The Paenibacillus thiaminolyticus SY20 strain,which was previously screened and identified as polymyxin A1-producing strain,was evaluated for antimicrobial activity at different stages of growth.Subsequently,the expression levels of five genes,namely pmxA,pmxB,pmxC,pmxD,and pmxE in the polymyxin A1 synthetic gene cluster(pmx),were investigated during the fermentation process using real-time PCR.Finally,the expression levels of regulatory genes for polymyxin(sfp,ectB,spo0A,and abrB)were also explored.The results indicated that,in the M63T medium,the antimicrobial substances were produced from P.thiaminolyticus SY20 in the early logarithmic phase of bacterial growth,and reached a maximum value at the end of the logarithmic phase or early stationary phase(84 h).Pmx expression showed a synchronous trend of significant increase in the early logarithmic stage(36 h).The ectB expression was synchronized with the pmxA and pmxE genes.The sfp and spo0A expression was positively correlated with antimicrobial activity,while abrB expression indicated the opposite.In conclusion,during fermentation in P.thiaminolyticus SY20,the pmx cluster expression reached a maximum before exhibiting antimicrobial activity,and ectB was verified as closely related to polymyxin A1 synthesis.Both sfp and spo0A were identified as positive regulatory genes,while abrB was a negative one.This study provides a theoretical basis for understanding the synthesis and regulation mechanisms of polymyxin.
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