Minimizing Ochratoxin A Contamination through the Use of Actinobacteria and Their Active Molecules

Abstract

Ochratoxin A (OTA) is a secondary metabolite produced by fungal pathogens such as Penicillium verrucosum, which develops in food commodities during storage such as cereals, grapes, and coffee. It represents public health concerns due to its genotoxicity, carcinogenicity, and teratogenicity. The objective of this study was to evaluate the ability of actinobacteria and their metabolites to degrade OTA and/or to decrease its production. Sixty strains of actinobacteria were tested for their ability to prevent OTA formation by in vitro dual culture assays or with cell free extracts (CFEs). In dual culture, 17 strains strongly inhibited fungal growth, although it was generally associated with an increase in OTA specific production. Seventeen strains inhibited OTA specific production up to 4% of the control. Eleven actinobacteria CFEs reduced OTA specific production up to 62% of the control, while no substantial growth inhibition was observed except for two strains up to 72% of the control. Thirty-three strains were able to degrade OTA almost completely in liquid medium whereas only five were able to decrease it on solid medium, and two of them reduced OTA to an undetectable amount. Our results suggest that OTA decrease could be related to different strategies of degradation/metabolization by actinobacteria, through enzyme activities and secretion of secondary metabolites interfering with the OTA biosynthetic pathway. CFEs appeared to be ineffective at degrading OTA, raising interesting questions about the detoxification mechanisms. Common degradation by-products (e.g., OTα or L-β-phenylalanine) were searched by HPLC-MS/MS, however, none of them were found, which implies a different mechanism of detoxification and/or a subsequent degradation into unknown products.

Aspergillus flavus Growth Inhibition and Aflatoxin B1 Decontamination by Streptomyces Isolates and Their Metabolites

“…All isolates were able to decrease AFB 1 -specific production to at least 54% of the control during the dual culture assay, particularly IX07 and IX31, which diminished it almost entirely (0.71% and 0.83% of the control, respectively). Moreover, no aflatoxin overproduction was observed when the Streptomyces isolates were confronted in dual culture, which contrasts the previous results obtained with P. verrucosum (Figure S4), where strong fungal inhibitions were accompanied by a boost in OTA production [29]. The analysis of CFEs' effect on AFB 1 sp, and the degradation abilities of the isolates and their CFEs, can help in highlighting the various mechanisms potentially involved in the observed reduction in AFB 1 during the dual culture assays.…”

“…The effect of Streptomyces isolates and their CFEs on fungal growth and aflatoxin-specific production was evaluated, in addition to their ability to degrade aflatoxin B 1 . A study on the effect of the same bacterial collection against the storage fungus Penicillium verrucosum and its ochratoxin A was previously conducted [ 29 ]. As the preceding work brought out isolates with promising features, the collection was evaluated against A. flavus , another post-harvest wheat pathogen [ 11 ].…”

“…The attenuated effect of CFEs in comparison to dual culture assays also suggests that bacterial antifungal metabolites and/or enzymes production could be positively induced by the presence of the fungus, as demonstrated by Wakefield et al during co-culture of Aspergillus fumigatus and Streptomyces leeuwenhoekii [ 31 ]. Interestingly, bacterial isolates able to decrease A. flavus growth in dual culture were also able to reduce P. verrucosum development ( Figure S3 ) [ 29 ], which implies that growth reduction could also partly originate from a general inhibition mechanism such as hydrolytic enzymes, pH variation or competition. For instance, the production of chitinase is frequently described in the literature for bacteria from the genus Streptomyces [ 12 , 32 , 33 ].…”

“…This suggests that the differentiated metabolism followed by Streptomyces isolates could be influenced by the culture environment [ 30 , 54 ] but is still rather similar in both conditions regarding AFB 1 degradation. In contrast, degradation of OTA by the same Streptomyces isolates was scarce on solid medium, whereas it was largely spread in liquid medium ( Figure S5 ) [ 29 ], which highlights the differences in the degradation mechanisms involved for both mycotoxins. Of note, Streptomyces isolates that were efficient at degrading OTA in liquid medium were also capable of degrading AFB 1 in both liquid and solid environments ( Figure S5 ).…”

PCR Assay and its Application to Identify Mycotoxigenic Fungi

“…Ochratoxin A (OTA) is a secondary metabolite created by Aspergillus and Penecillium fungi contaminated a wide variety of foodstuffs such as oats, beans coffee, instant coffee, beer, wins, cocoa, dried fruits, grapes as well as different tissues of animal origin [50,51]. OTA have variety of harmful impacts, including nephrotoxic-having been connected to the Balkan Endemic Nephropathy, immunotoxic, cancer-causing, teratogenic incidences [52,53].…”