| There is an old saying that “food is the paramount necessity of people and food safety is the top priority”,food safety is a matter of concern to thousands of households.With the development of national economy,the improvement of people’s living standard and the continuous growth of edible fungui industry in China,people put forward greater demands on taste and quality of edible fungi products,and begin to pay more attention to their nutrition and safety issues.Research on key factors affecting safety issues pertaining to the upstream and downstream of edible fungui industrial chain,such as control of harmful substances in mushroom products and microbial contamination in cultivation process,is crucial to improve quality and safety of edible fungui products.To study microbial contamination problem of during edible fungi production,samples of contaminated culture materials,strains and fruiting bodies of Hypsizigus marmoreus were collected from factories of a large-scale mushroom production enterprise located in three provinces,respectively.Then pathogenic microorganisms in these samples were isolated and identified in order by morphological characteristics of colonies,microscopic staining observation,and molecular sequencing.The effect of these pathogenic bacteria on mycelial growth of H.marmoreus was analyzed by the plate confrontation experiment.In total,there were 11 pathogenic microorganisms belonging to 3 families and 7 genera 10 of which were bacteria and 1 was a species of fungi.Enterobacteriaceae was the dominant family and Bacillus was the dominant genus.Two isolates of bacteria belonging to Bacillus and Enterobacter respectively were likely to be new species.The results of the plate confrontation experiment showed that 7 bacteria and 1 fungus inhibited mycelial growth of H.marmoreus significantly.Phylogenetic analysis showed that 5 strains of Bacillus subtilis and their related species formed a distinct clade independent of other typical species of Bacillus.Based on these findings,substrate sterilization and fruiting management are critical control points for disease prevention in H.marmoreus cultivation.Using Lentinula edodes as the studying material,upstream genetic mechanism of endogenous harmful substance biosynthesis in edible fungi product was analyzed.Content of endogenous formaldehyde during the growth of Lentinula edodes was monitored,expression of five Csl genes was analyzed by RT-qPCR,and the key enzyme C-S lyase in the sulfur compound pathway that is associated with endogenous formaldehyde production in L.edodes was studied.The results showed that temporal kinetics of both formaldehyde content and expression of Csl genes increased initially and then decreased in the development of L.edodes fruit-body.Beside Csl1 that is known to play a catalytic role in the sulfur compound biosynthetic pathway associated with formaldehyde production in L.edodes,Csl2 gene was also found to have catalytic activity for the first time in this study.In addition,five CSL proteins were heterologously expressed for the first time in this study.The HPLC detection condition for analysis of C-S lyase catalytic reaction in vitro was explored,and catalytic reactions of these heterologous proteins were attempted in vitro.The research results provide theoretical references for strengthening management of safety production in upstream and downstream of edible fungi industrial chain,provide a reference for contamination prevention and control in factory production of H.marmoreus and other edible fungi,and lay a scientific foundation for development of molecular marker assisted quality related metabolite detection methods of edible fungi products. |
