scholarly journals Evidence for Niche Partitioning Revealed by the Distribution of Sulfur Oxidation Genes Collected from Areas of a Terrestrial Sulfidic Spring with Differing Geochemical Conditions

2012 ◽  
Vol 79 (4) ◽  
pp. 1171-1182 ◽  
Author(s):  
Brendan Headd ◽  
Annette Summers Engel
Keyword(s):  
Gene Sequence ◽  
Sulfide Oxidation ◽  
Niche Partitioning ◽  
Sulfur Oxidation ◽  
Reduced Sulfur Compounds ◽  
Content Type ◽  
Geochemical Conditions ◽  
Sequence Variations ◽  
Bacterial Genes ◽  
Outflow Channel

ABSTRACTThe diversity and phylogenetic significance of bacterial genes in the environment has been well studied, but comparatively little attention has been devoted to understanding the functional significance of different variations of the same metabolic gene that occur in the same environment. We analyzed the geographic distribution of 16S rRNA pyrosequences andsoxBgenes along a geochemical gradient in a terrestrial sulfidic spring to identify how different taxonomic variations of thesoxBgene were naturally distributed within the spring outflow channel and to identify possible evidence for altered SoxB enzyme function in nature. Distinct compositional differences between bacteria that utilize their SoxB enzyme in theParacoccussulfide oxidation pathway (e.g.,Bradyrhizobium,Paracoccus, andRhodovulum) and bacteria that utilize their SoxB enzyme in the branched pathway (e.g.,Chlorobium,Thiothrix,Thiobacillus,Halothiobacillus, andThiomonas) were identified. Different variations of thesoxBgenes were present at different locations within the spring outflow channel in a manner that significantly corresponded to geochemical conditions. The distribution of the differentsoxBgene sequence variations suggests that the enzymes encoded by these genes are functionally different and could be optimized to specific geochemical conditions that define niche space for bacteria capable of oxidizing reduced sulfur compounds.

scholarly journals Impact of Seasonal Hypoxia on Activity and Community Structure of Chemolithoautotrophic Bacteria in a Coastal Sediment

2017 ◽  
Vol 83 (10) ◽  
Author(s):  
Yvonne A. Lipsewers ◽  
Diana Vasquez-Cardenas ◽  
Dorina Seitaj ◽  
Regina Schauer ◽  
Silvia Hidalgo-Martinez ◽  
...  
Keyword(s):  
Community Structure ◽  
Bacterial Community ◽  
Nitrate Reduction ◽  
Sulfide Oxidation ◽  
Niche Partitioning ◽  
Sulfur Oxidation ◽  
Electron Acceptors ◽  
Content Type ◽  
Sulfur Oxidizing ◽  
Seasonal Hypoxia

