Date of Award

Spring 5-2016

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Sciences

Committee Chair

Shiao Y. Wang

Committee Chair Department

Biological Sciences

Committee Member 2

Mohamed O. Elasri

Committee Member 2 Department

Biological Sciences

Committee Member 3

Kevin A. Kuehn

Committee Member 3 Department

Biological Sciences

Committee Member 4

Glenmore Shearer Jr.

Committee Member 4 Department

Biological Sciences

Committee Member 5

Dmitri V. Mavrodi

Committee Member 5 Department

Biological Sciences

Abstract

Lignocellulose decomposes slowly in nature because it consists of complex polymers resistant to enzymatic degradation by most organisms. Some bacteria are capable of producing cellulolytic enzymes but the way in which bacteria interact within a community to enhance degradation of the recalcitrant substrate is poorly understood. A better understanding of how bacterial interactions affect lignocellulose degradation would provide potential approaches to improve the efficiency of lignocellulose degradation for biofuel production.

To study whether bacterial interactions enhance lignocellulose degradation, I grew environmental bacterial isolates in mixed cultures and pure cultures. I found that bacterial synergism in mixed cultures was common in lignocellulose medium. Bacterial synergism promoted bacterial growth, metabolic activity and the production of β-1,4-glucosidase in mixed cultures. I also found that the complexity of carbohydrates mediated bacterial interactions. The synergistic growth found in lignocellulose medium was not observed in glucose medium, suggesting that bacterial synergism was substrate-dependent. Pairwise antagonistic interactions among bacteria showed that the frequency of antagonism in carboxymethyl cellulose (CMC)-xylan medium was only half of that in glucose medium, suggesting that reliance on complex polysaccharides as carbon source reduces bacterial antagonism. The frequency of antagonistic interactions among bacteria was not randomly distributed. Firmicutes and Gamma-Proteobacteria were among the most antagonistic groups whereas Bacteroidetes and Actinobacteria were the most susceptible groups. In addition, I also found different interaction network structures between bacteria relying on glucose and CMC-xylan as carbon sources.

Overall, results from the study showed that complex polysaccharides as the main carbon source promote bacterial synergism and reduce the frequency of bacterial antagonism. They support the potential use of bacteria synergism from different bacteria combinations to enhance plant biomass degradation/conversion for biofuel production.

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