Chapter 4 Microbial Metabolism (MIC461) PDF

CHAPTER 4: MICROBIAL METABOLISM MIC461  LEARNING OUTCOMES At the end of this topic, students should be able to: Explain the catabolism and anabolism reactions. Differentiate three forms of Microbial Metabolism. Discuss the extrinsic and intrinsic parameters affecting Mic...

CHAPTER 4: MICROBIAL METABOLISM MIC461  LEARNING OUTCOMES At the end of this topic, students should be able to: Explain the catabolism and anabolism reactions. Differentiate three forms of Microbial Metabolism. Discuss the extrinsic and intrinsic parameters affecting Microbial Growth.  MICROBIAL METABOLISM What is Metabolism? Is the sum of all growth processes that takes place in the body of all living cells. It involves about 2000-3000 biosynthetic reactions. all governed by enzymes. These reactions are classified into two: 1. Catabolism 2. Anabolism These reactions generate the materials for growth. MICROBIAL METABOLISM  ANABOLISM Anabolism: Biosynthesis Enzyme-regulated energy requiring reactions. The building of complex organic molecules from simpler ones. All reactions associated with the building of cellular components and cell mass. Uses products of catabolism: 1. The building blocks are linked to form cellular components. 2. Requires energy from ATP or reducing powers. These reactions are called anabolic or biosynthetic and they are generally dehydration synthesis reactions (reactions that release water), and they are endergonic (consume more energy than they produce). Eg. Formation of proteins from amino acids, nucleic acids from nucleotides, polysaccharides from simple sugars, photosynthesis process: makes energy-rich sugar molecules using energy in SUNLIGHT.  CATABOLISM CATABOLISM: Breakdown Enzyme-regulated chemical reactions that release energy. Complex organic compounds are broken down into simpler ones. These reactions are called catabolic or degradative reactions. Breakdown releases energy from breaking of chemical bonds (Energy is neither created nor destroyed). They are generally hydrolytic reactions (reactions that use water and in which chemical bonds are broken), and they are exergonic (produce more energy than they consume). Ex. Cells break down sugars (glucose) into CO₂ and H₂O. Cellular respiration also releases energy and heat and produces products but is able to use the released energy to perform work  CATABOLISM The objectives of Catabolism are to generate: i. Energy. ATP Breakdown of nutrients releases energy. Energy is captured in Substrate level ii. Reducing power: Phosphorylation and Oxidative level NADH,FADH, NADPH Phosphorylation. In microbes this takes place in the vicinity of the inner CM. Nicotinamide adenine dinucleotide (NAD) + hydrogen (H)- High energy electron carrier used to transport electrons generated in Glycolysis, Kreb Cycle, Electron Transport Chain. Precursor metabolites : Small building blocks (materials for cell mass synthesis) are tapped from the breakdown process. Ex: R-COOH (carboxylic acid) for amino acid and protein synthesis. CATABOLISM VS ANABOLISM TYPES OF BACTERIAL METABOLISM Three common forms: i. Aerobic pathway ii. Anaerobic pathway iii. Facultative pathway These form differs in what is the final electron acceptor. SOD - Superoxide dismutase Catalase Peroxidase  AEROBIC PATHWAY a. Aerobic pathway: Substrate or nutrients are broken down in the presence of oxygen as the final electron acceptor. It generates the most available energy for living cells. Ex. E.coli gets 28 molecules of ATP from 1 molecule of glucose. Catabolic activity = exergonic*  ANAEROBIC PATHWAY B) Anaerobic pathway: Also known as the fermentation pathway. Substrate (usually intermediate carbohydrate; eg: glucose are broken down in the absence of oxygen (toxic to strict anaerobes)). The resulting intermediate carbohydrate acts as the final electron acceptor. The end product is either alcohols or organic acids. Only small amount of energy and reducing power is obtained. Eg: 2 ATP per Glucose. Therefore for microbes to survive by fermentation, it must be given high concentration of nutrient (Pasteur effects in fermentation).  FACULTATIVE PATHWAY C) Facultative pathway: Some microorganisms show ability to live in the presence and also absence of oxygen. These are called facultative organisms. Given a preference they will choose to live in aerobic environments. Majority of bacteria are facultative.  