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Pretreatments to enhance the digestibility of recalcitrant waste—current trends
Published in Małgorzata Pawłowska, Artur Pawłowski, Advances in Renewable Energy Research, 2017
Following another trend, the researchers constructed microbial consortia dedicated for degrading different recalcitrant waste. Poszytek et al. (2016) tested a microbial consortium with high cellulolytic activity (MCHCA) for maize silage decomposition. The consortium included 16 selected strains (representatives of Bacillus, Providencia, and Ochrobactrum genera) which had a high endoglucanase activity and exhibited wide tolerance to various physical, and chemical conditions. The MCHCA was found to be capable of efficient hydrolysis of the substrate. This resulted in an increase of biogas production by up to 38%. Thermophilic microbial consortium (MC1) with great lignocellulose degradation ability was involved by Yuan et al. (2016) for enhancement of methane yield as well as methane production rate from cotton stalk. The MC1 contained Clostridium straminisolvens (CSK1), Clostridium sp. FG4b, Pseudoxanthomonas sp. strain M1-3, Brevibacilus sp. M1-5, and Bordetella sp. M1-6. The predominant volatile organic products in the MC1 hydrolysate were ethanol, acetic acid, propionic acid, and butyric acid. It was shown that biogas and methane yields were significantly increased following MC1 pretreatment. Moreover, the methane production rate was enhnaced. In contrast, Baba et al. (2016) used a natural consortium of microbes present in cattle rumen fluid to improve the methane production from rapeseed (Brassica napus L.). The cattle rumen fluid contains 1010–1011 bacteria per gram and exhibits a high capacity of converting lignocellulose to saccharides and short-chain fatty acids. Hence, using such a consortium for waste pretreatment could result in an effective substrate solubilization and, subsequently, in enhanced biogas production. It was shown that methane production from solubilized rapeseed exceeded the values obtained from untreated substrate by 1.5 times. While analyzing microbial community during rumen fluid treatment, some changes were observed, i.e. predominant phylum shifted from Bacteroidetes, composed of amylolytic Prevotella spp., to Firmicutes, composed of cellulolytic and xylanolytic Ruminococcus spp., in only 6 h. Moreover, 7 cellulolytic, 25 cello-oligosaccharolytic, and 11 xylanolytic bacteria were detected while investigating the most abundant sequences of detected taxa.
Guided dietary fibre intake as a means of directing short-chain fatty acid production by the gut microbiota
Published in Journal of the Royal Society of New Zealand, 2020
Cellulosomes are multi-enzyme complexes at the bacterial cell surface that facilitate the degradation of cellulose and hemicelluloses by bacteria in the rumen and soil (Bayer et al. 2004). One species, Ruminococcus champanellensis, with this property has been detected in the human gut microbiota (Ben David et al. 2015). Cellulosomes bring hydrolytic enzymes, carbohydrate-binding domains, substrate, and cell surface into close proximity, facilitated by molecules called ‘dockerins’ and ‘cohesins’ (Bayer et al. 2004). A simpler type of multi-enzyme complex (the ‘amylosome’) is present on the cells of the starch-degrading species Ruminococcus bromii (Ze et al. 2015). This species has an exceptional ability to degrade particulate resistant starches when compared with other amylolytic bacterial species inhabiting the gut. The importance of starch in the life of R. bromii is confirmed by analysis of the genome sequence of strain L2-63: it encodes 21 glycosyl hydrolases of which 15 belong to the family GH13 (amylases, pullulanases) (Ze et al. 2012).