11- Microbiology of water

Question 1

What are the biological activity aquatic systems depend on? and what are “they” depending on?

Answer 1

The biological activity of an aquatic ecosystem depends, ultimately, on the activities of the primary producers (oxygenic photoautotrophs, phytoplankton; phyto = plant):
– Algae
– Cyanobacteria (also fix nitrogen)

• These organisms serve as a food source for chemoheterotrophs: bacteria, protozoa (zooplankton, zoo = animal), fish, and other aquatic organisms.
• The ac:vi:es and net numbers of phytoplankton depend on a variety of factors:
– Temperature
– Light received
– Availability of specific limiting nutrients such as nitrogen and phosphorus.

Question 2

What is the photic zone?

Answer 2

In clear water, light will penetrate to a maximum depth of 300m: photic zone

Microorganisms must be able to harvest light that reaches them (accessory pigments)

Question 3

Marine environment characteristic

Answer 3

High salinity (3%): organisms are halotolerant.

• 75% of the ocean is deeper than 1000 m (deep sea, pelagic zone); at its deepest,
11 km below the surface, pressure is about 1100 atmospheres (~1 atm / 10 m)

• Below 100 m the temperature is constant at 2-3°C.

Question 4

What is the open ocean? What is the productivity state? T?

Answer 4

In the open ocean (pelagic zone), primary productivity is very low due to the lack
of inorganic nutrients (nitrogen, phosphorus, iron) that are required by phytoplankton. The open ocean is OLIGOTROPHIC.

• Temperatures are cooler and more constant than in area closer to shore.
• In some regions, wind and ocean currents cause an upwelling of water from the ocean floor bringing nutrients to the surface and promoting productivity.

Question 5

What are the organisms in the open ocean? Trichodesmium?

Answer 5

Bulk of primary productivity comes from prochlorophytes, tiny phototrophs phylogene:cally related to cyanobacteria: Prochlorococcus.

• General adaptations seen in pelagic (open ocean) microorganisms:
– Reduced size (high surface/volume ratio)
– High affinity transport systems

• Trichodesmium:
– Filamentous cyanobacteria
– Contains phycobilins
– Nitrogen fixation

Question 6

What about the organisms in coastal water? Productivity?

Answer 6

Primary producers:
algae, cyanobacteria

• Productivity is usually higher due to the influx of nutrients from rivers and other polluted water sources (ex: agricultural runoff = excess nitrogen, phosphorus). EUTROPHIC

• Can cause red tides (algal bloom,
dinoflagellates, neurotoxins). Nitrogen is a limiting nutrient.

• A higher level of primary productivity
supports a higher concentration of zooplankton and aquatic animals.

Question 7

What are the organisms in the deep sea; btw 300-1000m and below 1000m?

Answer 7

Between 300 and 1000 m, chemoheterotrophs degrade organic matter that falls from the photic zones. 2-3°C, psychrophiles.

• Below 1000 m, organic carbon is very scarce, oligotrophic, no light. Very few
microorganisms (psychrophilic and barophilic or barotolerant).

Question 8

What are hydrothermal vent? Tube worms?

Answer 8

Source of heat, source of nutrients,velectron donors, electron acceptors.

• Community of microorganisms, animals.
• Tube worms: symbiosis with sulfur oxidizing chemoautotrophs. Tube worms trap and transport nutrients to the bacterial symbionts.

Question 9

What are the characteristics of freshwater environment?

Answer 9

Highly variable (isolated system compared to ocean)

• Microbial populations will depend on the availability of nutrients, and the availability of light and oxygen.
Limited by the availability of nitrogen and phosphorus.
• Lakes (poor mixing/aera:on)
• Rivers (good mixing/aera:on)

Question 10

What are oligotrophic lakes?

Answer 10

Lakes with limiting N and P

Primary production is low, availability of organic matter is low.

• Growth of aerobic chemoheterotrophs is limited by nutrient supply; oxygen concentration remains high.
Rate of oxygen dissolution is higher than the
consumption rate.

• Lake remains aerobic even at depth and organic matter is degraded completely.
• Oxygen saturated.
• Clear water (deep penetration of light)

Question 11

What are eutrophic lakes? Characteristics, bottom sediment, anaerobic photosynthesis,

Answer 11

Nutrient rich lakes

Primary production is high (algal bloom), availability of organic matter is high.

• Rapid growth of chemoheterotrophs, rapid depletion of dissolved oxygen.

• Low oxygen concentration
• Anaerobic zones are created.
• Poor light penetration
• Health risk: pathogens, bloom of
cyanobacteria/algae (secrete toxins).

