Griffith's experiment in 1928 showed that bacteria can undergo transformation through uptake of DNA. He found that non-lethal heat-killed bacteria, when mixed with live harmless bacteria, could make the mixture lethal. Later it was found the "transforming principle" was DNA, which could be taken up by other bacteria and confer new traits like capsule formation and virulence. This provided early evidence that DNA carries genetic information that can be transferred between bacteria.

1. SPONTANEOUS MUTATIONS IN MICRO
ORGANISMS.
SUBMITTED TO:
Dr.A.VIJAYA GOPAL
ASST.PROFESSOR
SUBMITTED BY:
B.PRASANNA KUMAR
ID.NO:RAM/14-81

2. Griffith's experiment, was an experiment done in 1928 by Frederick Griffith.
It was one of the first experiments showing thatbacteria can
get DNA through a process called transformation.[1][2]
Griffith used two strains of Pneumococcus. These bacteria infect mice. He
used a type III-S (smooth) and type II-R (rough) strain. The III-S strain
covers itself with a polysaccharide capsule that protects it from the
host's immune system. This means that the host will die. The II-R strain does
not have that protective shield around it and is killed by the host's immune
system.
In this experiment, bacteria from the III-S strain were killed by heat, and
their remains were added to II-R strain bacteria. While neither harmed the
mice on their own, the blend of the two was able to kill mice.
Griffith was also able to get both live II-R and live III-S strains
of pneumococcus from the blood of these dead mice. He concluded that the
type II-R had been "transformed" into the lethal III-S strain by a
"transforming principle" that was somehow part of the dead III-S strain
bacteria.[3]

3. Today, we know that the "transforming principle"
Griffith saw was the DNA of the III-S strain
bacteria. While the bacteria had been killed, the
DNA had survived the heating process and was
taken up by the II-R strain bacteria. The III-S
strain DNA contains the genes that form the
shielding polysaccharide part from attack. Armed
with this gene, the former II-R strain bacteria
were now protected from the host's immune
system and could kill the host.
The exact nature of the transforming principle
(DNA) was confirmed in the experiments done
by Avery, McLeod and McCarty and by Hershey
and Chase.

5.  Definition:
 A sudden and heritable change in the nucleotide
sequence of a gene.
 A mutation is a change in phenotype, which is sudden,
heritable and is not produced due to segregation or
recombination.
 Mutation is the ultimate source of all the genetic
variation existing in any organism.
 Mutations always change the genotype and thus the
phenotype of the microorganism.

7.  Spontaneous mutations are those that arise occasionally
in the absence of a known cause i.e., without exposure
to external agents.
 These mutations may result from errors in DNA
replication, or from the action of transposons,or even
from the effect of some mutagenic agents present in the
environment.
 In India, the first mutation
breeding programme began
in the early 1930’s.

8.  Mutations are random events interms of the time of
their occurrence and the gene inwhich they occur.
 Most mutations have harmful effects, but some
mutations are beneficial.
 Mutations are recurrent.i.e., the same mutation may be
expected to occur in different individuals of a given
generation.
 Mutations can occur in any tissue or cell of an
organism.

9.  Mutations occur in both forward & reverse directions.
 Generally the rate of forward mutations are much higher
than those for reverse mutations.
 Mutations occur at very low frequencies in nature such
mutations are called spontaneous mutations.
 The rate of spontaneous mutations for most of the genes
is very low ranging between 10⁻7 and 10⁻4.
 Some genes increase the spontaneous mutation rates of
some other genes of the genome.
 Such genes are called mutator genes.

10.  The spontaneous mutation rate varies. Large gene provide
a large target and tend to mutate more frequently.
 Organisms possess a variety of cellular functions to
suppress spontaneous mutagenesis, and the specificity
and effectiveness of each function strongly affect the
pattern of spontaneous mutations.
 spontaneous mutations occur more randomly and much
less frequently.