ABSTRACT Seasonal hypoxia in coastal systems drastically changes the availability of electron acceptors in bottom water, which alters the sedimentary reoxidation of reduced compounds. However, the effect of seasonal hypoxia on the chemolithoautotrophic community that catalyzes these reoxidation reactions is rarely studied. Here, we examine the changes in activity and structure of the sedimentary chemolithoautotrophic bacterial community of a seasonally hypoxic saline basin under oxic (spring) and hypoxic (summer) conditions. Combined 16S rRNA gene amplicon sequencing and analysis of phospholipid-derived fatty acids indicated a major temporal shift in community structure. Aerobic sulfur-oxidizing Gammaproteobacteria (Thiotrichales) and Epsilonproteobacteria (Campylobacterales) were prevalent during spring, whereas Deltaproteobacteria (Desulfobacterales) related to sulfate-reducing bacteria prevailed during summer hypoxia. Chemolithoautotrophy rates in the surface sediment were three times higher in spring than in summer. The depth distribution of chemolithoautotrophy was linked to the distinct sulfur oxidation mechanisms identified through microsensor profiling, i.e., canonical sulfur oxidation, electrogenic sulfur oxidation by cable bacteria, and sulfide oxidation coupled to nitrate reduction by Beggiatoaceae. The metabolic diversity of the sulfur-oxidizing bacterial community suggests a complex niche partitioning within the sediment, probably driven by the availability of reduced sulfur compounds (H2S, S0, and S2O3 2−) and electron acceptors (O2 and NO3 −) regulated by seasonal hypoxia. IMPORTANCE Chemolithoautotrophic microbes in the seafloor are dependent on electron acceptors, like oxygen and nitrate, that diffuse from the overlying water. Seasonal hypoxia, however, drastically changes the availability of these electron acceptors in the bottom water; hence, one expects a strong impact of seasonal hypoxia on sedimentary chemolithoautotrophy. A multidisciplinary investigation of the sediments in a seasonally hypoxic coastal basin confirms this hypothesis. Our data show that bacterial community structure and chemolithoautotrophic activity varied with the seasonal depletion of oxygen. Unexpectedly, the dark carbon fixation was also dependent on the dominant microbial pathway of sulfur oxidation occurring in the sediment (i.e., canonical sulfur oxidation, electrogenic sulfur oxidation by cable bacteria, and sulfide oxidation coupled to nitrate reduction by Beggiatoaceae). These results suggest that a complex niche partitioning within the sulfur-oxidizing bacterial community additionally affects the chemolithoautotrophic community of seasonally hypoxic sediments.

scholarly journals Comparative Genome Analysis of the Genus Thiothrix Involving Three Novel Species, Thiothrix subterranea sp. nov. Ku-5, Thiothrix litoralis sp. nov. AS and “Candidatus Thiothrix anitrata” sp. nov. A52, Revealed the Conservation of the Pathways of Dissimilatory Sulfur Metabolism and Variations in the Genetic Inventory for Nitrogen Metabolism and Autotrophic Carbon Fixation

2021 ◽  
Vol 12 ◽  
Author(s):  
Nikolai V. Ravin ◽  
Tatyana S. Rudenko ◽  
Dmitry D. Smolyakov ◽  
Alexey V. Beletsky ◽  
Andrey L. Rakitin ◽  
...  
Keyword(s):  
Core Genome ◽  
Carbon Fixation ◽  
Tricarboxylic Acid Cycle ◽  
Sulfur Metabolism ◽  
Sulfide Oxidation ◽  
Calvin Cycle ◽  
Sulfur Oxidation ◽  
Rrna Gene ◽  
Reduced Sulfur Compounds ◽  
Hybridization Data

Two strains of filamentous, colorless sulfur bacteria were isolated from bacterial fouling in the outflow of hydrogen sulfide-containing waters from a coal mine (Thiothrix sp. Ku-5) and on the seashore of the White Sea (Thiothrix sp. AS). Metagenome-assembled genome (MAG) A52 was obtained from a sulfidic spring in the Volgograd region, Russia. Phylogenetic analysis based on the 16S rRNA gene sequences showed that all genomes represented the genus Thiothrix. Based on their average nucleotide identity and digital DNA-DNA hybridization data these new isolates and the MAG represent three species within the genus Thiothrix with the proposed names Thiothrix subterranea sp. nov. Ku-5T, Thiothrix litoralis sp. nov. AST, and “Candidatus Thiothrix anitrata” sp. nov. A52. The complete genome sequences of Thiothrix fructosivorans QT and Thiothrix unzii A1T were determined. Complete genomes of seven Thiothrix isolates, as well as two MAGs, were used for pangenome analysis. The Thiothrix core genome consisted of 1,355 genes, including ones for the glycolysis, the tricarboxylic acid cycle, the aerobic respiratory chain, and the Calvin cycle of carbon fixation. Genes for dissimilatory oxidation of reduced sulfur compounds, namely the branched SOX system (SoxAXBYZ), direct (soeABC) and indirect (aprAB, sat) pathways of sulfite oxidation, sulfur oxidation complex Dsr (dsrABEFHCEMKLJONR), sulfide oxidation systems SQR (sqrA, sqrF), and FCSD (fccAB) were found in the core genome. Genomes differ in the set of genes for dissimilatory reduction of nitrogen compounds, nitrogen fixation, and the presence of various types of RuBisCO.

