High Genetic Potential for Proteolytic Decomposition in Northern Peatland Ecosystems

Abstract

33Nitrogen (N) is a scarce nutrient commonly limiting primary productivity. Microbial 34 decomposition of complex carbon (C) into small organic molecules (e.g., free amino acids) has 35 been suggested to supplement biologically-fixed N in high latitude peatlands. We evaluated the 36 microbial (fungal, bacterial, and archaeal) genetic potential for organic N depolymerization in 37 peatlands at Marcell Experimental Forest (MEF) in northern Minnesota. We used guided gene 38 assembly to examine the abundance and diversity of protease genes; and further compared to 39 those of N-fixing (nifH) genes in shotgun metagenomic data collected across depth at two 40 distinct peatland environments (bogs and fens). Microbial proteases greatly outnumbered nifH 41 genes with the most abundant gene families (archaeal M1 and bacterial Trypsin) each containing 42 more sequences than all sequences attributed to nifH. Bacterial protease gene assemblies were 43 diverse and abundant across depth profiles, indicating a role for bacteria in releasing free amino 44 acids from peptides through depolymerization of older organic material and contrasting the 45 paradigm of fungal dominance in depolymerization in forest soils. Although protease gene 46 assemblies for fungi were much less abundant overall than for bacteria, fungi were prevalent in 47 surface samples and therefore may be vital in degrading large soil polymers from fresh plant 48 inputs during early stage of depolymerization. In total, we demonstrate that depolymerization 49 enzymes from a diverse suite of microorganisms, including understudied bacterial and archaeal 50 lineages, are likely to play a substantial role in C and N cycling within northern peatlands. 51 52

Substratum‐associated microbiota

“…Using shotgun metagenomic sequencing, Graham, Yang, Bell, and Hofmockel (2019) studied the proteolytic degradation of complex organic matter in northern peatlands to help determine how various microbes influence C and N cycling. Microbial succession was associated with anaerobic chitin degradation in the littoral sediment of Lake Constance (Wörner & Pester, 2019).…”