Denitrification by Pseudomonas stutzeri coupled with CO2 reduction by Sporomusa ovata with hydrogen as an electron donor assisted by solid-phase humin.

A co-culture system comprising an acetogenic bacterium, Sporomusa ovata DSMZ2662, and a denitrifying bacterium, Pseudomonas stutzeri JCM20778, enabled denitrification using H2 as the sole external electron donor and CO2 as the sole external carbon source. Acetate produced by S. ovata supported the heterotrophic denitrification of P. stutzeri. A nitrogen balance study showed the reduction of nitrate to nitrogen gas without the accumulation of nitrite and nitrous oxide in the co-culture system. S. ovata did not show nitrate reduction to ammonium in the co-culture system. Significant proportions of the consumed H2 were utilized for denitrification: 79.9 ± 4.6% in the co-culture system containing solid-phase humin and 62.9±11.1% in the humin-free co-culture system. The higher utilization efficiency of hydrogen in the humin-containing system was attributed to the higher denitrification activity of P. stutzeri under the acetate deficient conditions. The nitrogen removal rate of the humin-containing co-culture system reached 0.19 kg NO3(-)-N·m(-3)·d(-1). Stable denitrification activity for 61 days of successive sub-culturing suggested the robustness of this co-culture system. This study provides a novel strategy for the in situ enhancement of microbial denitrification.

Peptidoglycan remodeling and conversion of an inner membrane into an outer membrane during sporulation.

Two hallmarks of the Firmicute phylum, which includes the Bacilli and Clostridia classes, are their ability to form endospores and their "Gram-positive" single-membraned, thick-cell-wall envelope structure. Acetonema longum is part of a lesser-known family (the Veillonellaceae) of Clostridia that form endospores but that are surprisingly "Gram negative," possessing both an inner and outer membrane and a thin cell wall. Here, we present macromolecular resolution, 3D electron cryotomographic images of vegetative, sporulating, and germinating A. longum cells showing that during the sporulation process, the inner membrane of the mother cell is inverted and transformed to become the outer membrane of the germinating cell. Peptidoglycan persists throughout, leading to a revised, "continuous" model of its role in the process. Coupled with genomic analyses, these results point to sporulation as a mechanism by which the bacterial outer membrane may have arisen and A. longum as a potential "missing link" between single- and double-membraned bacteria.

Thermosinus carboxydivorans gen. nov., sp. nov., a new anaerobic, thermophilic, carbon-monoxide-oxidizing, hydrogenogenic bacterium from a hot pool of Yellowstone National Park.

A new anaerobic, thermophilic, facultatively carboxydotrophic bacterium, strain Nor1(T), was isolated from a hot spring at Norris Basin, Yellowstone National Park. Cells of strain Nor1(T) were curved motile rods with a length of 2.6-3 microm, a width of about 0.5 microm and lateral flagellation. The cell wall structure was of the Gram-negative type. Strain Nor1(T) was thermophilic (temperature range for growth was 40-68 degrees C, with an optimum at 60 degrees C) and neutrophilic (pH range for growth was 6.5-7.6, with an optimum at 6.8-7.0). It grew chemolithotrophically on CO (generation time, 1.15 h), producing equimolar quantities of H(2) and CO(2) according to the equation CO+H(2)O-->CO(2)+H(2). During growth on CO in the presence of ferric citrate or amorphous ferric iron oxide, strain Nor1(T) reduced ferric iron but produced H(2) and CO(2) at a ratio close to 1 : 1, and growth stimulation was slight. Growth on CO in the presence of sodium selenite was accompanied by precipitation of elemental selenium. Elemental sulfur, thiosulfate, sulfate and nitrate did not stimulate growth of strain Nor1(T) on CO and none of these chemicals was reduced. Strain Nor1(T) was able to grow on glucose, sucrose, lactose, arabinose, maltose, fructose, xylose and pyruvate, but not on cellobiose, galactose, peptone, yeast extract, lactate, acetate, formate, ethanol, methanol or sodium citrate. During glucose fermentation, acetate, H(2) and CO(2) were produced. Thiosulfate was found to enhance the growth rate and cell yield of strain Nor1(T) when it was grown on glucose, sucrose or lactose; in this case, acetate, H(2)S and CO(2) were produced. In the presence of thiosulfate or ferric iron, strain Nor1(T) was also able to grow on yeast extract. Lactate, acetate, formate and H(2) were not utilized either in the absence or in the presence of ferric iron, thiosulfate, sulfate, sulfite, elemental sulfur or nitrate. Growth was completely inhibited by penicillin, ampicillin, streptomycin, kanamycin and neomycin. The DNA G+C content of the strain was 51.7+/-1 mol%. Analysis of the 16S rRNA gene sequence revealed that strain Nor1(T) belongs to the Bacillus-Clostridium phylum of the Gram-positive bacteria. On the basis of the studied phenotypic and phylogenetic features, we propose that strain Nor1(T) be assigned to a new genus, Thermosinus gen. nov. The type species is Thermosinus carboxydivorans sp. nov. (type strain, Nor1(T)=DSM 14886(T)=VKM B-2281(T)).

Desulfosporomusa polytropa gen. nov., sp. nov., a novel sulfate-reducing bacterium from sediments of an oligotrophic lake.

Five strains of sulfate-reducing bacteria were isolated from the highest positive dilutions of a most probable number (MPN) series supplemented with lactate and inoculated with sediments from the oligotrophic Lake Stechlin. The isolates were endospore-forming and were motile by means of laterally inserted flagella. They stained Gram-negative and contained b-type cytochromes. CO difference spectra indicated the presence of P582 as a sulfite reductase. Phylogenetic analyses of the 16S rDNA sequences revealed that the isolates were very closely affiliated with the genus Sporomusa. However, sulfate and amorphous Fe(OH)(3), but not sulfite, elemental sulfur, MnO(2), or nitrate were used as terminal electron acceptors. Homoacetogenic growth was found with H(2)/CO(2) gas mixture, formate, methanol, ethanol, and methoxylated aromatic compounds. The strains grew autotrophically with H(2) plus CO(2) in the presence or absence of sulfate. Formate, butyrate, several alcohols, organic acids, carbohydrates, some amino acids, choline, and betaine were also utilized as substrates. The growth yield with lactate and sulfate as substrate was 7.0 g dry mass/mol lactate and thus two times higher than in sulfate-free fermenting cultures. All isolates were able to grow in a temperature range of 4-37 degrees C. Physiologically and by the presence of a Gram-negative cell wall, the new isolates resemble known Desulfosporosinus species. However, phylogenetically they are affiliated with the Gram-negative genus Sporomusa belonging to the Selenomonas subgroup of the Firmicutes. Therefore, the new isolates reveal a new phylogenetic lineage of sulfate-reducing bacteria. A new genus and species, Desulfosporomusa polytropa gen. nov., sp. nov. is proposed.