scholarly journals A Comparative Quantitative Proteomic Study Identifies New Proteins Relevant for Sulfur Oxidation in the Purple Sulfur Bacterium Allochromatium vinosum

2014 ◽  
Vol 80 (7) ◽  
pp. 2279-2292 ◽  
Author(s):  
Thomas Weissgerber ◽  
Marc Sylvester ◽  
Lena Kröninger ◽  
Christiane Dahl
Keyword(s):  
Sulfur Metabolism ◽  
Sulfur Oxidation ◽  
Hypothetical Protein ◽  
Mrna Levels ◽  
Reduced Sulfur Compounds ◽  
Allochromatium Vinosum ◽  
Purple Sulfur Bacterium ◽  
Content Type ◽  
Protein Levels ◽  
New Genes

ABSTRACTIn the present study, we compared the proteome response ofAllochromatium vinosumwhen growing photoautotrophically in the presence of sulfide, thiosulfate, and elemental sulfur with the proteome response when the organism was growing photoheterotrophically on malate. Applying tandem mass tag analysis as well as two-dimensional (2D) PAGE, we detected 1,955 of the 3,302 predicted proteins by identification of at least two peptides (59.2%) and quantified 1,848 of the identified proteins. Altered relative protein amounts (≥1.5-fold) were observed for 385 proteins, corresponding to 20.8% of the quantifiedA. vinosumproteome. A significant number of the proteins exhibiting strongly enhanced relative protein levels in the presence of reduced sulfur compounds are well documented essential players during oxidative sulfur metabolism, e.g., the dissimilatory sulfite reductase DsrAB. Changes in protein levels generally matched those observed for the respective relative mRNA levels in a previous study and allowed identification of new genes/proteins participating in oxidative sulfur metabolism. One gene cluster (hyd; Alvin_2036-Alvin_2040) and one hypothetical protein (Alvin_2107) exhibiting strong responses on both the transcriptome and proteome levels were chosen for gene inactivation and phenotypic analyses of the respective mutant strains, which verified the importance of the so-called Isp hydrogenase supercomplex for efficient oxidation of sulfide and a crucial role of Alvin_2107 for the oxidation of sulfur stored in sulfur globules to sulfite. In addition, we analyzed the sulfur globule proteome and identified a new sulfur globule protein (SgpD; Alvin_2515).

scholarly journals Acidity and sulfur oxidation intermediate concentrations controlled by O2-driven partitioning of sulfur oxidizing bacteria in a mine tailings impoundment

2021 ◽  
Author(s):  
Kelly J Whaley-Martin ◽  
Lin-Xing Chen ◽  
Tara Colebrander Nelson ◽  
Jay Gordon ◽  
Rose Kantor ◽  
...  
Keyword(s):  
Mine Tailings ◽  
Niche Partitioning ◽  
Sulfur Oxidation ◽  
Reduced Sulfur Compounds ◽  
Rna Detection ◽  
Anoxic Waters ◽  
Tailings Impoundment ◽  
Global Environmental ◽  
Sulfur Oxidizing ◽  
Sulfur Oxidizing Bacteria

