Abstract
BackgroundImproved carbohydrate-active enzymes (CAZymes) are needed to fulfill the goal of producing food, feed, fuel, chemicals, and materials from biomass. Little is known about how the diverse microbial communities in anaerobic digesters (ADs) metabolize carbohydrates or which CAZymes that are present, making the ADs a unique niche to look for CAZymes that can potentiate the enzyme blends currently used in industry.ResultsEnzymatic assays showed that functional CAZymes were secreted into the AD environments in four full-scale mesophilic Danish ADs fed with primary and surplus sludge from municipal wastewater treatment plants. Metagenomes from the ADs were mined for CAZymes with Homology to Peptide Patterns (HotPep). 19,335 CAZymes were identified of which 30% showed 50% or lower identity to known proteins demonstrating that ADs make up a promising pool for discovery of novel CAZymes. A function was assigned to 54% of all CAZymes identified by HotPep. Many different α-glucan-acting CAZymes were identified in the four metagenomes, and the most abundant family was glycoside hydrolase family 13, which contains α-glucan-acting CAZymes. Cellulytic and xylanolytic CAZymes were also abundant in the four metagenomes. The cellulytic enzymes were limited almost to endoglucanases and β-glucosidases, which reflect the large amount of partly degraded cellulose in the sludge. No dockerin domains were identified suggesting that the cellulytic enzymes in the ADs studied operate independently. Of xylanolytic CAZymes, especially xylanases and β-xylosidase, but also a battery of accessory enzymes, were present in the four ADs.ConclusionsOur findings suggest that the ADs are a good place to look for novel plant biomass degrading and modifying enzymes that can potentiate biological processes and provide basis for production of a range of added-value products from biorefineries.
Highlights
Improved carbohydrate-active enzymes (CAZymes) are needed to fulfill the goal of producing food, feed, fuel, chemicals, and materials from biomass
A study of switchgrass degraded in cow rumen showed that only 12% of the identified CAZymes had 75% or more identity to known proteins and 43% had less than 50% identity to known proteins
The microorganisms in unexplored habitats may have evolved novel CAZymes in order to cope with both deconstruction of the biomass they use as carbon source and the environment their secreted enzymes must act in
Summary
Improved carbohydrate-active enzymes (CAZymes) are needed to fulfill the goal of producing food, feed, fuel, chemicals, and materials from biomass. The use of biomass to produce more food and feed from biomass and renewable biobased chemicals, materials, Wilkens et al Biotechnol Biofuels (2017) 10:158 metagenomics, combined with use of synthetic genes for production of CAZymes through heterologous expression, has revolutionized our opportunities for CAZyme discovery from microbes often living in complex communities. This enables us to study microbial communities [2, 4,5,6] and finds new enzymes for industrial uses. The microorganisms in unexplored habitats may have evolved novel CAZymes in order to cope with both deconstruction of the biomass they use as carbon source and the environment their secreted enzymes must act in
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