MMG301 Dr. Frank Dazzo Aquatic & Wastewater Microbiology

• Natural aquatic habitats for microorganisms include lakes, ponds,rivers, springs, oceans estuaries, marshes.

• The concentration, mixing and movement of nutrients, O2, andwaste products are the dominant factors controlling the abundance,distribution, and diversity of aquatic microbial communities

Trophic levels and the microbial loop in aquatic ecosystems:In contrast to soil, phytoplankton (algae and cyanobacteria) are thepredominant photosynthetic organisms in aquatic habitats

• Much of the organicmatter synthesized byphytoplankton duringphotosynthesis isreleased as dissolvedorganic matter (DOM).

• This DOM isconsumed bybacterioplanktonwhich become part ofthe suspendedparticulate organicmatter (POM) pool.

• A portion of thesebacteria are thenconsumed as food byprotozoa predators.

• Some of the nutrients immobilized in bacteria and protozoa aremineralized and then assimilated directly by phytoplankton withouttransfer to higher trophic levels (e.g. fish) in the aquaticecosystem. This is called the "microbial loop" (arrows in red).

O2 plays a key role in microbial activity in aquatic habitats:Photic zone, oxic zone, anoxic zone in lakes:

O2 and organic nutrients are inversely interrelated in aquatichabitats. Nutrient-poor (oligotrophic, A) lakes recyclenutrients only within the water whereas nutrient-rich(eutrophic, B) lakes have major nutrient inputs from outside.

Oligotrophic lakes are typically O2-saturated and have lowmicrobial populations. Eutrophic lakes develop highmicrobial populations that deplete the dissolved O2 byaerobic respiration during decomposition of abundantorganic matter, producing deep anoxic zones.

Oligotrophic lakeEutrophic lake

Temperature also impacts on the status of O2 and nutrients intemperate lakes.

• Anoxic conditions develop in the depths of the lake as a result ofthermal stratification.

• The cool bottom waters (hypolimnion) are more dense and containH2S from anaerobic bacterial sulfate reduction.

• The depth zone of rapid temperature change is the “thermocline.”• Typically as lake surface waters (epilimnion) cool in the fall and

early winter, they reach the temperature and density of thehypolimnionic waters and then they sink, displacing bottom watersand the sediments, affecting “lake turnover” and the redistributionof nutrients for the aquatic microorganisms.

Marine microorganisms (eubacteria, archaea, and eukaryotes)• True marine microorganisms are moderate osmiophiles, requiring

the salinity and ions (esp. Na+) of seawater for cultivation• Most are psychrophiles (5°°°°C for most of ocean volume)• Barophiles in deep sea (hydrostatic pressures ≤≤≤≤ 1,100 atmospheres)• Most are oligocarbophiles adapted to the extremely low

concentration of organic C in ocean seawater (∼∼∼∼ 1-2 mg C / liter)• Recent exciting find of endosymbiotic bacteria inside Riftia tube

worms that develop on sides of black smoker vents at deep seaocean floor →→→→ life sustained by geothermal energy rather than sun.

Concept of Biochemical Oxygen Demand:• The amount of biologically usable organic carbon in water is

indirectly measured by its Biochemical Oxygen Demand (BOD).• It represents the portion of total carbon that can be oxidized by

microorganisms in a 5-day period under standard conditions.• It equals the amount of dissolved O2 needed for microbial

oxidation of biodegradable organic matter in a water sample.

The effect of a point source discharge of an organic pollutant (e.g.,untreated sewage) into a clean flowing river system is profound:

• Heterotrophic bacteria, organic carbon, and BOD immediatelyincrease at the pollutant input, and correspondingly, dissolved O2levels decline due to the burst in microbial respiration. Kills allaquatic life (fish, etc) dependent on dissolved O2.

• Microbes mineralize and oxidize the organic N and P into inorganicnutrients (NO3

-, NH4+, and PO4

-3), resulting in eutrophication, withdevelopment of noxious algal / cyanobacterial blooms.

