Lecture 9 - Microbial ecosystems, Symbioses, Frontiers

Soil

Environment: Thousands of different microbe species with tons of diversity between layers

Subsurface

Environment: Thought to be very microbe-lacking but recent exploration uncovered a diverse microbiome

Lakes

Environment: Typically with 4 layers with each layer having different biological and nutrient concentrations. Water column mixing changes the concentrations of those layers during seasonal changes

Ocean

Environment: Very low nutrient, oxygen, and light levels leading to low numbers of microbes

Biological Soil Crusts (BSC)

• Microbial habitats that exist on the surface of the soil on exposed rock, cracks, and fissures

• Mostly composed of cyanobacteria that do nitrogen fixation

• Provide soil cohesion and eliminating erosion from wind and water

Desertification

Occurs when the biological soil crusts gets disturbed and the earth gets eroded

Nitrogen fixation

Converting nitrogen gas to forms that plants can use (nitrate or ammonium)

Phototrophic microbes

Located in the top layer of a lake; produce organic carbon and O2 (Photosynthesis)

Heterotrophic microbes

Located in the second layer of a lake; consume organic carbon from the autotrophs, dead autotrophs, and oxygen

Anaerobic microbes

Eat organic carbon that sinks to the bottom of the lake

Water column mixing

When the bottom water brings nutrients to the top and top water brings oxygen to the bottom

Healthy water

High levels of dissolved oxygen (fish survive) and a low level of organic carbon (prevent microbe “blooms”)

Unhealthy water

Low levels of dissolved oxygen (fish die) and a high level of organic carbon (microbe “blooms”)

Eutrophication

When organic carbon and nutrients (from farm runoff) cause a sudden increase in the growth of both phototrophic and heterotrophic microbes

Phototrophic bloom

When microbes multiply rapidly and block out the sunlight → Plants below surface of water die off

Heterotrophic bloom

When microbes multiply rapidly and take up all the oxygen in the water → Creates anoxic zones that kill fish in large numbers

Pelagibacter

• Most abundant microbe in the ocean and planet

• Successful:

  • High SA:V ration

  • Genome encodes enzymes needed for low-nutrient lifestyle

  • Highly compact genome reduces cost of replication

• Has poteorhodopsin

Proteorhodopsin

Light driven proton pump that makes ATP. Allows microbe to survive starvation to compensate for lack of organic carbon

Prochlorophytes

Account for half of the photosynthetic biomass in tropical and subtropical regions of the ocean creating lots of CO2

Tichodesmium

Form “puffs” or colonies of filaments with each puff containing up to 200 cells. Preform nitrogen fixation which is important for the marine nitrogen cycle

Great pacific garbage patch

Large span of trash spanning from the West Coast of North America to Japan and mostly made up of microplastics

Microplastics

Small plastic pieces less than 5mm long

• Fish can ingest them

• Sea turtles often mistake them for jellies

• Albatrosses will feed them to their chicks killing them

Symbiosis

Two organisms living together in close contact

Mutualism

Both organisms give and receive for beneficial means

Coevolution

The mutualistic partners ave evolved to benefit each other overt time

Obligate mutualism

Mutualism to the extend they can’t live without each other

Legumes

Flowering plants that bear seed in pods (soybeans, clover, alfalfa, beans, peas)

Legumes - Rhizobia

Bacteria that infects these plants to form root nodules. In these root nodule, the bacteria will do nitrogen fixation giving nitrogen to plants while bacteria receives photosynthetic sugars. Plant used as a cover crop to replenish soil nitrogen

Endosymbionts

Intracellular bacteria localized at specialized organs within insects. Provide insects nutritional advantage or protection from parasites

Termites - Trichonumpha

Endosymbiotic relationship where protist helps insect digest cellulose

Whiteflies - Rickettsia

Endosymbiotic relationship where bacteria help insect produce offspring at about twice the rate of uninfected insects and more survive to adulthood

Flies - Spiroplasma

Endosymbiotic relationship where bacteria provide protection against parasitic wasp

Hawaiian Bobtail squid

Harbors a large population of bioluminescent gram-negative bacteria in a light organ that offers camouflage from predators

Coral

Made up of hundreds of to thousands of tiny creatures called polyps

Polyps

Secrete a hard outer skeleton of limestone (calcium carbonate) that attaches either to rock or the dead skeletons of others

Zooxanthellae

Single celled dinoflagellets that live inside polyps. Photosynthetic so they provide their host with organic carbon products whilst they receive nutrients, CO2, and an elevated position to reach light

Coral bleaching

Increased CO2 → Increased ocean acidity → Killing zooxanthellae → Killing coral

Human Microbiome

1:1 ratio between microbes and human cells

First year of life

Most important time to assemble the guy microbiota

• Vaginal birth or C-section

• Breast milk or formula