Sulfurimonas is a bacterial genus within the class of Campylobacterota, known for reducing nitrate, oxidizing both sulfur and hydrogen, and containing Group IV hydrogenases. This genus consists of four species: Sulfurimonas autorophica, Sulfurimonas denitrificans, Sulfurimonas gotlandica, and Sulfurimonas paralvinellae. The genus' name is derived from "sulfur" in Latin and "monas" from Greek, together meaning a "sulfur-oxidizing rod". The size of the bacteria varies between about 1.5-2.5 μm in length and 0.5-1.0 μm in width. Members of the genus Sulfurimonas are found in a variety of different environments which include deep sea-vents, marine sediments, and terrestrial habitats. Their ability to survive in extreme conditions is attributed to multiple copies of one enzyme. Phylogenetic analysis suggests that members of the genus Sulfurimonas have limited dispersal ability and its speciation was affected by geographical isolation rather than hydrothermal composition. Deep ocean currents affect the dispersal of Sulfurimonas spp., influencing its speciation. As shown in the MLSA report of deep-sea hydrothermal vents Campylobacterota, Sulfurimonas has a higher dispersal capability compared with deep sea hydrothermal vent thermophiles, indicating allopatric speciation.
Characteristics +Table 1. Specific characteristics of the four species within Sulfurimonas genusSpeciesSize Morphology MovementTemperature dependenceHabitat conditions Optimal conditions Doubling time under optimal conditions(hours)Sulfurimonas autotrophica1.5-2.5 x 0.5-1.0 μm Rod A single polar flagellum Mesophilic Temperature: 10 - 40 °C pH: 5 - 9 Temperature: 23 - 26 °CPH= 6.51.4Sulfurimonas denitrificansVariable length with width ~0.3μmShort Rod or Spirilla-liked N/A Mesophilic Temperature: 10-30 °C; pH: 7Temperature: 22 °C PH=712 Sulfurimonas gotlandica0.66±0.083 x 62.1±0.54 μm Curved Rod or Spirilla-liked One polar flagella or two flagella at opposite poles PsychrotolerantTemperature: 4 – 20 °C pH: 6.7–8.0 Temperature: 15 °C13Sulfurimonas paralvinellae1.50–2.50 μm × 0.6–0.8 μm Rod moving flagellum 1.5–2.5 μm long and 0.6–0.8 μm wide Mesophilic Temp: 4-35 °C pH: 5.4-8.6 Temperature: 30 °C pH=6.113-16
History of recognition "Auto" and 'trophicos" are derived from Greek words, where "auto" means self and 'trophicos" refers to nursing, tending or feeding, which indicates its autotrophy. The abundance and distribution of subgroups within the Campylobacterota and the genusSulfurimonas have been detected in the water column using a number of techniques including 16S rRNA cloning, catalyzed reporter deposition and fluorescence in situ hybridization (CARD-FISH), and quantitative PCR measurements. Water samples were collected at different depths and the concentrations of nutrients, oxygen, and sulfur measured immediately after sampling. The sample was measured for carbon fixation rate, and the DNA extracted and specific sequences amplified by PCR.
The "denitrificans" portion in the name Sulfurimonas denitrificans (S. denitrificans) refers to its ability to reduce nitrate into di-nitrogen gas, a process known as denitrification. In 2006, Sulfurimonas denitrificans was the last species to be placed in the genus Sulfurimonas, as in 2000 it had been wrongly classified into the genus Thiomicrospira.
Studies of Sulfurimonas gotlandica (S. gotlandica) have mostly been from the Baltic Sea, using transmission electron microscopy and fluorescence microscopy with phosphotungstic acid and DAPI stain as forms of visualization.
