Non-Toxin-Producing Bacillus cereus Strains Belonging to the B. anthracis Clade Isolated from the International Space Station

• Published in: mSystems Vol. 2; no. 3
• Main Authors: Venkateswaran, Kasthuri, Singh, Nitin K, Checinska Sielaff, Aleksandra, Pope, Robert K, Bergman, Nicholas H, van Tongeren, Sandra P, Patel, Nisha B, Lawson, Paul A, Satomi, Masataka, Williamson, Charles H D, Sahl, Jason W, Keim, Paul, Pierson, Duane, Perry, Jay
• Format: Journal Article
• Language: English
• Published: United States American Society for Microbiology 01.05.2017
• Subjects: Comparative analysis; Hybridization; Peptidoglycans; Phages; Population dynamics; ISS; Bacillus anthracis; genomics; Bacillus cereus; spores; Bacillus
• ISSN: 2379-5077; 2379-5077
• DOI: 10.1128/mSystems.00021-17

In an ongoing Microbial Observatory investigation of the International Space Station (ISS), 11 strains (2 from the Kibo Japanese experimental module, 4 from the U.S. segment, and 5 from the Russian module) were isolated and their whole genomes were sequenced. A comparative analysis of the 16S rRNA gene sequences of these isolates showed the highest similarity (>99%) to the - - group. The fatty acid composition, polar lipid profile, peptidoglycan type, and matrix-assisted laser desorption ionization-time of flight profiles were consistent with the group. The phenotypic traits such as motile rods, enterotoxin production, lack of capsule, and resistance to gamma phage/penicillin observed in ISS isolates were not characteristics of . Whole-genome sequence characterizations showed that ISS strains had the non- ancestral "C" allele and lacked anthrax toxin-encoding plasmids pXO1 and pXO2, excluding their identification as . The genetic identities of all 11 ISS isolates characterized via analyses arbitrarily identified them as members of the group, but traditional DNA-DNA hybridization (DDH) showed that the ISS isolates are similar to (88% to 90%) but distant from the (42%) and (48%) type strains. The DDH results were supported by average nucleotide identity (>98.5%) and digital DDH (>86%) analyses. However, the collective phenotypic traits and genomic evidence were the reasons to exclude the ISS isolates from . Nevertheless, multilocus sequence typing and whole-genome single nucleotide polymorphism analyses placed these isolates in a clade that is distinct from previously described members of the group but closely related to . The International Space Station Microbial Observatory (Microbial Tracking-1) study is generating a microbial census of the space station's surfaces and atmosphere by using advanced molecular microbial community analysis techniques supported by traditional culture-based methods and modern bioinformatic computational modeling. This approach will lead to long-term, multigenerational studies of microbial population dynamics in a closed environment and address key questions, including whether microgravity influences the evolution and genetic modification of microorganisms. The spore-forming group consists of pathogenic ( ), food poisoning ( ), and biotechnologically useful ( ) microorganisms; their presence in a closed system such as the ISS might be a concern for the health of crew members. A detailed characterization of these potential pathogens would lead to the development of suitable countermeasures that are needed for long-term future missions and a better understanding of microorganisms associated with space missions.