Heeji Hong

Hydrogen peroxide detoxification is a key mechanism for growth of ammonia-oxidizing archaea

Significance Ammonia-oxidizing archaea (AOA) are major players in global nitrogen cycling, but the AOA carbon-nutrition paradigm is poorly understood. Once considered strict autotrophs, AOA also have been reported to assimilate organic carbon. We used a marine AOA isolate to test hypotheses about the role of fixed carbon in AOA nutrition. Results were confirmed with tests with four additional marine and terrestrial AOA. We discovered that α-keto acids (pyruvate, oxaloacetate) were not directly incorporated into AOA cells. Instead, the α-keto acids functioned as chemical scavengers that detoxified intracellularly produced H2O2 during ammonia oxidation. H2O2 toxicity was also counteracted by co-inoculating the AOA with bacteria harboring catalases. Thus, H2O2 toxicity in AOA may be an evolutionary force controlling AOA communities and global ammonia cycling. Ammonia-oxidizing archaea (AOA), that is, members of the Thaumarchaeota phylum, occur ubiquitously in the environment and are of major significance for global nitrogen cycling. However, controls on cell growth and organic carbon assimilation by AOA are poorly understood. We isolated an ammonia-oxidizing archaeon (designated strain DDS1) from seawater and used this organism to study the physiology of ammonia oxidation. These findings were confirmed using four additional Thaumarchaeota strains from both marine and terrestrial habitats. Ammonia oxidation by strain DDS1 was enhanced in coculture with other bacteria, as well as in artificial seawater media supplemented with α-keto acids (e.g., pyruvate, oxaloacetate). α-Keto acid-enhanced activity of AOA has previously been interpreted as evidence of mixotrophy. However, assays for heterotrophic growth indicated that incorporation of pyruvate into archaeal membrane lipids was negligible. Lipid carbon atoms were, instead, derived from dissolved inorganic carbon, indicating strict autotrophic growth. α-Keto acids spontaneously detoxify H2O2 via a nonenzymatic decarboxylation reaction, suggesting a role of α-keto acids as H2O2 scavengers. Indeed, agents that also scavenge H2O2, such as dimethylthiourea and catalase, replaced the α-keto acid requirement, enhancing growth of strain DDS1. In fact, in the absence of α-keto acids, strain DDS1 and other AOA isolates were shown to endogenously produce H2O2 (up to ∼4.5 μM), which was inhibitory to growth. Genomic analyses indicated catalase genes are largely absent in the AOA. Our results indicate that AOA broadly feature strict autotrophic nutrition and implicate H2O2 as an important factor determining the activity, evolution, and community ecology of AOA ecotypes.

Rhodanobacter aciditrophus sp. nov., an acidophilic bacterium isolated from mine wastewater.

A novel strain (designated sjH1T), characterized as aerobic, Gram-stain-negative, oxidase-positive, catalase-negative, motile and rod-shaped, was isolated from mine wastewater. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain sjH1T belonged to the genus Rhodanobacter. Strain sjH1T was closely related to Rhodanobacter thiooxydans LCS2T (98.0% 16S rRNA gene sequence similarity), Rhodanobacter denitrificans 2APBS1T (97.7%), Rhodanobacter soli DCY45T (97.2%) and Rhodanobacter caeni MJ01T (97.0%). The DNA G+C content of strain sjH1T was 69.2 mol%. DNA-DNA relatedness ( < 60%) indicated that strain sjH1T represents a distinct species that is separate from R. thiooxydans, R. denitrificans, R. soli and R. caeni. The major ubiquinone was Q-8, and major fatty acids were summed feature 9 (iso-C17 : 1ω9c and/or C16 : 0 10-methyl), iso-C15 : 0, iso-C17 : 0, iso-C16 : 0 and anteiso-C15 : 0. Based on data from this polyphasic study, it is proposed that sjH1T ( = KCTC 42660T = JCM 30774T) is the type strain of a novel species, Rhodanobacter aciditrophus sp. nov.

Draft genome sequence of an aromatic compound‐degrading bacterium, Desulfobacula sp. TS, belonging to the Deltaproteobacteria

Herein, we report a high-quality draft genome sequence of an uncultivated aromatic compound-degrading bacterium, obtained by the stable isotope probing method from a sulfate-reducing microcosm from an oil-contaminated tidal flat. The obtained genome was closely related with that of Desulfobacula toluolica Tol2. Abundant genes for various anaerobic aromatic degradation pathways and putative mobile elements were detected in the genome.