Sulfurimonas paralvinellae was first obtained from a nest of deep-sea polychaete worms, particularly from the family Alvinellidae. Members from the genus Paralvinellae were found at a sulfide mound at a deep-sea hydrothermal vent in the Iheya North Field in the Mid-Okinawa Trough. The strain was initially separated from the nest via dilution-to-extinction technique. The strain was called GO25 T and had resembling physiological and phylogenetic characteristics of Sulfurimonas autotrophica. It was later determined that this species differs from Sulfurimonas autotrophica by having a distinct energy metabolism.
Phylogeny The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN) and National Center for Biotechnology Information (NCBI).
16S rRNA based LTP_10_2024 120 marker proteins based GTDB 10-RS226 Unassigned species: "S. diazotrophicus" Zhong et al. 2025 "Ca. S. kebritensis" Alamoudi et al. 2025 "S. microaerophilus" Zhong et al. 2025
Metabolism Generally, bacteria have many pathways for metabolism, and in the case of members of the genus Sulfurimonas, this is how they are categorized into taxa. Members of the genus Sulfurimonas live in a wide range of environments, and play a vital role in chemoautotrophic processes, depending on the environment. Isolates of the four species in this genus have been shown to grow with a wide variety of electron acceptors and donors, allowing for members of the genus Sulfurimonas to grow in a wide variety of environments. Therefore, the success of Sulfurimonas spp. is credited to its ability to be a chemolithotroph, its flexible metabolism of changing electron acceptors/donors and sources of inorganic carbon, its oxygen tolerance and its ability to change with the environment. With differing environments, four types of energy metabolism are seen; including sulfur, hydrogen, nitrogen and carbon metabolism.
Sulfur metabolism As a sulfur-oxidizing Epsilonproteobacterium, studies have found that Sulfurimonas spp. use a wide variety of electron donors for growth including sulfide, sulfur, thiosulfate, and sulfite. However, as shown below, not all species can use each of the mentioned electron donors (Table 2). Multiple strains of the genus are capable of Microbial Sulfur Disproportionation (MSD) of elemental sulfur and thiosulfate.
Sulfurimonas paralvinellae is able to use both molecular hydrogen and reduced sulfur for metabolism, which makes it only the second deep-sea Campylobacterota discovered to do so. Sulfurimonas paralvinellae is also capable of using yeast extract as a sulfur source. Molecular hydrogen is observed to yield a higher growth rate and is favored by Sulfurimonas paralvinellae over free reduced sulfur, even if the latter is present in the environment is excess. This can possibly be explained by the smaller amount of molecular hydrogen required to sustain growth in a bacterial cell as compared to reduced sulfur.
Table 2. List of electron donors for Sulfurimonas species. Sulfurimonas autorophicaSulfurimonas denitrificansSulfurimonas gotlandicaSulfurimonas paralvinellaeSulfide✓✓✓XSulfur✓✓✓✓Thiosulfate✓✓✓✓SulfiteXX✓XHydrogenX✓✓✓ Sulfur Oxygenase Reductase (SOR) catalyzes sulfur, creating sulfite, thiosulfate and sulfide. SOR genes are found in S. gotlandica and S. autotrophica, but are absent in S. denitrificans. It's hypothesized that S. denitrificans lost SOR genes because of the low sulfide habitat in the Dutch Wadden Sea.