11.  There are several ways in which mutations can be
classified; some of the common ones are
 1.Direction of mutation:
 a. Forward mutation:(mutation from wild type allele)
 b.Reverse mutation:(mutation from a mutant allele to
the normal one)
 2.Cause of mutation:
 a. Spontaneous mutation:(occur naturally without any
apparent cause)

13.  Induced mutations:(originate due to a treatment with
some physical or chemical agent)
 3.Dominance relationship:
 a. Dominant mutation:
 b.Recessive mutation:(most often recessive)
 c.Codominant mutation:(occationally codominant)
 d.incompletely dominant mutation:(partially dominant)
 4.Tissue of origin:
 a.Somatic mutation:(mutation occuring in somatic cell)
 Bud mutation:(somatic mutation occurs in an
axillarybud)

15.  b.Germinal mutation:(occur in reproductive tissue)
 In an sexually reproducing species only germinal
mutations are transmitted to the next generation.
 5.Effect on survival:
 a.Lethal mutations:(kill all the individuals having them in
appropriate genotype)
 b.Sublethal mutations:(kill most of the individuals)
 c.subvital mutations:(kill some of the individuals)
 d.vital mutations:(do not affect survival)
 e.supervital mutations:(increase the survival)

16.  6.Type of affected:
 a.Morphological/visible mutations:(mutation that alters
mutant allele is visually detected)
 b.Biochemical mutations:(mutations prevent the
production of a biochemical by the organism)
 7.Quantum of morphological effect produced:
 a.Macro mutations:(produce large enough changes in the
phenotype detected without any confusion) e.g:short
legged mutation in sheep.
 b.Micro mutations:(quantitative characters generally
produce small morphological effects,special techniques
required for their detection)

17.  8.Cytological basis:
 a.chromosomal mutations:(detectable changes in either
chromosome number or structure)
 e.g.,bar eye mutation in drosophila
 b.gene mutations/point mutations:(produced by
alternations in the base sequencens of genes)
 c.cytoplasmic or plasmagene mutations:(changes in
mitochondria or chloroplast DNA)
 e.g.,cytoplasmic male sterility in maize, sorghum.

18.  9.Molecular basis:
 a.base substitution:(single base in a DNA molecule is
replaced by another base)
 b.deletion mutation:(one or more bases are deleted or lost
from a gene)
 c.addition mutation:(insertion of one or more bases in a
gene)
 10.Type of amino acid replacement:
 a.missense mutation:(replacement of a single amino acid
of the respective polypeptides by another amino acid)
 They are produced by base substitutions.

20.  b.nonsense mutation:(a codon does not code for any
amino acid)
 c.frameshift mutations:(all the amino acids of the
polypeptide chain located beyond the site of mutation are
substituted)
 Frameshift mutations are produced due to deletion or
addition of bases.

21.  1.Errors during DNA replication.
 2.mutagenic effects of the natural environments of
organisms.
 3.transposons and incertion sequences.
 4.methylation followed by spontaneous deamination of
DNA bases, esp cytocine.
 5.some of the solar radiations are surely mutagenic.
 Both eukaryotic and prokaryotic genomes contain some
transposable elements.e.g.,incersion
sequences(IS),transposons,etc.

22.  The rate of spontaneous mutations is very low.
 It generally ranges between 10⁻⁵to10⁻⁷ /gene
/generation for prokaryotes.
 10⁻⁴ to 10⁻⁶/gene/generation for eukaryotes.
 Spontaneous mutation rates per generation are
comparatively higher in eukaryotes than in prokaryotes.
 But some eukaryotic genes are highly stable and mutate
at a very low rate.
 e.g.,the waxy locus in maize.
 Estimated mutatin rates in man appear to be much higher
than those for other eukaryotes.

23.  The rate of forward mutations to yellow body colour and
to brown eye colour in drosophila are estimated as 1.2 х
10⁻⁴ and 3 х 10⁻⁵,respectively.

24.  Mutations produced due to the treatment with either a
chemical or physical agent.
 The agents capable of inducing mutations are known as
mutagens.
 The capacity of an agent for inducing mutations is
termed as mutagenic property.
 Induced mutations are useful in two different ways:
 1.in genetic and biochemical studies.
 2.in crop improvement.

25.  The process of induced mutations through treatment with
a mutagen is known as mutagenesis.
 The exploitation of induced mutations for crop
improvement is called mutation breeding.
 Some potent chemical mutagens may produce mutations
at the rate of more than 1% per gene per generation in
bacteria and bacteriophages.
 This represents a more than 10,000-fold increase in the
mutation rate.

