Microbial Growth And Nutrition Lecture Notes PDF

MICROBIAL GROWTH AND NUTRITION BY Dr. Benson E.A Course code: MCB 311 Course Title: Microbial Physiology 1 INTRODUCTION  Like all living organisms, microorganism grow.  Growth can be defined as;  an orderly increase the q...

MICROBIAL GROWTH AND NUTRITION BY Dr. Benson E.A Course code: MCB 311 Course Title: Microbial Physiology 1 INTRODUCTION  Like all living organisms, microorganism grow.  Growth can be defined as;  an orderly increase the quantity of all cellular constituents.  Increase in cell number and cell population  The cell population and population mass typically increase with time  Growth of microorganisms follows a specific pattern 2 described in the microbial growth curve.  MICROBIAL GROWTH CURVE 3 4 GENERATION TIME  The time taken by the bacteria to double in number during a specified time period is known as the generation time.  The generation time tends to vary with different organisms.  Thus, if we start with a single bacterium, the increase in population is geometric progression: 1 2 22 23 24……………..2n n= the number of generations. Each succeeding generation, assuming no cell death, doubles the population.  The total population N at the end of a given time period would be expressed N = 1 x 2n  However, under practical conditions several thousands of bacteria are introduced into the medium at zero time and not one, so the formula now becomes.  N = NO x 2n  Where No = number of organisms at zero time.  N = number of organisms after n generations.  n= number of generations 5 6 7   Microorganisms have certain requirements for growth which may be grouped as;  Nutritional Requirements  Environmental Requirements 8  NUTRITIONAL REQUIREMENTS  Microorganisms may require certain nutrients in large amounts because they utilize them to make up carbohydrates, proteins, lipids and nucleic acids. These are known as MACRO-NUTRIENTS. Some examples include; Carbon, Oxygen, Nitrogen, Hydrogen, Phosphorus, Sulfur etc.  Other nutrients may be required only in minute amounts and these are referred to as MICRO-NUTRIENTS. Most are minerals that are essential for the activity of enzymes known as Cofactors. They include; manganese, zinc, cobalt, molybdenum, nickel and copper etc. 9   Bacteria have three major growth factors;  A source of energy (ATP) necessary for cellular functions  A source of Carbon for making Carbohydrates  A source of Nitrogen for making Proteins 10  ENERGY SOURCE  Two basic forms of energy are suitable energy sources for living organisms namely chemical and light energy.  Organisms that utilize light energy are referred to as Phototrophs. Phototrophs are able to convert energy from the sun into chemical energy.  Organisms that utilize chemical energy are referred to as Chemotrophs. 11  CARBON SOURCE  All living organisms require energy and carbon sources for growth.  Carbon can be obtained from organic materials in the environment, or it may be derived from an inorganic source e.g carbon dioxide.  Organisms that use (oxidize) organic sources of carbon are heterotrophs while  Organisms that use CO2 as a sole source of carbon for growth are called autotrophs.  Autotrophs are able to synthesize their own organic requirements from simple inorganic materials. 12   Heterotrophic Bacteria can be grouped into the following;  Saprophytic Bacteria  Symbiotic bacteria  Parasitic Bacteria 13  Saprophytic Bacteria  These bacteria obtain their nutritional requirements from dead organic matter  They breakdown the complex organic matter into simple soluble form by secreting exogenous enzymes  Subsequently they absorb the simple nutrients and assimilate them, during which they release energy  These bacteria have a significant role in the ecosystem, functioning as decomposers  The aerobic breakdown of organic matter is called decay or decomposition. It is usually complete and not accompanied by the release of foul gases 14   Anaerobic breakdown of organic matter is called fermentation. It is usually incomplete and is always accompanied by the release of foul gases. Anaerobic breakdown of proteins is called putrefaction.  The property of decomposition of organic compounds is employed in several industrial processes such as ripening of cheese, in the retting of fibres and in the curing of tobacco. 