• Bottom sediments are anaerobic and contain organic matter (dead primary
producers, etc.) which support the growth of denitrifiers, methanogens and sulfate reducers (H2S).

• Anaerobic photosynthesis uses H2S as electron donor and produces sulfate, which is used by sulfate reducers.
• Excessive production of H2S and the production of organic acids from fermentation can give the water a bad odor. The lack of oxygen and/or presence of H2S may kill fish and other aerobic organisms.

Question 12

What about lakes in temperate climates? upper and bottom layer

Answer 12

• Anaerobic zones may develop as a result of summer stratification. Lakes become thermally stratified.
• As the air temperature increases, the surface water is warmed resulting in the formation of a warm upper layer –epilimnion – less dense, aerobic.

• The colder, bottom layer –hypolimnion, denser, anaerobic – is separated from the epilimnion by a zone of rapid temp. change –
thermocline.

• Mixing in the spring and fall only. Brings
nutrient back up the water column.

Question 13

Tell me about rivers

Answer 13

Rivers: good mixing/aeration ensures that organic matter, within limits, is degraded effectively (no fermenta:on, no H2S production).

• Excess organic matter may still result in anaerobiosis with consequences similar to
those seen in eutrophic lakes.

Question 14

Tell me about water pollution; freshwater, sewage, organisms biochemical oxygen demand

Answer 14

Pollution of freshwater: deliberate discharge of effluents into a waterway– major source is sewage.

• Sewage is rich in organic matter and
contains a large number of organisms
(some may be pathogens).

• Aerobic and facultative organisms oxidize organic matter using the dissolved oxygen.

• Biochemical oxygen demand (BOD) is high (used as a measure of the extent of pollution by organic matter).
Water tends to become anaerobic, microbial
metabolisms: fermenta:on, sulfate reduction, nitrate reduction…

Question 15

What are biofilms?

Answer 15

Biofilm: microbial cells embedded inside an extracellular matrix.

• Usually produced by a mixed population of species.
• Extracellular matrix composed of proteins, polysaccharides, DNA.
• Cells inside the biofilm are more resistant to stresses than planktonic (free-living) cells.
• Biofilms are found in water systems (natural and man-made), on wet surfaces, growing on medical devices, etc.

Question 16

What are the sources of water-borne pathogens? Where are they born usually? Tell me few of them

Answer 16

Most of these pathogens grow in the intestinal tract and transmission is mediated by fecal contamination of water supplies.

• Sources of infection:
– Potable water (drinking and food preparation)
– Recreational water (swimming)

Salmonella typhi: typhoid fever in humans, systemic infection, healthy carriers.

• Vibrio cholerae: cholera, severe diarrhea (enterotoxin)
• Shigella spp.: shigellosis; bacterial dysentery (bloody diarrhea, inflamma:on of the intestinal mucosa)
• Salmonella spp. (other than typhi): salmonellosis, gastroenteritis.
• Campylobacter spp.: gastroenteritis, most common cause of gastroenteritis in Canada.
• Enterovirus: poliovirus, norovirus, rotavirus (children)
• Hepatitis A virus.

Question 17

What are the water-borne pathogenic protozoa?

Answer 17

Entamoeba histolytica: amoebic dysentery.

• Giardia lamblia: giardiasis (backpacker’s
disease/beaver fever), chronic diarrhea, owen
associated with drinking water in wilderness
areas (beavers and muskrats are frequent
carriers – source of contamination of streams).

• Cryptosporidium parvum: chronic and accute
diarrhea, self limiting in healthy individuals,
major problem in immunocompromised
individuals, no reliable treatment. Present in
90% sewage samples, 75% river waters and
28% of drinking waters. (Intracellular C.
parvum)

Both form cysts (G.lamblia n C parvum) that are resistant to a number of disinfectants, including chlorine.
• C. parvum cysts are not effectively removed by the filtration process in water plants (too small).

Question 18

What is water quality control? 2 indicators

Answer 18

Impossible to check for all pathogens. Most water-borne pathogens are associated with fecal material.

• Test the water for organisms that are present in large numbers in feces – use these organisms as indicators of fecal pollution – if these organisms are present, there is a chance that the water may also contain pathogens.

• Two indicators:
– Coliforms: facultative aerobic, Gram-negative, non spore-forming, rod-shaped bacteria that can ferment lactose with gas formation within 48 hours at 35°C. Includes a variety of bacteria not all of intestinal origin.

– Fecal coliforms: coliforms derived from the intestines of warm-blooded animals (can
grow at 44.5°C, thermotolerant)

• The presence of fecal coliforms, especially E. coli, indicate fecal contamination and
that the water is unsafe for human consumption.
• The absence of fecal coliforms does not ensure good water quality (cysts are more
resistant than fecal coliforms).

