We studied five strains of psychrotolerant Bacillus cereus(B.cereus)isolated from Antarctic snow(BCsn),ice(BCic),lake water(BCwr),sediment(BCsd),and soil(BCsl)samples in terms of their growth,biochemical properties,and heat shock responses.Analyses of growth kinetics at 4℃showed that BCsn had the fastest generation time(16.1 h),whereas BCwr had the slowest(30.8 h).Strain BCsd formed the largest zone of lipid hydrolysis(18 mm)whereas BCsn formed the smallest zone(3 mm).Only BCsd produced gelatinase.These physiological differences illustrate adaptations of B.cereus isolates to different niches.Strains BCsl andBCwr were resistant to all 12 of the antibiotics tested.Strains BCsn,BCic,and BCsd 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 BCsn,BCic,and BCwr 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.
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