| Bacillus cereus group strains are widespread in nature,mainly in soil,decaying organic matter and water.They have been found to be distributed in marine environments such as the deep sea recently.Bacillus cereus group strains are members of the most important foodborne pathogens;they have strong resistance to environmental stress becasus of their endospores and can cause gastrointestinal diseases such as diarrheal syndrome and non-gastrointestinal diseases such as sepsis.In this study,we identified two strains of the Bacillus cereus group isolated from the deep-sea hydrothermal vent and the deep-sea cold seeps,and named them Bacillus wiedmannii SR52 and Bacillus cereus H2,respectively.In addition,we expounded the characteristics of infection and virulence of these bacteria using genomics analysis and in vitro/vivo experimental studies.Strain SR52 was isolated from the gills of shrimp Alvinocaris longirostris that dwelled on the hydrothermal vent of Okinawa Trough.SR52 is most closely related to Bacillus wiedmannii FSL W8-0169,a member of the Bacillus cereus group.SR52 is aerobic,motile,and able to form endospores.SR52 can grow in high concentrations(up to 9%)of NaCl.SR52 has a circular chromosome of 5,448,361 bp and a plasmid of 137,592 bp,encoding 5,709 and 189 genes,respectively.The chromosome contains 297 putative virulence genes,including those encoding enterotoxins and hemolysins.Fourteen rRNA operons,107 tRNAs,and 5 sRNAs are present in the chromosome,and 7 tRNAs are present in the plasmid.SR52 possesses 13 genomic islands(GIs),all on the chromosome.Comparing to FSL W8-0169,SR52 exhibits several streaking features in its genome,notably an exceedingly large number of non-coding RNAs and GIs.In vivo studies showed that following intraperitoneal injection into mice Mus musculus,SR52 was able to disseminate in tissues and cause acute mortality.In vitro studies showed that SR52 possessed hemolytic activity.We isolated the other bacteria,strain H2,from the setae of the galatheid crab Shinkaia crosnieri collected at a deep-sea cold seep in South China Sea.In vivo study showed that H2 was capable of tissue dissemination and causing acute mortality in mice and turbot Scophthalmus maximus following intraperitoneal/intramuscular injection.In vitro study showed that H2 caused death of epithelial cells and macrophages.Study using macrophages revealed that H2-infected cells exhibited pyroptotic death in a manner that was dependent on NLRP3.H2 infection activated p38,JNK,and ERK,but only JNK proved to participate in H2-triggered pyroptosis.The production of reactive oxygen species(ROS)increased after infection and was essential to H2-induced activation of JNK and NLRP3 inflammasome.Similarly,intracellular Ca2+ was also important to the activation of JNK and NLRP3 inflammasome during H2 infection.This study demonstrated for the first time the cytotoxicity and infectivity of two deep-sea bacteria belonging to the Bacillus cereus group and provided new insights into the mechanism of Bacillus cereus infection. |
