TITLE: Dynamic utilization of low-molecular-weight organic substrates across a microbial growth rate gradient
–Aim: Low-molecular-weight organic substances (LMWOSs) are at the nexus between microorganisms, plant roots, detritus, and the soil mineral matrix. Nominal oxidation state of carbon (NOSC) has been suggested a potential parameter for modeling microbial uptake rates of LMWOSs and the efficiency of carbon incorporation into new biomass.
–Methods and Results: In this study, we assessed the role of compound class and oxidation state on uptake kinetics and substrate-specific carbon use efficiency (SUE) during the growth of three model soil microorganisms, a fungal isolate (Penicillium spinulosum) and two bacterial isolates (Paraburkholderia solitsugae, and Ralstonia pickettii). Isolates were chosen that spanned a growth rate gradient (0.046-0.316 h-1) in media containing 34 common LMWOSs at realistically low initial concentrations (25 μM each). Clustered, co-utilization of LMWOSs occurred for all three organisms. Potential trends (p < 0.05) for early utilization of more oxidized substrates were present for the two bacterial isolates (P. solitsugae and R. pickettii), but high variability (R2 < 0.15) and a small effect of NOSC indicate these relationships are not useful for prediction. The SUEs of selected substrates ranged from 0.16-0.99 and there was no observed relationship between NOSC and SUE. –Conclusion: Our results do not provide compelling population-level support for NOSC as a predictive tool for either uptake kinetics or the efficiency of use of LMWOS in soil solution.
–Significance and Impact of the Study: Metabolic strategies of organisms are likely more important than chemical identity in determining LMWOS cycling in soils. Previous community-level observations may be biased towards fast-responding bacterial community members. [Link to Article]