• Further downstream, self-purification processes result in a declineof BOD, the oligotrophic conditions and phototrophic microbialcommunities regain dominance, and dissolved O2 levels replenish.

Microbiology of Domestic Sewage Wastewater Treatment• The treatment of human fecal wastes (→→→→ organic matter plus many

bacterial, protozoan & viral pathogens) is one of the mostimportant factors in maintaining an advanced healthy society.

• Effects of discharging organic wastes into aquatic ecosystemscan be drastic as described earlier

• Fecal pathogens are shed from patients with disease and fromcarriers (maintain infection without expression of symptoms).

• Conventional sewage treatment is a controlled intensification ofnatural self-purification processes involving 1°°°°, 2°°°°, and 3°°°° treatment.

Primary treatment: removal ofinsoluble particulate materialsfrom raw sewage by screening gravitational settling in tanks.The resultant solid material iscalled sludge.Secondary treatment:microbial conversion oforganic matter into microbialbiomass and finaldecomposition products (90-95% reduction in BOD), plusremoval of many bacterialpathogens.Tertiary treatment: biologicaland chemical removal of inor-ganic nutrients (e.g., N and P)to reduce eutrophication ofreceiving ecosystem, virusremoval or inactivation, tracechemical removal.

Role of microorganisms in secondary treatment of domestic sewage:

Activated sludge process:Microbes (e.g., Zooglea ramigera)in a forced aeration tank formzooglea of activated sludge (activebiomass of suspended flocs) thataerobically decomposes organicmatter. A portion of the activatedsludge is recycled as inoculum tomaintain the process.

Trickling filter system: arotating arm of an aerationbasin trickles wastewaterover a bed of rocks. Eachrock develops a largemicrobial biofilm thatabsorbs and aerobicallydecomposes the dissolvedorganic matter in thewastewater as it tricklesover the rocks.

Anaerobic (anoxic) sludge digestion process:

The bioreactor has a lid cover tomaintain anoxic conditions. A verycomplex community of anaerobesactively decompose polymers bythe processes indicated to finalanaerobic metabolites dominatedby methane (CH4) and CO2 as themajor products of anaerobic bio-degradation. The CH4 is burned orused to power the treatment plant.

Anaerobicsludge digestor

Use of Indicator Microorganisms to Detect Fecal Pollution

A wide range of bacterial, protozoan, and viral diseases result fromconsuming water and food contaminated with human fecal wastes:• Bacterial diseases; diarrhea caused by Salmonella, Shigella,

enteropathogenic E. coli; cholera (Vibrio cholerae)• Protozoan diseases: amoebic dysentery (Entamoeba histolitica),

amoebic meningocephalitis (Naegleria fowleri)• Viral diseases: hepatitis A, poliomyelitis, diarrhea (enteroviruses)• Many bacteria from the intestinal tract become physiologically

stressed when introduced into the aquatic environment, and theygradually lose their ability to form colonies on differential &selective media. Also, enumeration of many intestinal pathogens inwastewater is difficult. Therefore, various indicator microbes areused to detect fecal wastes in food and water (used for bothpotable and recreational uses).

Criteria for use of indicator microbes as an index of fecal pollution:

1. Its normal habitat should be the gut of warm-blooded animals.2. It should be suitable for the analysis of all types of water.3. It should be present whenever enteric pathogens are present.4. It should survive longer than the hardiest enteric pathogens.5. It should not reproduce in the contaminated water so its population

level can indicate the degree of fecal pollution.6. The methods to detect and enumerate them should be specific, very

sensitive, standardized, and easy to perform, yield results quickly.Present status: The “ideal” indicator organism hasn’t been found.The search continues….. Ones currently used as indicators include:1. Fecal coliforms: (e.g., Escherichia coli ) Gram (-) non-sporulating

facultative anaerobic rods from the intestine of warm-bloodedanimals that ferment lactose with the production of gas at 44.5 °°°°C

2. Fecal streptococci: (Streptococcus faecalis), useful indicator offecal contamination in estaurine and marine waters, where itsurvives better than E. coli.

3. Lytic bacteriophages of E. coli (viruses survive chlorination betterthan bacteria