Prescott's Microbiology,4/e

		Microbiology, 4/e Prescott, Harley, Klein
		Instructor Resources

41 Marine and Freshwater Environments

CHAPTER OVERVIEW

This chapter discusses the general characteristics of microorganisms that are associated with marine and freshwater environments. Aquatic environments are dominated by the liquid phase, and the only oxygen available is that which can be dissolved in water. This dissolved oxygen can be quickly depleted, creating anaerobic conditions. The use of surface and subsurface waters for drinking water sources and for waste disposal is also discussed. The chapter concludes with a discussion of the contamination of groundwaters by domestic and industrial wastes and the use of microorganisms to restore this important resource.

CHAPTER OBJECTIVES

After reading this chapter you should be able to:

! discuss the nature of marine and freshwater environments

! describe the complex microbial communities found in these environments

! discuss hydrothermal vents and hydrocarbon seeps

! discuss biofilms and the consequences of their formation

! discuss microbial mats

! discuss the recent concern over Pfeisteria piscicida, a protozoan parasite of fish

! discuss the influence of microorganisms in the oceans on carbon, nitrogen, phosphorus and sulphur cycling

! describe the possible cyclic changes in dissolved oxygen content of aquatic environments because of the unbalanced nature of oxygen depletion and replenishment

! discuss sewage treatment systems and their logical design according to the predictable sequences of the biological utilization of organic wastes

! describe the use of indicator organisms to measure the microbiological quality of water and describe the desirable characteristics of such an organism

! discuss the recent concern over the protozoan, Cyclospora, which causes long-lasting diarrheal disease

! discuss the limitations of indicator organisms with regard to the potential presence of viruses and protozoa in water sources

! discuss the ways that pathogenic organisms may be introduced into water sources other than by contamination with human wastes

! discuss the increasing concern about contamination of groundwater sources

CHAPTER OUTLINE

I. The Nature of Marine and Freshwater Environments

A. Nutrient concentrations

1. Can vary from extremely low (e.g., micrograms organic matter per liter) to levels approaching those in laboratory media

2. Changes in nutrient levels can cause shifts between low-nutrient responsive (oligotrophic) and high-nutrient responsive (copiotrophic) microorganisms

3. Nutrient turnover rates can vary from hundreds to thousands of years (marine environments) to very rapid turnover (marsh and estuarine environments)

B. Gradients

1. Movement of materials in aquatic environments causes concentration gradients to form

2. Microorganisms are able to respond rapidly to these gradients to select their most suitable environment

3. Mixing occurs more readily than in soil habitats

4. Aquatic habitats are only marginally aerobic unless they are vigorously agitated

5. Stagnant waters can develop distinct microbial growth zones that are dependent on the release of nutrients provided by other microorganisms that have already grown in that zone

6. A Winogradsky column is a microcosm in which these microbial interactions can be studied

C. Surfaces and biofilms

1. Microorganisms and nutrients tend to accumulate at surfaces rather than in the bulk phase of water

2. Surface attachment is advantageous to microorganisms at concentrations of dissolved organic matter below 25 mg per liter

3. Biofilms are layers of microorganisms and nutrients adhering to various surfaces

4. Simple biofilms are monolayers

5. Complex biofilms are multilayered with different microorganisms in different layers and may contain cell aggregates, interstitial pores and conduit channels between layers; these conduits are shaped by protozoans that graze the bacteria and allow nutrients to reach the biomass

6. Confocal scanning laser microscopy (CSLM) is a new technique that assists in our study of biofilms by generating optical Athin sections@ across some complex biofilms

7. Computer simulations can be constructed from these Athin sections@ in order to better understand how microorganisms function in these complex environments

8. Biofilms have a wide impact in environmental and public health microbiology (e.g., biofilms may be a major source of Legionella in heated waters and also potable water systems)

D. Microbial Mats

1. Microbial mats result from biofilms that become so large that they are visible and have macroscopic dimensions

2. Bands of microbes are usually evident

3. They are found in many freshwater and marine environments on rocks and sediments

4. They form extreme gradients (e.g., light may only penetrate 1 mm into these communities and below this conditions are anaerobic)

II. The Microbial Community in Marine and Freshwater Environments

A. Important microorganisms

1. PhotoautotrophsCsulfur and nonsulfur photosynthetic bacteria

2. ChemoheterotrophsCinclude some unique species of sheathed, sessile, prosthecate, budding, and/or gliding bacteria

3. ChemoautotrophsCaerobic hydrogen sulfide oxidizers (Beggiatoa and Thiotrix) are found in waterlogged zones where hydrogen sulfide is present

