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Aquatic Bacteria & Fungi Objective To know the main cellular features, physiology and function of bacteria & fungi in water and wastewater environments To know the species interactions in anaerobic digestion to understand how substrate conditions and nutritional requirements determine the competitive success of these microbes in pollutant degradation processes. References Gray N.F. Biology of Wastewater Treatment Lester J.N. & Birkett J.W. Microbiology and Chemistry for Environmental Scientists & Engineers Madigan M.T., Martinko J.M., Parker J. Brock - Biology of Microorganisms Stanier R.Y. General Microbiology Kiely G Environmental Engineering Lecture Outline Bacteria - Cell Structure Physiology & Function Fungi- Cell Structure Physiology & Function Bacteria What are they? Prokaryotic organisms Bacteria (eubacteria), Archaea (archaebacteria) Importance in Environmental Engineering Biodegradation Nutrient Cycling Pathogens in Contaminated Waters Bacterial Cell Structure Size smallest living organisms, 1m. Shape typically cocci or rods (bacilli), spiral, stalked, filamentous. multicellular swarms (gliding myxobacteria, myxococcus) DNA circular, supercoiled, no nuclear membrane. Extranuclear DNA or Plasmids. Reproduction Asexual = Binary fission, Conjugation via Pili. Cell Structure Cell Wall Two types, Gram Positive, Gram Negative Both have Peptidoglycan Gram Negatives also have Lipopolysaccharide (LPS) Archaea similar to G+ve, have pseudopeptidoglycan Cell Structure Flagellum May be present - Motile Polar or peritricious Driven by Proton motive Force (PMF) Chemotaxis - tumble frequency increases. Cytoplasm complex subcellular organelles usually absent. vesicular and lamellar structures (mesosomes) form by invagination of cytoplasmic membrane (e.g. N-fixing, Nitrifying, and Phototrophic bacteria). cytoplasmic membrane essential (maintains PMF). Ribosomes - Protein synthesis Enzymes - metabolism Granules (Inclusions) Gas Vesicles (buoyancy, e.g. cyanobacteria) Characteristics Oxygen Requirements Aerobic Microaerophilic Facultative (aerobe) Anaerobic (strict) Growth Requirements - Organic substrates Heterotrophic (Chemoorganotrophs) – Pseudomonas, Bacillus, Zoogloea, etc. Key role in Nutrient Cycling Biodegradation of Organic Detritus Soluble low molecular weight substrates e.g. acetate, methanol, sugars. Polymers degraded by extracellular hydrolytic Enzymes. Metabolism Growth Requirements - Inorganic substrates Autotrophic (Chemolithotrophic, Phototrophic) – Nitrosomonas, Nitrobacter, Methanococcus, Chlorobium, etc. Reduced forms of sulphur H2S, S0, S2O32-, SO3Reduced forms of nitrogen NH3 Hydrogen H2 Iron Fe2+ Growth Requirements - Light Photosynthetic (phototrophic) light and CO2 oxygenic blue-green (cyanobacteria) anoxygenic green-sulphur (Chlorobium sp.) Bacteria in Aquatic Environments Natural Waters Energy source (depends on metabolism and dissolved species) Cellular Nutrient Requirements C, H, O, N, P, S. vitamins, growth factors, trace elements. Dissolved Gases (O2, CO2, H2S) Nitrogen is usually limiting in oligotrophic waters. Origin of Nutrients Algal secretions, death. Zooplankton feeding, death. Soil run-off discharge of treated (& untreated) effluents. Bacteria in Aquatic Environments Planktonic suspended free cells vertical movement – O2 – stratified nutrients (in anoxic zone) Particulate associated with POM Biofilms surfaces of stones and plants (epiphytic) can be slow growing, psychrophilic environments. Methanogenesis Methanogenic Bacteria (Archaea) Chemolithotrophic (autotrophs) H2 and CO2 e.g. Methanobacterium, Methanococcus, Methanospirillum 4H2 + H+ + HCO3CH4 + 3H2O Energy -136kJ (but as low concentrations = -30kJ) Low pE (anaerobic) environments Inhibited in Marine sediments Other substrates include Acetate, Methanol, Formate etc. METHANOGENESIS Complex polymers Protein, Cellulose Hydrolysis Monomers Sugars, amino acids Fermentation H2 + CO2 Acetogenesis Acetate Propionate Butyrate Alcohols Acetate Syntrophs Fermentation H2 + CO2 Methanogens Acetoclastic METHANE Acetate Methanogens H2-Utilising, Acetoclastic Methanogenesis Methanogenesis involves Co-operation Inter-species Hydrogen transfer Several Steps from a complex