Question 19

What is the most probable number (MPN)?

Answer 19

Test for coliforms:
samples are added to lactose broth. If gas
production is detected, test is positive.

Use statistical tables to estimate the MPN of
coliforms in the original sample.
Presumptive tests, further tests needed for
confirma:on.

Question 20

What is a membrane filtration?

Answer 20

Coliforms and fecal coliforms
• Test large volume of water (100 mL)
• Faster and easier than MPN

Question 21

What is water treatment? (Aims)

Answer 21

Aims:
– remove pathogens
– improve clarity of water
– remove compounds that give bad smell or taste
– sowen the water
• Extent of treatment needed depends on the quality of the source of water

Question 22

What are the steps in water treatment? (4)

Answer 22

1) Sedimentation:
• Water is lew to stand in a reservoir (sedimentation basin).
• Allow large particle (sands) to settle

2) Flocculation treatment (chemical coagulation):
-A flocculating chemical (coagulant) is added.
• Water is transferred to a flocculation basin and allowed to settle for ~6h.
• As the flocs (flaky precipitates) form, they trap fine particles (clay, bacteria, viruses, protists).
• Some organic chemicals are also absorbed by the flocs.
• ~80% of bacteria, color and particulates have been removed.

3) Filtration:
The water is filtered through sand to remove remaining particles, even more bacteria and any remaining G. lamblia cysts.
• Awer this stage, 98-99.5% of the bacteria have been removed.
• Filter is backflushed regularly to prevent clogging.

4) Disinfection:
• Chlorination:
– Chlorine is very reactive in water, it forms strong oxidizing agents.
– Kills remaining microorganisms (some are resistant).
– Neutralizes most of the chemicals that give water a bad smell/taste.

• Residual chlorine: amount of chlorine that remains in the water that lew the treatment plant. Desired/required to protect the distribution system.
• Ozone: more effective that chlorine (kills G. lamblia and C. parvum cysts) but very short half-life.

• The water is now safe for human consumption.
• Quality control (Montreal): < 10 coliforms/100ml; <1 fecal coliform/100ml
• Walkerton tragedy: hOp://www.cbc.ca/news/background/walkerton/
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Question 23

What are the aims of wastewater (sewage) treatments? What are the treatments (primary, secondary (trickling filter and activated sludge), tertiary)?

Answer 23

Aims:
– Reduce BOD (remove/destroy organic matter)
– Destroy pathogens

1) Primary treatment:
Sedimentation tanks: 40-70% of suspended solids settle. Flocculating chemical can be added. Produces PRIMARY SLUDGE (Dried and incinerated or secondary treatment).

• Reduces the BOD of wastewater to 25-40% and the bacteria by 25-75%.
• Wastewaters can be discharged to waterways or go through secondary treatment: use microorganisms to reduce the BOD and the concentration of bacteria further.

2) Secondary treatment (liquid):

Trickling filter: liquid from primary treatment is sprayed over a bed of rock or plastic honeycomb, microorganisms form biofilms, coating the surface and oxidize the organic matter present in the sewage. BOD reduced by 80-95%, bacteria by 90-95%.

• Activated sludge: air is blown through the liquid from primary treatment. Slime-forming bacteria grow and clump together to form flocs (activated sludge) that oxidize the organic matter. Then, the material passes to a settling tank, sludge is removed for disposal or secondary treatment. BOD reduced by
85-95%, bacteria by 90-98%.

The primary and secondary sludge, containing cellulose and other organic compounds, is subjected to microbial digestion under anaerobic conditions.
• CH4 produced can be used to power the treatment plant. BOD reduced by 90%. Material that remains is incinerated or buried.

3) Tertiary treatment (liquid):
Further reduces the BOD, bacteria and the concentrations of N and P.
• May involve any or a combination of the following:
– Biological treatment (ponds: algae)
– Flocculation
– Filtration
– Chlorination or ozonation

• The final liquid effluent that come from wastewater treatment plant that uses primary, secondary and tertiary treatments may be suitable for drinking (coliforms and fecal coliforms below limits).

Question 24

What are septic tank?

Answer 24

Minimal treatment of sewage.
• Within the tank: settling of the material and minimal sludge digestion
– requires periodic emptying.

• BOD of effluent reduced by 60%.

• Effluent flows to a leaching field (tile field):
– Still contains > 10,000 coliforms/ml.
– Reduce amount of water in the tank.
– Soils act as a filter and organisms decompose organic matter. Care has to be
taken to prevent contamination of groundwater and nearby waterways.