4. Eucaryotic photosynthetic algaeCprimary producers

5. ProtozoansCincrease nutrient cycling by grazing on other organisms

6. Fungi that are specially adapted to an aquatic existence including oomycetes and chytrids

7. Filamentous fungi that can sporulate under water play an important role in the processing of organic matter

B. The marine environment

1. Contains 97% of the earth=s water

2. The ocean has been called a Ahigh pressure refrigerator@ with temperatures near 3EC and pressures up to 1,000 atm

3. Three types of bacteria

a. BarotolerantCgrow at 0 to 400 atm; best growth is at atmospheric pressures

b. Moderate barophilesCgrow best at 400 atm, but will grow at 1 atm

c. Extreme barophilesCgrow only at higher pressures

4. Other major types of microorganisms include large numbers of viruses and high levels of archaeobacteria

5. The major source of organic matter is photosynthesis

6. Nitrogen and sulfur cycles function at an Aocean scale@ with nitrogen frequently being the limiting nutrient

7. Dimethyl sulfoxide (DMS) release from algae can influence atmospheric acidity and cloud formulation on a global scale

8. Most of the nutrient cycling occurs in the upper 300 meters, which is where light penetrates

9. Organic matter falls, but only 1% of the photosynthetically derived materials reach the deep-sea floor (the rest is decomposed); conditions there are oligotrophic (low nutrient concentration)

10. Massive deposits of methane are found below 500 meters, and are trapped in latticelike cages of crystalline water

11. Ultra microbacteria that resist grazing by nanoflagellates have been found to be the dominant bacteria in these environments

12. Because of increasing urban development in coastal areas, nutrient enrichment and microbial pollution are increasing and taxing the ocean=s seemingly inexhaustible ability to absorb and process pollutants

13. Shellfish beds are sensitive to contamination from urban runoff

14. Pfeisteria piscicida, a protozoan fish parasite, sense the presence of fish and attack them

C. The freshwater environment

1. Lakes and rivers provide microbial environments that are very different from those of oceanic systems

2. Lakes

a. Mixing and water exchange can be limited in lakes, allowing large-scale vertical gradients

(1) EpilimnionCwarm, aerobic, upper layer

(2) ThermoclineCregion of rapid temperature decrease

(3) HypolimnionCcold, often anaerobic (particularly in nutrient rich lakes) lower layer

b. Stratified waters undergo seasonal turnovers because of temperature and specific gravity changes

c. EutrophicationCstimulation of growth by addition of nutrients (enrichment) to a body of water

d. Oligotrophic watersCnutrient poor; aerobic; seasonal temperature shifts do not result in distinct chemical and microbial stratification

e. Eutrophic watersCnutrient rich; often stratified; anaerobic, except at the surface; layers will turn over in spring and fall, causing migration of microorganisms

f. Cyanobacteria can fix nitrogen and accumulate nutrients if phosphorus is added to oligotrophic waters

g. Cyanobacteria compete more effectively with eucaryotic algae at higher pH and temperatures

h. Cyanobacteria and eucaryotic algae contribute to massive algal blooms in strongly eutrophied lakes

3. Rivers

a. Horizontal movement minimizes vertical stratification

b. Most of the functional biomass is attached to surfaces

c. Nutrients can be from in-stream production (autochthonous) or from out-stream sources (allochthonous)

d. The ability to process organic matter is limited

e. Organic material can be released into streams and rivers from a variety of sources

(1) Nonpoint sources of pollution include field and feedlot run-offs

(2) Point sources of pollution include inadequately treated municipal wastes and other materials from specific locations

f. If the amount of organic material is excessive, oxygen is used faster than it can be replenished, which causes an oxygen sag curve

g. If the amount of organic material is not excessive, algae will grow, which leads to oxygen production in the daytime and respiration at night (diurnal oxygen shifts)

h. Organic matter can be measured in several ways

(1) Chemical oxygen demand (COD)Cquantifies the amount of organic matter present by reacting organic material with a strong acid

(2) Total organic carbon (TOC)Cquantifies carbon concentration by reacting (reducing) organic compounds to produce carbon dioxide

(3) Biochemical oxygen demand (BOD)Camount of oxygen needed to utilize organic material as growth substrates; indirectly measures the amount of organic material in a sample; can be affected by presence of ammonia so nitrogen oxygen demand (NOD) is inhibited by nitrapyrin addition to the sample

(4) BiomassCmeasured by filtration, followed by dry weight measurement or specific content measurements

(5) Chlorophyll measurementsCindicate the mass of photosynthetic organisms in water

(6) Number of microorganisms can be determined directly, by immunofluorescence, or by viable cell counts

i. Filtration may be needed to concentrate the bacteria from the water prior to making some of these measurements

j. If too much nutrient is added, the cycling cannot occur, which creates an anaerobic, foul-smelling body of water that is considered Abiologically dead,@ although microorganisms may still be functioning; can be reversed only by major remediation procedures

k. Silicon removal (by dams) is reducing the diatom population, resulting in increases in toxic nitrate-utilizing algae

D. The Role of Microbial Communities in Water Quality

1. Sewage treatmentCcontrolled self-purification; can involve the use of large basins (conventional sewage treatment) where mixing and gas exchange are carefully controlled; can also involve constructed wetlands where reed and aquatic plant communities and their associated microbes facilitate the processing of dissolved nutrients

2. Primary (physical) treatmentCremoval of particulates (20 to 30% of the BOD)

3. Secondary (biological) treatmentCremoval of dissolved carbonaceous materials (90 to 95% of the BOD) and many bacterial pathogens; produces a sludge which must be further processed or disposed of

a. Aerated activated sludge systemsChorizontal flow, sludge recycling, utilization of organic matter by microorganisms

b. Trickling filtersCvertical flow over gravel on which microorganisms have developed in surface films

c. Extended aeration systemsCreduce the amount of sludge produced by the process of biological self-consumption (endogenous respiration)

4. Anaerobic sludge digestionCreduces the amount of sludge for disposal and produces methane, which can be used as a fuel for generation of electrical power

5. Tertiary treatment (physical/chemical and/or biological)Cremoves inorganic nitrogen, phosphorus, recalcitrant organics, viruses, etc.

