Molecular identification of a Bacillus cereus strain from Murrah buffalo milk showed in vitro bioremediation properties on selective heavy metals

Objective: This study aims for molecular identification of naturally growing Bacillus cereus strain from a unique source, able to survive, and alleviate heavy metals from the nature.

Materials and methods: Pure isolate from Murrah buffalo milk was prepared in B. cereus selective Polymyxin pyruvate egg-yolk mannitol-bromothymol blue agar (PEMBA) medium through a cascade of contamination free subcultures. The morphological and biochemical tests were done prior to 16S rRNA gene sequencing for strain identification and further physiological tests. The test strain was inoculated in both solid and suspension culture medium supplemented individually with Cd, Cu, Ag, and Zn to reveal the qualitative and quantitative heavy metal tolerance properties, respectively. Finally, the data collected from the in vitro assessment was statistically analyzed.

Results: Molecular analysis revealed that the test strain was B. cereus BF2, which was motile, catalase positive and Gram positive rod. B. cereus BF2 was found significant at 0.3% bile salt tolerance [two-way analysis of variance (ANOVA)-p value is < 0.0001] where, t-test p value is < 0.0002 between Control Group (CG) and TGR-1; p < 0.037 between TGR-1 and 2; p < 0.0014 between CG and TGR-2. Similarly, B. cereus BF2 was significant in pH tolerant up to 8.0 with p < 0.0115 (in scale p < 0.05). The heavy metal tolerance test revealed that the test metals could not stop the growth of B. cereus BF2 even after 24 h of incubation but partially suppressed the growth kinetics for letting into stationary phase. Among the four heavy metals, Cd and Zn showed partial antagonism to the growth of B. cereus BF2. The survivability was highly significant in the medium supplemented with Zn (p < 0.0001) and Ag (p < 0.018).

Conclusion: Bacillus cereus BF2 can survive in selective heavy metals with metal resistance and biodegradation capacity.