Bacterial Growth Requirements

BACTERIAL GROWTH REQUIREMENTS Microbial Growth Refers to an increase in cell size and number. Bacteria grow on solid media as colonies. A colony is defined as a visible mass of microorganisms all originating from a single mother cell Bacteria grow and divide by binary fission, a rapid and relatively simple process. Bacterial Growth: Binary Fission Binary fission in bacteria starts with the replication of DNA as the cell elongates. A division septum forms in the center of the cell. Two daughter cells of similar size form and separate, each receiving a copy of the original chromosome. Generation Time: Time required for a cell to divide, and its population to double. Generation time varies considerably: E. coli divides every 20 minutes. U Most bacteria divide every 1 to 3 hours. Some bacteria require over 24 hours to divide. U Phases of Growth 1.Lag phase: During this phase, metabolic activity occurs but cells do not divide. This can last a few minutes up to many hours. 2.Log phase(logarithmic or exponential):The cells start dividing & their number increase with time. 3. Stationary phase: The rate of multiplication & death becomes almost equal, because of depletion of nutrient & accumulation of toxic product . 4. Decline phase: In this phase population decreases due to death of cells. Factors Affecting Bacterial Growth Bacterial requirements for growth PHYSICAL OR ENVIRONMENTAL FACTORS • oxygen (presence or absence) • Temperature • pH • osmotic pressure • moisture • radiation Bacterial requirements for growth CHEMICAL OR NUTRITIONAL FACTORS • • • • • • • • carbon nitrogen phosphorous sulphur metal ions trace elements vitamins growth factors PHYSICA L OR ENVIRON MENTAL FACTORS OXYGEN OXYGEN REQUIREME NTS OBLIG ATE AEROB ES OBLIGA TE ANAERO BES FACULTA TIVE ANAERO BES AEROTOLER ANT MICXR O AEROPHI LES  Obligate aerobes are organisms that grow only in the presence of oxygen. They obtain their energy through aerobic respiration.  Obligate anaerobes are organisms that grow only in the absence of oxygen and, in fact, are often inhibited or killed by its presence. They obtain their energy through anaerobic respiration or fermentation.  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  Aerotolerant anaerobes do not use oxygen to pathogenic bacteria anaerobes. transform energy but are can facultative tolerate and grow in its presence. They obtain energy only by fermentation and are also known as obligate fermenters.  Microaerophiles are organisms that require a low concentration of oxygen (2% to 10%) for growth, but OXYGEN REACTIVITY  Oxygen is a very reactive molecule and is a potent cellular poison unless a cell has a mechanisms to enzymatically inactivate it.  Various reactive oxygen radicals (ROS) are invariably generated by cells in the  These ROS are H2O2 (peroxide), 2 presence of O2.oxygen (O ),(O peroxide anions and superoxide ), singlet hydroxyl radicals (OH-). OXYGEN DETOXIFICATION All organisms which can live in the presence of O2 (whether or not they utilize it in their metabolism) contain enzyme (O2- ) superoxide dismutase, which destroys superoxide ion. Nearly all organisms also contain the enzyme catalase, which decomposes H2O2. Some organisms decompose H2O2 by means of peroxidase enzymes which derive electrons from NADH2 to reduce peroxide The action of superoxide dismutase, catalase and peroxidase enzymes on toxic oxygen radicals Terms used to describe O2 Relations of Microorganisms Group Aerobic Anaerobic O2 Effect Obligate aerobe Growth No growth Required (utilized for aerobic respiration) Obligate anaerobe No growth Growth Toxic Facultative anaerobe (Facultative aerobe) Growth Growth Preferentially utilized when available Microaerophile Growth if level not too high No growth Required but at levels below 0.2 atm Aerotolerant anaerobe Growth Not required and not utilized Growth Capnoph iles  A small amount of CO2 is required by all organisms for growth, which is provided by metabolism.  Some organisms requires relatively high concentrations of carbon dioxide (1-5%) for their optimum growth, particularly for primary isolation; these are known as capnophiles, e.g., Brucella abortus TEMPERATUR E TEMPERAT URE REQUIREM ENT PSYCHROP HILES MESOPHI LES THERMOPH ILES HYPER THERMOPH ILES Bacteria have a minimum, optimum, and maximum temperature for growth and can be divided into following groups based on their optimum growth temperature (temperature at which an organism grows best):  Psychrophiles are cold-loving bacteria. Their optimum growth temperature is between -5°and 15°C with maximum up to 20°C. They are usually found in the Arctic and Antarctic regions and in streams fed by glaciers.  Mesophiles are bacteria that grow best at moderate temperatures. Their optimum growth temperature is between 25° and 40°C with maximum below 45°C. Most bacteria are mesophilic and include common soil bacteria and PATHOGENS.  Thermophiles are heat-loving bacteria. Their optimum  Hyperthermophil grow at very high Thei es temperatures. r optimum growth temperature is between 70° and 110°C. usually Theymembers of the Archae ar hydrothermal and are found vents growing at great depths in e the ocean, e.g. Sulfolobus acidocaldarium nea r  Obligate psychrophiles – are unable to grow above 20ºC.  Facultative psychrophiles - are able to grow above 20ºC, but not in mesophilic range.  Psychrotroph - A variant psychrophile which can grow temperature in the range of mesophiles  Thermoduric- Mesophilicorganisms of at a that can TEMPERATURE TOLERANCE  Psychrophilic bacteria are adapted environment unsaturated membranes. due fatty to their cool to high concentration of acids in their plasma  Thermophilic bacteria adapted to their hot environment due to high concentration of highly saturated fatty acids in their plasma membranes.  