L. Dalia Kamal Eldien MSc in Microbiology Bacteria L. Dalia Kamal Eldien MSc in Microbiology Lecture NO: 2

Questions for revision Define microbiology& microorganisms? Enumerate the discipline of microbiology? Which of the microorganisms is non pathogenic? List the benefits of microorganisms Identify the biological classification of living cells?

Objectives At the end of this lecture, the student should know The characteristics of bacteria Classification of bacteria Bacterial structure External bacterial structures

The general characteristics of bacteria All bacteria are prokaryotic cell Unicellular organism Micron or micrometer is the measurement unit of bacteria Varying in size from 0.1–10 μm. The bacteria contain both deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) Reproduce by binary fission

Classification of bacteria Prokaryotic bacteria are divided into two major groups: Eubacteria, are usually found in variety of conditions, in the human body, in some foods and practically everywhere around us& include all bacteria of medical importance Archaebacteria, are usually found under extremes conditions.

Mrs.:Dalia Kamal Eldien MSC in microbiology Bacterial structure Bacteria, despite their simplicity, contain a well developed cell structure which is responsible for many of their unique biological structures. Mrs.:Dalia Kamal Eldien MSC in microbiology

Bacteria cell anatomy Bacteria cell structure consist of:- Cell wall Cytoplasmic membrane Mesosomes. Chromosome Ribosome Cytoplasm External structures(depending on species) including a capsule, fimbriae (pili), flagella& spore

Bacterial structure

Cell wall Bacterial cells are often surrounded by several layers, which are collectively called the cell envelope. The bacterial cell walls all consist of  phospholipid& peptidoglycan (murein or mucopeptide) Peptidoglycan is composed of many identical subunits, a polymer of disaccharides (glycan) cross-linked by short chains of amino acids (peptide) Each subunit contains two sugar derivatives, N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM), and several different amino acids

Cell wall Functions of bacterial cell wall: The cell wall of bacteria protects the cell from osmotic shock and physical damage. Confers rigidity and shape of bacterial cells. The cell wall also determines whether the bacterium is classified as Gram positive or Gram negative

Atypical bacteria Atypical bacteria include groups of organisms such as Mycoplasma, Chlamydia, and Rickettsia that, although prokaryotic, lack significant characteristic structural components or metabolic capabilities Nearly all bacteria, with the exception of the Mycoplasma, have a rigid cell wall

Cytoplasmic membrane The cytoplasmic membrane encloses the cytoplasm. Composed of phospholipid, the molecules of which form two parallel surfaces (bilayer) The polar phosphate groups are on the outside of the bilayer The nonpolar lipid chains are on the inside. The cell membrane function is to regulates the specific transport of substance between the cell and the environment.

Mesosomes Mesosomes are the infoldings in the plasma membrane Rich in enzymes that helps to perform functions like: Cellular respiration DNA replication Cell division

Chromosome The chromosome in bacteria is typically a single, closed circle DNA (deoxyribonuclic acid) that is concentrated in a nucleoid region Genetic information in bacteria is stored in the sequence of DNA in two forms, that is bacterial chromosome and plasmid The plasmids is extra-chromosomal fragments, replicate independently, and can exist in the cell as one copy or as many copies.

Ribosome Bacterial cells can contain thousands of ribosomes, which are the sites of protein synthesis. Bacterial cells contain 70S ribosomes (Svedberg units)

Cytoplasm Cytoplasm or protoplasm It is gel-like in consistency Most of cell organelles are floating in cytoplasm Containing the bacterial chromosome (genome), ribosomes, stored energy inclusions, plasmids, vitamins, ions, fatty acids & amino acids, ect…………

External structures 1-Flagella:- A flagellum is a whip-like structure that allows a cell to move toward favorable environments. A flagellum comprises of three parts, filament, hook and basal body. The flagellum is attached to the cell body by hook and basal body. While the filament called an axoneme is free Flagella made of protein chains, name as flagellin Bacterial cells may have one or many flagella. Flagella are highly antigenic

Main parts of flagella

Flagella arrangement in bacteria There are basically four different types of flagella arrangements: A single flagellum can extend from one end of the cell - if so, the bacterium is  Monotrichous. 2. A single flagellum can extend from both ends of the cell –name as Amphitrichous.

Flagella arrangement in bacteria 3. Several flagella can extend from one end or both ends of the cell - Lophotrichous. 4. Multiple flagella may be randomly distributed over the entire bacterial cell - Peritrichous.

Flagella arrangement in bacteria

Identify the following types of flagella???

External structures 2-Fimbriae Are short, hair-like structures called fimbriae. Made up of protein known as pilin Arise from plasma membrane They enable organisms to adhere the host cells and to one another. Specialized fimbriae named as sex pili enable genetic material to be transferred from one bacterium to another Fimbriae are shorter and straighter or flexible than flagella and are more numerous.  Visible with the use of an electron microscope

Fimbriae

Flagella& fimbriae

External structures 3- Capsule Many bacteria secrete around themselves a polysaccharide substance (or sometimes protein) which may become sufficiently thick to form a definite capsule. Possessing a capsule usually increases the virulence of an organism.

Capsule under microscope

External structures 3-Spores: When conditions for vegetative growth are not favorable, especially when carbon and nitrogen become unavailable, bacteria of the genera Bacillus and Clostridium are able to survive by forming resistant Endospores. This process is known as sporulation. Spore formation involves a change in enzyme activity and morphology. The spore may be positioned at the end (terminal) of the bacterium or centrally (median)

It may be round, oval, or elongate. When the condition became favorable signal the process of endospore germination. Germination of a spore results in a break in the spore wall and the outgrowing of a new vegetative cell. The newly formed vegetative cell is capable of growth and reproduction.

Spore structure

Spore under microscope

Identify?

Identify?

Identify?

Sources Lippincott's Illustrated Reviews: Microbiology, 3rd Edition (2012)- Richard A. Harvey- Bruce D. Fisher- Richard A. Harvey- (chapter 6, 1& 3) http://www.differencebetween.net/science/health/difference-between-eubacteria-and-archaebacteria/#ixzz4Wf3zKsx2