Chapter 7 Microbial Genetics Plasmids Circular genetic elements that reproduce autonomously and have an extra chromosomal existence 1-1000 KB in size Most are circular double- stranded dna. some linear ds DNA Transmitted from cell to cell via conjugation process Some can integrated into chromosome Can carry a variety of genes for production of toxin, resistance to antibiotics and heavy metals
Chapter 7 Microbial Genetics Plasmids • Circular genetic elements that reproduce autonomously and have an extrachromosomal existence. – 1-1000 KB in size – Most are circular doublestranded DNA, some linear ds DNA – Transmitted from cell to cell via conjugation process – Some can integrated into chromosome – Can carry a variety of genes for production of toxin, resistance to antibiotics and heavy metals
Mutations and Mutants Phenotype: the observable characteristics of an organism designated by a capital letter followed by two small letters, with either a plus and minus superscript to indicate the presence or absence of that property His. Glut et al Genotype: The precise genetic make-up of an organism designated by three lower case letters followed by a capital letter(all in italics) indicating the particular gene involved: hisC, mutations in the hisc gene would be designated as hisEl, hisC2 et al
Mutations and Mutants • Phenotype:the observable characteristics of an organism – designated by a capital letter followed by two small letters, with either a plus and minus superscript to indicate the presence or absence of that property: His- , Glu+ et al • Genotype: The precise genetic make-up of an organism – designated by three lower case letters followed by a capital letter (all in italics) indicating the particular gene involved: hisC, mutations in the hisC gene would be designated as hisC1, hisC2 et al
Isolation of mutants Pigmented and nonpigmented mutants Antibiotic-resistant mutants within the inhibition zone · Genetic marker, such as the expression ofβ- galactosidase that produces the blue color
Isolation of Mutants • Pigmented and nonpigmented mutants • Antibiotic-resistant mutants within the inhibition zone • Genetic marker, such as the expression of bgalactosidase that produces the blue color
Replica plating Technique: Isolation of Mutants Velveteen(锦绒布) ∵ Auxotroph(营养缺陷型) Mutants do not grow Prototroph(原养型) 合-合 growth on complete medium Press plate onto velveteen Velveteen with imprint of all Animal medium Complete medium colonies Velveteen Plastic hoop ∵: Wooden block Transfer imprint of colonies to
Replica Plating Technique: Isolation of Mutants Velveteen (锦绒布） Auxotroph (营养缺陷型) Prototroph (原养型)
Replica plating Technique: Isolation of Mutants FIGURE 7.2 (a) Replica plating method for detection of nutritional mu- tants. (b) Nutritional mutants, as re- vealed by the replica plating method The left photo shows the master plate The colonies not appearing on the epoca plate are marked with an x. The replica plate lacked one nutrient leucine) present in the master plate Penicillin-Selection method Penicillin kills only growing cells. If penicillin is added to a population growing in a medium lacking the growth factor required by the designed mutant, the parent cells will be killed whereas the non-growing mutant cells will be unaffected
Replica Plating Technique: Isolation of Mutants • Penicillin-Selection Method – Penicillin kills only growing cells. If penicillin is added to a population growing in a medium lacking the growth factor required by the designed mutant, the parent cells will be killed, whereas the non-growing mutant cells will be unaffected