Fulvimarina pelagi gen. nov., sp. nov., a marine bacterium that forms a deep evolutionary lineage of descent in the order "Rhizobiales".

Three brownish-yellow bacterial strains were isolated from the western Sargasso Sea by high-throughput culturing methods and characterized by polyphasic approaches. All isolates were Gram-negative, strictly aerobic, chemoheterotrophic, non-motile short rods that contained carotenoid pigments. Phylogenetic analyses based on 16S rRNA gene sequences, DNA-DNA hybridization and DNA G+C content, along with phenotypic characteristics, revealed that they belonged to the same species. The strains utilized a wide range of substrates, including pentoses, hexoses, oligosaccharides, sugar alcohols, organic acids and amino acids, as sole carbon sources. The DNA G+C content of the isolates ranged from 57.6 to 59.9 mol%. The predominant cellular fatty acid constituent was C(18 : 1)omega7c, whilst C(16 : 0), C(18 : 0) and C(19 : 0)omega8c cyclo were also abundant. The organism related most closely to these strains, as determined by 16S rDNA sequence comparison, was the recently described species Aurantimonas coralicida (93.3-93.8 % similarity). Phylogenetic analyses indicated that the strains formed a distinct and deep evolutionary lineage of descent, together with A. coralicida, within the order "Rhizobiales" of the alpha-Proteobacteria. This lineage could not be associated with any of the ten known families in the order "Rhizobiales". From polyphasic evidence, it is proposed that the strains be placed into a novel genus and species, Fulvimarina pelagi gen. nov., sp. nov. (type strain, HTCC2506(T)=ATCC BAA-666(T)=KCTC 12091(T)=DSM 15513(T)).

Methylocapsa acidiphila gen. nov., sp. nov., a novel methane-oxidizing and dinitrogen-fixing acidophilic bacterium from Sphagnum bog.

A novel genus and species, Methylocapsa acidiphila gen. nov., sp. nov., are proposed for a methane-oxidizing bacterium isolated from an acidic Sphagnum peat bog. This bacterium, designated strain B2T, represents aerobic, gram-negative, colourless, non-motile, curved coccoids that form conglomerates covered by an extracellular polysaccharide matrix. The cells use methane and methanol as sole sources of carbon and energy and utilize the serine pathway for carbon assimilation. Strain B2T is a moderately acidophilic organism with growth between pH 4.2 and 7.2 and at temperatures from 10 to 30 degrees C. The cells possess a well-developed system of intracytoplasmic membranes (ICM) packed in parallel on only one side of the cell membrane. This type of ICM structure represents a novel arrangement, which was termed type III. The resting cells are Azotobacter-type cysts. Strain B2T is capable of atmospheric nitrogen fixation; it possesses particulate methane monooxygenase and does not express soluble methane monooxygenase. The major phospholipid fatty acid is 18:1omega7c and the major phospholipids are phosphatidylglycerols. The G+C content of the DNA is 63.1 mol%. This bacterium belongs to the alpha-subclass of the Proteobacteria and is most closely related to the acidophilic methanotroph Methylocella palustris KT (97.3% 16S rDNA sequence similarity). However, the DNA-DNA hybridization value between strain B2T and Methylocella palustris K(T) is only 7%. Thus, strain B2T is proposed to comprise a novel genus and species, Methylocapsa acidiphila gen. nov., sp. nov. Strain B2T (= DSM 13967T = NCIMB 13765T) is the type strain.

Identification and characterization of a novel Bradyrhizobium japonicum gene involved in host-specific nitrogen fixation.

To understand the genetic mechanism of host specificity in the interaction between rhizobia and their hosts, it is important to identify genes that influence both early and late steps in symbiotic development. This paper focuses on the little-understood genetics of host-specific nitrogen fixation. A deletion mutant of Bradyrhizobium japonicum, strain NAD163, was found to induce effective, nitrogen-fixing nodules on soybean and siratro plants but produced ineffective nodules on cowpea plants. Additional transposon and deletion mutants defined a small region that conferred this phenotype, and this region was sequenced to identify two putative open reading frames (ORFs). Data indicate that only one of these ORFs is detectable in bacteroids. This ORF was termed hsfA, with a predicted protein product of 11 kDa. The transcriptional start site of hsfA was determined and found to coincide with a predicted RpoN-dependent promoter. Microscopic studies of nodules induced by the wild type and hsfA mutants on cowpea and soybean plants indicate that the cowpea mutant nodules are slow to develop. The data indicate that hsfA appears to play a crucial role in bacteroid development on cowpea but does not appear to be essential for nitrogen fixation on the other hosts tested.