The document discusses various forms of bacterial chromosomes, highlighting that most bacteria possess a single circular DNA molecule while some have multiple chromosomes or linear chromosomes. Examples include Vibrio cholerae and Brucella melitensis, which exhibit two dissimilar chromosomes, and Lactococcus lactis, which remains diploid with two non-replicating chromosomes. The study also notes differences in chromosome organization across bacterial species, including linear and circular structures, and explores the implications of linear genomes in prokaryotes.

1. by S.Palizban
different forms of
bacterial chromosomes

2.  in most of the bacteria:
 single circular DNA
molecule
Haploid

3. Exceptions:
•Bacteria with linear
chromosomes
•Bacteria with more than
one chromosome

4. Bacteria with more than one
chromosome
bacteria have 2, 3 or 4 dissimilar chromosomes
Vibrio cholerae and Brucella melitensis have 2
dissimilar chromosomes
The existence of multiple chromosomes in bacteria has been known for some time. Yet the
extent of functional solidarity between different chromosomes remains unknown.

5. Rhodobacter sphaeroides
•Multichromosomal
•a kind of purple bacteria;
• photosynthetic eubacterium
•a rod-shaped, Gram-negative
bacterium

6. The genome of R. sphaeroides .
two chromosomes,
one of 3 Mb (CI) and one of 900 Kb (CII),
five naturally occurring plasmids.
Many genes are duplicated between the two
chromosomes but appear to be differentially
regulated.
Moreover, many of the (ORFs) on CII seem to
code for proteins of unknown function.

7. When genes of unknown function on CII are
disrupted, many types of auxotrophy result,
emphasizing that the CII is not merely a
truncated version of CI

8. Vibrio cholerae;
the etiologic agent of the
diarrheal disease, is a Gram-
negative bacterium
.

9. V. cholerae has two
circular chromosomes ,
together totaling 4 million bp of
DNA sequence and 3,885
predicted genes

10. Chromosome 1;
The larger first chromosome
contains the crucial genes for
toxicity, regulation of toxicity,
and important cellular functions,
such as transcription and
translation

11. The second chromosome
•Which is determined to be different from a plasmid or
megaplasmid due to the inclusion of housekeeping and
other essential genes in the genome,
•including essential genes for metabolism, heat-shock
proteins, and 16s rRNA genes
• Also relevant in determining if the replicon is a
chromosome is whether it represents a significant percentage
of the genome, and chromosome 2 is 40% by size of the
entire genome.
•And, unlike plasmids, chromosomes are not self-
transmissible.

12. However, the second
chromosome may have once
been a megaplasmid because it
contains some genes usually
found on plasmids.

13. The V. cholerae Genome Contains Two
Replicons

14. Brucella sp.
a small, Intracellular
Gram-negative coccobacillus,
can causes brucellosis.

15. contains two unique and
independent replicons
The availability of 10
different genomes consisting
of two chromosomes and

16. General features of the genomes:
All genomes studied have two circular chromosomes
of about 2,100 and 1,150 kb.
Both have similar G+C content,

17. Lactococcus lactis
is a Gram-positive bacterium used
extensively in the production of
buttermilk and cheese

18. In contrast to this general rule for bacteria,
we found that Lactococcus lactis, is born with
two complete non-replicating
chromosomes.
L. lactis therefore remain diploid throughout
its entire life cycle.

19. .laboratory strains of Lactococcus lactis:
MG1363 and IL1403 Laboratory Strains
This strain thus fulfills the criterion of being
diploid without overlapping chromosomal
replication cycles.

20. we found that some of these strains were born
with two complete nonreplicating
chromosomes.
We determined the cellular content of DNA
by flow cytometry and by radioactive labeling
of the DNA.
These strains thus fulfill the criterion of
being diploid.
MG1363 and IL1403 are diploid in slow-
growing cultures.

22. The diploid and haploid strains differed in :
•their sensitivitytoward UV light,
•in their cell size,
•and in their D period,
•the period between termination of DNA replication
•and cell division.

24. Bacteria can carry plasmids and can be infected with viruses,
each of which are capable of carrying copies of bacterial
genes.
Thus bacteria can be partially diploid, or merodiploid, for
some genes.

25. Some prokaryoteshavea linear chromosome;
Borrelia burgdorferi.

26. Borrelia burgdorferi;
the aetiological agent of Lyme disease,
of spirochete

28. The chromosome of Borrelia behaved as a eukaryotic
linear chromosome with a size of around 1,000 kb.
The genome also comprised several circular and
linear plasmids which varied in size from 15 to 60 kb.

29. Bacteria Chromosome Organization
Agrobacterium tumefaciens One linear and one circular
Bacillus subtilis Single and circular
Bacillus subtilis Single and linear
Borrelia burgdorferi Two circular
Brucella abortus Two circular
Brucella melitensis Two circular
Brucella ovis Two circular
Brucella suis biovar 1 Two circular
Brucella suis biovar 2 Two circular
Brucella suis biovar 4 Two circular
Escherichia coli Single and circular
Paracoccus denitrificans Three circular
Pseudomonas aeruginosa Single and circular
Rhodobacter sphaeroides Two circular
Streptomyces griseus Linear
Vibrio cholerae Two circular
Vibrio fluvialis Two circular
Vibrio parahaemolyticus Two circular
Vibrio vulnificus Two circular
Summary of Currently Known Bacterial Chromosome
Organizations

30. Linear chromosomes are also found in other
bacterial lineages,
including the pathogenic spirochaetes
Borrelia afzelii, Borrelia
burgdorferi and Borrelia garinii
and several Streptomyces spp
and the α-proteobacterium Agrobacterium
tumefaciens.

31. A remarkable property of the 8.2-Mb chromosome of
S. erythraea was that, contrary to the expectations and
the earlier data (Reeves et al., 1998), it proved to be circular.
The chromosomes of its close relatives,
Streptomyces coelicolor and Streptomyces
avermitilis, are both linear, as is the
chromosome of Rhodococcus sp. strain RHA1.

32. It is examined the properties of the Escherichia coli K-12
strains with a linear chromosome.

33. Chromosomes in eukaryotes are linear, whereas those of most, but not
all, prokaryotes are circular. To explore the effects of possessing a
linear genome on prokaryotic cells, we linearized the Escherichia coli
genome using the lysogenic lambda-like phage N15. Linear genome E.
coli were viable and their genome structure was stable. There were no
appreciable differences between cells with linear or circular genomes in
growth rates, cell and nucleoid morphologies, genome-wide gene
expression (with a few exceptions), and DNA gyrase- and
topoisomerase IV-dependent growth.
However, under dif-defective conditions, only cells with a circular
genome developed an abnormal phenotype. Microscopy indicated that
the ends of the linear genome, but not the circular genome, were
separated and located at each end of a new-born cell. When tos - the
cis-element required for linearization - was inserted into different
chromosomal sites, those strains with the genome termini that were
more remote from dif showed greater growth deficiencies.

34. In fact linear chromosome even offered certain
advantages: E. coli strains with circular chromosomes
whose chromosomal recombination was affected by a
mutation in the XerCD recombinase or by a deletion of
the dif site, exhibited much slower growth than the same
mutants carrying linearized chromosomes

35. Thanks for your
attention