Bacteria growth Flashcards
Definition of bacterial growth
-change in the total population rather than an increase in mass or size of the individual organism
Method for bacterial reproduction
Bacteria divide by binary fission:
- increase of cell mass
- duplication of genome
- cell membrane and cell wall separation
Stages in Binary fission
1) cell elongates and DNA is replicated
2) cell wall and plasma membrane begin to divide
3) cross wall forms a completely around divided DNA
4) cells separate
What shapes can binary fission form?
- A chain of cocci is formed when the cell devides in one plane (coccus –> diplococcus–>chain of cocci (tetrad)
- A packet of cocci whent he cell divides in two or more planes perpendicular to one another
- A cluster of cocci when cell divides in several planes at random
what are the growth phases?
- lag phase
- log/exponential growth phase
- stationary phase
- death or logarithmic decline phase
Describe Lag Phase
- population remains unchanged TEMPORARILY
- bacterial cells may be growing in volume or mass, synthesize enzymes, proteins, RNA and increasing in metabolic activity
Describe exponential growth phase
- expressed as generation time or doubling time of the bacterial population
- generation time= time(t) per generation (n=number of generations)
Stationary phase - describe
- exhaustion of available nutrients
- accumulation of inhibitory metabolites or end products
- exhaustion of space
Exponential growth phases
- one cell divides producing 2 daughter cells
- increase in population is by GEOMETRIC PROGRESSION
- total population b at the end of a given period (starting with one cell) = 1 x 2^n where n is the number of generation assuming no cell death
GENERATION TIME - DEFINITION
The time interval required for the cells(or population) to divide
G=t/n, where G=generation time; t = time in minutes or hours; n=number of generations
b=B x 2^n (expression of growth by binary fission)
G= t/(3.3 log b/B)
Chemostat
-chemostat =bioreactor to which fresh medium is continuously added, while culture liquid is continuously removed to keep the culture volume constant
This: controls growth rate and optimizes production
-continuous fermentation and batch fermentation
What are the chemical requirements for growth
- Energy source: CHEMOTROPHS (chemical compounds); PHOTOTROPHS (radiant energy- light)
- Source of electrons: LITOTROPHS (reduced inorganic compounds) and ORGANOTROPHS (use of organic compounds)
- Carbon source: AUTOTROPHS (CO2 as their major source of carbon); HETEROTROPHS (organic compounds as their main carbon source)
- Nitrogen source: ATMOSPHERIC NITROGEN;INORGANIC NITROGEN (nitrate,nitrite or ammonium salts); organic compounds (amino acids)
- Ions
- Oxygen, sulphur and phosphorus
Describe OXYGEN, SULPHUR AND PHOSPHORUS AS CHEMICAL REQUIREMENTS
- -Oxygen: water,nutrients, molecular oxygen
- Sulphur: needed for the synthesis of certain amino acids:cysteine, cystine and methionine): use of organic sulphur or elemental sulphur
- phosphorus: usually supplied in the form of phsphate nucleotides, nucleic acids, phospholipids, teichoic acids
ions as a chemical requirement for growth
- metal ions such as K+, Ca2+, Mg2+, Fe2+ for normal growth
- trace elements (low concentrations in support of growth): Zn2+, Mn2+, Cu2+, Mo6+, Ni2+, B3+, Co2+
- enzyme cofactors: Zn2+, Mn2+, Cu2+, Mo6+, Mg2+, Fe2+
Aerobic bacteria requirements for growth
- aerobic bacteria need oxygen for growth
