Bacteria of Morphology, Structure, Types , flagella.

Bacteria

Father of bacteriology is Louis Pasteur.

Father of bacteriological technique  is Robert koch-given Koch postulates.

Anton von leeuwenhoek first time seen bacteria and protozoa under a self-made microscope and regard them  as Animalcules.

 F.J .Cohn coined the term bacteria.

 Morphology of bacteria

•  Coccus - spherical shaped.

• Diplococcus - cocci from paired cells .

• Tetracoccus - four cells arranged in a cube.

•  Streptococcus - chain of cocci.

•  Sarcina - division in three planes produces eight cells arranged in a

 cube.

•  Staphylococcus - grape-like cluster.

• Bacillus - rod or capsule.

• Vibrio - comma shaped.

• Spirillum - rigid, wavy shaped.

•  Spirochaete - cork-screw shaped.

• Star-like - star-shaped bacteria.

Types of bacteria

• Stalked bacteria: e.g. Caulobacter, Gallionella.

• Budding bacteria: e.g. football shaped, network of cells

• Myxobacteria: e.g. gliding bacteria, lack rigid cell wall and flagella, cigar shaped

• Spirochaetes: e.g. Spirochaeta, Cristispira – large, helical or spiral, flagella is absent.

• Actinomycetes: e.g. Streptomyces – thread-like mycelial bacteria

Structure of bacterial cell

• Surface appendages – flagella, fimbriae and pilli.

• Surface adherents – capsule and slime layers.
• Cell wall – made up of mucopeptide.

• Cytoplasm and organelles – lack organized 

nucleus, nucleoid is circular, genome is 

not organized into chromosomes, ribosomes are free.

• Special structures – endospores, stalks, mesosome.

Flagellation in bacteria

• Atrichous – e.g. Lactobacillus.
•  Monotrichous – e.g. Xanthomonas.
• Lophotrichous – e.g. Spirilla.
• Amphitrichous – e.g. Pseudomonas.
• Cephalotrichous:- e.g.spirilla
• Peritrichous:- e.g. Erwinia.

Phases of Growth Bacterial Growth Curve :

 

When bacteria are inculcate into growth medium, we can plot of the number of cells in the population over time.

Four phases of Bacterial Growth:

Lag Phase:

• Period of adjustment to new conditions.
• Little or no cell division occurs, population size doesn’t increase.

Log (Exponential) Phase:

• Period of most rapid growth.
• Number of cells produced > Number of cells dying
• Cells are at highest metabolic activity.

Stationary Phase:

• Population size begins to stabilize. Number of cells produced =Number of cells dying.
• Overall cell number does not increase.
• Cell division begins to slow down.
• Factors that slow down microbial growth: • Accumulation of toxic
• waste materials • Acidic pH of media • Limited nutrients • Insufficient oxygen supply.

Death or Decline Phase:

• Population size begins to decrease. Number of cells dying >Number of cells produced.
• Cell number decreases at a logarithmic rate.
• Cells lose their ability to divide.
• A few cells may remain alive for a long period of time.