Metagenomics investigation of agarlytic genes and genomes in mangrove sediments

Mangrove sediments (MGSs) provide a special environment for enriching carbohydrate-active enzyme (CAZyme) genes. However, the potential of MGSs as a repertory of CAZyme genes has been poorly evaluated. In this study, the environmental DNA (eDNA) of MGSs was deeply sequenced. Comparable or even higher numbers of complete CAZyme genes were annotated in our datasets compared with the datasets of cattle rumen and termite intestines, which are two proven outstanding repertories for CAZyme genes. Our work emphasized the agarlytic genes and genomes because of the great potential of agar in the bio-energy field. The agarose-degrading activities of 30 agarases derived from MGSs were determined by heterologous expression based on the numerous complete open-reading frames rarely obtained in most metagenomic sequencing studies. Accordingly, 4 agarases with potential for practical production were found. Analysis of signal peptides showed a probable economical and collaborative process in agarose utilization among the MGSs. Six draft genomes were recovered, and the metabolic pathway of agarose was speculated through the first attempt in investigating the metagenomics of MGSs. Our results showed the great value of MGSs in mining CAZyme genes. The MGSs may serve as a powerful tool for solving the problem in degrading different complex polysaccharides.