Microbiology Lect 23 Flashcards
What are the members of the microbiome of the large intestine/colon
-Two main components:
-Firmicutes: gram +, including Lactobacillus, Clostridium, Christensenella
-Bacteroidetes: Gram -, including Bacteroides and Prevotella
-Also many Proteobacteris (E. Coli) and Actinobacteria (Bifidobacterium)
Biochemical/metabolic contributions of intestinal microbes
-Vitamin synthesis
-Amino acid synthesis
-Organic acid production
-Breakdown of large polymers using extracellular enzymes
-Production of neurological agents
-Nitrogen fixation
-Results in gas and odor production
Why does the most abundant virus in the human colon infect a Bacteroides species?
To keep the population in check
Vicuna dung gardens
-Vicunas leave dung piles high up in the mountains where there are no other nutrients or living things
-Vicunas have been seen eating out of them
-Bacteroidetes dominate the poop piles, but they are aerobic coil Bacteroidetes, not from the vicunas
What are archaea in the colon?
-About 10-30% of microbes in the colon, mostly methanogens
-Many live syntropically with fermentative members of the Clostridiales including M. smithii
-Removal of H2 by M. smithii allows more fermentation and the production of more acetate by Clostridiales
-Excess acetate is associated with lipid production in the liver
Methanogenesis reaction:
4H2 + CO2 = CH4 + 2H2O
Syntrophy
Ethanol fermenter ferments ethanol to acetate, the methanogen takes the hydrogen that was produced and uses it with CO2 to form CH4
What do methanogens do in the colon, and what is the result of that?
-Methanogens remove H2, which increases acetate, which increases fat production
-More methanogens also results in more flatulence (CH4)
Experiment with microbiome and mice
-Two mice with no microbiomes were infected, one with microbiome of an obese person, and the other with the microbiome of a lean person
-Microbiome from obese human cause them to be obese
-Microbiome from lean human caused them to be lean
-Obese mice living with lean mice acquired lean microbiome and lost weight
How can different species of the microbiome affect body fat?
-Christensenella minuta reduced body fat in experiments with germ-free mice
-Levels of C. minuta in humans correlates with body mass index (BMI)
Christensenella minuta
-Non-spore-forming, strict anaerobe in the Phylum Firmicutes, order Clostridiales
-Produces both butyric and acetic acids via fermentations-
-Also anti-inflammatory
Bifidiobacterium (Actinobacteria)
-Many gut Bifidiobacterium ferment milk-based oligosacchardies
-Important in early development of the gut microbiome and infant nutrition
-Decreases as breastfeeding stops, around 12 months
-Also added to yogurt as a probiotic
Succession of the entire microbial community
-Greatest as an infant, decreases as one gets older
What are Probiotics
-Live microorganism which confers a health benefit when consumed
-Concept introduced in 1907 by Elie Metchnikoff, considered heretical
-Two main genera:
-Lactobacillus and Bifidiobacterium
-Many new candidates: Bacteroides, Christensenella, Cutinbacterium
How do probiotics work?
- inactivation of bacterial toxins/metabolites
- competition with pathogens for nutrients/adhesion sites
- up-regulation of immunity
- suppression of inflammation
- promotion of intestinal barrier function.
