Abstract
Bacillus toyonensis is a group of Gram-positive bacteria belonging to the Bacillus cereus group and used in some cases as probiotics or biocontrol agents. To our knowledge, B. toyonensis from the deep sea (depth >1,000 m) has not been documented. Here, we report the isolation and characterization of a B. toyonensis strain, P18, from a deep sea hydrothermal field. P18 is aerobic, motile, and able to grow at low temperatures (4°C) and high concentrations of NaCl (8%). P18 possesses a circular chromosome of 5,250,895 bp and a plasmid of 536,892 bp, which encode 5,380 and 523 genes, respectively. Of these genes, 2,229 encode hypothetical proteins that could not be annotated based on the COG database. Comparative genomic analysis showed that P18 is most closely related to the type strain of B. toyonensis, BCT-7112T. Compared to BCT-7112T, P18 contains 1,401 unique genes, 441 of which were classified into 20 COG functional categories, and the remaining 960 genes could not be annotated. A total of 319 putative virulence genes were identified in P18, including toxin-related genes, and 24 of these genes are absent in BCT-7112T. P18 exerted strong cytopathic effects on fish and mammalian cells that led to rapid cell death. When inoculated via injection into fish and mice, P18 rapidly disseminated in host tissues and induced acute infection and mortality. Histopathology revealed varying degrees of tissue lesions in the infected animals. Furthermore, P18 could survive in fish and mouse sera and possessed hemolytic activity. Taken together, these results provide the first evidence that virulent B. toyonensis exists in deep sea environments.
Highlights
Deep hydrothermal vents are localized areas of the deep sea with high tectonic activities that cause the escaping of hot, mineral-rich water from the sea floor, which forms chimney-like black or white smokers
We examined the biological features of a B. toyonensis strain, P18, isolated from a deep hydrothermal field
We found that P18 was able to form spores and grow at conditions resembling that of the local deep sea environment
Summary
Deep hydrothermal vents are localized areas of the deep sea with high tectonic activities that cause the escaping of hot, mineral-rich water from the sea floor, which forms chimney-like black or white smokers. B. cereus can be a transient presence in the guts of mammals, and for some insects, B. cereus is part of the gut microbial communities (Jensen et al, 2003). They have been studied mostly as probiotics for animal feeds and medicines (Cutting, 2011; Elshaghabee et al, 2017). Some members of the Bacillus cereus group can produce several toxins, including the single-protein toxin, cytotoxin K (CytK), and the two protein toxin complexes formed by hemolysin BL (Hbl) and the non-hemolytic enterotoxin (Nhe) (Stenfors Arnesen et al, 2008; Ehling-Schulz et al, 2019)
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