Microorganisms play an essential role in the processing of plant-derived matter in nature and in industrial settings. Decomposition of plant matter in nature is a key process in the feedback between soils and the atmosphere and an important parameter to incorporate into climate models to increase their predictive value. The mechanisms that enable decomposers to process plant matter in nature are not known. To gain insights, I investigated the response of Cellulomonas decomposers to nitrogen disturbances such as those caused by the addition of fertilizers or atmospheric deposition of greenhouse gases. These decomposers adapt to low nitrogen by specifically colonizing plant-derived substrates as biofilms and sequestering significant amounts of carbon in the biofilm matrix. The biofilm strategy enabled cells to be closer to the substrate and to degrade it more efficiently despite the low availability of nitrogen sources. The process is reversible and potentially manageable, thus showing promise for its use as a carbon remediation technology to mitigate the accumulation of greenhouse gases. Knowledge gained from studying Cellulomonas uda can be utilized in industry as interest in cellulolytic microorganisms has increased in recent years due to their role in bioethanol production. To minimize the cost of bioethanol, agricultural residues and dedicated bioenergy crops are preferable as substrates instead of starch and sugar. These lignocellulosic substrates are more recalcitrant and require a chemical pretreatment step plus an additional step of enzymatic hydrolysis to make them fermentable. Consolidated bioprocessing (CBP), i.e. a combined platform that catalyzes the breakdown and fermentation of cellulose in one single step, is a cost-effective approach to producing ethanol from lignocellulosic substrates. C. uda is an attractive candidate for industrial consolidated bioprocessing of lignocellulose. The activities of this organism is limited, however, by the accumulation of ethanol and fermentation byproducts, which in nature are rapidly removed by other organisms. Our lab has developed a platform for the bioprocessing of chemically-pretreated agricultural residues such as corn stover by C. uda and Geobacter sulfurreducens into ethanol and biohydrogen using a microbial electrochemical cell (MEC). As predicted, nitrogen supplementation prevented the accumulation of carbon as a curdlan biofilm matrix and resulted in 2-fold increases in the energy recoveries from the fermentation of Ammonia Fiber Expansion pretreated corn stover (AFEX-CS). Improving culture conditions and developing a faster fermenting strain led to a 12-fold increase in ethanol productivity. Another bioprocessing scheme of industrial significance is the generation of value-added co-products from glycerol, the major waste product in the production of biodiesel. Harnessing the glycerin waste stream to produce value-added products will diminish the cost and waste of biodiesel production. We identified a glycerol-fermenting bacterium (Clostridium cellobioparum) that converts glycerol into ethanol at high rates and generates waste fermentation byproducts that are converted into hydrogen in Geobacter-driven MECs. This scheme shows promise as a wastewater treatment method as optimization of the platform resulted in glycerol consumption of 50g/L.
Read
