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(Strain improvement techniques), Formation of new gene combinations among…

- - - - Recombination
        
        Types:
        
        3.Transformation
        
        Bacteria take up DNA from their environment (recipient cells)
        
        The DNA remnants in the environment most commonly originate from death bacteria cells
        
        The DNA incorporating it into recipient own genome, where the cell is described as being competent
        
        4. Conjugation
        
        Bacterium connects itself to another through protein tube structure - pillus
        
        Genes are transferred from one bacterium to another through the pillus
        
        5. Transduction
        
        Bacterial DNA is exchanged thru a virus that infects bacteria - bacteriophage
        
        The transfer of DNA from one bacteria to another by bacteriophage
        
        2. Translocation
        
        Crossing over that occurs in non-homologous chromosomes
        
        When a chromosome segments detaches from one chromosome and move to a new position on another non-homologous chromosome's
        
        6. Protoplast fusion
        
        During fusion, two or more protoplasts come in contact and adhere with one another either spontaneously or in presence of fusion inducing chemicals
        
        The cytoplasm of the two protoplasts intermingle
        
        The fusion between non-antibiotic producing strains of two species has yielded a strain that produce indolizomycin, a new indolizine antibiotic
        
        1. Cross over
        
        Occurs during prophase 1 of meiosis
        
        The chiasma breaks and the broken chromosome segments get switched onto homologous chromosome
        
        The broken chromosome from the maternal chromosomes get joined to its homologous paternal chromosome
        
        Exchange of gene code
      - Recombinant DNA technology
        
        Feedback regulation - biosynthesis of amino acids, nucleotides, vitamins:
        
        1. Feedback inhibition
        
        The final product of the metabolite pathways, inhibits the action of the first enzyme of the pathway.
        
        This to prevent further synthesis of intermediates and products of the pathways
        
        It happens when the final product is sufficient quantities
        
        Example:
        
        High conc. of D will inhibit conversion of A to B
        
        D is specifically able to bind and inhibit enzyme convert A to B
        
        D thus acts as a negative allosteric effector or feedback inhibitor of the enzyme
        
        2. Feedback repression and attenuation
        
        Involves turn off of enzyme synthesis
        
        Happens in gene level
        
        When the sufficient amount of the product have been made and it starts to accumulate :arrow_right: the feedback regression take place
        
        The end-product of the pathway acts as co-repressor
        
        Example:
        
        In bacteria, the presence of the synthesized particular amino acid in the culture medium prevents new synthesis of the amino acid via repression
        
        A small molecule such as histidine or leucin, acting as co-repressor, can ultimately block synthesis of the enzymes involved in its own synthesis
        
        In the presence of co-repressor, an active repressor is formed which binds to the operator to prevent transcription by RNA polymerase and prevent enzyme synthesis
      - Mutation selection
        
        4 methods to isolate mutants:
        
        1. Replica planting technique
        
        Used to detect auxotrophic mutants which differentiates between mutants and wild type strains on the basis of ability to grow in the absence of an amino acid
        
        4. Carcinogenicity test
        
        Used to identify the environmental carcinogens that cause mutation and induce cancer in organisms
        
        Based on detecting potential of carcinogens & testing for mutagenicity in bacteria
        
        Ames test - mutational reversion assay
        
        Salmonella typhimurium carry mutation on gene that encodes histidine - His-salmonella
        
        The bacteria loss the ability to synthesis histidine utilizing the ingredients of culture media - Histidine is required in growth media
        
        Culturing His-salmonella in a media containing certain chemical (mutagens), causes mutation in histidine encoding gene
        
        Bacteria regain the ability to synthesize histidine gene - Reverse mutation
        
        3. Substrate utilizing method
        
        Several bacteria utilize only a few primary carbon sources
        
        The cultures bacteria are seeded onto medium containing an alternate carbon sources
        
        Any colony that grows on medium can use the substrate and are possibly mutants
        
        Can be isolated
        
        2. Resistance selection methods
        
        The wild type cells are not resistant either to antibiotics or bacteriophages
        
        It is possible to grow the mutant bacterium in the presence of antibiotics or bacteriophage and look for survivors
        
        4 types:
        
        Spontaneous mutation
        
        Occurs without any specific treatment
        
        Naturally it happens due to external factors
        
        Happens during cell division
        
        Induced mutation
        
        Due to treatment with certain agents - chemical or physical agents
        
        Major mutation
        
        Extreme changes in biochemical characteristics
        
        Used in strain improvement
        
        eg. Streptomyces griseus & Streptomyces aurofaciens - produce 6-methyl tetracylcine in place of tetracycline
        
        Minor mutations
        
        Stepwise changes take place in the biochemical characteristic
        
        Eg. Penicillium chrysogenum - yield 55% more penicillin than the original strain