Water Microbiology Essentials

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Water Microbiology Definition: The study of microorganisms (viruses, bacteria, algae, protozoa, and microscopic fungi) and their activities in fresh, estuarine, and marine waters, including springs, lakes, rivers, and seas. The Aquatic Environment: Physical & Chemical Conditions The microbial population in natural water is largely determined by physical and chemical conditions. Temperature Surface water temperature varies from $0^\circ C$ in polar regions to $30-40^\circ C$ in equatorial regions. Over $90\%$ of marine environments are below $5^\circ C$ (psychrophilic microorganisms). Hot springs: Microorganisms like Thermus aquaticus thrive at $75-80^\circ C$ (optimum temp. $70-72^\circ C$). Geothermal vents (Pacific Ocean): Some microorganisms grow at $250^\circ C$. Hydrostatic Pressure Definition: Pressure exerted by a fluid at equilibrium due to gravity. Varies significantly between surface water and oceanic depths. Affects chemical equilibrium, lowering seawater pH, and changing nutrient solubility (e.g., $HCO_3^-$). Increases the boiling point of water, maintaining its liquid state at high temperatures and pressures. Rule of thumb: Hydrostatic pressure increases by $1 \text{ atm}$ per $10 \text{ m}$ of depth. Example: Barophilic microorganisms are found at depths of $1000-10000 \text{ m}$, where pressure exceeds $100 \text{ atm}$. Light Most aquatic life depends on photosynthetic organisms. Primary producers (algae) are restricted to the upper water layer where light can penetrate. Salinity Ranges from zero in fresh water to saturation in salt lakes. Sea water salt concentration: $33-37 \text{ g/kg}$. Major salts: Chlorides, Sulphates, and Carbonates of $Na, K, Ca, Mg$. Most marine microorganisms are halophilic , growing best at $2.5-4\%$ salt concentration. Lake and river microorganisms are salt-sensitive and do not grow at salt concentrations above $1\%$. Turbidity Variation in the clarity of surface waters. Suspended material causing turbidity includes: Mineral particles from land. Detritus (e.g., cellulose, hemicellulose, chitin fragments). Suspended microorganisms. Turbidity affects light penetration, thus impacting the photosynthetic zone. Hydrogen Ion Concentration (pH) Aquatic microorganisms generally grow at pH $6.5-8.5$. Sea pH: $7.5-8.5$. Optimum growth for most marine species: pH $7.2-7.6$. Lakes and rivers show wider pH ranges depending on local conditions. Aquatic Microorganisms The microbiology of fresh waters is part of limnology (study of flora and conditions for life in lakes, ponds, and streams). Lakes and Ponds: Characteristic Zones Littoral zone: Along the shore, with rooted vegetation and light penetration to the bottom. Limnetic zone: Open area after the littoral zone, determined by the light compensation level (depth of effective light penetration). Profundal zone: Beneath the limnetic zone in deeper open waters; photosynthesis decreases due to poor light penetration. Benthic zone: Deepest zone, composed of soft mud at the bottom. Streams Obtain nutrients from surrounding terrestrial systems or lakes/ponds. Microbial flora reflects immediate terrestrial conditions, including effects of agriculture and industrial practices. The Sea Microorganisms are present at all depths and latitudes. Occur as plankton and in ocean sediments. Open sea offers a less variable environment than other aquatic systems. Marine Plankton: Phytoplankton: Diatoms, cyanobacteria (blue-green algae), dinoflagellates (flagellate protists), silicoflagellates (unicellular algae). Responsible for converting radiant energy to chemical energy. Zooplankton: Feed on phytoplankton, bacteria, or detritus. Many exhibit diurnal migration, avoiding light during the day and grazing on phytoplankton at the surface at night. Benthic Population Offshore sediments are inhabited by protozoa and bacteria. Bacterial populations at the mud-water interface can range from hundreds to millions per mm. Sediment counts can be as high as $10^8$ bacteria per gram. Many bacteria are facultative or strict anaerobes (e.g., Desulfovibrio , Clostridium , methane bacteria). Waterborne Diseases Water ($H_2O$) acts as a vector for bacterial, viral, and protozoan agents causing mainly intestinal diseases. Can also be linked to viral/protozoan diseases transmitted by insects (aquatic hosts or breeding in $H_2O$). Responsible for approximately $80\%$ of all infectious diseases globally. Spread and Symptoms Infection: Direct drinking of contaminated water or contact with contaminated water. Common symptoms: Abdominal pain, fever, diarrhea. Conditions are more severe in individuals with weakened immune systems. Indicator Microorganisms Used to indicate increased risk of pathogen contamination due to fecal contact. Not dangerous themselves but signal a potential health risk. Coliform Bacteria E. coli -like bacteria, most often used for water quality assessment. Serve as indicators of sanitary quality in food and water. Their presence suggests potential fecal contamination (from animals or humans). Widespread, easy to detect, and respond to environmental conditions similarly to many pathogenic bacteria. Function: Indicate a potential risk of contamination by more dangerous bacteria (e.g., E. coli , Salmonella ). Safety: While not directly harmful, water contaminated with coliforms can cause gastrointestinal upset if pathogens are also present. Testing: Used to determine the likelihood of other pathogens. A positive result necessitates further investigation. Characteristics of Coliforms Aerobic or facultative. Gram-negative. Non-spore forming. Bacilli. Ferment lactose to form acid and/or gas within $24$ hours at $35^\circ C$. Gas production (carbon dioxide and hydrogen) is a key characteristic for identification and can cause defects in products like cheese. Most Probable Number (MPN) Method A statistical technique to estimate microorganism concentration, especially in water and food. Checks potability (safety for drinking) of water. Detects potential pathogenic bacteria due to water supply contamination. Used for water supplies derived from ground sources to check bacterial contamination safety levels. MPN Technique Steps Sample preparation and dilution: Sample is diluted in a series of $10$-fold dilutions. Inoculation: Multiple tubes of liquid broth are inoculated with different volumes from each dilution. Incubation: Tubes are incubated at a suitable temperature (e.g., $24-48$ hours) for microbial growth. Observation: Tubes are examined for signs of microbial growth (turbidity, gas production). Interpretation: Count positive tubes at each dilution and compare to a standard MPN reference table to determine microbial density. Applications and Advantages Estimates viable microorganisms, even in low-concentration samples. Useful for turbid samples with high particulate matter, where traditional plate counts are difficult. Commonly used in water quality testing to detect fecal coliforms. Disadvantages Labor-intensive, requires large amounts of glassware. Lack of precision, prone to large errors. Still requires survival and culture of organisms in the lab. Membrane Filtration Categorized into four processes based on membrane pore size: Microfiltration Ultrafiltration Nanofiltration Reverse Osmosis Reverse Osmosis Pore size: $0.0001$ microns. Removes: Natural organic substances, pesticides, cysts, bacteria, viruses. Used in desalination. Membrane Filter Methods Filter water through a membrane filter (bacterial cells cannot pass). Place membrane on selective media (e.g., EMB). Incubate at $35^\circ C$. Count colonies. Results: Coliform bacteria produce colonies with a characteristic "metallic green sheen." Membrane Filtration Method Advantages More than $100 \text{ ml}$ samples can be tested. Effective and acceptable technique, used to monitor drinking water in government laboratories. Rapid. Lower chance of contamination, especially on a small scale. More accurate. Membrane Filtration Method Disadvantage Not suitable for turbid or waste water.