15  Symbiotic Bacteria  These are bacteria which live in a mutually beneficial association with other organisms. Such bacteria derive the essential nutrients from their host organisms and in that process help the host through some of their biological activities  EXAMPLES  The nitrogen fixing bacteria found in the root nodules of leguminous plants.  Bacteria such as Rhizobium and Pseudomonas reside in the root nodules and reduce atmospheric nitrogen directly to ammonia.  This becomes the source of nitrogen for the host plants.  The plants in return provide bacteria with nutrients and protection. 16   2. Escherichia coli is a bacteria found in the human alimentary canal. They are non-pathogenic.  The bacteria check the growth of harmful putrefying bacteria.  The human host provides shelter and food for the bacteria  3. Cellulose digesting bacteria which occur in the alimentary canal of ruminant mammals such as cows and goats also performs the same function 17  Parasitic Bacteria  These are bacteria which occur in the body of animals and plants, obtaining their organic food from their host  Most of these bacteria are pathogenic  They cause serious diseases in the host organisms  They do this either by exploiting them or by releasing poisonous secretions called toxins 18  COMBINING ENERGY AND CARBON SOURCE  Photoautotrophs  Photoheterotrophs  Chemoautotrophs  Chemoheterotrophs: 19  Photoautotrophs: They are organisms that carry out photosynthesis. Using energy from sunlight, carbon dioxide and water are converted into organic materials to be used in cellular functions such as biosynthesis and respiration.  Photoheterotrophs: They are organisms that make use of light energy as their energy source. They also cannot use carbon dioxide as their sole carbon source. They use organic compounds from the environment.  Chemoautotrophs: They utilize chemical energy to synthesize their food from inorganic sources such as co2  Chemoheterotrophs: They utilize chemical energy to synthesize their food from organic compounds such as carbohydrates, proteins and 20 lipids. NUTRITIONAL TYPE ENERGY SOURCE CARBON SOURCE PHOTOAUTOTROPHS LIGHT INORGANIC COMPOUND CO2 PHOTOHETEROTROPHS LIGHT ORGANIC COMPOUNDS CHEMOAUTOTROPHS CHEMICAL ENERGY INORGANIC (LITOTROPHS) COMPOUNDS CO2 CHEMOHETEROTROPHS CHEMICAL ENERGY ORGANIC COMPOUND (HETEROTROPHS) (OFTEN IN FORM OF GLUCOSE) 21  NITROGEN SOURCE  Nitrogen requirements of organisms for growth may be;  Organic e.g amino acids, pepetides and proteins or  Inorganic e.g ammonium salts and nitrates.  Nitrogen is used for the synthesis of proteins, amino acids, RNA, and DNA.  Bacteria that obtain nitrogen directly from the atmosphere are called nitrogen-fixing bacteria. 22  GROWTH FACTORS  They are required in small amounts by cells because they fulfill specific roles in metabolism.  Growth factors are organized into three categories.  Purines and Pyrimidines: required for synthesis of nucleic acids (DNA and RNA)  Amino acids: required for the synthesis of proteins. These are often supplied in the form of partially digested proteins called peptone  Vitamins : needed as co-enzymes and functional groups of certain enzymes 23  CRITICAL THINKING Now we know the major nutritional requirements for microbial growth. Is it possible to compound a simple medium for culturing microorganisms from local sources considering that most synthetic media are expensive to purchase? 24  ENVIRONMENTAL FACTORS  Temerature  Thermophiles Osmotic pressure Osmotolerant  Mesophiles Halophiles  Psychrophiles  Oxygen  Obligate aerobes  Microaerophiles  Facultative aerobes  Aerotolerant anaerobes  Obligates anaerobes  pH Alkalophiles Neutrophiles 25  Acidophiles  TEMPERATURE REQUIREMENTS  Temperature is the most important factor that determines the rate of microbial growth.  At high temperature, enzymes and other proteins responsible for the normal functioning of the cells are denatured.  Microbial membranes are also disrupted by extreme temperatures. 26 27 28  PSYCHROPHILES  Also referred to as cryophiles.  These are microorganisms that are able to grow and reproduce in cold environments.  Temperature requirements ranges between -20oc to +20oc. Optimum temperature is 15oc.  Examples include; Aeromonas hydrophila, Clostridium botulinum, andYersinia enterocolitica. 29  MESOPHILES  These are microorganisms which grows best at moderate temperature.  Their temperature requirement ranges between 20oc to 45oc.  Optimum temperature 30oc to 40oc.  