Acidification of freshwater in mining impacted areas is a major global environmental problem catalyzed by sulfur-oxidizing bacteria (SOB). To date, little is known about the active bacteria in mine tailings impoundments and their environmental niches. Here, biological sulfur oxidation was investigated over four years in a mine tailings impoundment, integrating sulfur geochemistry, genome-resolved metagenomics and metatranscriptomics. We demonstrated oxygen driven niche partitioning of SOB and their metabolic pathways that explain acidity generation and thiosulfate persistence. Four chemolithoautotrophic SOB, Halothiobacillus, Thiobacillus, Sulfuricurvum and Sediminibacterium comprised 37% to 73% of the analyzed communities. The impoundment waters alternated between the dominance of Halothiobacillus versus a Thiobacillus, Halothiobacillus, Sulfuricurvum and Sediminibacterium consortia. Halothiobacillus dominance was associated with lower pH values (~4.3), higher [H+]/[SO42-] and lower [S2O32-], collectively indicative of extensive sulfur oxidation. Halothiobacillus, which couple sulfur oxidation via the Sox pathway to aerobic respiration or NO2- reduction, were present throughout the depth profile, yet their expression of sox genes occurred only in upper highly oxygenated waters. Conversely, when consortia of Thiobacillus, Halothiobacillus, Sulfuricurvum and Sediminibacterium dominated, recycling/disproportionating reactions were more prevalent. Thiobacillus, which dominated deeper micro-oxic/anoxic waters, oxidized sulfur primarily through the rDSR pathway, coupled to NO3-/NO2- reduction, resulting in lower [H+]/[SO42-] and higher [S2O32-] relative to upper waters. These field results mirror the Sox/rDSR-geochemical patterns of experimental SOB enrichments and reveal opportunities for biological treatments of recalcitrant reduced sulfur compounds, as well as gene-based monitoring and in situ RNA detection to predict the onset of problematic geochemistry.

scholarly journals The Heterotrophic Bacterium Cupriavidus pinatubonensis JMP134 Oxidizes Sulfide to Sulfate with Thiosulfate as a Key Intermediate

2020 ◽  
Vol 86 (22) ◽  
Author(s):  
Yufeng Xin ◽  
Rui Gao ◽  
Feifei Cui ◽  
Chuanjuan Lü ◽  
Honglei Liu ◽  
...  
Keyword(s):  
Gene Deletion ◽  
Heterotrophic Bacteria ◽  
Heterotrophic Bacterium ◽  
Sulfide Oxidation ◽  
Sulfur Oxidation ◽  
Content Type ◽  
Sulfide:Quinone Oxidoreductase ◽  
Main Pathway ◽  
Cell Assays ◽  
Sulfur Oxidizing

ABSTRACT Heterotrophic bacteria actively participate in the biogeochemical cycle of sulfur on Earth. The heterotrophic bacterium Cupriavidus pinatubonensis JMP134 contains several enzymes involved in sulfur oxidation, but how these enzymes work together to oxidize sulfide in the bacterium has not been studied. Using gene-deletion and whole-cell assays, we determined that the bacterium uses sulfide:quinone oxidoreductase to oxidize sulfide to polysulfide, which is further oxidized to sulfite by persulfide dioxygenase. Sulfite spontaneously reacts with polysulfide to produce thiosulfate. The sulfur-oxidizing (Sox) system oxidizes thiosulfate to sulfate. Flavocytochrome c sulfide dehydrogenase enhances thiosulfate oxidation by the Sox system but couples with the Sox system for sulfide oxidation to sulfate in the absence of sulfide:quinone oxidoreductase. Thus, C. pinatubonensis JMP134 contains a main pathway and a contingent pathway for sulfide oxidation. IMPORTANCE We establish a new pathway of sulfide oxidation with thiosulfate as a key intermediate in Cupriavidus pinatubonensis JMP134. The bacterium mainly oxidizes sulfide by using sulfide:quinone oxidoreductase, persulfide dioxygenase, and the Sox system with thiosulfate as a key intermediate. Although the purified and reconstituted Sox system oxidizes sulfide, its rate of sulfide oxidation in C. pinatubonensis JMP134 is too low to be physiologically relevant. The findings reveal how these sulfur-oxidizing enzymes participate in sulfide oxidation in a single bacterium.

scholarly journals Sulfide Consumption in Sulfurimonas denitrificans and Heterologous Expression of Its Three Sulfide-Quinone Reductase Homologs