substrate (Cellulose) 1. Hydrolysis (depolymerisation) to cellobiose (G-G) 2. Fermentation of Glucose to Fatty acids, H2 and CO2 3. Fatty acids oxidised to H2 and CO2 (SYNTROPHS) 4. Methanogens produce CH4 Syntrophs require H2 to be consumed Typically H2 < 10-4 M Fungal Cells Size Typically 5m diameter filament, variable length Structure Filamentous – hyphae bundled as Mycelia (moulds) Usually branched Rods (Yeasts ) Chitin and cellulose cell walls DNA chromosomes, nuclear membrane. Reproduction Asexual = tip cell, sexual = spores called conidia. Physiology of Fungi No chlorophyll, produce extra-cellular enzymes. Heterotrophic nutrition. Parasitic or Saprophytic Very slow rate of growth cf. bacteria. Tolerate low DO, low pH, High C:Nratios. Dairy & Trade wastes Environmental Requirements 1. Nutrients - Only organic C - or Organic C + N } and some need vitamins C10H17O6N i.e. low ratio N:C therefore tolerate N deficiency. 2. Moisture relatively low concentration H2O (75-80%) (Usually 95-98% in bacteria etc.) Therefore can grow on moist and aquatic environments. Physiology of Fungi 3. pH Normally prefer low pH (produce acid themselves) 4. Oxygen Normally prefer O2 (i.e. aerobic) although some species can tolerate anaerobic conditions temporarily. Aerobic respiration: C6H12O6 6CO2 + 6H2O Anaerobic respiration fermentation: C6H12O6 2C2H5OH + 2 CO2 (Yeasts) 5. Temperature Grow in range 2 - 25oC, optimum = 15oC i.e. psychrophilic - cold-loving Importance of Fungi in Freshwater 1. Fungi play similar role to bacteria. Very important in breakdown of complex organics to simpler substances for algae (i.e. NH3 mineralization) White rot fungi (Phenaerochete) degrade lignin and produce enzymes that degrade complex pollutant molecules Associated with polluted waters because of high nutrient requirements. 2. Indicators of pollution Fusarium, Leptomitis and Geotrichum associated with a mesosaprobic zone in Saprobian system. Importance of Fungi in Freshwater 3. Actinomycetes and Fungi Give Taste and Odour problems in treated water. a) Grow on reservoir walls, and release complex organic compounds when dead. (TASTE AND ODOUR). Also grow on dead algae. Very common after algal blooms. Saprophytic b) Grow in cold water systems in buildings, especially where cold and hot water pipes are adjacent. 4. Sewage Fungus growths in rivers receiving certain industrial wastes (e.g. wood pulping and dairy wastes). 5. Marine Waters Sewage Fungus WRC Survey of 90 Sewage Fungus Associations thick, slimy growths on river bed pulp mill, dairy or strong sewage Leptomitis lacteus Geotrichum Fusarium aqueductum Other fungi 4% 7% 3% 10% Sphaerotilus natans Zoogloea 89% 94% Stigeoclonium Diatoms Ulothrix 10% 18% Sewage Fungus - FUNGI BACTERIA* ALGAE 4% therefore a misnomer Mainly bacteria Fungi in Activated Sludge Rare, unless high proportion of trade wastes (e.g. Canneries, Dairies, Distilleries) High C:N ratio Low pH Low DO Overloading Under aeration Give rise to BULKING SLUDGE. *Geotrichum Pullularia pullulans Sporotrichum Also filamentous bacteria give rise to same problem e.g. Nocardia, Sphaerotilus natans, Thiothrix, Microthrix + many others Fungi in Trickling Filters Leptomitis lacteus Fusarium aqueductum Geotrichum candidum Sepedonium spp. Subbaromyces speldens Ascoidea rubescens often present in feed channels. Colonise surface of filter Able to withstand impact of sewage. Common in sub-surface zone. Phoma, Saprolegnia, Leptomitis lacteus occasionally present. In winter, species with low optimum temperature e.g. Sepedonium dominate. Fungi in Trickling Filters Industrial Wastes e.g. from Canneries, Dairies, Distilleries etc. encourage growth of fungi (High C:N ratio) Problems caused by Fungi: Heavy growth causes PONDING, especially in winter. Operational procedures: Film accumulation controlled by Recirculation, Alternating double filtration low frequency dosing. Colonisation of Trickling Filters Fungi, high energy of maintenance (40-50 mg/l BOD) Bacteria have much lower saturation constants than fungi (Ks = 0-20 mg/l BOD for sewage bacteria) Therefore bacteria continue to grow at low substrate concentrations i.e. Bacteria have a competitive advantage over fungi at low substrate concentrations. Vice versa at high substrate concs.
