Bacteria Flashcards
What are bacteria
Prokaryotic unicellular organisms that do not have a membrane bound nucleus and membrane bound organelles. They are omnipresent
Characteristics of bacteria
1.Bacteria cell wall is composed of peptidoglycan ( protein, lipids and glucans).
2. They lack chloroplasts and the carbohydrates form reserves consist of granules of glycogen and oil
3. The nuclear materials are not enclosed in a nuclear membrane and some genera have flagella therefore can move.
Criteria for classifying bacteria
- Based on shape
- Based on flagellation
- Based on nutrition
- Based on respiration
Classification based on shape
- Cocci
- Bacilli
- Spirilla
The ___________________ determines the shape of a cell
Rigid bacterial cell wall
The cocci or bacilli may be _________
Joined to form colonies or filaments
What’re pleomorphic bacterial cells
They can exhibit a variety of shapes e.g arthrobacter
Cocci
This group of bacteria is spherical, ellipsoidal or bean shaped, and is subdivided into six groups
1.Micrococci
2. Diplococci
3. Streptococci
4. Tetracocci
5. Staphylococci
6. Sarcinae
Types of cocci
- Micrococci: cells are arranged singly or irregularly. Members are saprophytes that live in water and air.
- Diplococci: cells divide along one plane and remain attached in pairs. Examples include those that cause deadly diseases like: Pneumonia, Cerebral meningitis and Gonorrhoea
- Streptococci: Cells here divide in one plane and remain attached to form chains of different lengths. Some cause disease of humans.
- Tetracocci: cells divide in two planes and form group of four cells.
- Staphylococci: cells divide in several planes results in an irregular pattern, producing bunches of cocci. Some cause disease in man and animals
- Sarcinae: cells divide in three planes, in a regular pattern, producing a cuboidal arrangement of cells. They are often found in air.
Types of bacilli
- Diplobacilli: occur in pair
- Streptobacilli: occur in chains of different lengths
- Palisades: those that are not arranged in a regular pattern
Types of spirilla
- Spirillum: are coiled forms of bacteria which may be twisted e.g spirillum minus ( rat-bite fever )
- Vibrioses: are curve/ comma shaped e.g the virio comma which causes cholera
All spirilla have_____ , about _____ of the bacilli and ___________ number of cocci are flagellated
Flagella, half, a small number
In a polar arrangements
The flagella are attached at one or both ends of the cell.
Types of flagellation ( polar arrangements)
1.Monotrichous- with a single flagellum at one end of the cell e.g cholera vibrio
2. Lophotrichous- with small bunches or tuft of flagella emerging from one end e.g alcaligenes faecalis.
3. Amphitrichous- with one or more flagella at both poles of the cell e.g spirillum volutans
4. Peritrichous- flagella are dispersed randomly over the surface of the cell e.g colibacillium.
5. Atrichous bacteria lack flagellum
Nutrition in bacteria
- Autotrophic nutrition
- Heterotrophic nutrition
Photoautotrophic nutrition
- Photoautotrophic bacteria:
They use sunlight as their source of energy to synthesize food. Unlike photosynthetic eukaryotic cells they do not split water to obtain reducing power.
Oxygen is not evolved during bacterial photosynthesis
Types of photoautotrophic nutrition
- Photolithotrops:
- In this hydrogen donor is an inorganic substance.
- In green sulphur bacteria ( e.g chlorobium) hydrogen sulphide ( H2S) is hydrogen donor. The chlorophyll is bacteriovirdin
Photo-organolithotrops:
- In this hydrogen donor is a organic acid or alcohol e.g purple non- sulphur bacteria ( e.g Rhodospirillum)
chemoautotrophic bacteria
- They do not have photosynthetic pigments and hence they cannot use sunlight energy
- They obtain energy in the form of ATP by oxidizing inorganic or organic compounds.
- The energy this obtained is used to reduce CO2 to organic matter.
Types of chemoautotrophs
Chemolithotrophs:
-Inorganic compound in oxidized to release energy.
- e.g sulphur bacteria ( e.g thiobacillus ) iron bacteria ( e.g Ferrobacillus ), hydrogen bacteria e.g Hydrogenomonas and nitrifying bacteria ( e.g Nitrosomonas and nitro bacter )
Chemo-organotrophs:
- An organic compound is oxidized to release energy. e.g methane bacteria ( methanococcus ) ; acetobacteria and lactobacillus
Heterotrophic
They may be saprotrophic e.g ( bacillus subtilis) parasitic e.g Plant parasite ( xanthomonas citrii ) animal parasite e.g ( bacillus anthracis ) or symbiotic on association with roots of the family leguminosae e.g ( rhizobium )
Respiration in bacteria
Aerobic bacteria:
- these bacteria require oxygen as a terminal acceptor of electrons and will not grow under anaerobic conditions ( in the absence of O2 )
Anaerobic bacteria:
- these bacteria do not use oxygen for growth and metabolism but obtain Thier energy from fragmentation reaction e.g clostridium sp
Facultative anaerobes:
- bacteria can grow either oxidatively using O2 as a terminal electron acceptor or anaerobically using fermentation reaction to obtain energy, bacteria that are facultative anaerobes are often termed “aerobes”
When s facultative anaerobes present at the site of am infection like an abdominal abscess it can rapidly consume all available O2 and change to anaerobic metabolism, producing an anaerobic environment and thus, allow the anaerobic bacteria that are present to grow and cause disease
Endospores: are structures formed in bacillus bacteria during unfavorable conditions. Fortunately most pathogenic bacteria do not form endospores
Reproduction in bacteria
Reproduction by binary fission is very common, the other form of reproduction is sexual reproduction
Sexual reproduction methods
Typical sexual reproduction involving the formation and fusion of gametes is absent in bacteria
However, Gene’s recombination can occur in bacteria by three different methods
- Conjugation
- Transduction
- Transformation
Explain Conjugation
-In this method of gene transfer, the donor cell gets attached to the recipient cell with the help of pili
- The pilus grows in size and forms the conjugation tube
- The plasmid of donor cell which has the F+ ( fertility factor ) undergoes replication
- Only one strand of DNA is transferred to the recipient cell through the conjugation tube.
- The recipient completes the structure of double DNA by synthesizing the strand that compliments the strand acquired from the donor
