1. Prokaryotic Cells
Bacteria

2. The Prokaryotic Cell
Members of the prokaryotic world make up a vast heterogeneous group of very small single-celled organisms.
Include bacteria and archae, although the majority are bacteria
The thousands species of bacteria are differentiated by many factors such as:
Morphology (shape), chemical composition (often detected by staining reactions), nutritional requirements, biochemical activities, and sources of energy (sunlight or chemicals)
These differences can only be seen with the use of a microscope

3. Size, Shape, and Arrangement
Bacteria come in many sizes, and several shapes.
Most range from 0.2 to 2.0 µm in diameter and 2-8 µm in length
Basic shapes include:
Cocci- round shaped
Bacillus- rod shaped
Spirillum- spiral shaped, helical shape like corkscrew, have rigid bodies, and use flagella to move
Vibrio- curved
Spirochetes- helical and flexible, move by axial filaments found within flexible external sheath
Square
Star

4. Cell Cluster Formation
Streptobacillus
Bacteria are also classified according to cell cluster formation:
Cluster formation
Description
Diplococci
Two cocci cells paired
Staphylococci
Number of cells clustered together (grape-like)
Streptococci & Streptobacillus
Number of cells arranged in a chain
Staphylobacilli do not exist because bacilli only divide along their long axis which means they will never form clusters of rods.

5. Learning Check: What Shape are these bacteria?1. 2. 3.
bacillus
spirillum
coccus 5. 6.
spirochete
vibrio
bacillus

6. Shape and Arrangement The shape of bacteria is determined by heredity.
Most bacteria are monomorphic: maintain a single shape
Environmental factors can alter that shape
Some bacteria like Rhizobium and Corynebacterium are pleomorphic: can have many shapes, not just one.
Source for figure:

7. Basic Components of Bacteria
Cell wall-this gives the cell its shape and retains the constituents
Cell membrane-used for filtering in food constituents and discharging waste products
Nucleoid-where the genetic material of the cell is stored;
Cytoplasm- a semiliquid proteinaceous substance which contains starch, fat and enzymes.
*Cell wall- Most bacteria have a cell wall but there are some that do not like Mycoplasma species

8. Structures External to the Cell Wall
Possible structures external to the prokaryotic cell wall are:
Glycolax
Flagella
Axial filaments
Fimbrae
and Pili
In certain species, capsules are important in contributing to bacterial virulence (the degree to which a pathogen causes disease). Capsules often protect pathogenic bacteria from phagocytosis by the cells of the host. For example Streptococus pneumoniae which causes pneumonia only when the cells are protected by a polysaccharide capsule

9. What is the Glycocalyx?
Means sugar coat & is the general term used for substances that surround cells
Bacterial glycocalyx is a viscous (sticky), gelatinous polymer that is external to the cell wall
Composed of a polysaccharide, polypeptide, or both
Two types:
Capsule: substance is organized and is firmly attached to the cell wall
Slime layer: substance is unorganized and only loosely attached to the cell wall glycocalyx
Fig. 1
Polysaccharide: a carbohydrate (e.g., starch, cellulose, or glycogen) whose molecules consist of a number of sugar molecules bonded together.
Polypeptide: a linear organic polymer consisting of a large number of amino-acid residues bonded together in a chain, forming part of (or the whole of) a protein molecule.
Source for Fig. 1:

10. (a) Micrograph of Streptococcus pneumoniae, the common cause of pneumonia, showing a prominent capsule. (b) Bacteroides, a common fecal bacterium, has a slime layer surrounding the cell

12. Learning Check
What advantage does a glycocalyx provide a cell? (think about its composition)

13. Glycocalyx Very important component of biofilms
Biofilms are densely packed communities of microbial cells that grow on living or inert surfaces
A glycocalyx that helps cells in a biofilm attach to their target environment and to each other is called an extracellular polymeric substance (EPS)
EPS protects the cells within it
Facilitates communication among them
and enables the cells to survive by attaching to various surfaces in their natural environment
Fig. 2
Through attachment, bacteria can grow on diverse surfaces such as rocks in fast-moving streams, plant roots, human teeth. Streptococcus mutans, an important cause of dental cavities, attaches itself to the surface of teeth by a glycocalyx. Vibrio cholerae, the cause of cholera produces a glycocalyx that helps it attach to the cells of the small intestine.
Source for Fig. 2

14. Flagella
Some prokaryotes have flagella which are long filamentous appendages that propel bacteria
Peritrichous: flagella distributed over the entire cell
Polar: at one or both poles or ends of the cell
Monotrichous: A single flagellum at one pole
Lopothrichous: a tuft of flagella coming from one pole
Amphitrichous: flagella at both poles of the cell
Bacteria that lack flagella re referred to as atrichous (without projections)
Motility enables a bacterium to move toward a favorable environment or away from an adverse on. This is called taxis. Motile bacteria contain receptors in various locations which pick up chemical stimuli, such as oxygen, ribose.

15. Flagellar Movement
The flow of hydrogen ions (H ) or of sodium ions (Na ) through the cytoplasmic membrane near the basal body powers the rotation, propelling the bacterium through the environment at about 60 cell lengths per second—equivalent to a car traveling at 670 miles per hour
Figure 3.9 Motion of a peritrichous bacterium. In peritrichous bacteria, runs occur when all of the flagella rotate counterclockwise and become bundled. Tumbles occur when the flagella rotate clockwise, become unbundled, and the cell spins randomly. In positive chemotaxis (shown), runs last longer than tumbles, resulting in motion toward the chemical attractant.

16. Axial Filaments Spirochetes have unique structure and motility
Move my means of axial filaments
Bundles of fibrils that arise at the ends of the cell beneath an outer sheath and spiral around the cell
The rotation of the filaments produces a movement of the outer sheath that propels the spirochetes in a spiral motion

17. Fimbriae and Pili
Many gram-negative bacteria contain hair-like appendages that are shorter, straighter, and thinner than flagella
are used for attachment and transfer of DNA rather than for motility
Fimbrae can occur at the poles of the bacterial cell or entire surface of cell
Have a tendency to adhere to each other and to surfaces
Pili are usually longer than fimbrae but shorter than flagella and are found as one or two per cell
Involved in motility and DNA transfer

18. Conjugation Pili

19. Learning Check Several Escherichia coli cells are connected by
conjugation pili. How are pili different from bacterial flagella?
Bacterial flagella are flexible structures that rotate to propel the cell; pili are hollow tubes that mediate transfer of DNA from one cell to another