Combinatorial co-expression of xanthine dehydrogenase and chaperone XdhC from Acinetobacter baumannii and Rhodobacter capsulatus and their applications in decreasing purine content in food

This study investigated the combinatorial expression of xanthine dehydrogenase(XDH)and chaperone XdhC from Acinetobacter baumannii and Rhodobacter capsulatus and their applications in decreasing purine content in the beer,beef and yeast.Naturally occurring xdhABC gene clusters of A.baumannii CICC 10254 and R.capsulatus CGMCC 1.3366 as well as two refactored clusters constructed by exchanging their xdhC genes were overexpressed in Escherichia coli and purified to near homogeneity.RcXDH chaperoned by AbXdhC showed nearly the same catalytic performance as that by RcXdhC,except for the decreased substrate affinity.While the AbXDH co-expressed with RcXdhC displayed enhanced acidic adaptation but weakened catalytic activity.All the XDHs degraded purines in beer,beef and yeast extract effectively,indicating potential applications in low-purine foods to prevent hyperuricemia and gout.The study also presents a method for exploiting the better chaperone XdhC and novel XDHs by functional complement activity using existing XdhCs such as RcXdhC.

Complete genome sequence of Lactobacillus fermentum 9-4,a purine-degrading Lactobacillus probiotic isolated from Chinese fermented rice-flour noodles

Lactobacillus fermentum 9-4 is a purine-degrading probiotic firstly isolated from traditional fermented rice-flour noodles with special characteristics of southern China's Guangxi Zhuang Autonomous Region.L.fermentum 9-4 could efficiently reduce the purine contents in foods with excellent purine-nucleoside assimilation and purine-metabolizing enzymatic activities.Crude cell lysate of L.fermentum 9-4 showed strong purine degradation abilities on nucleosides including inosine,guanosine,and purines including xanthine and uric acid,indicating a complete purine metabolic pathway to degrade purine substances to allantoin.In this study,the whole genome of L.fermentum 9-4 was sequenced.Its genome consisted of a 2085632 bp circular chromosome without plasmid.The GC content of circular chromosome was 51.25%,including 2089 coding sequences(CDs),15 rRNA operons and 59 tRNA coding genes.Genetic analysis showed that at least 5 protein coding genes were related to purine lowering ability.In addition,neither toxic virulence factor nor drug resistance gene was identified by searching the virulence factor database and drug resistance gene database,suggesting good safety of L.fermentum 9-4.The results showed that L.fermentum 9-4 has a good potential for the development and utilization as a purine-degrading probiotic for low-purine foods.