Identification of a Novel Aflatoxin B1-Degrading Strain, Bacillus halotolerans DDC-4, and Its Response Mechanisms to Aflatoxin B1.

Abstract

Aflatoxin B1 (AFB1) contamination is a food safety issue threatening human health globally. Biodegradation is an effective method for overcoming this problem, and many microorganisms have been identified as AFB1-degrading strains. However, the response mechanisms of these microbes to AFB1 remain unclear. More degrading enzymes, especially of new types, need to be discovered. In this study, a novel AFB1-degrading strain, DDC-4, was isolated using coumarin as the sole carbon source. This strain was identified as Bacillus halotolerans through physiological, biochemical, and molecular methods. The strain's degradation activity was predominantly attributable to thermostable extracellular proteins (degradation rate remained approximately 80% at 90 °C) and was augmented by Cu2+ (95.45% AFB1 was degraded at 48 h). Alpha/beta hydrolase (arylesterase) was selected as candidate AFB1-degrading enzymes for the first time as a gene encoding this enzyme was highly expressed in the presence of AFB1. Moreover, AFB1 inhibited many genes involved in the nucleotide synthesis of strain DDC-4, which is possibly the partial molecular mechanism of AFB1's toxicity to microorganisms. To survive under this stress, sporulation-related genes were induced in the strain. Altogether, our study identified a novel AFB1-degrading strain and explained its response mechanisms to AFB1, thereby providing new insights for AFB1 biodegradation.