertidal environments were used for comparative analysis in this study. The genome size range of the non-vent Sulfurovum species was 2.1–2.6 Mb, and the G+C content ranged from 38.4 to 43.6%, while the genome size range of the vent strain was 2.2–2.6 Mb and the range of G+C content was 42.5–45.7%. The results showed that Sulfurovum species from deep-sea hydrothermal vent environments had relatively higher G+C values ( Table 2 ). In addition, comparative genomic analysis revealed 1051 core genes in all Sulfurovum genomes ( Supplementary Figure S5 ). The percentage of core genes per genome ranged from 42.8% to 50.9%, and the percentage of unique genes per genome ranged from 5.4% to 19.6%. Sulfurovum genomes belonging to Group I had 12.2–19.3% of unique genes, and those genomes from Group II had 11.9–17.9%. Group III from non-vent genomes had the lowest percentage of unique genes (< 9%) ( Table S1 ).

For sulfide oxidation, Sulfurovum species contain four sulfoquinone oxidoreductase (Sqr) types, including Type II, Type III, Type IV, and Type VI ( Supplementary Figure S7 ). Type II Sqr was present in all strains ( Table 3 ), implying that it is essential for sulfide oxidation in Sulfurovum species. Notably, the vent strains contained more copies of Type II Sqr, up to four copies in strain NBC37-1 and S. riftiae, in contrast to the single copy in the non-vent strains. Type III Sqr was present only in the non-vent strain HSL1-3, whereas Type VI Sqr was present in all strains in a single copy. Phylogenetic analysis showed that the vent and non-vent branches of Sqr were located in different evolutionary clusters, and Sqr from different groups of Sulfurovum clustered together.

In addition, all Sulfurovum species encode the complete sox gene cluster (soxABXYZ and soxCDYZ) for thiosulfate oxidation. The phylogenetic tree based on the SoxB protein showed a topology similar to that of the phylogenomic analysis of Sulfurovum, suggesting that the SoxB gene in Sulfurovum species is acquired by vertical inheritance within the lineage ( Supplementary Figure S8 ). For elemental sulfur respiration, all Sulfurovum strains have polysulfide reductase (Psr) of the three groups, which can reduce elemental sulfur to sulfide ( Table 3 ). Phylogenetic analysis showed that polysulfide reductase Group I was detected in all Sulfurovum species from non-vent environments, encoded by five genes, psrA1B1CDE. Groups II and III were also present in some non-vent strains, such as TSL6, XGS-02, and HSL1-3 ( Supplementary Figure S9 ).

Genes encoding superoxide dismutase and catalase, which are involved in oxidative stress, were found in non-vent strains ( Table 3 ), while superoxide dismutase was absent in vent strains NBC37-1, S. lithotrophicum and S. riftiae, and catalase was absent in S. indicum and S. riftiae. In addition, all Sulfurovum strains contain genes encoding cytochrome c peroxidase and thiol peroxidase, which scavenge peroxides and provide defense against oxidative damage (Missall et al., 2004). Vent Sulfurovum genomes usually have more copies of cytochrome c peroxidase than those from non-vent environments. Multiple terminal oxidases are present in the Sulfurovum genomes, all containing cbb3-type cytochrome c oxidase ( Table 3 ). Phylogenetic analysis showed that cbb3 type cytochrome c oxidase clustered into two groups: CcoN I and CcoN II ( Supplementary Figure S10 ). All strains containing CcoN I and CcoN II were of vent origin. The coxA-encoded caa3 type terminal oxidase was present in non-vent strains and absent in vent strains ( Table 3 ). In addition, some Sulfurovum strains, such as zt1-1, HSL1-3, TSL1, and S. indicum, contained genes encoding cytochrome bd ubiquinone oxidase.

To our knowledge, this is the first report of a novel species of non-vent origin in Sulfurovum. The combined phenotypic, chemotaxonomic, and phylogenetic characteristics demonstrated that strains XTW-4 and zt1-1 represent two new species in the genus Sulfurovum, for which the names Sulfurovum xiamenensis sp. nov. and Sulfurovum zhangzhouensis sp. nov. are proposed, both of which showed the closest 16S rRNA gene sequence similarity to S. aggregans Monchim33^T (95.8% and 95.4%, respectively). They differed from other type strains in phenotypical features, such as optimum salinity and oxygen concentrations and the utilization of electron acceptors. Intriguingly, the two coastal species both respired for thiosulfate, while the vent strains could not; however, while the vent strains could respire nitrate, the two coastal strains could not ( Table 1 ).

