Abstract
Monosaccharides and oligosaccharides produced by agarose degradation exhibit potential in the fields of bioenergy, medicine, and cosmetics. Mangrove sediments (MGSs) provide a special environment to enrich enzymes for agarose degradation. However, representative investigations of the agarlytic genes in MGSs have been rarely reported. In this study, agarlytic genes in MGSs were researched in detail from the aspects of diversity, abundance, activity, and location through deep metagenomics sequencing. Functional genes in MGSs were usually incomplete but were shown as results, which could cause virtually high number of results in previous studies because multiple fragmented sequences could originate from the same genes. In our work, only complete and nonredundant (CNR) genes were analyzed to avoid virtually high amount of the results. The number of CNR agarlytic genes in our datasets was significantly higher than that in the datasets of previous studies. Twenty-one recombinant agarases with agarose-degrading activity were detected using heterologous expression based on numerous complete open-reading frames, which are rarely obtained in metagenomics sequencing of samples with complex microbial communities, such as MGSs. Aga2, which had the highest crude enzyme activity among the 21 recombinant agarases, was further purified and subjected to enzymatic characterization. With its high agarose-degrading activity, resistance to temperature changes and chemical agents, Aga2 could be a suitable option for industrial production. The agarase ratio with signal peptides to that without signal peptides in our MGS datasets was lower than that of other reported agarases. Six draft genomes, namely, Clusters 1–6, were recovered from the datasets. The taxonomic annotation of these genomes revealed that Clusters 1, 3, 5, and 6 were annotated as Desulfuromonas sp., Treponema sp., Ignavibacteriales spp., and Polyangiaceae spp., respectively. Meanwhile, Clusters 2 and 4 were potential new species. All these genomes were first reported and found to have abilities of degrading various important polysaccharides. The metabolic pathway of agarose in Cluster 4 was also speculated. Our results showed the capacity and activity of agarases in the MGS microbiome, and MGSs exert potential as a repertory for mining not only agarlytic genes but also almost all genes of the carbohydrate-active enzyme family.
Highlights
Given the demand for bioenergy, researchers have isolated numerous genes and genomes with biomass-degrading functions (Harris et al, 2010; Langston et al, 2011; Sheydina et al, 2014; Yang et al, 2016) to produce fermentable monosaccharides
The results proved that Mangrove sediments (MGSs) are potential repertories of agarlytic genes and almost all families of CAZyme genes
The organic carbon content in MGSs was studied in former studies
Summary
Given the demand for bioenergy, researchers have isolated numerous genes and genomes with biomass-degrading functions (Harris et al, 2010; Langston et al, 2011; Sheydina et al, 2014; Yang et al, 2016) to produce fermentable monosaccharides. Most of these works have focused on screening cellulase genes, and cellulose is the usual material for producing fermentable monosaccharides. Natural cellulose fibrils exclude water and cellulases (Lynd et al, 2002; Zhang and Lynd, 2003). Producing fermentable monosaccharides through cellulose hydrolysis by cellulases still has limited application. The solubility of agarose is higher than that of celluloses, and agarases could directly function on agarose dissolved in water. The enzymatic hydrolysis efficiency of agarose is significantly increased compared with that of celluloses. Agarose can be extracted and dissolved by heating, which is easier and cost saving than the current pre-treatment methods for cellulose. Agarose is a potential alternative to cellulose for fermentable monosaccharide production. The demand for enzymes with outstanding agarose-degrading activity is high
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
