Deadwood-Inhabiting Bacteria Show Adaptations to Changing Carbon and Nitrogen Availability During Decomposition.

Vojtěch Tláskal,Petr Baldrian

doi:10.3389/fmicb.2021.685303

Vojtěch Tláskal, Petr Baldrian

Open Access

https://doi.org/10.3389/fmicb.2021.685303

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Abstract

Deadwood decomposition is responsible for a significant amount of carbon (C) turnover in natural forests. While fresh deadwood contains mainly plant compounds and is extremely low in nitrogen (N), fungal biomass and N content increase during decomposition. Here, we examined 18 genome-sequenced bacterial strains representing the dominant deadwood taxa to assess their adaptations to C and N utilization in deadwood. Diverse gene sets for the efficient decomposition of plant and fungal cell wall biopolymers were found in Acidobacteria, Bacteroidetes, and Actinobacteria. In contrast to these groups, Alphaproteobacteria and Gammaproteobacteria contained fewer carbohydrate-active enzymes and depended either on low-molecular-mass C sources or on mycophagy. This group, however, showed rich gene complements for N2 fixation and nitrate/nitrite reduction—key assimilatory and dissimilatory steps in the deadwood N cycle. We show that N2 fixers can obtain C independently from either plant biopolymers or fungal biomass. The succession of bacteria on decomposing deadwood reflects their ability to cope with the changing quality of C-containing compounds and increasing N content.

Highlights

The decomposition of deadwood in forests is a complex process during which plant polymers such as cellulose, hemicellulose, and lignin are exploited by members of the microbial community
Our isolation, which resulted in 959 deadwood bacterial isolates, was partly redundant, with many taxa repeatedly captured (Supplementary Figure 1), yet due to the presence of several members of dominant deadwood OTUs, the collection represented a relatively large portion of the bacterial community—on average, approximately one-third of the bacteria present in CWD
We identified strains with an increased potential for the utilization of complex carbohydrates, including cellulose, chitin, hemicelluloses, and pectin

Summary

Introduction

The decomposition of deadwood in forests is a complex process during which plant polymers such as cellulose, hemicellulose, and lignin are exploited by members of the microbial community. N accumulates in Adaptations of Deadwood Bacteria deadwood during decomposition either due to transport via the mycelium of ectomycorrhizal and soil foraging fungi (Philpott et al, 2014) or via the activity of the diazotrophic bacterial community (Rinne et al, 2016; Tláskal et al, 2021a). Such an increase gradually alleviates N limitation, leading to a more favorable C:N ratio of the whole habitat (Weedon et al, 2009)

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