A Microbial Biorealm page on the genus Bacterioides cellulosilyticus
Higher order taxa
Bacteria; Bacteroidetes; Bacteroidia; Bacteroidales; Bacteroidaceae; Bacteroides; Bacteroides cellulosilyticus
Description and significance
Extensive research has been performed to identify many of the microbes within the human gut. These microbes assist in the catabolism of foods that are consumed providing valuable nutrients and energy that the body needs. Most of these microbes have been classified within the phylum Bacteroidetes. Bacteroides cellulosilyticus (identified as strain CRE21) are a species of bacteria within the Bacteroides genus. These bacteria play an important role in the degradation of cellulose (cellulolytic) within the human microbiota. Cellulose is a polysaccharide that is found in plant cells walls and is an important source of dietary fiber. Most bacteria of the human gut are unable to break down plant polysaccharides (Flint, 2008). Degradation of cellulose by B. cellulsilyticus produce acetate, propionate and succinate (Robert, 2007). The mechanism by which this strain of bacterium degrade polysaccharides could prove useful in the understanding and development of biotechnological tools to break apart polysaccharides into monosaccharides.
The circular genome for B. cellulosilyticus is a total of 7,678,005 base pairs long with a G-C content of 43.05% (Integrate Microbial Genomes/Eduation Site, 2013). As a comparison, the human genome is 3 billion base pairs long (National Human Genome Research Institute, 2010). The 16S rRNA gene of strain CRE21 was sequenced with analysis revealing a close relationship to members of the phylum Bacteroidetes; sharing 97-98% similarity of 16S rRNA gene sequence with species B. intestinal (Robert, 2007). Although 97-98% similarity is a strong relationship to B. intestinalis, researchers agreed that there was enough variation to identify this as a new strain and provided it the name CRE21. Analysis of the genome revealed the total number of protein coding genes is 6,368. Additional genome statistics can be found at JGI Integrated Microbial Genomes/Education Site.
Cell and colony structure
B. cellulosilyticus are gram-negative, strictly anaerobic, non-spore-forming, rod-shaped, non-motile bacteria. Cells of strain CRE21 where evidenced as rods with rounded ends, with a mean length of 1.7 micrometers and mean width of 0.9 micrometers (Robert, 2007). As with other gram-negative cells, these bacteria have an outer membrane, peptidoglycan layer and a cytoplasmic membrane. The negatively stained cells lacked the presence of flagella. (Microbewiki, 2010) In studies, colonies were grown on glucose-BC agar medium producing translucent, white to slightly brown and circular colonies with a diameter of 2-5 mm. B. cellulosilyticus is a component of the bacterial florae within mucous membranes of the human gut and colon. Optimal growth environments for strain CRE21 include a temperature range of 25-45 0C and a pH of 6.8; these environmental conditions are consistent with that of the human colon (Robert, 2007).
B. cellulosilyticus, strain CRE21 was shown in studies to degrade, by fermentation, different types of cellulose producing acetate, propionate and succinate as metabolic by-products. This degradation occurred under anaerobic conditions. Additionally, strain CRE21 was shown to ferment glucose, sucrose, fructose, maltose, xylose, galactose, ribose, lactulose, pectin and starch. In the presence of lactose, raffinose, arabinose, cellobiose, aesculin, xylan and salicin poor growth was seen. Studies have shown that no growth was seen in the presence of trehalose, mannitol, inositol, sorbitol or fructose (Robert, 2007).
B. cellulosilyticus are found in the human intestine and gut microbiota where they are thought to play an important role in the degradation of complex molecules like cellulose. They have a symbiotic-host-bacterial relationship with humans whereby enhancing health by catabolizing complex molecules into metabolic byproducts that the body can use as sources of energy and essential nutrients (Microbewiki, 2010).
Research is limited on the pathological effects of B. cellulosilyticus as a strain of the genus Bacteriodes. Research however does support that species within the genus Bacteriodes have a significant pathological effect on their host if found outside of the human gut. If retained within the human gut these bacteria maintain a complex and mutually beneficial relationship with their host. The pathological effects of this bacterium present outside of the human gut are bacteremia and abscess formation in multiple sites of the body (Wexler, 2007). Species of this genus have formed antibiotic resistance and exhibit the highest resistance rates of all anaerobic pathogens (Wexler, 2007). Studies have shown that these bacteria have increasing resistance to many antibiotics including cefoxitin, clindamycin, metronidazole, carbapenems, and fluoroquinolones (Wexler, 2007).
Celine Robert, C. C.-D. (2007). Bacteroides cellulolyticus sp. nov., a cellulolytic bacterium from human gut microbial community. International Journal of Systematic and Evolutionary Microbiology (57), 1515-1520.
Harry J. Flint, E. A. (2008, February 1). Polysaccharide utilization by gut bacteria: potential for new insights from genomic analysis. Retrieved November 2, 2015, from nature Reviews Microbiology: http://www.nature.com/nrmicro/journal/v6/n2/execsumm/nrmicro1817.html
Integrate Microbial Genomes/Eduation Site. (2013, August 23). Bacteroides cellulosilyticus CL02T12C19. Retrieved November 2, 2015, from IJG Integrated Microbial Genomes/Education Site: https://img.jgi.doe.gov/cgi-bin/edu/main.cgi?section=TaxonDetail&page=taxonDetail&taxon_oid=2531839301
Microbewiki. (2010, July 23). Microbewiki. Retrieved November 2, 2015, from Bacteroides: https://microbewiki.kenyon.edu/index.php/Bacteroides National Human Genome Research Institute. (2010, October 30). The Human Genome Project Completion: Frequently Asked Questions. Retrieved November 2, 2015, from NHI: Advancing human health through genomics research: https://www.genome.gov/11006943
Wexler, H. M. (2007, October 20). Bacteroides: the Good, the Bad, and the Nitty-Gritty. Retrieved November 2, 2015, from Clinical Microbial Reveiws: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2176045/
Edited by Molly Tanguay of Dr. Lisa R. Moore, University of Southern Maine, Department of Biological Sciences, http://www.usm.maine.edu/bio