Bacillus safensis sp. nov., isolated from spacecraft and assembly-facility surfaces

Summary auto-generated

Researchers isolated 13 strains of a previously unknown spore-forming bacterium from spacecraft surfaces, including the Mars Odyssey Orbiter, and from assembly facilities at NASA's Jet Propulsion Laboratory and Kennedy Space Center. Initial analysis suggested these isolates were Bacillus pumilus based on 16S rRNA gene sequencing (99.9% similarity), but comprehensive polyphasic taxonomy revealed they represent a distinct species. The gyrB gene analysis showed only 91.2% similarity to B. pumilus, and DNA-DNA hybridization demonstrated only 54-66% relatedness, well below the species threshold of 70%. Additional discriminatory analyses including rep-PCR fingerprinting, MALDI-TOF mass spectrometry protein profiling, and phenotypic characterization confirmed the isolates formed a separate cluster from B. pumilus. Key distinguishing features included acid production and utilization of inositol, along with differences in acid phosphatase production and Tween 80 hydrolysis. Based on these comprehensive analyses, the authors established a new species, Bacillus safensis, with FO-36bT designated as the type strain. The discovery is significant for spacecraft sterilization protocols and planetary protection, as these resilient spore-formers represent a previously uncharacterized contaminant in spacecraft assembly facilities.

Key findings

Thirteen bacterial strains isolated from spacecraft and assembly facility surfaces represent a novel species, Bacillus safensis, distinct from the closely related Bacillus pumilus
Polyphasic taxonomy using gyrB gene sequences, DNA-DNA hybridization (54-66% relatedness), rep-PCR fingerprinting, and MALDI-TOF mass spectrometry definitively separated B. safensis from B. pumilus despite 99.9% 16S rRNA similarity
B. safensis is distinguished phenotypically from B. pumilus by acid production and utilization of inositol, along with differences in specific enzymatic activities
The species represents a resilient, spore-forming bacterium adapted to low-biomass, controlled spacecraft assembly environments, raising concerns for planetary protection and mission contamination

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Abstract

Thirteen strains of a novel spore-forming, Gram-positive, mesophilic heterotrophic bacterium were isolated from spacecraft surfaces (Mars Odyssey Orbiter) and assembly-facility surfaces at the Jet Propulsion Laboratory in California and the Kennedy Space Center in Florida. Phylogenetic analysis of 16S rRNA gene sequences has placed these novel isolates within the genus Bacillus, the greatest sequence similarity (99.9 %) being found with Bacillus pumilus. However, these isolates share a mere 91.2 % gyrB sequence similarity with Bacillus pumilus, rendering their 16S rRNA gene-derived relatedness suspect. Furthermore, DNADNA hybridization showed only 5466 % DNA relatedness between the novel isolates and strains of B. pumilus. rep-PCR fingerprinting and previously reported matrix-assisted laser desorption/ionization time-of-flight mass spectrometry protein profiling clearly distinguished these isolates from B. pumilus. Phenotypic analyses also showed some differentiation between the two genotypic groups, although the fatty acid compositions were almost identical. The polyphasic taxonomic studies revealed distinct clustering of the tested strains into two distinct species. On the basis of phenotypic characteristics and the results of phylogenetic analyses of 16S rRNA and gyrB gene sequences, repetitive element primer-PCR fingerprinting and DNADNA hybridization, the 13 isolates represent a novel species of the genus Bacillus, for which the name Bacillus safensis sp. nov. is proposed. The type strain is FO-36b^T (=ATCC BAA-1126^T=NBRC 100820^T).