Exam 2…Mean = 72 (after adding 7 points to all tests)Q. 19 - answers were messed up (real answer isc) so part of the 7 points was for that question.Spend a little time going over the test…..Bacterial Genetics - we will only discussmechanisms of genetic exchange (genetransfer) in bacteria….Read pages 323-334 and 203-215.Three modes of genetic exchange:1. Transduction (figs. 8.16 and 13.11)2. Transformation (persp. 8.1, pg. 205)3. Conjugation (Figs. 8.18 - 8.22)Transduction…..Transfer of host DNA via bacteriophage2 types: Specialized & Generalized TransductionGeneralized results from the lytic cycle ofcertain phage (see Fig. 8.16)Specialized results from lysogeny followed bythe lytic cycle (Fig. 13.11)In order to understand transductionwe need to know…..Viruses ofBacteria (bacteriophage or phage)Always are naked viruses (no membrane)why?Huge variety - One species of bacteria canhave many different phage… Table 13.2Important for:1. Genetic transfer (transduction)2. Control of Bacteria in Nature(read Persp. 13.1 pg. 330)3. Some can cause bacteria to become pathogens (e.g. diphtheria - see Table 13.3)Table 13.2. Note the variety of shapes,nucleic acid content, and “life cycle”…See Fig. 13.1cHost ranges of phage:Phage are usually very specific to the speciesthey infect - they attach to specific receptorson the outer layers of the bacterium -e.g. some phage of E. coli attach specificallyto the proteins of the flagellum…see Figures 13.12 and 8.17Phage for a particular bacterium also haveDNA methylation patterns like their host andthus avoid having their DNA cleaved byrestriction enzymes when the DNA entersthe cell…. See Figure 13.13Bacteriophageattached to pilus ofE. coliPhage tail fibersentwined aroundflagellumPhage T4 attached tospecific receptors(cell wall proteins)of E. coli.Fig. 13.12Virus interactions with host cells orReplication Cycles of phage…..See Figs. 13.4 - 13.7Fig. 13.04Fig. 13.4Latent state =Lysogenic stateFig. 13.5. Example of the lytic cycle: T4 of E.colFig. 13.6. Phage Lambda can undergo a lyticor the lysogenic cycleFig. 13.7. Insertion of Lambda into a specificspot the bacterial chromosome….Summary of lytic and lysogenic cyclesConsequences of the lysogenic cycle:Cells are immune to further infection by thatphageCan lead to specialized transduction (later)Can cause “lysogenic conversion” = viral genesthat change the phenotype of the host cell - e.g.some phage have genes for toxin production andcan convert a non-pathogenic bacterium to apathogenic one…. See Table 13.3 for examples….Table 13.3. Lysogenic conversion of bacteriaconferring pathogenic properties….Prophage = the lysogenic phage incorporatedinto the bacterial chromosome…..Back to Bacterial GeneticsTransduction…..Transfer of host DNA via bacteriophage2 types: Specialized & Generalized TransductionGeneralized results from the lytic cycle ofcertain phage (see Fig. 8.16)Specialized results from lysogeny followed bythe lytic cycle (Fig. 13.11)Fig. 8.16Generalized transduction results from the lytic cycle.Chromosome is digested into small pieces - some of which end upbeing packaged in virus particles…Fig. 13.11. Specialized transduction by a temperatephage. Results from the lysogenic cycle… Specificpieces of DNA (near insertion sites) are transferred…Fig. 13.11b. Specialized transduction by a temperatephageBacterial Genetics2. Transformation… uptake andincorporation (into the chromosome) of“naked” DNA from the environment….Expression of this new DNA can alter thephenotype of the organism, e.g. converting anon-pathogen into a pathogen….e.g. Streptococcus pneumoniae… Fig. 19.10. Streptococcuspneumoniae is pathogenic only when it produces a capsule(which helps it avoid detection by antibodies and phagocytes)Persp. 8.1, pg. 205. Experiment carried out by Griffin,showing that something was transferred from dead,pathogenic, S. pneumoniae to live nonpathogenic cells -transforming them into pathogens…It was later (1944) shown that the “transformingprinciple” was DNA (thus studies of transformation led to identificationof DNA as the genetic material in cells).Fig. 8.14. Transformation of a cell from non-resistant (StrS) to resistant to streptomycin (StrR).Fig. 8.15. There are many artificial ways to makebacterial cells “competent” for transformation, e.g.electroporation, and many chemical treatments thatmake temporary holes in the cell wall and membraneTransformation can take place between evenunrelated bacteria (but it is rarer thanbetween related because most foreign DNA isdegraded before it can be methylated - seefigure 8.26)There are also genetic platforms (integrons)within bacterial chromosomes that canmobilize large pieces of DNA and integratelarge pieces of foreign DNA behind apromoter so that they are easilytranscribed…Fig. 8.26Bacterial GeneticsConjugation (bacterial sex) Usually occursbetween a + strain (has a conjugative plasmid)and a - strain (no plasmid)….Fig. 8.17. Conjugation between F+ and and F- E. coli…Quick review of Plasmids - Extrachromosomal,circular, double-stranded DNA molecules.Plasmids divide and copies go to both daughter cellsduring asexual reproduction.Many plasmids can be transmitted between closely relatedspecies but some are not limited to close relatives.Not usually essential for a given organism, rather they allow theorganism to adapt to specific environmental conditions.Therefore, plasmids are often unstable in a host bacterium dueto the increased metabolic load.Also found in Archaea, Fungi and other euks………All sorts of traits can be transferred viaconjugative plasmids - the most relevant traitsfor us are antibiotic resistance genes…. Butother important genes are also found onplasmids.. (Table 8.4)Antibiotic resistance - usually by coding for anenzyme that renders the antibiotic non-functional.Beta-lactamase (inactivates Beta-lactams) is oneexample. Penicillin is a Beta-lactam.Special metabolic properties - some plasmids allowbacteria to take advantage of situations that might beotherwise harmful. Breakdown of complex organicmolecules is often plasmid encodedTable 08.04Virulence Plasmids - there are a number of ways that aplasmid can confer virulence in a bacterium.1) The production of one or more toxins thatcan be directed toward the host or towards otherbacteria (bacteriocins).2) The ability to form a capsule.The recent anthrax scare is an example: Virulent B.