2016 ◽  
Vol 198 (8) ◽  
pp. 1260-1267 ◽  
Author(s):  
Yuchen Han ◽  
Mirjam Perner
Keyword(s):  
Experimental Evidence ◽  
Rhodobacter Capsulatus ◽  
Sulfide Oxidation ◽  
Quinone Reductase ◽  
Good Growth ◽  
Reduced Sulfur Compounds ◽  
Content Type ◽  
Type Iii ◽  
Sulfur Oxidizing ◽  
Bacterial Type

ABSTRACTSulfurimonas denitrificansis a sulfur-oxidizing epsilonproteobacterium. It has been reported to grow with sulfide and to harbor genes that encode sulfide-quinone reductases (SQRs) (catalyze sulfide oxidation). However, the actual sulfide concentrations at whichS. denitrificansgrows and whether its SQRs are functional remain enigmatic. Here, we illustrate the sulfide concentrations at whichS. denitrificansexhibits good growth, namely, 0.18 mM to roughly 1.7 mM. Around 2.23 mM, sulfide appears to inhibit growth.S. denitrificansharbors three SQR homolog genes on its genome (Suden_2082 for type II SQR, Suden_1879 for type III SQR, and Suden_619 for type IV SQR). They are all transcribed inS. denitrificans. According to our experiments, they appear to be loosely bound to the membrane. Each individualS. denitrificansSQR was heterologously expressed in theRhodobacter capsulatusSB1003sqrdeletion mutant, and all exhibited SQR activities individually. This suggests that all of these three genes encode functional SQRs. This study also provides the first experimental evidence of a functional bacterial type III SQR.IMPORTANCEAlthough the epsilonproteobacteriumSulfurimonas denitrificanshas been described as using many reduced sulfur compounds as electron donors, there is little knowledge about its growth with sulfide. In many bacteria, the sulfide-quinone reductase (SQR) is responsible for catalyzing sulfide oxidation.S. denitrificanshas an array of different types ofsqrgenes on its genome and so do several other sulfur-oxidizingEpsilonproteobacteria. However, whether these SQRs are functional has remained unknown. Here, we shed light on sulfide metabolism inS. denitrificans. Our study provides the first experimental evidence of active epsilonproteobacterial SQRs and also gives the first report of a functional bacterial type III SQR.

scholarly journals Faecalicoccus acidiformans gen. nov., sp. nov., isolated from the chicken caecum, and reclassification of Streptococcus pleomorphus (Barnes et al. 1977), Eubacterium biforme (Eggerth 1935) and Eubacterium cylindroides (Cato et al. 1974) as Faecalicoccus pleomorphus comb. nov., Holdemanella biformis gen. nov., comb. nov. and Faecalitalea cylindroides gen. nov., comb. nov., respectively, within the family Erysipelotrichaceae

2014 ◽  
Vol 64 (Pt_11) ◽  
pp. 3877-3884 ◽  
Author(s):  
Celine De Maesschalck ◽  
Filip Van Immerseel ◽  
Venessa Eeckhaut ◽  
Siegrid De Baere ◽  
Margo Cnockaert ◽  
...  
Keyword(s):  
16S Rrna ◽  
16S Rrna Gene ◽  
Type Species ◽  
Gene Sequence ◽  
Sequence Similarity ◽  
16S Rrna Gene Sequence ◽  
Rrna Gene ◽  
Rrna Gene Sequence ◽  
Content Type ◽  
Link Type

