Identification of Putative NADP-Dependent Oxidoreductase Gene curA in Diverse Environmental Bacteria Isolated from Winogradsky Columns Challenged with Turmeric and Ginger

Curcumin is the active unstable polyphenol found in turmeric root (Curcuma longa) capable of fully reducing twice while collecting free radicals from the environment. While curcumin reduction and demethylation are potential pathways for microbial metabolism, in E. coli, a two-step NADPH-dependent curcumin metabolic pathway, via an NADP-dependent curcumin/dihydrocurcumin reductase (CurA) was identified. Curcumin has been confirmed as a fantastic oxidative agent because of its ability to fully reduce into dihydrocurcumin and tetrahydrocurcumin which can take place in a wide range of pH environments and temperatures. Unfortunately, the utilization of curcumin by the human body alone is often minimal, due to curcumin’s natural hydrophobicity and low bioavailability for oral absorption. Curcumin metabolism has been investigated in vitro using fermentation with E. coli and human gut microbes, but the identification of either curA or other molecular mechanisms in vitro or in situ for such metabolism has not been reported. Elucidation of curA has led to the identification of the putative gene product in Vibrio vulnificus, which was able to be produced and crystallized in the pure protein form. Another study which focused on identifying differential pathogenicity in Shigella sp. has recently sequenced the curA gene within the S. sonnei whole genome. Due to a lack of knowledge of the elucidated curA and its function in microbial metabolism, studies seeking to identify diverse species of curcumin-converting bacteria are scarce. However, given the evidence of three identified Gram-negative bacteria possessing the putative gene, this study aims to identify and characterize an array of environmental isolates possessing the putative curA which were extracted from soil Winogradsky columns. The soil isolates were harvested from Winogradsky columns containing 1% ground turmeric root within the column and were maintained on 1% powdered turmeric-containing. Isolates were characterized using 16s rRNA sequencing and phylogeny was observed through phylogenetic tree creation. Primers were designed based on the two curA sequences available from E. coli str. K-12 and S. sonnei str. ECH+12, which share a 98% curA sequences similarity. Phylogenetic analysis exemplifies the diverse nature of this gene and its conservation within the genome that has persisted throughout a diverse array of Gram-negative bacteria. Further understanding of curcumin metabolic activity encourages the prospect of effective curcumin therapies in clinical settings, such as the use of curcumin therapy to inhibit tumor growth in mice with colorectal, pancreatic, and breast.