C/N Ratio Drives Soil Actinobacterial Cellobiohydrolase Gene Diversity

Alexandre B. de Menezes, Miranda T. Prendergast-Miller, Pabhon Poonpatana, Mark Farrell, Andrew Bissett, Lynne M. Macdonald, Peter Toscas, Alan E. Richardson, Peter H. Thrall

Cellulose accounts for approximately half of photosynthesis fixed carbon, however the ecology of its degradation in soil is still relatively poorly understood. The role of actinobacteria in cellulose degradation has not been extensively investigated, despite their abundance in soil and known cellulose degradation capability. Here, the diversity and abundance of the actinobacterial glycoside hydrolase family 48 (cellobiohydrolase) gene was determined in soils from three paired pasture-woodland sites using T-RFLP and clone libraries with gene-specific primers. For comparison, the diversity and abundance of general bacteria and fungi were also assessed. Phylogenetic analysis of the nucleotide sequences of 80 clones revealed significant new diversity of actinobacterial GH48 genes, and analysis of translated protein sequences showed that these are likely to represent functional cellobiohydrolases. Soil C:N ratio was the primary environmental driver of GH48 community composition across sites and land uses, demonstrating the importance of substrate quality in their ecology. Furthermore, mid infrared (MIR) spectrometry-predicted humic organic carbon was distinctly more important to GH48 diversity than to total bacterial and fungal diversity. This suggests a link between actinobacterial GH48 community and soil organic carbon dynamics and highlights the potential importance of actinobacteria in the terrestrial carbon cycle.