Calculibacillus koreensis gen. nov., sp. nov., an anaerobic Fe(III)-reducing bacterium isolated from sediment of mine tailings

A strictly anaerobic bacterium, strain B5T, was isolated from sediment of an abandoned coal mine in Taebaek, Republic of Korea. Cells of strain B5T were non-spore-forming, straight, Gram-positive rods. The optimum pH and temperature for growth were pH 7.0 and 30°C, respectively, while the strain was able to grow within pH and temperature ranges of 5.5–7.5 and 25–45°C, respectively. Growth of strain B5T was observed at NaCl concentrations of 0 to 6.0% (w/v) with an optimum at 3.0–4.0% (w/v). The polar lipids consisted of phosphatidylethanolamine, phosphatidylglycerol, an unknown phospholipid and three unknown polar lipids. Strain B5T grew anaerobically by reducing nitrate, nitrite, ferric-citrate, ferric-nitrilotriacetate, elemental sulfur, thiosulfate, and anthraquinone-2-sulfonate in the presence of proteinaceous compounds, organic acids, and carbohydrates as electron donors. The isolate was not able to grow by fermentation. Strain B5T did not grow under aerobic or microaerobic conditions. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain B5T is most closely related to the genus Tepidibacillus (T. fermentans STGHT; 96.3%) and Vulcanibacillus (V. modesticaldus BRT; 94.6%). The genomic DNA G+C content (36.9 mol%) of strain B5T was higher than those of T. fermentans STGHT (34.8 mol%) and V. modesticaldus BRT (34.5 mol%). Based on its phenotypic, chemotaxonomic, and phylogenetic properties, we describe a new species of a novel genus Calculibacillus, represented by strain B5T (=KCTC 15397T =JCM 19989T), for which we propose the name Calculibacillus koreensis gen. nov., sp. nov.

Anaerosolibacter carboniphilus gen. nov., sp. nov., a strictly anaerobic iron-reducing bacterium isolated from coal-contaminated soil

A strictly anaerobic, mesophilic, iron-reducing bacterial strain, IRF19(T), was isolated from coal-contaminated soil in the Republic of Korea. IRF19(T) cells were straight, rod-shaped, Gram-staining-negative and motile by means of flagella. The optimum pH and temperature for their growth were determined to be pH 7.5-8.0 and 40 °C, while the optimum range was pH 6.5-10.0 and 20-45 °C, respectively. Strain IRF19(T) did not require NaCl for growth but it tolerated up to 2% (w/v). Growth was observed with yeast extract, D-glucose, D-fructose, D-ribose, D-mannitol, D-mannose, L-serine, L-alanine and L-isoleucine. Fe(III), elemental sulfur, thiosulfate and sulfate were used as electron acceptors. Phylogenetic analysis based on the 16S rRNA gene sequences indicated that strain IRF19(T) is affiliated to the family Clostridiaceae and is most closely related to Salimesophilobacter vulgaris Zn2(T) (93.5% similarity), Geosporobacter subterraneus VNs68(T) (93.2%) and Thermotalea metallivorans B2-1(T) (92.3%). The major cellular fatty acids of strain IRF19(T) were C14 : 0, iso-C15 : 0 and C16 : 0, and the profile was distinct from those of the closely related species. The major respiratory quinone of strain IRF19(T) was menaquinone MK-5 (V-H2). The main polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, an unknown phospholipid and two unknown polar lipids. The G+C content of the genomic DNA of strain IRF19(T) was determined to be 37.4 mol%. On the basis of phenotypic, chemotaxonomic and phylogenetic results, strain IRF19(T) is considered to represent a novel species of a novel genus of the family Clostridiaceae , for which we propose the name Anaerosolibacter carboniphilus gen. nov., sp. nov., with the type strain IRF19(T) ( =KCTC 15396(T) =JCM 19988(T)).

Comparative genomic analysis of Geosporobacter ferrireducens and its versatility of anaerobic energy metabolism

Members of the family Clostridiaceae within phylum Firmicutes are ubiquitous in various iron-reducing environments. However, genomic data on iron-reducing bacteria of the family Clostridiaceae, particularly regarding their environmental distribution, are limited. Here, we report the analysis and comparison of the genomic properties of Geosporobacter ferrireducens IRF9, a strict anaerobe that ferments sugars and degrades toluene under iron-reducing conditions, with those of the closely related species, Geosporobacter subterraneus DSM 17957. Putative alkyl succinate synthase-encoding genes were observed in the genome of strain IRF9 instead of the typical benzyl succinate synthase-encoding genes. Canonical genes associated with iron reduction were not observed in either genome. The genomes of strains IRF9 and DMS 17957 harbored genes for acetogenesis, that encode two types of Rnf complexes mediating the translocation of H+ and Na+ ions, respectively. Strain IRF9 harbored two different types of ATPases (Na+-dependent F-type ATPase and H+-dependent V-type ATPase), which enable full exploitation of ion gradients. The versatile energy conservation potential of strain IRF9 promotes its survival in various environmental conditions.