Quantitative assessment of bacterial and fungal degradation of glucose and cellulose [thesis]

Rene N. Miller
Quantitative assessment of bacterial and fungal degradation of glucose and cellulose Rene Miller Fungi are known for having metabolic capabilities that allow them to decompose complex organic material and are abundant in the organic soil horizon. The mineral horizon has a greater proportion of bacteria. These trends suggest that fungi are the predominate decomposers of complex polymeric substrates while bacteria focus on simpler substrates. However multiple strains of cellulose degrading
more » ... se degrading bacteria have been identified making the relative contribution of these groups to decomposition less clear. The goal of this research was to quantify the assimilation of cellulose and glucose derived carbon by bacterial and fungal taxa thus revealing their decomposition activity. To address this objective, we examined bacterial and fungal communities from soils with differing carbon substrate inputs by sampling the Detritus Input and Removal Treatment (DIRT) plots in Harvard Forest (Petersham, MA). We examined soils that have received twice the normal amount of leaf litter (double litter), had no leaf litter (no litter), or had normal litter inputs (control). We measured the decomposition of glucose and cellulose by incubating soils with 13 C-labeled substrates. Assimilation of substrates by microbial taxa was assessed by quantitative stable isotope probing. This method measures the incorporation of isotopically labeled (i.e. 13 C) compounds into the DNA of microorganisms. The rate of glucose decomposition was greater than that of cellulose regardless of treatment, with the majority of mineralization occurring in the first two weeks. The rate of decomposition varied across treatments. Both microbial groups showed significant 13 C incorporation from glucose and cellulose. On average fungal operational taxonomic units (OTUs) had a higher 13 C excess atom fraction (EAF) compared to bacterial OTUs for both substrates. A significant number of bacterial OTUs had little to no 13 C EAF suggesting that those OTUs may be dormant or utilizing alternative substrates. The metabolically active bacterial OTUs may be important in cellulose degradation and competitive in glucose assimilation. Bacterial OTUs 13 C EAF was not significantly different between substrates and across treatments, whereas fungal OTUs 13 C EAF varied. Substrate usage by bacteria was not impacted by environmental variance, whereas fungal usage may vary. iii
doi:10.33915/etd.7215 fatcat:dd74xrsmevhhvo2a7wrwz4md6m