Methylobacterium ajmalii sp. nov., Isolated From the International Space Station

Abstract

Four strains belonging to the family of <i>Methylobacteriaceae</i> were isolated from different locations on the International Space Station (ISS) across two consecutive flights. Of these, three were identified as Gram-negative, rod-shaped, catalase-positive, oxidase-positive, motile bacteria, designated as IF7SW-B2^T, IIF1SW-B5, and IIF4SW-B5, whereas the fourth was identified as <i>Methylorubrum rhodesianum</i>. The sequence similarity of these three ISS strains, designated as IF7SW-B2^T, IIF1SW-B5, and IIF4SW-B5, was <99.4% for 16S rRNA genes and <97.3% for <i>gyrB</i> gene, with the closest being <i>Methylobacterium indicum</i> SE2.11^T. Furthermore, the multi-locus sequence analysis placed these three ISS strains in the same clade of <i>M. indicum.</i> The average nucleotide identity (ANI) values of these three ISS strains were <93% and digital DNA-DNA hybridization (dDDH) values were <46.4% with any described <i>Methylobacterium</i> species. Based on the ANI and dDDH analyses, these three ISS strains were considered as novel species belonging to the genus <i>Methylobacterium.</i> The three ISS strains showed 100% ANI similarity and dDDH values with each other, indicating that these three ISS strains, isolated during various flights and from different locations, belong to the same species. These three ISS strains were found to grow optimally at temperatures from 25 to 30°C, pH 6.0 to 8.0, and NaCl 0 to 1%. Phenotypically, these three ISS strains resemble <i>M. aquaticum</i> and <i>M. terrae</i> since they assimilate similar sugars as sole carbon substrate when compared to other <i>Methylobacterium</i> species. Fatty acid analysis showed that the major fatty acid produced by the ISS strains are C₁₈ _: ₁-ω7<i>c</i> and C₁₈ _: ₁-ω6<i>c</i>. The predominant quinone was ubiquinone 10, and the major polar lipids were diphosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, and an unidentified lipid. Therefore, based on genomic, phylogenetic, biochemical, and fatty acid analyses, strains IF7SW-B2^T, IIF1SW-B5, and IIF4SW-B5, are assigned to a novel species within the genus <i>Methylobacterium</i>, and the name <i>Methylobacterium ajmalii</i> sp. nov. is proposed. The type strain is IF7SW-B2^T (NRRL B-65601^T and LMG 32165^T).