Microbial Growth

Growth of Microbes Orderly increase of all of the chemical constituents of the cell. Bact.growth-both an increase in the size and no. of the cells. Net effect an increase in the total mass i.e.biomass. Bacteria divide by binary fission. Nuclear division precedes cell division.

Factors Regulating Growth Chemical requirements( macro n micronutrients) Growth factors(essential n accessory) like thiamine, riboflavin,nicotinic acid, folic acid, B12. Physical factors: Environmental conditions: temperature, pH, osmotic pressure,oxygen,co2,moisture n drying,light, mechanical n sonic stresses. Energy sources( photo n chemotrophs) Generation time( interval of time between two cell divisions or time required for a bacterium to give rise to two daughter cells under optimal conditions.)

I.Nutritional Requirements Major elements (CHONPS + K, Mg, Fe, Ca) Carbon, oxygen, hydrogen, nitrogen, sulfur, phosphorus, potassium, magnesium, iron, and calcium Organisms classified based on carbon usage Heterotrophs Use organic carbon as nutrient source. Autotrophs Use inorganic carbon (CO2) as carbon source Trace elements (Co, Cu, Ni, Zn, Se, Mg, Wo) Cobalt, zinc, copper, molybdenum and manganese Required in minute amounts Assist in enzyme function Nutritional diversity Different organisms require the same nutrients but may require different forms of the nutrients

Major elements

Element % dry wgt Source Carbon 50 organic compounds or CO2 Oxygen 20 H2O, organic compounds, CO2, and O2 Nitrogen 14 NH3, NO3, organic compounds, N2 Hydrogen 8 H2O, organic compounds, H2 Phosphorus 3 inorganic phosphates (PO4) Sulfur 1 SO4, H2S, So, organic sulfur compounds Potassium Potassium salts Magnesium 0.5 Magnesium salts Calcium Calcium salts Iron 0.2 Iron salts

Nutritional Categories Carbon sources CO2 = autotroph organic = heterotroph Energy sources sunlight = phototroph organic = chemotroph Derive both carbon and energy from organic compnds(chemohetero)

A “Chemoorganic autotroph would be…. Derives energy from organic compounds and carbon source from inorganic compounds A related ancient group….. Lithoautotroph Neither sunlight nor organics used, rather it relies totally on inorganics

Nutritional Categories Saprobe – lives on organic matter of dead organisms Parasite – lives on organic matter of living host = pathogens

II.Environmental Factors Influencing Growth Temperature O2 CO2 pH Osmotic Pressure(plasmolysis n plasmotysis) Moisture n drying( lyophilization or freeze drying) Light Mechanical n sonic stresses.(grinding n vigorous shaking with glass beads)

Temperature Optima Psychrophiles: cold-loving Mesophiles: moderate temperature-loving Thermophiles: heat-loving Each has a minimum, optmum, and maximum growth temperature

Temperature Optima Optimum growth temperature is usually near the top of the growth rang Death above the maximum temp. comes from enzyme inactivation Mesophiles most common group of organisms 40ºF (5°C) slows or stops growth of most microbes

Oxygen Requirements Obligate aerobes – require O2.e.g pseudomonas,vibrio. Facultative anaerobes – can use O2 but also grow without it.ecoli n staph. Obligate anaerobes – die in the presence of O2.clostridia n bacteroides.

pH Most bacteria grow between pH 6.5 and 7.5 Acid (below pH 4) good preservative for pickles n cheeses Acidophiles can live at low pHe.g lactobacillus. Vibrio grows at alkaline pH

Bacterial Division Bacteria divide by binary fission. No mitosis Colony: clone of cell derived from a single parent..millions of bacteria in a single colony Colonies on soid media Diffuse growty in liquid media Logarithmic growth,geometric progression or exponential growth

Fig. 7.13

Generation Time Time required for cell to divide/for population to double Average for bacteria is 1-3 hours E. coli generation time = 20 min 20 generations (7 hours), 1 cell becomes 1 million cells! Tubercle bacilli 20 hrs Lepra bacilli 20 days

Fig. 7.14a

Plotting growth on graphs

Standard Growth Curve

Phases of Growth 1.Lag phase After inoculation of microorg.in fresh culture medium, no immediate increase in cell no. Increase in cell size but no cell division, cells r not dormant making new enzymes in response to new medium(adaptation) Variable in length 2.Log phase : exponential growth Desired for production of products Most sensitive to drugs and radiation during this period Population is most uniform in physiological n chemical properties

Phases of Growth Stationary phase – nutrients becoming limiting or waste products becoming toxic,changes in Ph,decreased o2 tension death rate = division rate Death phase – death exceeds division