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Different forms of bacterial chromosom

Date post: 15-Apr-2017
Author: samaneh-palizban
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by S.Palizban different forms of bacterial chromosomes
  • by S.Palizbandifferent forms of bacterial chromosomes

  • in most of the bacteria:

    single circular DNA moleculeHaploid


  • Exceptions:

    Bacteria with linear chromosomes

    Bacteria with more than one chromosome


  • Bacteria with more than one chromosome

    bacteria have 2, 3 or 4 dissimilar chromosomesVibrio 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.

  • Rhodobacter sphaeroides

    Multichromosomal a kind ofpurple bacteria; photosynthetic eubacterium a rod-shaped, Gram-negative bacterium

  • The genome ofR. 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.

  • 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

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

  • V. choleraehas two circular chromosomes,

    together totaling 4 million bpof DNAsequence and 3,885 predicted genes

  • Chromosome 1; The larger first chromosome

    contains the crucial genes for toxicity, regulation of toxicity, and important cellular functions, such astranscription and translation

  • The second chromosome

    Which is determined to be different from a plasmid or megaplasmiddue to the inclusion of housekeeping and other essential genes in the genome,

    including essential genes for metabolism, heat-shock proteins, and16s rRNAgenes

    Also relevant in determining if the repliconis 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.

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

  • TheV. choleraeGenome Contains Two Replicons

  • Brucellasp.a small, IntracellularGram-negative coccobacillus,can causes brucellosis.

  • contains two unique and independent replicons

    The availability of 10 different genomes consisting of two chromosomes and

  • General features of the genomes:

    All genomes studied have two circular chromosomesof about 2,100 and 1,150 kb.Both have similar G+C content,

  • Lactococcus lactis

    is a Gram-positive bacterium used extensively in the production of buttermilk and cheese

  • 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.

  • .laboratory strains of Lactococcus lactis:

    MG1363 and IL1403 Laboratory Strains

    This strain thus fulfills the criterion of being diploid without overlapping chromosomal replication cycles.

  • 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.

  • 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 replicationand cell division.

  • 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.

  • Some prokaryotes have a linear chromosome;

    Borrelia burgdorferi.

  • Borrelia burgdorferi;

    the aetiological agent of Lyme disease, of spirochete

  • 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.

  • .

    Summary of Currently Known Bacterial Chromosome Organizations

    BacteriaChromosome OrganizationAgrobacterium tumefaciensOne linear and one circularBacillus subtilisSingle and circularBacillus subtilisSingle and linearBorrelia burgdorferiTwo circularBrucella abortusTwo circularBrucella melitensisTwo circularBrucella ovisTwo circularBrucella suis biovar 1Two circularBrucella suis biovar 2Two circularBrucella suis biovar 4Two circularEscherichia coliSingle and circularParacoccus denitrificansThree circularPseudomonas aeruginosaSingle and circularRhodobacter sphaeroidesTwo circularStreptomyces griseusLinearVibrio choleraeTwo circularVibrio fluvialisTwo circularVibrio parahaemolyticusTwo circularVibrio vulnificusTwo circular

  • Linear chromosomes are also found in other bacterial lineages,

    including the pathogenic spirochaetesBorrelia afzelii,Borrelia burgdorferiandBorrelia gariniiand several Streptomyces sppand the -proteobacteriumAgrobacterium tumefaciens.

  • A remarkable property of the 8.2-Mb chromosome ofS. erythraeawas that, contrary to the expectations and the earlier data (Reeveset al., 1998), it proved to be circular.

    The chromosomes of its close relatives, Streptomyces coelicolorandStreptomyces avermitilis, are both linear, as is the chromosome ofRhodococcussp. strain RHA1.

  • It is examined the properties of theEscherichia coliK-12 strains with a linear chromosome.

  • 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.

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

  • Thanks for your attention