33. Genetic Exchange in Bacteria. Transduction. Types of transduction.

Transfer of genetic material from a donor cell to a recipient cell using bacteriophage. Distinguish between non-specific and specific transduction. Non-specific transduction-accidental transfer of DNA fragments from one bacterial cell to another. Specific transduction is only moderate phage having the ability to include well-defined regions of the chromosome of the bacterial cells and transduce certain genes.

General (non-specific) transduction - the transfer of any part of a bacteriophage fragment of the bacterial chromosome. In cells infected with bacteriophage during assembly subsidiary population some phage heads can penetrate bacterial DNA fragment or plasmid or viral DNA, together with, or instead of it. This occurs because the bacterial DNA is fragmented after phage infection and a piece of bacterial DNA of the same size as the phage DNA enters the viral particle. In this form transduction recipient cells may be made virtually any gene. Unspecific transduction phenomenon can be used for mapping the bacterial chromosome.

Specific transduction observed in the case where the phage DNA integrates into the bacterium to form a prophage. With the exclusion of phage DNA from the bacterial chromosome as a result of a random process is captured adjacent to the site include a phage DNA fragment of the bacterial chromosome. Since most temperate phage integrates into the bacterial DNA at specific sites for bacteriophages such transfer characteristic in the recipient cell specific portion donor bacterial DNA. Transduction can serve as specific transport mechanism of bacterial virulence genes, provided that these genes are located in the immediate vicinity of the integration of prophage.

The most typical example is the transduction carried out by phage λ. He usually transduce certain genes: gal (encodes the synthesis of galactose) and bio (encodes the synthesis of biotin). When going into a state of phage λ prophage is included in a certain area of ​​the chromosome of the host bacterium - between genes gal and bio. Branch phage DNA from the bacterial chromosome can be inaccurate and some of its fragment remains in the chromosome, a gene located near the phage DNA to be captured. In the case of infection with phage transducing cells deficient in certain gene, e.g. gal -, recombination may occur with replacement of the defective gene own transduce intact bacteria to form a recombinant gene (transductants) gal +.

Abortive transduction. When introduced abortive transduction donor DNA fragment is not integrated into the chromosome of the host, but remains in the cytoplasm and it operates independently. He subsequently transferred to one of the daughter cells (ie, inherited unilinearly) and then lost to posterity.

31. Systemics and Taxonomy of microorganisms. Classification. Types of taxonomy: numerical, phylogenetic, polyphase. Nomenclature.

Taxonomy - the science of biological classification; the grouping of organisms according to

their mutual similarities (i.e., establishing relationships between one group of organisms and

another; to differentiate one group of organisms from another).

Systematics - The study of biodiversity in an evolutionary context (i.e., the study of the

evolutionary history of organisms)

Classification:

• Ordering organisms with like characteristics into groups or taxa (singular - taxon)

• Based on established procedures and rules

• Describes groups of organisms, their interrelationships and boundaries between groups.

Taxonomy:

Kingdom (American system has six: Animalia, Plantae, Fungi, Protista, Archaea, Bacteria)

Phylum (there are 23+ bacterial phyla)

Class

Order

Family

Genus (aka, generic name)

Species (aka, specific name, specific epithet)

Subspecies

Numerical taxonomy is a classification system in biological systematics which deals with the grouping by numerical methods of taxonomic units based on their character states. It aims to create a taxonomy using numeric algorithms like cluster analysis rather than using subjective evaluation of their properties.

Phylogenetic system: groups organisms based on shared evolutionary heritage. DNA and RNA sequencing techniques are considered to give the most meaningful phylogenies.

Polyphasic taxonomy takes into account all available phenotypic and genotypic data and integrates them in a consensus type of classification, framed in a general phylogeny derived from 16S rRNA sequence analysis. In some cases, the consensus classification is a compromise containing a minimum of contradictions. It is thought that the more parameters that will become available in the future, the more polyphasic classification will gain stability. 

Today, microorganism names originate from four different sources:

1. Descriptive – For example Staphylococcus aureus (grape-like

cluster of spheres, golden in color), Streptococcus viridans (chains of

spheres, green in colony color), Proteus vulgaris (first and common),

Helicobacter pylori (spiral shaped rod at the entrance to the duodenum)

2. Scientist’s names – e.g., Escherichia coli (Theodor Esherich),

Erlichia (Paul Erlich), Nessieria (Albert Neisser), Listeria (Joseph

Lister), Pasturella (Louis Pasteur), Yersinia (AlexandreYersin),

Bartonella (Alberto Barton), Morganella (H. de R. Morgan), Edwardsiella (P. R. Edwards)

3. Geographic places – e.g., Legionella longbeachiae (Long Beach, California), Pasturella

tularensis (Tulare County, California), Pseudomonas fairmontensis (Fairmount Park,

Pennsylvania), Mycobacterium genavense (Geneva, Switzerland), Blastomyces brasiliensis

(Brazil), Providencia spp. (Brown University, Providence, RI)

4. Organizations – e.g., Legionella (American Legion), Afipia felis (Air Force Institute of

Pathology), Cedecea spp. (Centers for Disease Control), Bilophila wadsworthia (VA Wadsworth

Medical Center in Los Angeles)