While cataloging cultivatable microbes from the airborne biological diversity of the atmosphere of the Regenerative Enclosed life-support Module Simulator (REMS) system at Marshall Space Flight Center, two strains that belong to one novel bacterial species were isolated. Based on 16S rRNA gene sequencing and the unique morphology and the taxonomic characteristics of these strains, it is shown that they belong to the family Intrasporangiaceae, related to the genus Tetrasphaera, with phylogenetic distances from any validly described species of the genus Tetrasphaera ranging from 96.71 to 97.76 percent.
The fatty acid profile supported the affiliation of these novel strains to the genus Tetrasphaera except for the presence of higher concentrations of octadecenoic acid (C18:0) and cis-9-octadecenoic acid (C18:1), which discriminates these strains from other valid species. In addition, DNA-DNA hybridization studies indicate that these strains belong to a novel species that could be readily distinguished from its nearest neighbor, Tetrasphaera japonica AMC 5116T, with less than 20 percent DNA relatedness. Physiological and biochemical tests show few phenotypic dissimilarities, but genotypic analysis allowed the differentiation of these gelatin-liquefying strains from previously reported strains. The name Tetrasphaera remsis sp. Nov. is proposed with the type strain 3-M5-R-4T (=ATCC BAA-1496T=CIP 109413T). The GenBank/EMBL/DDBJ accession numbers for the 16S rRNA gene sequence are DQ447774 and EF028236 for the strains 3-M5-R-4T and 3-M5-R-7, respectively.
The cells are Gram-positive, non-motile, cocci, in tetrad arrangement and clusters. Spore formation is not observed. The colonies are beige in color and convex with a glossy surface. The organisms are aerobic chemo- heterotrophic in nature. They do not reduce nitrate to nitrite. They show no anaerobic growth and do not ferment glucose. They are gelatin-liquefying and esculin hydrolyzed. Catalase and β- galactosidase are produced. The cells use D-glucose, D-mannose, D-mannitol, D-maltose, N-acetyl-glucosamine, and malate. Tests show that the cells do not assimilate the following compounds: L-arabinose, gluconate, capric acid, adipic acid, phenyl acetic acid, or citrate. Growth occurs at 15 to 45 ºC and at pH 6–9. The optimal growth temperature and pH are 25 ºC and 7, respectively.
No species of Tetrashpaera has ever been isolated from airborne samples. Previous discoveries have come from soil and activated sludge samples. As other species of this genus have demonstrated enhanced biological phosphorus removal activity, further tests are required to determine if this newly discovered species would have bioremediation applications.