ANAEROBIC RESPIRATION D) Anaerobic Respiration This pathway is present in some bacteria. It differs from aerobic and anaerobic in the final electron acceptor being some other elements than oxygen or intermediary carbohydrate. Nitrate reducing bacteria Sulfate reducing bacteria The Intrinsic and Extrinsic Parameters Affecting Microbial Growth Microorganisms have great influence on human life and activities, affecting food, materials, health, medical and environment. Knowing the factors affecting the growth of these microorganisms greatly assist in providing effective measures at controlling and retarding the effects microorganism exert on the previously stated areas. These parameters can be classified into 2 major classes:- 1. Intrinsic 2. Extrinsic The Intrinsic Parameters These parameters describe the factors that are associated to the nature of substance or materials that are inherent (characteristics/a part of) properties of the substance, that are called the substrate Substrate: substance on which microorganism can establish growth. These parameters are:- 1. pH 2. Moisture content 3. oxidation-reduction potentials 4. nutritional content 5. antimicrobial constituents 6. biological structures 1. pH Bacteria prefers pH between 6.5 - 7.5 (neutral to slightly acidic). Fungi are more suited to slightly alkaline pH of 7.5 - 8.5. with some yeasts and molds. Buffering (stabilizing the pH) using acid or alkaline would be an effective methods of material preservations. 2. Moisture content One of the oldest methods of material preservation is drying or desiccation. Water or moisture content of a material is a very profoundly important criteria that determine the ability of microorganisms to grow on it. This is technically known as the Water Activity (aw) of the substance. It describe the pure water quantity in the substance that is available for biological growth. All living cells require water for growth. 3. Oxidation - Reduction Potential (OR) The OR potential of a substrate is defined as how readily the substrate loses or gains electron. When a substrate loses electron it is said to be oxidized, when it gains, it is said to be reduced. The OR potential can be measured using a potentiometer and expressed as millivolts (mv). A highly oxidized compound (readily accept electron) is a good reducing agent and has a positive (+) Eh (redox potential) (This also means oxygen are readily available) and vice versa. For substances with high content of -SH, like meat, the Eh is commonly negative, favoring anaerobic growth (Eg.; solid meat Eh -200mv, minced meat and fruits Eh +200mv.) OIL - RIG Oxidation is Losing electron - Reduction is Gaining electron 4. Nutrient Content The ability of microorganisms to grow well on materials and substances are also greatly dependent on the nutritional content of substance. As biological life need:- 1. water 2. source of energy 3. source of nitrogen and elements 4. source of minerals, vitamins and growth factors the ability of these microorganism to colonize and grow on substance will be highly dependent on the chemical constituents of that substance and also on the capabilities of their enzymatic profiles. Materials of simple sugars would be highly vulnerable to microbial spoilage as compared to a more complex one. 5. Antimicrobial Content and Constituents Natural biological materials and most synthetic ones are known to naturally contain antimicrobial constituent that somehow protect or delay spoilage. Example, spices such as cloves and most plant-based compound has chemical such as eugenol, phenol and others that are known to deter microbial growth. 6. Biological Structures Eggs are contained in protective shells, human tissues are protected by the skin, wood are covered by resin and so on. These structural makeup somehow protects these materials from being easily spoilt by microorganisms. The Extrinsic Parameters Affecting Microbial Growth The extrinsic parameters affecting the spoilage of materials by microorganisms refer to those parameters associated to the environment surrounding those materials. They are limited to 3 specific parameters:- i. Temperature surrounding the material ii. Relative Humidity of the surrounding iii. Presence and concentration of gases in the environment. 1. Temperature Microorganisms grow over a wide range of temperature and are greatly affected by the temperature of their surroundings. As such the temperature surrounding the storage of materials would affect the colonization and proliferation of microorganisms on these materials. Controlling the surrounding temp in conjunction with the relative humidity would greatly enhance the durability of goods. 2. Relative Humidity As all biological lives need water, the relative humidity of the surrounding would greatly affect microorganism's growth on materials. Materials that are kept in low or high Rh would last longer. Drying agents such as salts, silica gels, talcum powders, refrigeration and so on helps in material preservation. 3. Gaseous content The gaseous content of the atmosphere surrounding materials, namely, carbon dioxide, oxygen and nitrogen have great effects on the ability of microorganisms to grow and proliferate. An environment with increased carbon dioxide (known as controlled or modified atmosphere) is commonly employed in the packaging of microbial sensitive materials to enhanced their shelf lives. A concentration of 10%, generated using dry ice or gaseous carbon dioxide is generally used.  LEARNING OUTCOMES At the end of this topic, students should be able to: Explain the catabolism and anabolism reactions. Differentiate three forms of Microbial Metabolism. Discuss the extrinsic and intrinsic parameters affecting Microbial Growth.