Metasecretome and biochemical analysis of consortium PM-06 during the degradation of nixtamalized maize pericarp

Abstract

Nixtamalized maize pericarp is an abundant by-product of the industrial processing of maize for tortilla production, and a potential source of prebiotics and biofuels. Consortium PM-06 is a bacterial community with the capacity to efficiently saccharify the nixtamalized pericarp; however, there is scarce information about the enzymatic mechanism involved. In this study, the soluble enzymes secreted by PM-06 in different stages of the degradation process were analyzed using biochemical approaches and label-free quantitative proteomics. Metasecretomic analysis revealed a marked abundance of glycosyl hydrolases in the initial stages of the process, mainly secreted by Bacillus and Paenibacillus. The main function of glycosyl hydrolases was the metabolism of soluble sugars released from maize pericarp. As degradation proceeded, substrate recalcitrance and oxidoreductase mass abundance increased. Actinobacteria, predominantly Microbacterium, secreted a great diversity of oxidoreductases with vanillyl alcohol oxidase as the most abundant enzyme. Lignin consumption in the last 48 h of culture and the lack of laccase and peroxidase sequences, suggest a role for Fenton chemistry. Different oxidoreductases secreted by PM-06 produce hydrogen peroxide, a co-substrate for various enzymes and a Fenton reactant. A strategy used by PM-06 to cope with substrate recalcitrance could be the use of hydroxyl radicals produced from H2O2 to attack polysaccharides and lignin. This study is the first report about a consortium secreting a great diversity of soluble oxidoreductases and provides information about possible synergistic interactions and functions of bacterial enzymes involved in lignocellulose degradation.