Often thermophiles have a high G + C content in their DNA  The membranes of hyperthermophiles are composed of repeating subunits of the C5 Terms used to describe microorganisms in relation to temperature requirements for Group Minimum Optimum Maximum Comments growth Psychrophile Below 0 10-15 Below 20 Psychrotroph 0 15-20 Above 25 Mesophile 10-15 25-40 Below 45 Grow best at relatively low T Able to grow at low T but prefer moderate T Most bacteria especially those living in association with warm-blooded animals Thermoduric 10-15 30-40 45-60 Mesophiles that can survive brief exposures to relatively high temperatures Thermophile 45 Above 100 ºC (boilin g) Above 121 Shows wide variation in optimum and maximum T Hyperthermophile 70 50-70 80-110 occurring in hot springs or deep sea vents in midocean ridges pH pH ACIDOPHI LES NEUTROPH ILES ALKALIPH ILES Microorganisms can be placed in one of the following groups based on their optimum pH requirements: Acidophiles - Organisms whose optimum pH is moderately to highly acidic, usually 5.5. Several genera of Archaea, including Sulfolobus and Thermoplasma, are obligate acidophiles. Among eukaryotes, many fungi are acidophiles. Neutrophiles - Organisms whose optimum pH is 7± 1.5 with a range of 5 to 8, e.g. Staphylococcus aureus (7.0-7.5), E. coli (6.07.0) WATER AVAILABILITY  Water is the solvent in which the molecules of life are dissolved, and the availability of water is, therefore, a critical factor that affects the growth of all cells.  The availability of water for a cell depends upon its presence in the atmosphere (relative humidity) or its presence in solution (water activity).  Microorganisms live over a range of Aw from 1.0 to 0.7.  The concept of lowering water activity in order to prevent bacterial growth is the basis for preservation of foods by drying (in sunlight or by evaporation) or by addition of high concentrations of salt or sugar. OSMOTIC PRESSURE Most bacteria require an isotonic environment or a hypotonic environment for optimum growth. Osmophiles organisms that are able to live in hypertonic environments high in salt or sugar. Osmotolerantorganisms that can tolerate salt concentration up to approximately 10%. Depending on the requirement of salt concentrations microorganisms are classified as follows:  Non-halophiles require less coli than 1% salt (E. or Pseudomonas)  mild halophiles require 1-6% salt  moderate halophiles require 6-15% salt (S. aureus)  Extreme halophiles require growt 15-30%such NaCl for h (archaea as Halococcus).  Halotolerant - bacteria that are able to grow at moderate salt concentrations, even though they grow best in the CHEMICAL OR NUTRITIONAL FACTORS NUTRITIONAL REQUIREMENTS All living organisms are grouped into different nutritional groups according to their energy source, carbon source and hydrogen / electrons source. Energy source Phototrophs use light as the primary source of energy Chemotrophs use chemical compounds as the primary source of energy Carbon source Autotrophs require only carbon dioxide as a carbon source. An autotroph can synthesize organic molecules from inorganic nutrients. Heterotrophs require organic forms of carbon. A heterotroph cannot synthesize organic molecules from inorganic nutrients. Hydrogen/Electron source Lithotroph use inorganic substrates such as ammonium, nitrite, hydrogen sulfide or elementary hydrogen as a source of hydrogen/ electron donor Organotroph use reduced organic compounds such as glucose and fatty acids as a source of hydrogen/ Major nutritional types of Nutritional Type Energy Carbon Examples prokaryotes Source Source Photoautotrophs Light CO2 Photoheterotrophs Light Organic Some Purple and compounds Green Bacteria Chemoautotrophs or Lithotrophs (Lithoautotrophs) Inorganic CO2 compounds, e.g. H2, NH3, NO2, H2S Chemoheterotrophs Organic or Heterotrophs compounds Cyanobacteria, some Purple and Green Bacteria A few Bacteria and many Archaea Organic Most Bacteria, compounds some Archaea NUTRITIONAL FACTORS  carbon  nitrogen  phosphorous  sulphur  metal ions  trace elements  vitamins  growth factors Major elements, their sources and functions in bacterial%cells Element of Source Function dry weight Carbon 50 organic compounds or CO2 Main constituent of cellular material Oxygen 20 H2O, organic compounds, CO2, and O2 Constituent of cell material and cell water; O2 is electron acceptor in aerobic respiration Nitrogen 14 NH3, NO3, organic Constituent of amino acids, nucleic acids compounds, N2 nucleotides, and coenzymes Hydrogen 8 H2O, organic compounds, H2 Main constituent of organic compounds and cell water Phosphorus 3 inorganic phosphates (PO4) Constituent of nucleic acids, nucleotides, phospholipids, LPS, teichoic acids Sulfur 1 SO4, H2S, So, organic sulfur Constituent of cysteine, methionine, glutathione, several coenzymes Main cellular inorganic cation, cofactor for enzymes Potassium 1 compounds Potassium salts Magnesium 0.5 Magnesium salts Inorganic cellular cation, cofactor for enzymes Calcium 0.5 Calcium salts Inorganic cellular cation, cofactor for certain enzymes, a component of endospores. Iron 0.2 Iron salts Component of cytochromes and certain nonheme iron-proteins, cofactor for some enzymes Growth factors  Growth factors are organic compounds such as amino acids, purines, pyrimidines, and vitamins that a cell must have for growth but cannot synthesize itself.  Organisms having complex nutritional requirements and needing many growth factors are said to be fastidious.