Cellulolytic potential under environmental changes in microbial communities from grassland litter - PubMed (original) (raw)

Cellulolytic potential under environmental changes in microbial communities from grassland litter

Renaud Berlemont et al. Front Microbiol. 2014.

Abstract

In many ecosystems, global changes are likely to profoundly affect microorganisms. In Southern California, changes in precipitation and nitrogen deposition may influence the composition and functional potential of microbial communities and their resulting ability to degrade plant material. To test whether such environmental changes impact the distribution of functional groups involved in leaf litter degradation, we determined how the genomic diversity of microbial communities in a semi-arid grassland ecosystem changed under reduced precipitation or increased N deposition. We monitored communities seasonally over a period of 2 years to place environmental change responses into the context of natural variation. Fungal and bacterial communities displayed strong seasonal patterns, Fungi being mostly detected during the dry season whereas Bacteria were common during wet periods. Most putative cellulose degraders were associated with 33 bacterial genera and predicted to constitute 18% of the microbial community. Precipitation reduction reduced bacterial abundance and cellulolytic potential whereas nitrogen addition did not affect the cellulolytic potential of the microbial community. Finally, we detected a strong correlation between the frequencies of genera of putative cellulose degraders and cellulase genes. Thus, microbial taxonomic composition was predictive of cellulolytic potential. This work provides a framework for how environmental changes affect microorganisms responsible for plant litter deconstruction.

Keywords: cellulase; global change; leaf litter; metagenomics; microbial community composition.

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Figures

FIGURE 1

FIGURE 1

(A) Cumulative precipitation at Loma Ridge study site. (B) Overall distribution of sequences with annotation in the major microbial phyla detected in the leaf litter metagenomes across treatments [control (C), added nitrogen (N), reduced precipitation (R)] and seasons. (C) Fluctuations of the overall frequency of cellulase sequences in the leaf litter metagenomes.

FIGURE 2

FIGURE 2

(A) Distribution of cellulolytic enzymes in potential bacterial cellulose degraders. (B) Relationship between the lineage specific cellulase frequency and the potential cellulose degrading genera in the leaf litter metagenomes (_P_Spearman < 0.01).

FIGURE 3

FIGURE 3

Effect of the cumulative precipitation during the 2 weeks prior to litter collection on the overall rarefied frequency of microbial glycoside hydrolases (GHs), carbohydrates binding modules (CBMs), β-glucosidases, and cellulases. Break in the _x_-axis was introduced to discriminate low from high precipitation.

FIGURE 4

FIGURE 4

(A) Linear dependence of the normalized abundance of potential cellulose degraders and their potential cellulase content, across the samples (PSpearman < 0.01). (B) Comparison between the observed and the predicted cellulase content based on microbial community composition [samples used to construct the linear regression model (○) and independent samples from the factorial reduced precipitation and added nitrogen treatment (●)]. The solid and dotted lines are the regression line and the 1:1 line, respectively.

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