lecture 9: genetics of bacteria & their viruses ii

LECTURE 9: GENETICS OF BACTERIA & THEIR VIRUSES II

bacterial conjugation (rev)

bacterial transformation

bacteriophage genetics

BACTERIAL CONJUGATION

interrupted-mating selective markers

donor is strs

recipient is strr origin of replication

transferred first 1st transferred markers

most frequent in exconjugants

BACTERIAL CONJUGATION

bias in recovery of markers

gradient of transfer used for determination of gene order only

Scha

um’s

Out

lines

– G

enet

ics

3rd E

d., C

H12

, pp.

321

– 3

254th

Ed.

, CH

10, p

p. 3

49 –

355

a) exogenote enters cell ... merozygote = partial diploid

b) single recombination event (3x, 5x, ...) nonviable

c) double recombination event (4x, 6x, ...) viable

BACTERIAL CONJUGATION

BACTERIAL CONJUGATION

bias in recovery of markers

gradient of transfer used for determination of gene order only

to determine map distances, select late marker to ensure transfer of all relevant genes ... high resolution mapping

BACTERIAL CONJUGATION high-resolution mapping by recombinant frequency

Scha

um’s

Out

lines

– G

enet

ics

3rd E

d., C

H12

, pp.

321

– 3

254th

Ed.

, CH

10, p

p. 3

49 –

355

TRANSFORMATION IN BACTERIA

conversion of one genotype to another by uptake of exogenous DNA

transformation principle – demonstrated that DNA was responsible for inherited differences in polysaccharide character of S. pneumoniae (CH8)

TRANSFORMATION IN BACTERIA

extracted DNA (in an experiment) breaks at random

co-transformation of 2 tightly linked donor genes is more likely than 2 distant donor genes

cells must be made competent to enable DNA entry detergents electrical fields

TRANSFORMATION IN BACTERIA dependent on concentration of DNA in the medium

TRANSFORMATION IN BACTERIA DNA must enter and recombine into the host

TRANSFORMATION IN BACTERIA practice question, p. 237, #18

A transformation experiment is performed with a donor train that is resistant to four drugs: A, B, C and D. The recipient is sensitive to all four drugs. The treated recipient cell population is divided up and plated on media containing various combinations of the drugs. The table below shows the results. DRUGS ADDED # COLONIES DRUGS ADDED # COLONIES NONE 10,000 BC 51 A 1,156 BD 49 B 1,148 CD 786 C 1,161 ABC 30 D 1,139 ABD 42 AB 46 ACD 630 AC 640 BCD 36 AD 942 ABCD 30 a. Which of the genes is quite distant from the other three? b. What is the probable order of the three tightly linked genes?

BACTERIOPHAGE GENETICS

bacteriophage = eaters of bacteria

T-phages well studied; T-even and T-odd

BACTERIOPHAGE GENETICS

bacteriophage = eaters of bacteria

T-phages well studied; T-even and T-odd

BACTERIOPHAGE GENETICS

BACTERIOPHAGE GENETICS

lysis = breaking of cell wall and release of phage particles

bacteriophage lytic cycle ...

BACTERIOPHAGE GENETICS

phage plaques on a lawn of bacteria

1 plaque forming unit PFU = 1 phage particle

plaque morphology

host range

BACTERIOPHAGE GENETICS phage cross:

h– r+ x h+ r–

h+ infect strain 1 h– infect strains

1 & 2 r+ slow lysis,

small plaques r– slow lysis,

large plaques

BACTERIOPHAGE GENETICS lawn of 2 E. coli strains – 1 immune to h+ phage

BACTERIOPHAGE GENETICS

phage cross:h– r+ x h+ r–

h+ clowdy h– clear r+ small r– large

RF = [h+ r+ + h– r–] TOTAL

TRANSDUCTION IN BACTERIA alternative life cycles of temperate bacteriophage

TRANSDUCTION IN BACTERIA generalized transduction… random incorporation lytic cycle, non-integrated phage

TRANSDUCTION IN BACTERIA co-transduction donor leu+ thr+ azir recipient leu– thr– azis

thr leu azi

TRANSDUCTION IN BACTERIA genetic map of the purB cysB region in E. coli

TRANSDUCTION IN BACTERIA

phage integration

TRANSDUCTION IN BACTERIA

specialized transduction… non- random incorporation lysogenic cycle, integrated phage

TRANSDUCTION IN BACTERIA

specialized transduction… non- random incorporation lysogenic cycle, integrated phage

TRANSDUCTION IN BACTERIA

transduction: phage acquire host genes and transfer them to other bacterial cells

generalized transduction: transfers any host gene; and occurs when phage randomly package host DNA

specialized transduction: faulty separation of prophage (phage incorporated into host genome); new phage contains adjacent host genes only

GENETIC MAPS IN BACTERIA

E. coli linkage map (minutes)

GENETIC MAPS IN BACTERIA

5 minutes of the E. coli linkage map

GENETIC MAPS IN BACTERIA

correlated genetic and physical maps in E. coli

SUMMARY: RECOMBINATION IN BACTERIA

BACTERIAL CONJUGATION AND RECOMBINATION MAPPING: PROBLEMS

in Griffiths chapter 5, beginning on page 179, add these questions to those listed at the end of lecture #8… #4, 14, 16-21, 24, 28 (eg. in class)-32

begin with the solved problems on page 177 if you are having difficulty

look Schaum’s Outline (pp. 358-9) try Schaum’s Outline questions 10.7 – 10.12