Abstract
Our previous study confirmed the protective potential of Lactobacillus plantarum (L. plantarum) strains in alleviation of cadmium (Cd) toxicity in vivo and demonstrated that the observed protection largely depended on the tolerance of the strains to Cd-induced stress. It was also observed that there were significant intra-species differences in Cd tolerance of L. plantarum strains. In this study, we investigated the mechanism of Cd induced stress response of L. plantarum strains using the isobaric tags for relative and absolute quantitation (iTRAQ) based comparative proteomics. L. plantarum CCFM8610 (strongly resistant to Cd) and L. plantarum CCFM191 (sensitive to Cd) were selected as target strains, and their proteomic profiles in the presence and absence of Cd exposure were compared. We propose that the underlying mechanism of the exceptional Cd tolerance of CCFM8610 may be attributed to the following: (a) a specific energy-conservation survival mode; (b) mild induction of its cellular defense and repair system; (c) an enhanced biosynthesis of hydrophobic amino acids in response to Cd; (d) inherent superior Cd binding ability and effective cell wall biosynthesis ability; (e) a tight regulation on ion transport; (f) several key proteins, including prophage P2b protein 18, CadA, mntA and lp_3327.
Highlights
Cadmium (Cd) is a representative non-essential element and known as an environmental hazard to human health
While increasing Cd concentration caused a continuous decrease in the growth rate of all strains, significant Cd tolerance diversity could be observed, and the 20 strains could be categorized into four general groups, minimum inhibitory concentration (MIC) > 50 mg/L, MIC = 50 mg/L, MIC = 20 mg/L and MIC = 10 mg/L
L. plantarum CCFM8610 belonged to one of the eight strains with the highest MIC values, which was in agreement with our previous study on the tolerance of Lactic acid bacteria (LAB) strains tested on Cd-containing agar plates[15]
Summary
Cadmium (Cd) is a representative non-essential element and known as an environmental hazard to human health. Lactic acid bacteria (LAB) are members of commensal inhabitants of the human intestinal microbiota that can confer health benefits on the host[7] Among these LAB, Lactobacillus plantarum (L. plantarum) strains have been widely used in the food industry as probiotics and functional food supplements[8]. It is of interest to understand the resistance mechanism of L. plantarum strains against Cd exposure, and to explore why CCFM8610 is highly tolerant to Cd. The physiological bases of heavy metal tolerance have been well investigated in environmental and industrial microorganisms such as Pseudomonas spp., Escherichia coli, Bacillus subtilis and Saccharomyces cerevisia[12, 13, 18,19,20]. Numbers of reports indicated the presence of these genes in some strains of L. plantarum species[25, 26], but the Cd stress response network in these strains is yet to be elucidated
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