Abstract
BackgroundBacillus strains producing highly resistant spores have been isolated from cleanrooms and space craft assembly facilities. Organisms that can survive such conditions merit planetary protection concern and if that resistance can be transferred to other organisms, a health concern too. To further efforts to understand these resistances, the complete genome of Bacillus safensis strain FO-36b, which produces spores resistant to peroxide and radiation was determined. The genome was compared to the complete genome of B. pumilus SAFR-032, and the draft genomes of B. safensis JPL-MERTA-8-2 and the type strain B. pumilus ATCC7061T. Additional comparisons were made to 61 draft genomes that have been mostly identified as strains of B. pumilus or B. safensis.ResultsThe FO-36b gene order is essentially the same as that in SAFR-032 and other B. pumilus strains. The annotated genome has 3850 open reading frames and 40 noncoding RNAs and riboswitches. Of these, 307 are not shared by SAFR-032, and 65 are also not shared by MERTA and ATCC7061T. The FO-36b genome has ten unique open reading frames and two phage-like regions, homologous to the Bacillus bacteriophage SPP1 and Brevibacillus phage Jimmer1. Differing remnants of the Jimmer1 phage are found in essentially all B. safensis / B. pumilus strains. Seven unique genes are part of these phage elements. Whole Genome Phylogenetic Analysis of the B. pumilus, B. safensis and other Firmicutes genomes, separate them into three distinct clusters. Two clusters are subgroups of B. pumilus while one houses all the B. safensis strains. The Genome-genome distance analysis and a phylogenetic analysis of gyrA sequences corroborated these results.ConclusionsIt is not immediately obvious that the presence or absence of any specific gene or combination of genes is responsible for the variations in resistance seen. It is quite possible that distinctions in gene regulation can alter the expression levels of key proteins thereby changing the organism’s resistance properties without gain or loss of a particular gene. What is clear is that phage elements contribute significantly to genome variability. Multiple genome comparison indicates that many strains named as B. pumilus likely belong to the B. safensis group.
Highlights
Bacillus strains producing highly resistant spores have been isolated from cleanrooms and space craft assembly facilities
Most are open reading frames that code for hypothetical proteins, six genes suggest that FO-36b has a CRISPR system
The likely presence of a CRISPR system is shared by 5 other B. safensis genomes and 8 other B. pumilus genomes (Additional file 2: Table S2)
Summary
Bacillus strains producing highly resistant spores have been isolated from cleanrooms and space craft assembly facilities. Understanding the survival mechanisms employed by these organisms is the key to controlling their impact on exobiology missions Their occurrence in the closed environments of the International Space Station, (ISS), could possibly impact the living conditions there as well [1,2,3, 25,26,27]. Two of the most studied organisms in the specialized econiches of spacecraft assembly facilities and the ISS are B. safensis FO-36bT [28] (referred to as FO-36b ) and B. pumilus SAFR-032 [16] (referred to as SAFR-032). These organisms are representative strains of the endospore producing Bacillus sp. A recent phylogenetic study of 24 B. pumilus and B. safensis strains, found FO-36b, and MERTA clustered together in a distinct group of B. safensis strains [37]
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