Nanoscale mono- and multi-layer cylinder structures formed by recombinant S-layer proteins of mosquitocidal Bacillus sphaericus C3-41

Regulator DegU is required for multicellular behavior in Lysinibacillus sphaericus

DegS and DegU make up a two component system belonging to a class of signal transduction systems that play important roles in a broad range of bacterial responses to the environment. However, little study has been done to explore the physiological functions of DegS-DegU in mosquitocidal Lysinibacillus sphaericus. In this study, it was found that deletion of degU or degS-degU inhibited the swarming motility, biofilm formation, sporulation and binary toxin production through regulating the related genes, and phosphorylation was necessary for the functions of DegU. Based on the findings, a regulation network mediated by DegU was delineated. Both DegU-pi and Spo0A-pi positively regulates genes which are linked with the transition from stage Ⅱ to the end of the sporulation process and also influences the production of binary toxins via regulation on sigE. Both DegU-pi and Spo0A-pi negatively regulate abrB/sinR and influence the biofilm formation. DegU-pi can positively regulate the motility via the regulation on sigD. Whether the regulations are directly or indirectly need to be explored. Moreover, Spo0A-pi may indirectly regulate the swarming motility through negatively regulating DegU. It was concluded that DegU is a global transcriptional regulator on cell swarming motility, biofilm formation, sporulation and virulence in L. sphaericus.

Genome comparison provides molecular insights into the phylogeny of the reassigned new genus Lysinibacillus

BACKGROUND

Lysinibacillus sphaericus (formerly named Bacillus sphaericus) is incapable of polysaccharide utilization and some isolates produce active insecticidal proteins against mosquito larvae. Its taxonomic status was changed to the genus Lysinibacillus in 2007 with some other organisms previously regarded as members of Bacillus. However, this classification is mainly based on physiology and phenotype and there is limited genomic information to support it.

RESULTS

In this study, four genomes of L. sphaericus were sequenced and compared with those of 24 representative strains belonging to Lysinibacillus and Bacillus. The results show that Lysinibacillus strains are phylogenetically related based on the genome sequences and composition of core genes. Comparison of gene function indicates the major difference between Lysinibacillus and the two Bacillus species is related to metabolism and cell wall/membrane biogenesis. Although L. sphaericus mosquitocidal isolates are highly conserved, other Lysinibacillus strains display a large heterogeneity. It was observed that mosquitocidal toxin genes in L. sphaericus were in close proximity to genome islands (GIs) and mobile genetic elements (MGEs). Furthermore, different copies and varying genomic location of the GIs containing binA/binB was observed amongst the different isolates. In addition, a plasmid highly similar to pBsph, but lacking the GI containing binA/binB, was found in L. sphaericus SSII-1.

CONCLUSIONS

Our results confirm the taxonomy of the new genus Lysinibacillus at the genome level and suggest a new species for mosquito-toxic L. sphaericus. Based on our findings, we hypothesize that (1) Lysinibacillus strains evolved from a common ancestor and the mosquitocidal L. sphaericus toxin genes were acquired by horizontal gene transfer (HGT), and (2) capture and loss of plasmids occurs in the population, which plays an important role in the transmission of binA/binB.