Download GENETICS – BIO 300

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
Schaum’s Outlines – Genetics 3rd Ed., CH12, pp. 321 – 325
4th Ed., CH10, pp. 349 – 355
BACTERIAL CONJUGATION
a) exogenote enters cell
... merozygote =
partial diploid
b) single recombination
event (3x, 5x, ...)
nonviable
c) double recombination
event (4x, 6x, ...)
viable
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
Schaum’s Outlines – Genetics 3rd Ed., CH12, pp. 321 – 325
4th Ed., CH10, pp. 349 – 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
NONE
A
B
C
D
AB
AC
AD
# COLONIES
10,000
1,156
1,148
1,161
1,139
46
640
942
DRUGS ADDED
BC
BD
CD
ABC
ABD
ACD
BCD
ABCD
# COLONIES
51
49
786
30
42
630
36
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