Microbes in Aquatic environments

Question 1

Diversity of Aquatic Environments

Answer 1

• Natural: Oceans, Lakes, Rivers & streams, Estuaries, Aquifers, (Ice)
• Artificial: Dams & reservoirs, Swimming pools, Aquaria, Wastewater effluents, Drink containers

Question 2

Microbes Found in Aquatic Environments

Answer 2

Bacteria - 2nd, Archaea - 3rd, Protists (protozoans + microalgae), Fungi, ‘Virioplankton’ - most

non-tailed virus, tailed virus, bacterium (coccal), bacterium (curved)

Question 3

Major environmental factors

Answer 3

Light: Tropical sunlight and high UV to total darkness

Temperature: Hydrothermal vents (113ºC) to ice flows (-15ºC)

Pressure: Atmospheric pressure (surface) to 1100 atmospheres

Salinity: Freshwater/estuarine/marine/ hypersaline lakes

pH: Soda lakes (pH 12) to acid springs (pH 1)

Nutrients: Oligotrophic (low nutrients; open ocean, mountain streams) to eutrophic (rich; estuaries, polluted rivers)

Oxygen: Aerobic to anaerobic

Question 4

Ecological Importance of Aquatic Microbes

Answer 4

• Nutrient generation
• Nutrient cycling
• Affecting environmental conditions
  –Oxygen depletion
  –Microbial activities affect oceanic climate
• Aquatic food webs

Question 5

Nutrient generation

Answer 5

• Approx. 40% of total global nitrogen fixation occurs in oceans
  –Biological N2 fixation is only carried out by certain bacteria
• Approx. 50% of total global primary producers (carbon fixation)
  –Due to single-celled phytoplankton (microalgae, cyanobacteria)
  –These produce ~50% of the earth’s oxygen!

Question 6

Nutrient cycling

Answer 6

Inorganics to organics
* Microbes are fundamental to cycles of major and minor nutrients (C, N, P, S)

• Key processes
  –Carbon cycling (cellulose to organic acids)
  –Stimulation of CO2 fixation
  –Sulphate to sulphide
  –Oxygen (presence/absence)
  –Maintenance of the cycle (ecosystem)

Question 7

Ecological processes in nutrient cycling with examples

Answer 7

1. Oxygen is removed by heterotrophic bacteria (produces CO2)
2. Oxygen removal allows anaerobes to ferment cellulose to organic acids (produces CO2) –Clostridium
3. Organic acids support the growth of sulphate-reducing bacteria, which produce sulphides –Desulfovibrio
4. Sulphides are used by anaerobic
   photosynthetic bacteria for anoxygenic
   photosynthesis (fix CO2; adds organic C)
5. Some sulphides are used by
   chemolithoautotrophic bacteria to fix CO2 (adds C) –Chlorobium, Chromatium
6. Phototrophic protists and cyanobacteria fix CO2 entering via air diffusion. Adds organic C and O2 at the surface

Question 8

Affecting environmental conditions

Answer 8

Because of their rapid growth, microbes can change environmental conditions
affecting entire ecosystems

Microbes can deplete O2 in water:
a) In the bottom layers of summer-stratified lakes
b) In polluted rivers
c) In ‘enclosed’ marine basins

Microbial activities affect the oceanic climate
* Phytoplankton osmoregulators are converted to volatile compounds by marine bacteria
* These compounds enter the atmosphere and act as condensation nuclei, leading to
cloud formation
* This process occurs as a feedback system influencing oceanic weather systems
(oceans cover 70% of the planet)

Question 9

Aquatic Food Webs

Answer 9

Bacteria are the simplest organisms that can take up dissolved nutrients in the water

These are consumed by phytoplankton and these are fed on by crustations and then fish, etc.

Question 9

Wastewater treatment

Answer 9

Secondary Wastewater treatment uses microbes:
1. Microbes (esp. bacteria) degrade organic matter in the waste stream:
* as a biofilm on solid surfaces (e.g. trickling filter)
* as flocs suspended in the water column (aerated tanks)

2. Products of microbial degradation of organic matter are formed:
   * CO2
   * Microbial biomass (huge) and any intransigent organic matter (“sludge”)
3. The sludge is processed further:
   * Used to seed the secondary treatment process
   * Further digested, often by anaerobic microbial processes
4. In anaerobic digestion:
   * Different anaerobic bacteria populations work in sequence to degrade the sludge
   * Organic polymers are fermented to organic acids
   * Organic acids are converted to acetate, CO2 and H2
   * Acetate, CO2 and H2 is converted to methane (CH4)
5. CH4 from anaerobic digestion is referred to as “Biogas”:
   * Harvested and used in heating and electricity generation