To understand their environmental adaptation, we performed comparative genomic analyses between the vent and non-vent Sulfurovum strains. Significant differences were observed in key metabolic mechanisms and stress responses between the vent and non-vent strains, implying that their adaptive evolution and species diversification were related to inhabitance.

Correspondingly, we found that all members of the genus Sulfurovum from deep-sea hydrothermal vents contained a complete denitrification pathway in addition to some genes involved in dissimilatory nitrate reduction to ammonia (DNRA) in part vent strains. Denitrification and DNRA processes are currently considered to be two competing pathways for nitrate reduction (Bu et al., 2017; Jia et al., 2020; Pandey et al., 2020; Li S. et al., 2022), and few studies have reported their coexistence except for Pseudomonas and Shewanella (Kuypers et al., 2018; Huang X. J. et al., 2021; Liu et al., 2021). The nitrate reduction pathway (NAP) is considered conserved and widespread in the phylum Campylobacterota based on bacteria from deep-sea hydrothermal vent habitats (Vetriani et al., 2014). However, these two processes were absent in our coastal strains. Sulfur oxidation coupled with nitrate reduction is considered the primary source of energy in vent ecosystems (Wang et al., 2009), whereas this process does not occur in coastal Sulfurovum species. The genome revealed that the denitrification and DNRA pathways were completely absent, and experimental validation showed that they could not use nitrate as an electron acceptor. To compensate, our two Sulfurovum species adapted to higher oxygen concentrations and preferred to use oxygen as an electron acceptor, which is in agreement with the loss of denitrification and DNRA-related genes, as well as other non-vent Sulfurovum strains (unpublished data).

Intriguingly, members of the genus Sulfurovum from coastal sediments possess genes for nitrogen fixation, which are absent in deep-sea vent Sulfurovum. Coastal mangrove sediments are recognized to be nitrogen-limited due to the unbalance of carbon and nitrogen caused by burying of carbon-rich plant litter (Lin et al., 2019; Luo et al., 2021). Nitrogen-fixing bacteria are considered to play a key role in nitrogen amendment (Alfaro-Espinoza and Ullrich, 2015; Tang et al., 2020; Luo et al., 2021). Therefore, Sulfurovum containing nitrogenase genes are of competitive advantage in coastal environments. Recently, the expression of Nif genes associated with Sulfurovum spp., as well as the presence of the nifH gene in a Sulfurovum metagenome-assembled genome (MAG) was demonstrated at a coastal gas vent site (Patwardhan et al., 2021). Certainly, not all coastal Sulfurovum have nitrogenase genes. This is probably due to highly variable environmental parameters in coastal sediments. In contrast, ammonia is relatively abundant in the vent fluid, which can reach micromolar level in situ (Xu et al., 2014), and can be oxidized to nitrate by ammonia-oxidizing archaea (Crepeau et al., 2011; Zhang et al., 2016; Ding et al., 2017). Thus, genes for nitrogen fixation in deep-sea vent may be redundant and lost in all vent Sulfurovum. The differentiation of Sulfurovum in accordance with unique habitats expands our understanding of the genus in terms of environmental adaptation ( Figure 4 ).

Reduced sulfur compounds, such as sulfides, are important energy sources for chemolithoautotrophs in deep-sea vents. Unexpectedly, we found that coastal isolates of Sulfurovum grew best with hydrogen as an electron donor and weakly with thiosulfate and sulfide. Moreover, all members of this genus contain an extensive suite of hydrogenases, including [NiFe]-hydrogenase groups 1b, 2d, and 4 (Hyc and Coo). The most frequently occurring hydrogenases belonged to Group I. Almost all Sulfurovum members contained multiple copies of this group, probably in response to different hydrogen concentrations, suggesting that hydrogenase in Group I plays an important role in energy draining to support bacterial growth (Grote et al., 2012; Berney et al., 2014).

Regarding sulfide oxidation, Sulfurovum species contain genes encoding different types of Sqr, classified as types II, III, IV, and VI. The diversification of these Sqr genes is thought to play important roles in sulfide oxidation, sulfide assimilation, energy production, heavy metal tolerance, detoxification, and sulfide signaling (Marcia et al., 2010). Additionally, Sulfurovum bacteria have one or more copies of Type II Sqr ( Table 3 ), which may compensate for other Sqrs under specific environmental conditions (Wang et al., 2021). Thiosulfate ( Figure 4 ) can commonly be oxidized by Sulfurovum of any origin, but as an electron acceptor, it can be used by non-vent Sulfurovum, as confirmed by our coastal pure cultures ( Table 1 ).

