This document summarizes the morphology and structure of bacteria. It discusses the capsule, cell wall, cell membrane, differences between gram-positive and gram-negative bacteria, and membrane structures like pili and flagella. Methods of bacterial reproduction include binary fission, fragmentation, budding, conjugation, transduction, and transformation. Endospore formation allows some bacteria to survive in harsh environments. Environmental oxygen levels influence bacterial growth, with some bacteria being obligate aerobes or anaerobes and others being facultative.

1. BACTERIOLOGY

2. CONTENTS

3. MORPHOLOGY & STRUCTURE

6. Capsule
Some bacteria (often
pathogens) are surrounded by a
thick polysaccharide capsule.
This is a loose jelly-like or
mucus-like layer. It helps
prevent immune system cells
from reaching the bacteria, and
it forms part of biofilms.

7. CELL WALL

8. Cell Membrane
• The cell membrane (often called the plasma
membrane) is composed of 2 layers of
phospholipids.
• Phospholipids have polar heads and non-polar
tails.
– “Polar” implies that the heads are hydrophilic:
they like to stay in an aqueous environment:
facing the outside world and the inside of the
cell.
– “non-polar” means that the tails are
hydrophobic: they want to be away from
water, in an oily environment. The tails are in
the center of the membrane
• A pure phospholipid membrane only allows
water, gasses, and a few small molecules to
move freely through it.

9. 9
GRAM POSITIVE
GRAM NEGATIVE
Cytoplasm
Cytoplasm
Lipoteichoic acid Peptidoglycan-teichoic acid
Cytoplasmic membrane
Inner (cytoplasmic) membrane
Outer Membrane
Lipopolysaccharide
Porin
Braun lipoprotein

10. Membrane Structures
• Pili (singular = pilus) are hairs projecting from the
surface. They are composed of pilin protein. There are
several types:
– DNA can be transferred between bacteria by conjugation,
which is initiated when sex pili on the donor cell attach to
and draw in the recipient cell.
– Fimbriae (singular = fimbria) are pili used to attach the
bacteria to target cells ( in infection) or to surfaces, where
they form a biofilm.
• Flagella are long hairs used to propel the cells. They are
composed of flagellin protein.
– At the base of each flagellum is a motor embedded in the
membrane and cell wall. It turns in a rotary motion,
driven by proton-motive force (the flow of protons i.e. H+
ions across the cell membrane).
– The suffix “-trichous” is used to describe the placement of
flagella: e.g. lophotrichous = several flagella all clustered
at one end.

11. Some inclusions in Bacterial Cells
Bacterial Inclusions. A. PHB granules; b. a parasporal BT crystal in
the sporangium of
Bacillus thuringiensis; c. carboxysomes in Anabaena viriabilis,
showing their polyhedral
shape; d. sulfur globules in the cytoplasm of Beggiatoa.

12. Vegetative
• Binary fission
• Fragmentation
• Budding
 Asexual
• Conidiospore & Sporangiospore
 Sexual
• Conjugation
• Transduction
• Transformation

13. Binary Fission
• method of bacterial
reproduction
• cell divides exactly in half
– single cell division
– reproduction of the
entire organism

14. Conjugation

15. Transduction

16. Transformation

17. Endospore formation is NOT a mechanism of reproduction. Rather it is a
mechanism for survival in deleterious environments. During the process of spore
formation, one vegetative cell develops into one endospore.
The sequential steps of endospore formation in a Bacillus species. The process of endospore formation
takes about six hours. Eventually the mature endospore is released from its “mother cell” as a free spore
Free endospore
Vegetative cell
Endospore
within mother cell

18. Under favorable nutritional and
environmental conditions, an endospore
germinates into a vegetative cell.

21. Environmental Influencing Factors: oxygen
• oxygen levels vary between environments and within the same
environment
• based on O2 requirements, prokaryotes are separated into the
following groups
– obligate aerobes
– obligate anaerobes
– facultative anaerobes
– microaerophiles
– aerotolerant anaerobes