Abstract
The occurrence of Cladosporium in cold ecosystems has been evidenced long before, and most of the knowledge about nutrient utilization of this genus is sporadic. An alpine soil isolate C. neopsychrotolerans SL-16, showing great cold tolerance and significant lignocellulose-degrading capability, was sequenced to form a 35.9 Mb genome that contains 13,456 predicted genes. Functional annotation on predicted genes revealed a wide array of proteins involved in the transport and metabolism of carbohydrate, protein and lipid. Large numbers of transmembrane proteins (967) and CAZymes (571) were identified, and those related to hemicellulose degradation was the most abundant. To undermine the hemicellulose (xyaln as the main component) utilization mechanism of SL-16, the mRNA levels of 23 xylanolytic enzymes were quantified, and representatives of three glycoside hydrolase families were functionally characterized. The enzymes showed similar neutral, cold active and thermolabile properties and synergistic action on xylan degradation (the synergy degree up to 15.32). Kinetic analysis and sequence and structure comparison with mesophilic and thermophilic homologues indicated that these cold-active enzymes employed different cold adaptation strategies to function well in cold environment. These similar and complementary advantages in cold adaptation and catalysis might explain the high efficiency of lignocellulose conversion observed in SL-16 under low temperatures.
Highlights
The large fraction of the Earth’s surface, up to 80%, is occupied by permanently cold ecosystems, which include deep sea as well as polar (Arctic and Antarctic) and alpine regions[1]
We suggest that the synergistic actions on xylan degradation and complementary advantages in cold adaptation of xylanolytic enzymes are important traits of C. neopsychrotolerans for hemicellulose utilization under low temperature conditions
It suggested that strain SL-16 is a eurypsychrophilic fungus with significant lignocellulose-degrading capability
Summary
The large fraction of the Earth’s surface, up to 80%, is occupied by permanently cold ecosystems (below 5 °C), which include deep sea as well as polar (Arctic and Antarctic) and alpine regions[1] Such habitats experience extreme conditions that are challenging to most life forms, various microorganisms that colonize these cold environments have adapted to low temperatures. For only a few Carbohydrate Active enZymes (CAZymes), including glucoamylase[39], xylanase[40,41] and α-galactosidase[42], have been functionally characterized This sporadic knowledge provides some clues to but still far away from the underlying mechanisms of lignocellulose utilization of Cladosporium, not to speak of eurypsychrophilic Cladosporium. We suggest that the synergistic actions on xylan degradation and complementary advantages in cold adaptation of xylanolytic enzymes are important traits of C. neopsychrotolerans for hemicellulose utilization under low temperature conditions
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