Microbial Observatory (ISS-MO): Molecular characterization of Bacillus issensis sp. nov. isolated from various quarters of the International Space Station

As part of an ongoing effort to catalogue microbial communities inhabiting the International Space Station (ISS) crew-associated environmental samples were collected from the Japanese Kibo Russian and US research modules. Initial analysis based on 16S rRNA gene sequencing identified 11 Bacillus isolates (two from Kibo Japanese Experiment Module (JEM) four from US Segment Harmony Node 2 and five from Russian Segment Zvezda module sites) all belonging to the Bacillus anthracis-B. cereus-B. thuringiensis group. Isolates were further characterized by whole genome comparative analysis. Each isolate was sequenced assembled and aligned against all members of the B. cereus sensu lato group. Based on genome size estimates (5.2 - 5.3 Mbp) strain nucleotide identity (>99.99%) and maximum likelihood phylogenetic placement all isolates were found to exhibit a very high level of similarity. With respect to gene content all isolates were inspected for cry proteins common to B. thuringiensis as well as toxins specific to B. cereus. No significant hits were found to any known cry genes while full-length matches were found for multiple B. cereus toxin genes. Finally the isolates were closely screened against B. anthracis genomes and no B. anthracis signatures were identified. Notably all isolates contained the plcR ancestral C allele and lacked significant hits to pXO1 and pXO2 plasmids and toxins. The collective results from the analysis confirm that these strains belong to a previously uncharacterized Bacillus species hereafter referred to as Bacillus issensis. The type strain is ISSFR-003T (=NRRL B-65389T= DSMZ 101676T).