Except for S. paralvinellae, all Sulfurimonas species can use sulfide as an electron donor, by oxidizing sulfide into sulfate. The sulfide oxidizing pathway that's used is called sulfide:quinone reductase (SQR), and is coded by genes involved in the pathway responsible for catalyzing sulfide oxidation. There are six known types of SQR proteins in all the kingdoms. Most isolates of Epsiolonproteobacteria have SQRs classified as Type II, IV and VI, never have Type I and occasionally have Type III and V. Sulfurimonas is the only known genus in the Campylobacterota that has Type III and V SQRs. Type III is only found in S. denitrificans and S. gotlandica. Type IV SQR is highly conserved, and is found in all four species of Sulfurimonas and so is thought to be the most important SQR for cell survival in the genus Sulfurimonas. According to a study looking at heterologous expression of SQR homologs in S. denitrificans, it has three functional SQRs; Type II, III and IV. Another study also found that Type VI SQR was not in S. denitrificans, but that it was in the other three species. The researchers found that Type VI SQR functioning in high sulfide environments, and hypothesized that S. denitrificans doesn't require Type VI SQR because members of the species would have a low probability of encountering free sulfide. On the other hand, S. autotrophic is the only one of the four species that contains Type V SQRs, and was associated with organisms living in acid mines The exact roles for the functional SQRs remains unknown. However, in general, SQRs are crucial for sulfide oxidation, assimilation and signaling, energy generation and heavy-metal tolerance. Therefore, members of the genus Sulfurimonas are significant contributors to the global sulfur cycle as all members of the species oxidize sulfur to sulfate.
Hydrogen metabolism All but one of the Sulfurimonas species can use hydrogen as an energy source to grow. Members of S. autotrophica are the only Sulfurimonas spp. to not use hydrogen, and has been shown to grow with hydrogen in aerobic and anaerobic conditions. In contrast, hydrogen is used as an electron donor at times by bacteria belonging to S. denitrificans, S. gotlandica, and S. paralvinellae, instead of sulfur-based compounds.
To catalyze hydrogen metabolism bacteria belonging to the genus Sulfurimonas use [NiFe]-hydrogenase. The reaction being . There are many different [NiFe]-hydrogenases that are classified into different groups (Groups I to IV) and are found in all four Sulfurimonas species. Since S. autotrophica contains hydrogenases, a study has concluded that under specific environmental conditions it may be able to consume hydrogen.
Another study shows that S. denitrificans grows more efficiently with hydrogen than with thiosulfate. The three Sulfurimonas species express active hydrogen uptake hydrogenase and can grow on hydrogen. Where the bacteria live (i.e. marine water, sediments or hydrothermal vents) will affect the level of oxygen in the environment and therefore the kind of metabolism that they use.
Nitrogen metabolism As far as we know, nitrogen metabolism occurs in all members belonging to Sulfurimonas species except S. autotrophica . It has been shown that S. autotrophica could not grow in a concentration of 5 mM sodium nitrate under laboratory conditions. Denitrification by Sulfurimonas spp. has a crucial role in nitrogen cycling. Nitrate turnover for S. denitrificans is 20 mM in three (with thiosulfate and hydrogen) to six days (thiosulfate and no hydrogen). The nitrate turnover in the other two species, S. gotlandica and S. paralvinellae, are quite different. S. gotlandica used only 1 mM nitrate within 9 days (with thiosulfate) and S. paralvinellae used 10 mM nitrate within 4 days (with hydrogen and sulfur). Additionally, S. gotlandica and S. denitrificans can use nitrite instead of nitrate as an electron acceptor. A list of the electron acceptors that Sulfurimonas species can use is summarized in Table 3.
Table 3. List of electron acceptors for Sulfurimonas species. Sulfurimonas autorophicaSulfurimonas denitrificansSulfurimonas gotlandicaSulfurimonas paralvinellaeNitrateX✓✓✓NitriteX✓✓XOxygen✓✓✓✓ To catalyze the reaction of nitrogen metabolism, all Sulfurimonas species have a periplasmic nitrate reductase (Nap) catalytic subunit (NapA) . These epsiolonproteobacterial NapAs have a high affinity for nitrate and may represent an adaptation by members of this genus to low environmental nitrate concentrations at deep-sea vents .
Isolates of S. gotlandica and S. denitrificans are well adapted to the fluctuating oxygen and hydrogen sulphide concentrations in the environment because they can both use nitrate, nitrite or oxygen as electron acceptors. Their ability to use nitrate or nitrite as an electron acceptor, instead of oxygen, extends their ecological niche beyond anoxic to much deeper areas in the water column.
Speciation