Microbial growth is defined as an increase in the number of cells in a population. The mere presence of optimum nutrients is not sufficient to grow microorganisms. Microbial growth is affected by various environmental factors such as:
Organisms that can utilize radiant energy (sunlight) are called phototrophs. Chemotrophs are organisms that can harvest energy from chemicals.
Most microorganisms grow best around neutral pH values (6.5 - 7.0), but some thrive in extreme pH conditions (pH10).
Psychrophiles can grow at 0°C, mesophiles have optimum temperature near 37°C, and thermophiles grow best at 50-60°C.
Typical growth curve of microorganisms in a closed system consists of distinct phases called lag phase, log phase, stationary phase, and death phase.