Microbial Genetics (Overview)

1. Microbial Genetics (Overview) Professor Sudheer Kher

2. There is nothing different between the basic structure of substances in livings carrying heritage Chromosome of an insect E. coli DNA spread

3. Phenotype & Genotype • Phenotype • The observed properties of an organism • Genotype • Alteration of genetic information

4. Genotypic Variation • The ability of microbes to alter genetic information is fundamental to their survival in a changing environment . • Such variation occur by: • Mutation • Recombination

5. Change is a common phenomenon: Mutation and variation

6. Bacterial DNA Bacterial Chromosome • Have only one chromosome. • Are a large covalently closed, circular DNA molecule. • The chromosome is organized into loops around a proteinaceous center. • Most have around 2,000 genes. • All essential genes are on the bacterial genome.

7. Nonessential Bacterial Genetic Elements • A bacterium has three types of non essential genetic material: • Plasmid(s) • Bacteriophage or prophage • Transposon

8. Phenotypical adaptation Genetic changes Mutation Spontaneous Mutagens-induced Transposones (Jumping genes) Gene exchange Transformation Conjugation Transduction Ways of change in bacteria

9. Genetic exchange between bacteria • Transfection - Process of introducing nucleic acids into cells by non-viral methods. • Transduction - Process by which DNA is transferred from one bacterium to another by a virus. • Conjugation. Transfer of genetic material between bacteria through direct cell-to-cell contact. Conjugation involves F+ male bacterium and F- female bacterium.

10. Transfection

11. Mutations • Mutation is a heritable change in DNA sequence that can lead to a change in phenotype. • By definition, a mutant differs from its parental strain in genotype, the nucleotide sequence of the genome.

12. Mutation • Change in genetic material • Mostly fatal, few may be beneficial (evolution) • Point Mutation (Base substitution): single base at one point in DNA sequence is replaced with a different base • Frameshift mutation: DNA deletion or insertion

13. Point Mutations • A point mutation, which results from a change in a single base pair, can lead to a single amino acid change in a polypeptide or to no change at all, depending on the particular codon involved

14. Point Mutations • In a nonsense mutation, the codon becomes a stop codon and an incomplete polypeptide is made. • In a missense mutation, the sequence of amino acids in the ensuing polypeptide is changed, resulting in an inactive protein or one with reduced activity. • In a silent mutation there is no change in the amino acid sequence of the the protein

16. Deletions and Insertions • Deletions and insertions cause more dramatic changes in the DNA, including frameshift mutations, and often result in complete loss of gene function

18. An English Example THEBOYANDTHEDOGRANFAR THE BOY AND THE DOG RAN FAR D Missense: THE BOY AND THE HOG RAN FAR Nonsense: THE BOY AND .

19. English Example-Frameshift THEBOYANDTHEDOGRANFAR THE BOY AND THE DOG RAN FAR DEletion: N THE BOY ADT HED OGR ANF AR Insertion: THE EBO YAN DTH EDO GRA NFA R

20. Mutagens • Mutagens are chemical, physical, or biological agents that increase the mutation rate • Radiation • Ionizing • Nonionizing • Chemicals • Base analogs

21. Plasmids • Circular extrachromosomal elements that replicate independently of the host chromosome. • Carry non-essential genes • May confer a variety of phenotypes upon the host cell. (R plasmids carry antibiotic resistance genes) • Used as vectors to move pieces of DNA around in Genetic Engineering.

22. Bacterial Recombination • Process of transferring plasmid DNA or chromosomal DNA fragments laterally from a donor cell to a recipient cell. - Vertical gene transfer, from parent to offspring. - Lateral gene transfer. • Mechanisms • Transformation • Conjugation • Transduction.

23. Gene exchange

24. Genetic Recombination in Bacteria • Transformation • Assimilation of foreign DNA from the surroundings • Transduction • Gene transfer via a bacteriophage • Conjugation • Bacterial sex? Direct transfer of genes between 2 cells that are temporarily joined by a sex pilus

25. Overview

26. Transformation • Transfer of genes involving free (outside the cell) DNA. • Competence – ability of a cell to take up a molecule of DNA and be transformed. • Some bacteria are naturally transformable (competent). Others can be artificially induced to become competent and take up DNA from their surroundings.

27. Transformation • Steps • Uptake of DNA • Gram + • Gram - • Recombination • Legitimate, homologous or general • recA, recB and recC genes • Significance • Phase variation in Neiseseria • Recombinant DNA technology

28. Fig. 9.27 Griffith’s classic experiment in transformation

29. Transduction • Transfer of host genes from one bacterium to another by a virus (bacteriophage)

30. Infection of Host Cells by Phages • Adsorption • Tail fibers • Receptor is LPS for T4 • Irreversible attachment • Base plate • Sheath Contraction • Nucleic acid injection • DNA uptake

32. Conjugation-HFR • The F plasmid may integrate into the host chromosome. • HFR (High Frequency of Recombination) • If this occurs some of the bacterial chromosome can also be transferred to the recipient cell. Not just the F plasmid.

33. F+ F- F+ F- F+ F+ F+ F+ Mechanism of F+ x F- Crosses • Pair formation • Conjugation bridge • DNA transfer • Origin of transfer • Rolling circle replication

34. Hfr F- Hfr F- Hfr F- Hfr F- Mechanism of Hfr x F- Crosses • Pair formation • Conjugation bridge • DNA transfer • Origin of transfer • Rolling circle replication • Homologous recombination

35. F’ F- F’ F- F’ F’ F’ F’ Mechanism of F’ x F- Crosses • Pair formation • Conjugation bridge • DNA transfer • Origin of transfer • Rolling circle replication

36. Transposable elements • Genetic elements that can move from one location on a chromosome to another location. • Insertion sequences (IS) • carry no genetic info except that required for them to move about • Transposons (Tn) • Larger than IS and carry additional genes • Both IS and Tn have a structure called an inverted repeat at their ends. Both encode a transposase (an enzyme that lets them move about

37. Viral Genetics

38. THE VIRAL GENOME • Obligate intracellular parasites. Completely dependent on host cell for • Replication • Transcription • Translation of mRNA transcripts into proteins • Only one type of nuclei acid either DNA or RNA which could be single stranded or double stranded. • RNA viruses • Positive sense RNA(+RNA) - Serves directly as mRNA • Negative sense RNA(-RNA) - Must use an RNA polymerase to synthesize a complimentary positive strand to serve as mRNA

39. Viral Replication

40. VIRAL GENETICS • VIRUSES GROW RAPIDLY • A SINGLE PARTICLE PRODUCES A LOT OF PROGENY • DNA VIRUSES SEEM TO HAVE ACCESS TO PROOF READING, RNA VIRUSES DO NOT SEEM TO

41. REASSORTMENT (Viruses)

43. Enjoy these links • Play a Microbial genetics quiz Genetics quiz • For Microbiology fun, presentations, online text book, MCQs, videos, slideshows Visit my website