BACTERIA

Introduction

• Bacteria (singular bacterium) are unicellular microorganism which are of microscopic size and cannot be seen with unaided eyes.
• Constitute large domain-prokaryotes.
• They are among the first life form evolve on the earth and present in most of the habitat.
• Bacteria inhabit normal to the extreme habitat like air, water, soil, radioactive waste, hot springs, deep seas, even in human gut, etc.
• Also live in symbiotic and parasitic relationship with plants and animals. Example rhizobium associate with leguminous plants.
• Length of bacteria ranges in few micrometres. E.coli (1.0-2.0 micrometre long and 0.5 micrometre in radius), Mycobacterium tuberculosis (2-4 micrometre long and 0.2-0.5 micrometre width), V cholerae (1-3 micrometre long and 0.5-0.8 micrometre radius).
• The study of this discipline of microbiology is called bacteriology.
• Bacteria are beneficial for human and other animals in a way that they produce various kind of vitamins, enzyme and food products. Example- vitamin B12, lactic acid, alcohol.
• They are key components of our biosphere playing important role in biogeochemical cycles, removal of toxic substance and decomposition of waste materials.
• Involve in nitrogen fixation hence improve soil fertility.
• With beneficial characteristics several bacteria are pathogenic and cause various kind of disease in human, plants and animals. Example- cholera, tuberculosis, syphilis, anthrax, and more.
• In industries bacteria are useful in waste water treatment and industrial fermentation for cheese and yogurt production.

Structure

• Bacteria is a prokaryotic organism their body lacks nucleus and cellular components.

• Bacteria are covered by a membrane called cell wall chiefly made up peptidoglycan (murein layer).
• Peptidoglycan layer mainly constitute of polysaccharide which are cross linked by peptide bonds.
• Peptidoglycan layer is made up of two glucose derivative N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) chain. The chain is linked with tertapeptide bonds
• Four protein in tetrapeptide bond are L-alanine, D-alanine, L-lysine or meso-diaminopimelic acid (DPA) and D-glutamine.
• Cell wall contributes to the survival of the bacteria, protection from harsh environment and antibiotics.
• Peptidoglycan layer in gram positive bacteria is 20-80 nm thick in contrast gran negative bacteria contain 2-7 nm thick layer.
• Gram negative bacteria contain acidic substance known as teichoic acids which provide rigidity to the cell wall.

Outer Membrane

• Over the cell wall gram negative bacterium contain an external layer called outer membrane it contain lipopolysaccharide, phospholipids, lipoprotein and proteins.

Glycocalyx

• It’s the carbohydrate enriched layer that covers the outside of the bacteria.
• It provides protection against host
• This glycocalyx layer associate with the pathogenic property to the bacteria.
• Glycoclayx in a tightly packed form is called as capsule, in contrast in loose packing it is called as slime layer.

Surface Auxiliary

FLAGELLA

FLAGELLA

• Hairlike structure, attach on the surface of the cell, main function is to provide mobility to the bacteria
• Both gram positive and gram negative bacteria contain flagella. Consist of three parts filament, hook and basal body.

PILLI

PILLI

• Thin hairlike structure on the surface of gram negative bacteria
• Play an Important role in conjugation process

Fimbrae

• Present on both kind of cells gram negative an gran positive
• Helps in attachment to the surface

Classification

• Shape

Type	Example
Bacillus (Rod-Shaped)	Escherichia coli (E. coli)
Coccus (Sphere)	Streptococcus pneumoniae
Vibrio (Comma Shaped)	Vibrio cholerae
Spirilla or spirochete (Spiral)	Spirillum volutans

• Mode of Nutrition

Type	Example
Autotrophic Bacteria	Purple bacteria
Heterotrophic Bacteria	All disease-causing bacteria

• Cell Wall

Type	Example
Gram positive	Staphylococcus aureus
Gram negative	Enterobacteriaceae

• Mode of Respiration

Types	Example
Aerobic	Psuedomonas aeruginosa
Anaerobic	Clostridium

Reproduction

• The mode of replication in bacterium is binary fission.
• In this process the parent bacterial cell divided into two identical daughter cells.
• Replication of DNA starts in the parent cell and each copy is transfer into the daughter cell.
• Rate of reproduction is depend on the conditions like temperature, nutrient availability, moisture this is called favourable condition. E.coli generation rate is 2 million bacteria in 7 hrs.
• In some rare cases they undergo sexual reproduction by conjugation, transduction and transformation. Helps in genetic modification in bacteria which results in the antibiotic resistant property.