Strains LMG 27428T and LMG 27427 were isolated from the caecal content of a chicken and produced butyric, lactic and formic acids as major metabolic end products. The genomic DNA G+C contents of strains LMG 27428T and LMG 27427 were 40.4 and 38.8 mol%. On the basis of 16S rRNA gene sequence similarity, both strains were most closely related to the generically misclassified Streptococcus pleomorphus ATCC 29734T. Strain LMG 27428T could be distinguished from S. pleomorphus ATCC 29734T based on production of more lactic acid and less formic acid in M2GSC medium, a higher DNA G+C content and the absence of activities of acid phosphatase and leucine, arginine, leucyl glycine, pyroglutamic acid, glycine and histidine arylamidases, while strain LMG 27428 was biochemically indistinguishable from S. pleomorphus ATCC 29734T. The novel genus Faecalicoccus gen. nov. within the family Erysipelotrichaceae is proposed to accommodate strains LMG 27428T and LMG 27427. Strain LMG 27428T ( = DSM 26963T) is the type strain of Faecalicoccus acidiformans sp. nov., and strain LMG 27427 ( = DSM 26962) is a strain of Faecalicoccus pleomorphus comb. nov. (type strain LMG 17756T = ATCC 29734T = DSM 20574T). Furthermore, the nearest phylogenetic neighbours of the genus Faecalicoccus are the generically misclassified Eubacterium cylindroides DSM 3983T (94.4 % 16S rRNA gene sequence similarity to strain LMG 27428T) and Eubacterium biforme DSM 3989T (92.7 % 16S rRNA gene sequence similarity to strain LMG 27428T). We present genotypic and phenotypic data that allow the differentiation of each of these taxa and propose to reclassify these generically misnamed species of the genus Eubacterium formally as Faecalitalea cylindroides gen. nov., comb. nov. and Holdemanella biformis gen. nov., comb. nov., respectively. The type strain of Faecalitalea cylindroides is DSM 3983T = ATCC 27803T = JCM 10261T and that of Holdemanella biformis is DSM 3989T = ATCC 27806T = CCUG 28091T.

Patulibacter medicamentivorans sp. nov., isolated from activated sludge of a wastewater treatment plant

2013 ◽  
Vol 63 (Pt_7) ◽  
pp. 2588-2593 ◽  
Author(s):  
Bárbara Almeida ◽  
Ivone Vaz-Moreira ◽  
Peter Schumann ◽  
Olga C. Nunes ◽  
Gilda Carvalho ◽  
...  
Keyword(s):  
Wastewater Treatment ◽  
Sequence Analysis ◽  
Type Species ◽  
Gene Sequence ◽  
Treatment Plant ◽  
Rrna Gene ◽  
Rrna Gene Sequence ◽  
Content Type ◽  
Link Type ◽  
Gene Sequence Analysis

A Gram-positive, aerobic, non-motile, non-endospore-forming rod-shaped bacterium with ibuprofen-degrading capacity, designated strain I11T, was isolated from activated sludge from a wastewater treatment plant. The major respiratory quinone was demethylmenaquinone DMK-7, C18 : 1 cis9 was the predominant fatty acid, phosphatidylglycerol was the predominant polar lipid, the cell wall contained meso-diaminopimelic acid as the diagnostic diamino acid and the G+C content of the genomic DNA was 74.1 mol%. On the basis of 16S rRNA gene sequence analysis, the closest phylogenetic neighbours of strain I11T were Patulibacter ginsengiterrae CECT 7603T (96.8 % similarity), Patulibacter minatonensis DSM 18081T (96.6 %) and Patulibacter americanus DSM 16676T (96.6 %). Phenotypic characterization supports the inclusion of strain I11T within the genus Patulibacter (phylum Actinobacteria) . However, distinctive features and 16S rRNA gene sequence analysis suggest that is represents a novel species, for which the name Patulibacter medicamentivorans sp. nov. is proposed. The type strain is I11T ( = DSM 25962T = CECT 8141T).

scholarly journals Coupling of Dimethylsulfide Oxidation to Biomass Production by a Marine Flavobacterium

