MICROPARA - MODULE 2

Microbial Growth

Increase in number of cells rather than size

Binary Fission

Primary method of bacterial reproduction where one cell divides into two identical daughter cells

Generation Time

Time required for a cell population to double

Growth Curve

Graph of bacterial population growth with four phases: lag, log, stationary, death

Lag Phase

Period of adjustment; cells metabolically active but not dividing

Log Phase

Exponential phase; rapid cell division; cells most sensitive to antibiotics

Stationary Phase

Equilibrium phase; growth rate slows as nutrients deplete and wastes accumulate

Death Phase

Decline phase; deaths exceed new cell growth

Batch Culture

Closed system with limited nutrients; follows standard growth curve

Continuous Culture

Open system with constant nutrient supply and waste removal; maintains steady growth

Temperature Requirement

Each species has minimum, optimum, and maximum growth temperatures

Psychrophiles

Cold-loving microbes; optimal growth -5°C to 15°C

Psychrotrophs

Grow at refrigeration temps but optimal at 20–30°C; cause food spoilage

Mesophiles

Optimal growth at 30–37°C; most human pathogens

Thermophiles

Heat-loving microbes; optimal growth at 50–60°C

Hyperthermophiles

Extreme thermophiles; grow at >80°C; found in hot springs and hydrothermal vents

Heat Shock Proteins

Protective proteins produced during sudden temperature rise

Cold Shock Response

Cellular stress triggered by sudden cooling

pH Requirement

Microbes grow best at certain pH range depending on species

Acidophiles

Grow optimally at low pH (below 3.0)

Neutrophiles

Grow optimally at near-neutral pH (6.0–8.0)

Alkaliphiles

Grow optimally at high pH (up to 10.5)

Osmotic Pressure

Force exerted by solutes in environment that affects microbial growth

Halophiles

Organisms requiring high salt concentration for growth

Extreme Halophiles

Organisms thriving in very high salt (e.g., Dead Sea, salt flats)

Osmophiles

Organisms that thrive in high sugar concentrations

Carbon Requirement

Structural backbone of all organic molecules; needed for microbial growth

Autotroph

Uses CO2 as principal carbon source

Heterotroph

Requires organic compounds as carbon source

Nitrogen Requirement

Needed for protein and nucleic acid synthesis

Nitrogen Fixation

Conversion of N2 into NH3 by prokaryotes

Ammonification

Conversion of organic nitrogen into NH3

Nitrification

Conversion of NH3 to NO2- and NO3-

Denitrification

Conversion of NO3- to N2 gas; returns nitrogen to atmosphere

Sulfur Requirement

Needed for amino acids and vitamins; obtained as sulfate (SO4-2)

Phosphorus Requirement

Needed for nucleic acids, ATP, phospholipids; obtained as phosphate (PO4-3)

Trace Elements

Inorganic elements (iron, copper, molybdenum, zinc) required in small amounts for enzyme cofactors

Growth Factors

Organic compounds (amino acids, vitamins, purines, pyrimidines) essential for some microbes

Obligate Aerobes

Require oxygen for growth; oxygen as final electron acceptor

Facultative Anaerobes

Can grow with or without oxygen; prefer oxygen

Obligate Anaerobes

Killed by oxygen; grow only without oxygen

Aerotolerant Anaerobes

Do not use oxygen but tolerate its presence

Microaerophiles

Require oxygen at low concentrations (2–10%)

Catalase

Enzyme that converts hydrogen peroxide into water and oxygen

Superoxide Dismutase

Enzyme that detoxifies superoxide radicals into hydrogen peroxide and oxygen

Peroxidase

Enzyme that breaks down hydrogen peroxide without releasing oxygen

Culture Medium

Nutrient material prepared for microbial growth in lab

Agar

Complex polysaccharide used as solidifying agent in culture media

Solid Medium

Medium with agar to isolate colonies

Liquid Medium

Broth medium for growing microbial populations

Defined Medium

Chemically prepared medium where composition is exactly known

Complex Medium

Contains extracts (yeast, meat, plant); exact composition varies

Selective Medium

Suppresses unwanted microbes and encourages desired microbes

Differential Medium

Allows distinction between different microbes based on colony appearance or biochemical reaction

Enrichment Culture

Encourages growth of desired microbes in low numbers

Anaerobic Culture Method

Uses reducing media or anaerobic chambers to grow obligate anaerobes

Reducing Media

Culture medium containing chemicals that deplete oxygen

Streak Plate Method

Isolates pure colonies by spreading inoculum over agar surface

Pour Plate Method

Separates organisms within agar to obtain colony counts and isolates

Pure Culture

Population of microbes derived from a single cell; required for study

Colony

Visible mass of microbial cells arising from one cell or group of identical cells