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Tesi etd-02272014-103750

Thesis type
Tesi di dottorato di ricerca
Functional analysis of bc5181 in Bacillus cereus
Settore scientifico disciplinare
Corso di studi
tutor Prof.ssa Ghelardi, Emilia
Parole chiave
  • virulence
  • swimming and swarming motility
  • Bacillus cereus
  • ybjq-like gene
Data inizio appello
Riassunto analitico
Previous studies on the systematic examination of the global transcriptional response of Bacillus cereus to disinfectant treatments showed a common up-regulation of stress-related genes. In this study, we focused our attention on one of these genes (bc5181) that encodes a protein belonging to the YbjQ-like superfamily. Since bc5181 expression was shown to be induced by mild or lethal concentrations of peracetic-acid (PAA), we examined its role under PAA treatment by evaluating the phenotypic response of B. cereus strains lacking or overexpressing this gene. A bc5181 null mutant (MP23) and a strain carrying an additional IPTG-inducible copy of this gene (MP25) were constructed from B. cereus ATCC 14579 and comparatively assayed. Treatment of mid-exponential phase cells with two PAA concentrations revealed that the lack or overexpression of bc5181 have no significant effect on bacterial survival to the mild PAA concentration. However, when the lethal concentration was used, a high resistance to PAA was observed in the strain MP25 compared to the wild-type, more pronouncedly following IPTG induction. Unexpectedly, a lower increase in the resistance to the lethal PAA concentration was also observed in the bc5181 null mutant MP23 compared to the wild type.<br>To evaluate whether deprivation of bc5181 or increase in its expression could have other effects on B. cereus physiology, bacterial growth, carbohydrate utilization, antibiotic resistance, motility, chemotactic response, as well as virulence and pathogenicity of all strains were evaluated. Moreover, the effect of heterologous expression of bc5181 in B. subtilis, a microorganism naturally lacking a bc5181 homologue, was investigated.<br>While no significant effect of bc5181 on bacterial growth, biochemistry and antibiotic resistance was evidenced, bc5181 overexpression was shown to cause a defect in swimming motility, chemotactic response toward the chemo-attractant L-glutamine, and swarming motility. In addition, increase in bc5181 expression level caused a significant reduction in B. cereus pathogenicity in an in vivo animal model of infection using the lepidoteran Galleria mellonella and in the production of some relevant B. cereus virulence factors, such as phosphatidylcholine-preferring phospholipase C (PC-PLC), proteases and general haemolysins. Heterologous expression of bc5181 in B. subtilis was shown to increase the production of proteases and the propensity to develop biofilm communities by this organism. <br> In conclusion, bc5181 appears to be a non-essential stress-related gene whose overexpression increases resistance to PAA treatment, causes alterations in the motility and chemotactic behaviors, and leads to a reduction in B. cereus pathogenicity and virulence. The observation that heterologous bc5181 expression in a microorganism lacking ybjQ-like genes causes an increase in protease secretion and biofilm formation is also relevant, and further support a role of this gene in exerting a pleiotropic effect on bacterial cells.<br>