6. Constructed wetlands use floating emergent and/or submerged plants to provide nutrients for microbial growth in their root zone; they help remove organic matter, inorganic matter and metals from waters

7. Surface flow soil treatment is also being used to allow aerobic microbial processing of waste

III. Water and Disease Transmission

A. Water purification is a critical link in promoting public health and safety

1. Aeration precipitates iron and manganese which must then be removed

2. Sedimentation in a sedimentation basin removes sand and large particles

3. Coagulation with alum, lime and/or organic polymers is followed by clarification in a settling basin

4. Filtration

a. Rapid sand filtrationCphysically traps particles (not efficient for removal of Giardia cysts, Cryptosporidium oocysts, Cyclospora and viruses)

b. Slow sand filtrationCbiologically removes Giardia, which adheres to microbial layer on the sand particles

5. Recently Cryptosporidium has become of even greater concern than Giardia

a. It is commonly found in sewage (90%), rivers (75%), and drinking water (28%)

b. Infection takes as few as ten oocysts

c. Companion and domestic animals are common reservoirs

d. It is self-limiting in healthy individuals but can be serious, and even fatal, in immunocompromised individuals

e. Its small size makes it even more dangerous than Giardia because it is not readily removed by sand filters

6. Disinfection with chlorine or ozone; formation of halomethanes (carcinogens) during chlorination is becoming an increasing concern

7. Viruses must be removed or inactivated

8. An Information Collection Rule (ICR) has been initiated to assess the threat of those pathogens to the waters of cities over 100,000 population

B. Microbiological Analysis of WaterCprimarily based on detecting human fecal contamination of water supplies; human fecal waste contains a variety of pathogens

1. Ideal indicator organisms indicate fecal contamination, but may not themselves be pathogenic

a. Indicator organism should be applicable to all types of water

b. Organism should be present whenever enteric pathogens are present

c. Organism should survive longer than the hardiest enteric pathogen

d. Organism should not reproduce in the contaminated water

e. Test should be highly specific for the indicator

f. Test should be easy and sensitive

g. Indicator should be harmless to humans (ensuring safety for laboratory personnel)

h. Concentration of indicator should directly reflect the degree of fecal pollution

2. Indicator organisms in use

a. ColiformsCall of the facultative anaerobic, gram-negative, nonsporing, rod-shaped bacteria that ferment lactose with gas formation within 48 hours at 35EC

(1) Escherichia coli, Enterobacter aerogenes, and Klebsiella pneumoniae

(2) Most probable number (MPN)Cstatistical estimation

(3) Presence-absence (P-A) testClimited quantitative estimate, but is gaining in acceptance

(4) Membrane filtration techniqueCwater is filtered, filter is placed on an absorptive pad containing liquid medium; this is incubated; and colonies are counted

(5) Defined substrate tests (e.g., Colilert) involve the production of a colored product (for total coliforms) or a fluorescent product (for E. coli) from a specific growth substrate

b. Fecal coliforms (FC)Cmore restrictive; test involves growing bacteria at 44.5EC, a temperature tolerated by fecal coliforms, but not by other coliforms

c. Fecal enterococci (more restrictive) are being used as indicators for brackish and marine waters because they survive longer than coliforms under these conditions

3. Potable waterCindicates bacteria are not detectable in a specific volume of water

C. Water and Human Diseases

1. BacterialCmany different types have been previously discussed

2. Protozoans include Giardia, Cryptosporidium, and Naegleria; the latter organism is of increasing concern worldwide because it causes a fatal neurological disease called primary amebic meningoencephalitis (PAM)

IV. Groundwater Quality and Home Treatment Systems

A. Microbiology and microbiological processes in groundwater are not well understood

B. Disease-causing organisms are removed by adsorption and trapping as they move through the subsurface

C. Home treatment

1. Anaerobic liquefaction and digestion in a septic tank

2. Aerobic digestion, adsorption, and filtration of organic material are accomplished by drainage through suitable soil in a leach (drain) field

3. If drainage is too rapid, there is little adsorption and filtration, with subsequent contamination of well waters

D. Contamination of groundwater can lead to nutrient enrichment of ponds, lakes, and rivers

E. Contamination sources other than septic tank leach fields include sites for land disposal of sewage sludges, illegal dumping of septic tank pumpage, improper toxic waste disposal, agricultural runoff, and deep-well injection of industrial wastes

F. Treatment procedures for groundwater to be used either in place or at the point of use are under investigation

Back