1. High molecular weight dna must bind to the cell surface.

2. The bound dna is taken up through the cell membrane.

3. The donor dna fragment is then integrated into the host chromosome or replicates autonomously as a plasmid.

Transformation occurs in nature and it can lead to increased virulence.

During transduction, a virus transfers the genes between mating bacteria.

Andre Lwoff reported that certain bacterial strains are able to survive for a long time even after infected by the bacteriophage and these is no lysis of bacterial cell. This bacteria is known as lysogenic bacteria and the phage is called as prophage. This bacterial cells can survive in lysogenic stage for many generations which is due to the synthesis of a special repressor protein. This protein inhibits the synthesis of phage particle inside the bacterial cell. As the synthesis of this protein is stopped the bacterial cell start the synthesis of phage components.

Types of transduction:

• Generalized transduction – all genes have an equal probability of being transduced. Any bacterial gene from the donor can be transferred to the recipient.

• Specialized or In restricted transduction, only those genes near the prophage attachment site are transduced.

22. Unlike eukaryote no true sexual reproduction is found in bacteria because: …. What are the features of the bacterial recombination

Unlike eukaryote no true sexual reproduction is found in bacteria because:

a) they lack sexual structures.

b) no gametic fusion takes place.

c) Karyogamy and meiosis is also absent in bacteria.

D) Bacteria are haploid organisms.

Genetic recombination can follow the transfer of DNA from one cell to another leading to the emergence of a new genotype (recombinant).

Features of the bacterial recombination:

• Gene transfer in bacterial cell do not produce zygotes but partial diploid called mero-zygotes.

• The original genome of recipient is named as endogenote.

• While the portion of DNA introduced from doner cell into recipient cell is called exogenote.

22. What are the functions of homologous associations of bacteria? Provide examples of homologous associations of bacteria.

Homologous associations- formed as a result of incomplete division or cell separation by:

1. Coagglutination of external coat containing polysaccharides:

• Zooglea (slimy matrix) Zooglea ramigera

• Sheath (vagina) – Sphaerotilus natans

2. Egestion of cellulose – mikoderma (cell skin) Acetobactor xylinum

3. Binding by cellular appendages protein nature- Fimbriae and pilli

Functions of homologous associations

1. Reducing the likelihood of removal favorable environment

2. Plays a role in differentiation interchange with signal metabolites substances

3. Realization of certain functions:

• Formation of fruiting bodies of Myxobacteria- provides mature of myxospores

• Formation of fruiting bodies of Clostridium in aerobic conditions – protect sporulating cells and endospores from oxygen by layer of mucus.

22. Heterologous associations formed with:… Enumerate the function of heterologous associations. Provide examples of homologous associations. Describe the possible interactions between the organisms in heterologous associations.

Heterologous associations formed with: other prokaryotes, unicellular eukaryotes, tissues of eukaryotes.

Function of heterologous associations:

1. Advantage in nutrition ( nitrogen fixation, photosynthesis)

2. Identification function (Luminescent bacteria in marine animals)

3. Microbial products contribute to the growth and reproduction, synthesis of pathogenicity factors.

4. Protection

Possible interactions between the organisms in heterologous associations

• Symbiosis (mutualism)- both species receives benefit to each other

• Parasitism – one species receive benefit to another, and second one live at the expense of first.

• Commensalism – one species receive benefit, another hasn’t affected

• Neutralism – each of species are independent from each other, And haven’t affected.

Examples:

- Green sulfur bacteria consortium with colorless: phototrophic consortia, association between a colorless bacterium and green or brown pigmented epibionts.

Such consortia can reach high concentrations in some environments, and it is believed that they represent important components of the carbon and sulfur cycles in freshwater environments.

- Prokaryote/ eukaryote symbiosis: Luminescent bacteria in marine animals.

- Prokaryote/ eukaryote symbiosis: Normflora of human body

- Prokaryote/ plant symbiosis: legume root with nitrogen fixing nodules. (rhizobium bacteria for example)

- Parasitic Chlamydia and tissues of eukaryotes.

29. Biofilm development occurs in five stages:… Within the biofilm bacteria combined intercellular contacts of two types:… Describe the role of biofilm. Why bacteria in biofilms are more resistant to unfavorable environmental factors?

Biofilm – is a living layer of the bacteria that is attached to a surface.

Biofilm development occurs in five stages:

1. Reversible attachment: Cells transiently affix to substratum and surface induced gene expression results in a protein profile significantly different from planktonic bacteria.

2. Irreversible attachment (fixation): Cells reorient themselves, clusters develop, motility is lost, and the last quorum sensing regulon becomes activated. At this stage, the microbes produce extracellular polymers that provide strong adhesion.

3. Maturation I: Cell clusters become thicker than 10 υm and the rhl quorum sensing system becomes active. Cell that attach to the surface, facilitate subsequent attachment of cells, extracellular matrix holds together the entire colony. Accumulate nutrients, the cells begin to divide.

4. Maturation II (growth): Cell clusters reach maximum thickness with the protein profile most different from planktonic cells. Formed a mature biofilm, and now it changes its size and shape. Extracellular matrix is a protection of cells against external threats.

5. Dispersion ( release of bacteria): Cluster structures change, and pores and channels form. Motile and non-motile bacteria are present as the protein profile begins to resemble planktonic cell once again. By dividing the periodic break away from the biofilm, individual cells that can over time attach to the surface and form a new colony.

Quorum sensing- is social behavior of bacteria. This enable populations of cells to control a diverse array of biological processes in synchrony from biofilm formation to bioluminescence.

Within the biofilm bacteria combined intercellular contacts of two types:

1. Cytoplasmic bridges- membrane tubes that connect the cytoplasm of various cells.

2. Close clumping of cells, which in certain parts of the bacteria have a common cell wall.

These allow for the generation of common responses to external stimuli and exchange by signaling molecules.

Role of biofilm:

Formation of biofilm has important biological significance because the microbial cells are better protected from:

• Antimicrobial immunity factor

• Antibiotics

• Adverse environmental factors

Mechanism of resistance

1. Labored and through the polysaccharides slow penetration of antimicrobial agents de matrix of biofilm

2. To slow the rate of growth of the bacteria in the biofilm

30. What methods are used to identify bacteria? Give a brief description.

Identification- is the process of observing and classifying organisms into a standard group that is recognized throughout the biological community.

1. Streak plate isolation

• The most commonly used isolation technique in microbiological laboratories is the streak plate method.

• The goal of streak plate isolation is to separate each of individual in a population for further study.

• Pure cultures (axenic cultures) composed of cells arising from a single progenitor called a colony-forming unit (CFU).

2. Microscopy and Staining one of the major characteristics that divide bacteria into different groups is their cell wall (Gram stain), shape, and arrangement.

Staining technique for Gram:

• Fixed smear stained for 1-2 min with a solution gentian violet. Poured into the dye, not washing the smear with water.

• Processes smear Lugol's iodine solution for 1-2 minutes, and not rinsing with water, pour it.

• 96o decolorized with alcohol during 0.5-1 min, washed with water.

• stained for 1-2 min with an aqueous solution of fuchsin.

• Pap rinsed with water and dried.

A gram-positive cell wall has many layers of peptidoglygan that retain the crystal of violet dye when the cell is stained. This gives the cell a purple color when seen under a microscope. A gram-negative cell wall is thin. The inside is made of peptidoglycan. The outer membrane is composed of phospholipids and lipopolysaccharides. The cell wall does not retain the crystal of violet dye when the cell is stained. The cell appears pink when viewed with a microscope.