A novel bacterial thiosulfate oxidation pathway provides a new clue about the formation of zero-valent sulfur in deep sea

Sideroxydans lithotrophicus ES-1 grows autotrophically either by Fe(II) oxidation or thiosulfate oxidation, in contrast to most other neutrophilic Fe(II)-oxidizing bacteria (FeOB) isolates. This provides a unique opportunity to explore the physiology of a facultative FeOB and constrain the genes specific to Fe(II) oxidation. We compared the growth of S. lithotrophicus ES-1 on Fe(II), thiosulfate, and both substrates together. While initial growth rates were similar, thiosulfate-grown cultures had higher yield with or without Fe(II) present, which may give ES-1 an advantage over obligate FeOB. To investigate the Fe(II) and S oxidation pathways, we conducted transcriptomics experiments, validated with RT-qPCR. We explored the long-term gene expression response at different growth phases (over days-week) and expression changes during a short-term switch from thiosulfate to Fe(II) (90 min). The dsr and sox sulfur oxidation genes were upregulated in thiosulfate cultures. The Fe(II) oxidase gene cyc2 was among the top expressed genes during both Fe(II) and thiosulfate oxidation, and addition of Fe(II) to thiosulfate-grown cells caused an increase in cyc2 expression. These results support the role of Cyc2 as the Fe(II) oxidase and suggest that ES-1 maintains readiness to oxidize Fe(II) even in the absence of Fe(II). We used gene expression profiles to further constrain the ES-1 Fe(II) oxidation pathway. Notably, among the most highly upregulated genes during Fe(II) oxidation were genes for alternative complex III, reverse electron transport and carbon fixation. This implies a direct connection between Fe(II) oxidation and carbon fixation, suggesting that CO 2 is an important electron sink for Fe(II) oxidation. Importance Neutrophilic FeOB are increasingly observed in various environments, but knowledge of their ecophysiology and Fe(II) oxidation mechanisms is still relatively limited. Sideroxydans are widely observed in aquifers, wetlands, and sediments, and genome analysis suggests metabolic flexibility contributes to their success. The type strain ES-1 is unusual amongst neutrophilic FeOB isolates as it can grow on either Fe(II) or a non-Fe(II) substrate, thiosulfate. Almost all our knowledge of neutrophilic Fe(II) oxidation pathways comes from genome analyses, with some work on metatranscriptomes. This study used culture-based experiments to test the genes specific to Fe(II) oxidation in a facultative FeOB and refine our model of the Fe(II) oxidation pathway. We gained insight into how facultative FeOB like ES-1 connect Fe, S, and C biogeochemical cycling in the environment, and suggest a multi-gene indicator would improve understanding of Fe(II) oxidation activity in environments with facultative FeOB.

Download Full-text

Enzymatic and Genetic Characterization of Carbon and Energy Metabolisms by Deep-Sea Hydrothermal Chemolithoautotrophic Isolates of Epsilonproteobacteria

Applied and Environmental Microbiology ◽

10.1128/aem.71.11.7310-7320.2005 ◽

2005 ◽

Vol 71 (11) ◽

pp. 7310-7320 ◽

Cited By ~ 133

Author(s):

Ken Takai ◽

Barbara J. Campbell ◽

S. Craig Cary ◽

Masae Suzuki ◽

Hanako Oida ◽

...

Keyword(s):

Enzyme Activity ◽

Deep Sea ◽

Genetic Characterization ◽

Hydrogenase Activity ◽

Direct Oxidation ◽

Genetic Analyses ◽

Bisphosphate Carboxylase ◽

Genetic Characteristics ◽

Oxidation Pathway ◽

Sulfur Oxidizing

ABSTRACT The carbon and energy metabolisms of a variety of cultured chemolithoautotrophic Epsilonproteobacteria from deep-sea hydrothermal environments were characterized by both enzymatic and genetic analyses. All the Epsilonproteobacteria tested had all three key reductive tricarboxylic acid (rTCA) cycle enzymatic activities—ATP-dependent citrate lyase, pyruvate:ferredoxin oxidoreductase, and 2-oxoglutarate:ferredoxin oxidoreductase—while they had no ribulose 1,5-bisphosphate carboxylase (RubisCO) activity, the key enzyme in the Calvin-Benson cycle. These results paralleled the successful amplification of the key rTCA cycle genes aclB, porAB, and oorAB and the lack of success at amplifying the form I and II RubisCO genes, cbbL and cbbM. The combination of enzymatic and genetic analyses demonstrates that the Epsilonproteobacteria tested use the rTCA cycle for carbon assimilation. The energy metabolisms of deep-sea Epsilonproteobacteria were also well specified by the enzymatic and genetic characterization: hydrogen-oxidizing strains had evident soluble acceptor:methyl viologen hydrogenase activity and hydrogen uptake hydrogenase genes (hyn operon), while sulfur-oxidizing strains lacked both the enzyme activity and the genes. Although the energy metabolism of reduced sulfur compounds was not genetically analyzed and was not fully clarified, sulfur-oxidizing Epsilonproteobacteria showed enzyme activity of a potential sulfite:acceptor oxidoreductase for a direct oxidation pathway to sulfate but no activity of AMP-dependent adenosine 5′-phosphate sulfate reductase for a indirect oxidation pathway. No activity of thiosulfate-oxidizing enzymes was detected. The enzymatic and genetic characteristics described here were consistent with cellular carbon and energy metabolisms and suggest that molecular tools may have great potential for in situ elucidation of the ecophysiological roles of deep-sea Epsilonproteobacteria.

Download Full-text

Thiosulfate oxidation and mixotrophic growth of Methylobacterium oryzae

Canadian Journal of Microbiology ◽

10.1139/w07-057 ◽

2007 ◽

Vol 53 (7) ◽

pp. 869-876 ◽

Cited By ~ 16

Author(s):

R. Anandham ◽

P. Indiragandhi ◽

M. Madhaiyan ◽

Kyounga Kim ◽

Woojong Yim ◽

...

Keyword(s):

Novel Species ◽

Sodium Succinate ◽

Sodium Thiosulfate ◽

Sulfur Oxidation ◽

Sulfur Source ◽

Mixotrophic Growth ◽

Inorganic Sulfur ◽

Oxidation Pathway ◽

Thiosulfate Oxidation ◽

Methylobacterium Oryzae

Thiosulfate oxidation and mixotrophic growth with succinate or methanol plus thiosulfate was examined in nutrient-limited mixotrophic condition for Methylobacterium oryzae CBMB20, which was recently characterized and reported as a novel species isolated from rice. Methylobacterium oryzae was able to utilize thiosulfate in the presence of sulfate. Thiosulfate oxidation increased the protein yield by 25% in mixotrophic medium containing 18.5 mmol·L–1of sodium succinate and 20 mmol·L–1of sodium thiosulfate on day 5. The respirometric study revealed that thiosulfate was the most preferable reduced inorganic sulfur source, followed by sulfur and sulfite. Thiosulfate was predominantly oxidized to sulfate and intermediate products of thiosulfate oxidation, such as tetrathionate, trithionate, polythionate, and sulfur, were not detected in spent medium. It indicated that bacterium use the non-S4intermediate sulfur oxidation pathway for thiosulfate oxidation. Thiosulfate oxidation enzymes, such as rhodanese and sulfite oxidase activities appeared to be constitutively expressed, but activity increased during growth on thiosulfate. No thiosulfate oxidase (tetrathionate synthase) activity was detected.

Download Full-text