ABSTRACT
A novel non-phototrophic, marine, sulfur-oxidizing bacterium, strain S-1T, was isolated from a coastal salt marsh in Massachusetts, USA. Cells are Gram-stain-negative vibrios motile by means of a single polar unsheathed flagellum. S-1T is an obligate microaerophile with limited metabolic capacity. It grows chemolithoautotrophically utilizing sulfide and thiosulfate as electron donors, converting these compounds to sulfate, and the Calvin-Benson-Bassham cycle for carbon fixation. Cells of S-1T did not grow on any of a large number of organic carbon sources and there was no evidence for chemoorganoheterotrophic growth. Cells produced internal sulfur globules during growth on sulfide and thiosulfate. S-1T is strongly diazotrophic, as demonstrated by 15N2 fixation and acetylene reduction activity by cells when a fixed nitrogen source is absent from the growth medium. The marine nature of this organism is evident from its ability to grow in 10 to 100â% artificial seawater but not at lower concentrations and NaCl alone cannot substitute for sea salts. The major cellular fatty acids are C16â:â1ω7c, C16â:â0, and C18â:â1ω7c. Phosphatidylethanolamine and phosphatidylglycerol are the major polar lipids. Q8 is the only respiratory quinone. S-1T genomic DNA has a G+C content of 67.6 mol%. Based on its 16S rRNA gene sequence, S-1T shows the closest phylogenetic relationship to non-phototrophic species within the family Thioalkalispiraceae of the class Gammaproteobacteria. The name Endothiovibrio diazotrophicus is proposed for this organism, with S-1T as the type strain (ATCC BAA-1439T=JCM 17961T).
Subject(s)
Gammaproteobacteria/classification , Nitrogen Fixation , Phylogeny , Water Microbiology , Wetlands , Bacterial Typing Techniques , Base Composition , DNA, Bacterial/genetics , Fatty Acids/chemistry , Gammaproteobacteria/genetics , Gammaproteobacteria/isolation & purification , Massachusetts , Nitrogen/metabolism , Phospholipids/chemistry , RNA, Ribosomal, 16S/genetics , Sequence Analysis, DNA , Sulfur/metabolismABSTRACT
Vibrioid- to helical-shaped magnetotactic bacteria phylogenetically related to the genus Magnetospirillum were isolated in axenic cultures from a number of freshwater and brackish environments located in the southwestern United States. Based on 16S rRNA gene sequences, most of the new isolates represent new Magnetospirillum species or new strains of known Magnetospirillum species, while one isolate appears to represent a new genus basal to Magnetospirillum. Partial sequences of conserved mam genes, genes reported to be involved in the magnetosome and magnetosome chain formation, and form II of the ribulose-1,5-bisphosphate carboxylase/oxygenase gene (cbbM) were determined in the new isolates and compared. The cbbM gene was chosen for comparison because it is not involved in magnetosome synthesis; it is highly conserved and is present in all but possibly one of the genomes of the magnetospirilla and the new isolates. Phylogenies based on 16S rRNA, cbbM, and mam gene sequences were reasonably congruent, indicating that the genes involved in magnetotaxis were acquired by a common ancestor of the Magnetospirillum clade. However, in one case, magnetosome genes might have been acquired through horizontal gene transfer. Our results also extend the known diversity of the Magnetospirillum group and show that they are widespread in freshwater environments.
Subject(s)
Bacterial Proteins/genetics , Locomotion , Magnetics , Magnetospirillum/genetics , Phylogeny , Cluster Analysis , DNA, Bacterial/chemistry , DNA, Bacterial/genetics , DNA, Ribosomal/chemistry , DNA, Ribosomal/genetics , Gene Transfer, Horizontal , Magnetospirillum/isolation & purification , Magnetospirillum/physiology , Molecular Sequence Data , RNA, Ribosomal, 16S/genetics , Sequence Analysis, DNA , Southwestern United States , Water MicrobiologyABSTRACT
Two novel magnetotactic bacteria (MTB) were isolated from sediment and water collected from the Badwater Basin, Death Valley National Park and southeastern shore of the Salton Sea, respectively, and were designated as strains BW-2 and SS-5, respectively. Both organisms are rod-shaped, biomineralize magnetite, and are motile by means of flagella. The strains grow chemolithoautotrophically oxidizing thiosulfate and sulfide microaerobically as electron donors, with thiosulfate oxidized stoichiometrically to sulfate. They appear to utilize the Calvin-Benson-Bassham cycle for autotrophy based on ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) activity and the presence of partial sequences of RubisCO genes. Strains BW-2 and SS-5 biomineralize chains of octahedral magnetite crystals, although the crystals of SS-5 are elongated. Based on 16S rRNA gene sequences, both strains are phylogenetically affiliated with the Gammaproteobacteria class. Strain SS-5 belongs to the order Chromatiales; the cultured bacterium with the highest 16S rRNA gene sequence identity to SS-5 is Thiohalocapsa marina (93.0%). Strain BW-2 clearly belongs to the Thiotrichales; interestingly, the organism with the highest 16S rRNA gene sequence identity to this strain is Thiohalospira alkaliphila (90.2%), which belongs to the Chromatiales. Each strain represents a new genus. This is the first report of magnetite-producing MTB phylogenetically associated with the Gammaproteobacteria. This finding is important in that it significantly expands the phylogenetic diversity of the MTB. Physiology of these strains is similar to other MTB and continues to demonstrate their potential in nitrogen, iron, carbon and sulfur cycling in natural environments.
