Evolution of cellulolytic activity in Streptomyces

Evolution of cellulolytic activity in Streptomyces

Understanding the complex processes driving the evolution of biomass deconstruction in bacteria.

The Science                              

The degradation of cellulose, the principal component of plant cell walls, is critical to ecosystem functioning and the global carbon cycle. The primary drivers of plant biomass deconstruction are fungi and bacteria found in the soil or associated with plant-eating eukaryotes.

The Impact

Understanding the evolution of cellulolytic activity in a bacterial genus is key to studying the ecological functions of microbes in the environment and how they contribute to the global carbon cycle. The genus Streptomyces, abundant in soil and symbiotic niches associated with insect hosts that feed on plant biomass, is widely considered to have the ability to rapidly degrade cellulose. This work demonstrates how high cellulolytic activity is not a conserved characteristic of the entire genus, but is surprisingly rare and enriched in Streptomyces strains associated with insect hosts that feed on plant biomass.

Summary

Researchers in the Great Lakes Bioenergy Research Center compared the phylogenetic diversity of over 1,100 strains of Streptomyces, measured the cellulose degrading activity of 223 diverse strains isolated from free-living and eukaryotic host-associated niches, and identified strains that exhibited high rates of cellulose degrading activity by using a  filter paper (FP) deconstruction assay. Only 13% of those strains tested (29/223) were found to rapidly deconstruct FP, and 86% of these grouped into 2 phylogenetically distinct clades (I and III) associated with insect hosts that feed on plant biomass such as wood wasps, pine beetles, and leaf cutter ants. Comparative genomics studies identified that while plant biomass degrading enzymes (CAZy) are widespread in Streptomyces, key enzyme families were obtained by horizontal gene transfer, and were retained in the most highly cellulolytic strains. By using a combination of transcriptomic and biochemical analyses, the researchers identified key changes in transcriptional control of expression that confer cellulolytic activity. This research has given new insight into how specialized interactions between microbes and insects have given rise to increased microbial capability to deconstruct plant biomass, and has identified the key genes, regulatory circuits, and enzymes used in this process.

Contacts (BER PM)

N. Kent Peters
Program Manager, Office of Biological and Environmental Research
kent.peters@science.doe.gov, 301-903-5549

(PI Contact)

Cameron R. Currie
University of Wisconsin - Madison
currie@bact.wisc.edu

Brian G. Fox
University of Wisconsin - Madison
bgfox@biochem.wisc.edu

Funding

The DOE Great Lakes Bioenergy Research Center is supported by the US Department of Energy, Office of Science, Office of Biological and Environmental Research, through contract number DE-FC02-07ER64494.

Publications

Book AJ, Lewin GR, McDonald BR, Takasuka TE, Wendt-Pienkowski E, Doering DT, Suh S, Raffa KF, Fox BG, Currie CR “Evolution of High Cellulolytic Activity in Symbiotic Streptomyces through Selection of Expanded Gene Content and Coordinated Gene Expression”. PLOS Biology. 55 (12), 14(6): e1002475 (2016) [DOI: 10.1371/journal.pbio.1002475]

Related Links

http://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.1002475

PM Recommendation for SC Web Publication

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