Abstract
BackgroundThermobacillus xylanilyticus is a thermophilic and highly xylanolytic bacterium. It produces robust and stable enzymes, including glycoside hydrolases and esterases, which are of special interest for the development of integrated biorefineries. To investigate the strategies used by T. xylanilyticus to fractionate plant cell walls, two agricultural by-products, wheat bran and straw (which differ in their chemical composition and tissue organization), were used in this study and compared with glucose and xylans. The ability of T. xylanilyticus to grow on these substrates was studied. When the bacteria used lignocellulosic biomass, the production of enzymes was evaluated and correlated with the initial composition of the biomass, as well as with the evolution of any residues during growth.ResultsOur results showed that T. xylanilyticus is not only able to use glucose and xylans as primary carbon sources but can also use wheat bran and straw. The chemical compositions of both lignocellulosic substrates were modified by T. xylanilyticus after growth. The bacteria were able to consume 49% and 20% of the total carbohydrates in bran and straw, respectively, after 24 h of growth. The phenolic and acetyl ester contents of these substrates were also altered. Bacterial growth on both lignocellulosic biomasses induced hemicellulolytic enzyme production, and xylanase was the primary enzyme secreted. Debranching activities were differentially produced, as esterase activities were more important to bacterial cultures grown on wheat straw; arabinofuranosidase production was significantly higher in bacterial cultures grown on wheat bran.ConclusionThis study provides insight into the ability of T. xylanilyticus to grow on abundant agricultural by-products, which are inexpensive carbon sources for enzyme production. The composition of the biomass upon which the bacteria grew influenced their growth, and differences in the biomass provided resulted in dissimilar enzyme production profiles. These results indicate the importance of using different biomass sources to encourage the production of specific enzymes.
Highlights
Thermobacillus xylanilyticus is a thermophilic and highly xylanolytic bacterium
T. xylanilyticus growth kinetics on various substrates Growth profiles were determined for three different cultures that included monosaccharide, polysaccharides and two different types of plant cell walls (WB and Wheat straw (WS)) by monitoring turbidity of the culture medium for 25 h
A maximal yield was obtained with glucose as a substrate (1972 ± 172 μg/ mL), whereas the culture grown on Wheat bran (WB) produced only 739 ± 53 μg/mL of proteins)
Summary
Thermobacillus xylanilyticus is a thermophilic and highly xylanolytic bacterium. It produces robust and stable enzymes, including glycoside hydrolases and esterases, which are of special interest for the development of integrated biorefineries. Various starting materials, including agricultural residues (such as sugarcane bagasse, corn stover, wheat bran (WB) and wheat straw (WS)) and forest residues, represent biomass substrates of interest to Lignocellulosic plant cell walls are an assembly of cellulose, lignin and hemicelluloses. These polymers are linked together by covalent and non-covalent linkages and form an organized network. Arabino-glucuronoxylans are the most abundant hemicelluloses found in graminaceous plants They are formed by linear chains of xylans that comprise β-(1,4)-linked D-xylopyranose residues. Lignin is a complex phenolic polymer responsible for the rigidity and impermeability of the plant cell wall, and it represents 10% to 35% of the dry matter in plant cell walls [6]
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