Identification and biochemical characterization of a novel GH113 β-mannanase from acid mine drainage metagenome

Acid mine drainage (AMD) is a highly acidic and heavy metal-bearing environment with marginal availability of nutrients. Indeed, recycling the scarce organic matter in such environments is of particular ecophysiological functions, and polymer-degrading enzymes from AMD sites remain mostly uncharacterized. Here, harnessing the acid mine drainage biocatalytic reservoirs via sequence-based metagenomic technology, a novel highly-active β-mannanase was identified. This new β-mannanase, designated Man113Ali9, belongs to the glycoside hydrolase (GH) 113 family, one that remained underexplored. Deduced Man113Ali9 exhibited the highest identity (68%) to a characterized GH113 β-mannanase from Alicyclobacillus sp. A4. Man113Ali9 displayed optimal activity at pH 6.0 and 50 ℃, with over 75% activity retained at pH 5.0–9.0. The addition of K+ and Tween 80 enhanced enzyme activity by 29% and 48%, respectively. Man113Ali9 was capable to hydrolyze various mannan substrates and displayed higher activity on glucomannan than on galactomannan. Man113Ali9 also appeared to exhibit transglycosylation activity toward mannotetraose to mannohexaose. Our results underlined the utility of the metagenomic approach to mine novel polymer-degrading enzymes with promising biotechnological applications from AMD.