impact of symbiosis on human health and disease

Lecture 16 MICR221

what are pathogens

bacteria that cause disease

commensals or mutualistic bacteria characteristics (3)

• don’t cause disease

• benefit from association with humans

• can provide benefits to humans (mutualistic)

symbiosis

‘living together’ of two organisms

what is commensalism

relationship where one organism benefits and the other is neither helped nor harmed

what is mutualism

relationship where both organisms benefit

what is pathogenesis

relationship where one organism is harmed

ways bacteria ‘help create us’ (3)

• intestinal flora help with human nutrition

• stimulate proper growth of intestine and immune system

• perturbation of normal bacterial flora can contribute to disease

areas of body colonised by commensal/mutualistic bacteria (5)

• skin

• oral cavity

• nasopharynx

• stomach

• gastrointestinal tract

classic approach to identifying bacteria that colonise certain sites in the body

culturing

limitations of culturing (2)

• many microbes in human body can’t be grown in lab conditions

• labour-intensive

modern approach to identifying bacteria that colonise certain sites in the body

DNA sequencing of 16S rRNA

what does the modern approach (DNA sequencing) allow

identification of bacteria at the genus level

in commensalism, what does the host provide? (2)

habitat and nutrients

in mutualism, what can the microbe provide to the host (human specific)? (4)

• vitamin synthesis

• facilitate digestion (enzymes)

• develop immune system

• develop physiology e.g. intestinal epithelium

main ways microbes assist with human nutrition (2)

• synthesise vitamins

• digest polysaccharides

pH factor microbes living in the stomach must adapt to

low pH

pH factor microbes living in the small intestine must adapt to

acidic (but less acidic than stomach)

factors microbes living in the colon must adapt to (2)

neutral pH, little to no oxygen

what about the 16S subunit in ribosomes makes it identifiable?

similarity in most amino acid positions but there are a few unique differences based on the species

what percent of bacteria weren’t able to be cultured in the Gill et al. study?

83%

metagenomics

study of genomic material recovered from natural bacterial communities

what is the approach used for metagenomics?

genome sequencing of the all bacterial genomes present

what does a value of greater than one in the red columns of this graph indicate, given the blue is human genes relating to that function

bacteria are providing more genes with the specified function

germ-free/gnotobiotic organism

born with no microbes present