Phenotypic plasticity in Bacillus cereus strains isolated from various Antarctic habitats

Abstract

We studied five strains of psychrotolerant Bacillus cereus ( B. cereus ) isolated from Antarctic snow (BC sn ), ice (BC ic ), lake water (BC wr ), sediment (BC sd ), and soil (BC sl ) samples in terms of their growth, biochemical properties, and heat shock responses. Analyses of growth kinetics at 4℃ showed that BC sn had the fastest generation time (16.1 h), whereas BC wr had the slowest (30.8 h). Strain BC sd formed the largest zone of lipid hydrolysis (18 mm) whereas BC sn formed the smallest zone (3 mm).Only BC sd produced gelatinase. These physiological differences illustrate adaptations of B. cereus isolates to different niches. Strains BC sl and BC wr were resistant to all 12 of the antibiotics tested. Strains BC sn , BC ic , and BC sd were resistant to cell wall synthesis inhibitors (penicillin and ampicillin) and susceptible to protein synthesis inhibitors (tetracycline and streptomycin). A carbon-substrate utilization assay revealed that BC sn , BC ic , and BC wr could specifically utilize D-glucose-6-phosphate, salicin, and 2’-deoxyadenosine, respectively, indicating a degree of metabolic diversity among these Antarctic B. cereus strains. An analysis of heat shock proteins (HSPs) produced in response to a 60℃ heat treatment revealed significant variations in the amounts of HSP33 ( p = 0.01, df = 4), HSP44 ( p = 0.003, df = 4), and HSP60 ( p = 0.04, df = 4) among the strains. This emphasizes the importance of HSPs in bacterial taxonomy. These results show that there are considerable adaptive variations among B. cereus strains from extremophilic environments. This could be significant in evaluating the taxonomy and evolution of this species.