Sulfurovum usually grows in a mixed zone with unsaturated oxygen concentration (Meier et al., 2017). Antioxidation systems may be essential for traveling across redox gradients to oxic areas. Reactive oxygen species (ROS) are formed by the intermediate products of oxygen reduction and can cause damage to cellular macromolecules (Cabiscol et al., 2000). Superoxide dismutase and catalase are the most well-characterized ROS defense mechanisms (Johnson and Hug, 2019). Interestingly, we found that the genes encoding both superoxide dismutase and catalase were present in the non-vent strains but were partially or completely absent in the vent strains ( Table 3 ). In addition, some terminal oxidases function in the defense against ROS (Kaminski et al., 1996; Hassani et al., 2010; Borisov and Siletsky, 2019), allowing certain strictly anaerobic bacteria to grow in microaerobic environments, such as cbb3-type hemocopper oxidase and cytochrome bd ubiquinone oxidase. All pure culture strains of Sulfurovum contain the CcoNOQP operon, which encodes a cbb3-type cytochrome c oxidase that supports bacterial growth under anaerobic and microaerobic conditions owing to its high affinity for oxygen. Some strains also encode cytochrome bd ubiquinone oxidase, which is an alternative oxidase found in many bacteria that oxidizes ubiquinone and reduces oxygen as part of the electron transport chain. In addition, unlike vent strains, non-vent strains have a caa3-type hemocopper oxidase that catalyzes the reduction of oxygen to water and may play an important role in oxygen adaptation. Hence, it is possible that the ROS defense mechanisms enable coastal Sulfurovum bacteria to deal with oxidative stress caused by increased O₂ concentrations in coastal environments. This is consistent with their wider growth ranges with regard to oxygen concentrations (1–15%) and higher optimum oxygen concentration compared the vent Sulfurovum bacteria ( Table 1 ).

Sulfurovum xiamenensis (xia.men.en’sis. N.L. masc. adj. xiamenensis of Xiamen, a city in Fujian, China, where the type strain was isolated).

Cells are Gram-negative short rods (0.4-1.2 × 0.2-0.4 μm) without flagella. Optimum oxygen concentration 8%-10%. Growth occurs at 15-45°C (optimum 32°C), pH 5.0-8.5 (optimum pH 6.0-6.5), and 0.5-5.0% (w/v) NaCl (optimum 2.5%). Obligate chemolithoautotrophic growth occurs with H₂ as electron donor, and oxygen, thiosulfate, and S⁰ can be utilized as electron acceptors. It also growth occurs with thiosulfate as an electron donor and oxygen as an electron acceptor. Organic substrates are not utilized as carbon sources and energy sources. Major cellular fatty acids are C_18:1ω7c, C_16:1ω7c and C_16:0.

The type strain, XTW-4^T (=MCCC 1A19406), was isolated from mangrove sediments in, Xiamen, Fujian Province, PR China. The genomic G+C content of the type strain is 39.1 mol%.

Sulfurovum zhangzhouensis (zhang.zhou.en′sis. N.L. masc. adj. zhangzhouensis of Zhangzhou, a city in Fujian, China, where the type strain was isolated).

Cells are Gram-negative short rods (0.4-1.2 × 0.2-0.5 μm) without flagella. Optimum oxygen concentration 15%. Growth occurs at 10-45°C (optimum 32°C), pH 4.5-8.5 (optimum pH 6.0-6.5), and 0.5-7.0% (w/v) NaCl (optimum 1.5%). Obligate chemolithoautotrophic growth occurs with H₂ as electron donor, and oxygen, thiosulfate, and S⁰ can be utilized as electron acceptors. It also growth occurs with thiosulfate as an electron donor and oxygen as an electron acceptor. Organic substrates are not utilized as carbon sources and energy sources. Major cellular fatty acids are C_16:1ω7c, C_18:1ω7c and C_16:0.

The type strain, zt1-1^T (=MCCC 1A19490), was isolated from the sediment of retirement ponds in Yunxiao County, Zhangzhou City, Fujian Province, PR China. The genomic G+C content of the type strain is 39.4 mol%.