Altered secretome of Burkholderia pseudomallei induced by salt stress.

Burkholderia pseudomallei is a saprophyte found in soil and water. It is a difficult microorganism to kill and can survive in these environments for many years. Mechanisms for its adaptive response to environmental changes remain largely unknown. We performed a proteomics study to examine alterations in secreted proteins (secretome) under a salt stress (with 150 mM NaCl) compared to the normal cultured condition in LB broth. The culture supernatants were filtrated and precipitated with 50% ethanol. The isolated proteins were recovered, separated with 2-D PAGE, and visualized with SYPRO Ruby stain (n=5 gels for each group). Differentially expressed protein spots were identified by Q-TOF MS and/or MS/MS analyses. A total of 42 protein spots representing 37 unique proteins were identified as the altered proteins during the salt stress, including metabolic enzymes, transcription/translation regulators, potential virulence factors, chaperones, phage capsid proteins, drug resistance protein, solute transport regulator, and hypothetical proteins. The presence of secreted GroEL only after NaCl exposure was confirmed by Western blot analysis. The increased level (19-fold) of a beta-lactamase-like protein suggested that the NaCl-exposed bacterium might resist to beta-lactam antibiotics. Functional analysis revealed that the NaCl-exposed bacterium had significantly greater survival rate after a treatment with ceftazidime. Our study provided the first dataset of the secretome of B. pseudomallei and its alterations, which may lead to novel insights into adaptive response of B. pseudomallei during the salt stress.