Microbiology - Microbial Cultivation and Growth - Quick Guides | Microbiology

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Study GuideMicrobiology–Microbial Cultivation and Growth1.Growth Requirements for MicroorganismsOne of the defining features of microorganisms is their ability togrow and multiply, forming largepopulations. Microbial growth occurs when cells increase in size and then divide. For this growth tohappen successfully, microorganisms need specificchemical and physical conditions.1.1Chemical Requirements for Microbial GrowthTo grow and survive, microorganisms must obtain a variety of chemical substances from theirenvironment.Water and Carbon•Wateris essential for all life processes.•Almost all organic compounds in microorganisms—such as proteins, carbohydrates, fats, andlipids—containcarbon.•About50% of the dry weight of a bacterial cell is carbon.Sources of carbon:•Organic carbonfrom environmental materials•Carbon dioxide (CO₂)from the atmosphereMicroorganisms that use CO₂as their carbon source include:•Chemoautotrophs–obtain energy from chemical reactions•Photoautotrophs–obtain energy from sunlight through photosynthesisNitrogen and Phosphorus•Nitrogenis required for making:

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Study GuideoProteinsoAmino acidsoDNA and RNASome bacteria can use nitrogen directly from the air. These are callednitrogen-fixing bacteria, suchas:•Rhizobium•Azotobacter•Phosphorusis essential for:oNucleic acidsoPhospholipids in cell membranesoATP productionOxygen RequirementsMicroorganisms vary greatly in their oxygen needs:•Aerobic organismsoRequire oxygenoUse oxygen as the final electron acceptor in cellular respiration•Anaerobic organismsoGrow without oxygenoOften produce gases like hydrogen sulfide or methaneoSome pathogens, such asClostridiumspecies, are anaerobic•Facultative organismsoCan growwith or without oxygen•Microaerophilic organismsoRequirelow levels of oxygen•Capnophilic organismsoGrow best in environments withhigh carbon dioxide levels

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Study Guide1.2Trace Elements and Growth FactorsMicroorganisms also require small amounts oftrace elements, including:•Iron•Copper•ZincThese are often needed forenzyme synthesis.Some microorganisms requireorganic growth factors, such as:•Vitamins•Amino acids•Purines•Pyrimidines1.3Physical Requirements for Microbial GrowthIn addition to chemicals,physical conditionsstrongly influence microbial growth.TemperatureEnzyme activity depends on temperature, so microorganisms are classified based on their preferredtemperature range.•PsychrophilesoPrefer cold temperaturesoAbout0°C to 20°C•MesophilesoPrefer moderate temperaturesoAbout20°C to 40°CoMost human pathogens fall into this group

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Study Guide•ThermophilesoPrefer high temperaturesoAbove40°CFigure 1Three types of bacteria and the temperature environments in which they thrive.Each microorganism has:•Aminimum growth temperature•Amaximum growth temperature•Anoptimum growth temperature, where growth is fastest

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Study GuidepH (Acidity and Alkalinity)ThepHof the environment affects enzyme function and growth.•Most bacteria grow best atpH 6.5–7.5•Human tissues have a pH of7.0–7.2, which supports many bacteria•AcidophilesoPrefer acidic conditions (pH ≤ 6.0)oFound in foods like yogurt and sauerkrautoMolds and yeasts often belong to this group1.4Osmotic Pressure and Salt ConcentrationMicrobial growth is also influenced byosmotic pressure, which depends on salt concentration.•Normal cytoplasmic salt concentration ≈1%•When external salt concentration is also 1%, conditions are idealEffects of imbalance:•High external saltoWater leaves the celloCell shrinks and may die (used in food preservation)•Low external saltoWater enters the celloCell may swell and burstHalophilesMicroorganisms that tolerate or require high salt concentrations are calledhalophiles.Examples include:•Diatoms•Dinoflagellates•Many marine bacteria, fungi, protozoa, and algaeThese organisms thrive in salty environments such as oceans and salt lakes.

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