27.  A large variety of microbial mutants have been isolated
and studied intensively by microbiologists . some
important ones:
 1.AUXOTROPHIC MUTANTS
 2.RESISTANT MUTANTS
 3.CRYPTIC MUTANTS
 4.CONDITIONALLY EXPRESSED MUTANTS
 5.ANTIGENIC MUTNTS
 6.METABOLIC MUTANT
 7.REGULATORY MUTANTS
 8.TEMPARATURE-SENSITIVE MUTANTS.

28.  1.AUXOTROPHIC MUTANTS:
 Those that are nutritionally deficient ,i.e., they are unable
to synthesize essential metabolites or growth
factors(amino acid ,purine ,pyramidine,vit.,).
 2.RESISTANT MUTANTS:
 It’s exhibit an increased tolerance to inhibitory agents,
particularly antibiotics and phases.
 Microbes may develop such mutants spontaneously
through a range of mechanisms.
 3.CRYPTIC MUTANTS:
 Those that have lost a specific function but retain the
intracellular activities.e.g,.loss of permease.

29.  4.CONDITIONALLY EXPRESSED MUTANTS:
 These mutants remain as wild type phenotype under one
set of conditions.
 5.ANTIGENIC MUTNTS:
 It’s show a change in the surface structure and
composition of the microbial cell.
 6.METABOLIC MUTANT:
 These exhibit altered metabolic ability particularly the
fermentation ability of decreased or increased capacity to
produce some end-product.

30.  7.REGULATORY MUTANTS:
 Mutation affects either regulatory region of the promoter
gene or the activity of a regulatory protein.
 Mutants of Bacillus subtilis are grossly deficient in the
enzymes.
 8.TEMPARATURE-SENSITIVE MUTANTS:
 These will grow at one temparature but not at another.
most of them are heat-sensitive ,some how-ever , are cold
sensitive.

31.  Stress Survival
 Adaptive mutation
Transformation of Escherichia coliwith the F' plasmid containing the lac operon. The
operon possesses a + 1 frameshift, so it is unable to express genes for lactose catabolism.
Following specific cultivation conditions with lactose containing medium, the lactose
operon on some of the plasmids revert to lac+.

32. The recombination-dependent mutation
model for adaptive mutations of the lactose
operon on the F' plasmid. The “leaky” +1
frameshift of thelac operon provides
enough energy from lactose catabolism to
initiate replication of the plasmid. (A)
Persistent nicks in the plasmid cause the
replication fork to collapse and leave
exposed dsDNA. (B) Exposed dsDNA
initiates DNA repair with RecA, which
inserts a ssDNA segment into the dsDNA.
(C) Replication of the DNA by the low
fidelity DNA polymerase IV gives an
increased potential of replication errors
leading to numerous mutations.

33. Genomic rearrangement resulting from activity of an indigenous IS
element. (A) IS5 inserts between the CRP-binding site and thecstA gene.
(B) IS5 then undergoes inversion with IS5D, which is already located
upstream of an ABC-type transporter operon. (C) The inversion causes
the regions between IS5 and IS5D to invert. Hence, the ABC-type
transporter operon is now positioned near the CRP-binding site and
becomes activated.

34. Confirmational change of the
carboxyesterase. The esterase (left) can
hydrolyze carboxy esters, but the
confirmation specificity of the
enzyme’s catalytic site does not allow
hydrolysis of other polymers, such as
nylon. Point mutations in the enzymes’
gene can cause a conformational
alteration of the enzyme’s catalytic site
so that specificity is reduced (right).
This reduced specificity now allows
the enzyme to hydrolyze a wider
variety of oligomers, including the
linear polymer, nylon-6.

36.  Bacteria frequently develop mutations that enable them
to survive and adapt to a variety of environmental
conditions.
 However, most of these mutations can be classified as a
form of antagonistic pleiotropy.
 Bacteria face a variety of environmental conditions and
stressful situations.
 If the environmental conditions change, the mutation
usually becomes less beneficial and perhaps even
detrimental.
 most bacteria need the ability to rapidly adapt to ever
changing environments and food sources.