Purification and characterization of the enzymes from Brevundimonas naejangsanensis that degrade ochratoxin A and B.

Ochratoxin A (OTA) and Ochratoxin B (OTB) co-contaminate many types of agricultural products. Screening enzymes that degrade both OTA and OTB has significance in food safety. In this study, four novel OTA and OTB degrading enzymes, namely BnOTase1, BnOTase2, BnOTase3, and BnOTase4, were purified from the metabolites of the Brevundimonas naejangsanensis ML17 strain. These four enzymes hydrolyzed OTA into OTα and hydrolyzed OTB into OTß. BnOTase1, BnOTase2, BnOTase3, and BnOTase4 have the apparent Km values for hydrolyzing OTA of 19.38, 0.92, 12.11, 1.09 µmol/L and for hydrolyzing OTB of 0.76, 2.43, 0.60, 0.64 µmol/L respectively. OTα and OTß showed no significant cytotoxicity to HEK293 cells, suggesting that these enzymes mitigate the toxicity of OTA and OTB. The discovery of the novel OTA and OTB degrading enzymes enriches the research on ochratoxin control and provides objects for protein rational design.

Truncated Expression of a Carboxypeptidase A from Bovine Improves Its Enzymatic Properties and Detoxification Efficiency of Ochratoxin A.

Ochratoxin A (OTA) is a toxic secondary metabolite produced mainly by Penicillium spp. and Aspergillus spp. and commonly found in foodstuffs and feedstuffs. Carboxypeptidase A (CPA) can hydrolyze OTA into the non-toxic product ochratoxin α, with great potential to realize industrialized production and detoxify OTA in contaminated foods and feeds. This study constructed a P. pastoris expression vector of mature CPA (M-CPA) without propeptide and signal peptide. The results showed that the degradation rate of OTA by M-CPA was up to 93.36%. Its optimum pH was 8, the optimum temperature was 40 °C, the value of Km was 0.126 mmol/L, and the maximum reaction rate was 0.0219 mol/min. Compared with commercial CPA (S-CPA), the recombinant M-CPA had an improve stability, for which its optimum temperature increased by 10 °C and stability at a wide range pH, especially at pH 3-4 and pH 11. M-CPA could effectively degrade OTA in red wine. M-CPA has the potential for industrial applications, such as can be used as a detoxification additive for foods and feeds.

Degeneration of industrial bacteria caused by genetic instability.

The fermentation of industrial bacteria encounters a serious problem in continuous culture, i.e. the production traits lose. However, current research on the mechanism of strain degeneration is not clear enough, and there are few methods to effectively control the degeneration. Under growth restriction, the mutation rate of fermentation strains increases. Many cellular processes and poor fermentation conditions can trigger the transposition of transposable elements, SOS response, and RpoS-controlled adaptive mutations, causing genetic instability. Genetic instability which resulted from point mutations and genomic rearrangements can be responsible for strain degeneration. This mini-review summarizes the degeneration phenomena and mechanisms in common industrial bacteria and highlights three mechanisms of strain degeneration, including the transposition of transposable elements, SOS response, and adaptive mutations. According to different mutation mechanisms, many promising strategies have been proposed to increase the stability and the yield of industrial strains, for example, developing platform strains free of insertion sequence to enhance the stability of recombinant plasmid, using SOS inhibitors to block the SOS response, and improving environmental tolerance capacity and fermentation conditions to reduce adaptive mutations.

Probiotic Bacillus subtilis CW14 reduces disruption of the epithelial barrier and toxicity of ochratoxin A to Caco-2 cells.

The multiple toxic effects of ochratoxin A (OTA) are a threat for human and animal. This study aimed to examine whether B. subtilis CW14 protected against OTA-induced barrier disruption and cell damage to Caco-2 cells. The results showed that Caco-2 cells treated with OTA led to microvilli disruption, tight junction protein (ZO-1 and claudin-1) damage, and inhibition of cell proliferation by arresting the cell cycle in the G2/M phase that promoted apoptosis. The treatment of B. subtilis CW14 mitigated the tight junction injury by improving ZO-1 protein expression, and it reduced apoptosis that was induced by OTA. Furthermore, transcriptome analysis indicated that OTA down-regulated genes that involved in the tight junction, cell cycle, and apoptosis-related signaling pathways. B. subtilis CW14 may have protected the ZO-1 protein by activating the toll-like receptor signaling pathway, and it reduced OTA damage by down-regulating the death receptor genes and up-regulating the DNA repair genes. These findings demonstrated the importance of B. subtilis CW14 in the regulation of tight junction proteins and in reducing death of intestinal epithelial cells. Thus, B. subtilis CW14 is a potential candidate as a food additive to protect against intestinal damage.