Germination Characteristics Of Bacillus Thuringiensis Spore And Function Of Its Germination Genes

There are three well studied species in Bacillus cereus groups. Both Bacillus anthracis andBacillus cereus can cause serious disease in livestock and humans. Bacillus anthracis canproduce anthrax, and Bacillus cereus can product a heat-stable emetic toxin resulted in diarrheadsyndromes after spore germination. Bacillus thuringiensis can be beneficial as an insecticide, andits spores can synergize toxicity of insect crystal protein, and the process of germination maybeinvolve in the synergism. Germanation characteristics of Bt and the function of plasmid pHT73in nutrient-germiantion was studied. Genes related to spore were analysised by the sequence ofthe whole genome in YBt1520,, and a new operon related to genes for nutrient-germiantion wasfound. It was different from the receptors which were well known, It was named "gerZ", and therole of gerZ operon was also determined.The conditions for measuring germination rates of Bt HD-73 was optimized. By measuringthe germination rates of spore in different germination medium, at different temperature and withdifferent germinants in half an hour, the optimum conditions were determined: the optimumgermination medium was NaH₂PO₄ (10mM) and NaCl (100mM), pH 7.2 and the optimumtemperature was 37℃.Compared the germination rates between Bt HD-73 and Bt HD-73^- spores, which was basedon the optimum germination conditions, germination rates of Bt HD-73^- spores was twice of thatof Bt HD-73 on the pathways of inosine (1mM)/Asp (100mM) and inosine (1mM)/Glu(100mM). This results supported that the plasmid pHT73 contained the germination genes whichpartly blocked those two pathways, because Bt HD-73^- was cured of plasmid pHT73.It was considered to be a tricistronic operons with gerZA,gerZB and gerZC by analysis ofthe DNA sequence of gerZ operons in Bt HD-73. Transmembrane regions can be found in thesethree proteins, and GerZB is excepted to play a major role in anchoring to the spore innermembrane.Deletion mutant was constructed by knocking gerZA out. Compared the spores germinationrates between mutant and its parental strain, which was based on the optimum germinationconditions, germination rate of mutant spores was half of that of its parental strain on thepathways of L-Ala (1mM) with Leu (100mM), Val (100mM), Trp (1mM), Cys (100mM)or Ile (100mM), so gerZ operon was respected a new germination-related gene.