2011 ◽  
Vol 77 (9) ◽  
pp. 3137-3140 ◽  
Author(s):  
David H. Green ◽  
Damodar M. Shenoy ◽  
Mark C. Hart ◽  
Angela D. Hatton
Keyword(s):  
Dimethyl Sulfoxide ◽  
Biomass Production ◽  
Sulfur Oxidation ◽  
Microbial Metabolism ◽  
Compatible Solute ◽  
Content Type

ABSTRACTDimethylsulfide (DMS) is an important climatically active gas. In the sea, DMS is produced primarily by microbial metabolism of the compatible solute dimethylsulfoniopropionate. Laboratory growth ofBacteroideteswith DMS resulted in its oxidation to dimethyl sulfoxide but only in the presence of glucose. We hypothesized that electrons liberated from sulfur oxidation were used to augment biomass production.

scholarly journals Differential RNA Sequencing Implicates Sulfide as the Master Regulator of S 0 Metabolism in Chlorobaculum tepidum and Other Green Sulfur Bacteria

2017 ◽  
Vol 84 (3) ◽  
Author(s):  
Jacob M. Hilzinger ◽  
Vidhyavathi Raman ◽  
Kevin E. Shuman ◽  
Brian J. Eddie ◽  
Thomas E. Hanson
Keyword(s):  
Gene Expression ◽  
Elemental Sulfur ◽  
Green Sulfur Bacteria ◽  
Electron Donors ◽  
Reduced Sulfur Compounds ◽  
Promoter Elements ◽  
Content Type ◽  
Sulfur Bacteria ◽  
Chlorobaculum Tepidum ◽  
Green Sulfur

ABSTRACT The green sulfur bacteria ( Chlorobiaceae ) are anaerobes that use electrons from reduced sulfur compounds (sulfide, S 0 , and thiosulfate) as electron donors for photoautotrophic growth. Chlorobaculum tepidum , the model system for the Chlorobiaceae , both produces and consumes extracellular S 0 globules depending on the availability of sulfide in the environment. These physiological changes imply significant changes in gene regulation, which has been observed when sulfide is added to Cba. tepidum growing on thiosulfate. However, the underlying mechanisms driving these gene expression changes, i.e., the specific regulators and promoter elements involved, have not yet been defined. Here, differential RNA sequencing (dRNA-seq) was used to globally identify transcript start sites (TSS) that were present during growth on sulfide, biogenic S 0 , and thiosulfate as sole electron donors. TSS positions were used in combination with RNA-seq data from cultures growing on these same electron donors to identify both basal promoter elements and motifs associated with electron donor-dependent transcriptional regulation. These motifs were conserved across homologous Chlorobiaceae promoters. Two lines of evidence suggest that sulfide-mediated repression is the dominant regulatory mode in Cba. tepidum . First, motifs associated with genes regulated by sulfide overlap key basal promoter elements. Second, deletion of the Cba. tepidum 1277 ( CT1277 ) gene, encoding a putative regulatory protein, leads to constitutive overexpression of the sulfide:quinone oxidoreductase CT1087 in the absence of sulfide. The results suggest that sulfide is the master regulator of sulfur metabolism in Cba. tepidum and the Chlorobiaceae . Finally, the identification of basal promoter elements with differing strengths will further the development of synthetic biology in Cba. tepidum and perhaps other Chlorobiaceae . IMPORTANCE Elemental sulfur is a key intermediate in biogeochemical sulfur cycling. The photoautotrophic green sulfur bacterium Chlorobaculum tepidum either produces or consumes elemental sulfur depending on the availability of sulfide in the environment. Our results reveal transcriptional dynamics of Chlorobaculum tepidum on elemental sulfur and increase our understanding of the mechanisms of transcriptional regulation governing growth on different reduced sulfur compounds. This report identifies genes and sequence motifs that likely play significant roles in the production and consumption of elemental sulfur. Beyond this focused impact, this report paves the way for the development of synthetic biology in Chlorobaculum tepidum and other Chlorobiaceae by providing a comprehensive identification of promoter elements for control of gene expression, a key element of strain engineering.

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