Topic 7- L1 - Microbial communities

Question 1

Fundamental Niche:

Answer 1

The theoretical range of environments where a given microbe could live

Question 2

Realized Niche:

Answer 2

The range of environments where that microbe actually lives in the real world

Question 3

Symbiosis:

Answer 3

A close, long-term interaction between different organisms. In a symbiotic relationship, organisms can benefit, be harmed or be unaffected. Often involves co-evolution.

Question 4

Lichens are microbial communities comprised of two dominant organisms:

Answer 4

(i) A fungus (eukaryote)
(ii) An alga (eukaryote) and/or a cyanobacterium

(Large life span)

Question 5

How do the fungi benefit in this relationship?

Answer 5

• Food! Photosynthetic partner produces organic compounds for fungus

Question 6

How do the algae/cyanobacteria benefit from this relationship?

Answer 6

• Fungus provides anchor & controlled environment for growth
• Structure helps retain water for algae/cyanobacterium
• Fungus releases lichen acids – dissolve surface compounds to free up inorganic metabolites for algae cyanobacterium

Question 7

Specific fungal species often obligate symbionts –

Answer 7

partner can sometimes live freely…but symbiotic relationship drastically expands ecological range of both partners

Question 8

controlled parasitism –

Answer 8

fungi drastically slow their partners’ growth - consume a great deal of their nutrients

Question 9

Microbial consortium:

Answer 9

Two or more microbes living in a symbiotic relationship

Question 10

In freshwater lakes, a commonly found consortium features:

Answer 10

(i) Numerous non-motile photosynthetic bacteria

(ii) A central motile non-photosynthetic bacterium

Question 11

Motile bacterium positions consortium in location optimal for phototroph’s metabolism (light/nutrients) –

Answer 11

photosynthetic bacteria provide nutrients to motile (chemoorganotrophic) bacterium.

Question 12

“Chlorochromatium aggregatum”

Answer 12

(quotes since not single species) Green sulfur bacteria (phototrophs) & a β-proteobacterium (motile)

Question 13

Chlorochromatium aggregatum

β-proteobacterium at center:

Answer 13

• Obligate symbiont – cannot live on
  its own.
• Has suffered significant gene less – metabolism dependent on consortium. Enriched for chemotaxis genes.

Question 14

Chlorochromatium aggregatum

Green sulfur bacteria (phototrophs)

Answer 14

• Can be cultured…but never
  observed as free-living in nature
• Not prosperous without ability to
  localize to optimal niches in lake

Question 15

Cross-feeding

Answer 15

(one organism’s waste is another’s food)

Question 16

Community-level metabolic processes

Answer 16

(metabolic processes that require many distinct organisms to complete)