Differential Gene Expression in the Model Actinomycete Streptomyces coelicolor A3(2) Supports Nitrogen Mining Dependent on the Plant Carbon to Nitrogen Ratio

Nitrogen mining is the process whereby microbial communities catabolise recalcitrant long-term organic matter (OM) to meet nutritional requirements that are not ensured by labile OM. Microbial degradation of recalcitrant OM impacts soil fertility and contributes to greenhouse gas emissions in agricultural systems. Here we conducted a transcriptomics study to track differential gene expression in the model soil Actinomycete Streptomyces coelicolor A3(2) during the decomposition of mung bean ( Vigna radiata L.) and wheat ( Triticum aestivum L.) residues of relatively low and high carbon-to-nitrogen (C:N) ratios (17.3 and 35.7, respectively) at 1, 7, and 14 days of incubation. A negative binomial general linear model showed that plant variety predominantly affected transcription ( p < 0.001), although time of incubation also had an effect ( p = 0.01). In the high C:N ratio treatment, the expression of cellulases, chitinase, N-acetylglucosaminidase, secreted peptidases, and mineral nitrogen (N) metabolism were increased after 24 h. The low C:N ratio treatment demonstrated preferential expression of glutamate dehydrogenase, transporters involved in glutamate uptake and glycolysis, indicating more efficient N and carbon (C) assimilation. After 14 days, the low C:N ratio treatment showed increased transcription of extracellular enzymes, glutamate dehydrogenase, and glutamate transport. These results show an important role for added plant organic N content in determining when the transcription of genes associated with N mining occurs.