Most soil bacteria and bacteria that live in and on the body are mesophiles.  Examples include; Salmonella sp, Staphylococcus aureus, Streptococcus pyrogenes, Streptococcus pneumoniae, Escherichia coli, 30  THERMOPHILES  They are heat-loving bacteria.  They are capable of growing in relatively high temperatures.  Their temperature requirements ranges between 45oc and 80oc.  Optimum temperature is 55oc to 65oc.  Examples include; Thermus aquaticus ,Thermococcus litoralis. 31  HYPERTHERMOPHILES  Hyperthermophiles are bacteria that grow at very high temperatures.  Their optimum growth temperature is between 70oc and 110oc.  They are usually members of the Archaea. 32  OXYGEN REQUIREMENTS 33  OBLIGATE AEROBES  Obligate aerobes are organisms that grow only in the presence of oxygen.  They obtain their energy through aerobic respiration.  Examples include; Bacillus cereus, Pseudomonas aeruginosa, Mycobacterium tuberculosis etc. 34  MICROAEROPHILIC  Microaerophiles are organisms that require a low concentration of oxygen (2% to 10%) for growth.  They obtain their energy through aerobic respiration.  Higher oxygen concentrations may be inhibitory to them.  Examples include; Campylobacter jejuni, Helicobacter pylori etc. 35  OBLIGATE ANAEROBES  Obligate anaerobes are organisms that grow only in the absence of oxygen.  They are often inhibited or killed by its presence.  They obtain their energy through anaerobic respiration or fermentation.  Examples include; Clostridium tetani, Clostridium botulinum, Clostridium perfringens etc. 36  FACULTATIVE ANAEROBES  Facultative anaerobes are organisms that grow with or without oxygen, but generally better with oxygen.  They obtain their energy through aerobic respiration if oxygen is present,but use fermentation or anaerobic respiration if it is absent.  Most bacteria are facultative anaerobes.  Examples include; Enterobacteriaceae group, Staphylococcus aureus 37  pH LEVELS  pH refers to the degree of acidity or alkalinity of a medium.  Most bacteria prefer pH near neutral and usually cannot tolerate pH values below 4.  Drastic variations from optimal pH my result in disruption of plasma membrane or inhibit the activities of enzymes. 38 39  CLASSIFICATION ACCORDING TO pH CONT’D.  Acidophiles; pH ranges between 0 and 5.5. Examples; microscopic algae Cyanidium caldarium and Dunaliella acidophila.  Alkaliphiles; pH ranges between 7.5 and 14. Examles; Thermococcus alcaliphilus  Neutrophiles; pH ranges between 5.5 an 8. Examples; Lactobacillus acidophilus, Escherichia coli, Pseudomonas aeruginosa 40 41 OSMOTIC PRESSURE  This is the pressure that must be applied to the solution side to stop fluid movement when a semipermeable membrane separates a solution from pure water.  It is often used to express the concentration of solute in a solution.  Osmosis is the diffusion of water across a membrane from an area of higher water concentration (lower solute concentration) to lower water concentration (higher solute concentration). 42  TYPES OF SOLUTION  In an isotonic solution, both the water and solute concentration are the same inside and outside the cell and water goes into and out of the cell at an equal rate.  In a hypertonic, the water concentration is greater inside the cell while the solute concentration is higher outside. Water goes out of the cell.  In a hypotonic solution, the water concentration is greater outside the cell and the solute concentration is higher inside. Water goes into the cell 43 44 CLASSIFICATION ACCORDING TO SALT CONCERNTRATION  Halotolerant; these are microorganisms that can grow at relatively high salt concentration (up to 10%).  Halophiles; these are microorganisms that require relatively high salt concentrations for growth, like some of the Archaea that require sodium chloride concentrations of 20 %. 45  CONCLUSION  Summarily, factors required for microbial growth can be classified into two broad groups;  Chemical/nutritional factors; carbon, nitrogen etc.  Environmental/physical factors; temperature, pH, osmotic pressure etc. 46  FURTHER READING  http://www.onlinebiologynotes.com/classification-of-bacteria/  http://www.textbookofbacteriology.net/nutgro_6.html  https://www.coursehero.com/sg/microbiology/physical-and- chemical-factors-affecting-microbial- growth/#:~:text=There%20are%20a%20variety%20of,basic%2C%2 0or%20neutral%20pH%20conditions.  Microbiology: A Human Perspective, 5th Edition, pages 92-102. 47 48