MKS-Cell division mecahnism

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Cell division in bacteria : 

Cell division in bacteria Dr. M.K. SATEESH Department of Microbiology & Biotechnology, Bangalore University, Bangalore -56

Slide 2: 

DIVISION

Slide 3: 

- Growth is an increase in cellular constituents that may result in an increase in cell size, an increase in cell number, or both. - An increase in cell number is an immediate consequence of cell division. - Increase in cell numbers occurs when microorganisms reproduce by a process like budding or binary fission. - The majority of bacteria reproduce by a mechanism termed binary fission. - More than 90% of the Earths biomass is microbial. Bacteria use a relatively simple form of cell division called binary fission. Conceptually this is a simple process; a cell just needs to grow to twice its starting size and then split in two.

Slide 4: 

- Binary fission generally involves the separation of a single cell into two more or less identical daughter cells, each containing, among other things, at least one copy of the parental DNA.

Bacterial Reproduction : 

Bacterial Reproduction Bacteria reproduce by the process of binary fission. The circular chromosome replicates its DNA. Then, the cell splits into 2 halves, each containing a single chromosome No spindle apparatus (as exists in eukaryotic mitosis and meiosis).

Slide 6: 

Electrom photomicrographs of Gram positive cell division (Bacillus subtilis; left) and Gram negative cell division (Escherichia coli; right). A to C represent a progression in cell division. CW = cell wall; CM = cytoplasmic membrane; S = septum; N = nucleoid; OM = outer membrane. Bar = 0.2 um.

FtsZ ring : 

FtsZ ring Many types of proteins that comprise the cell division machinery assemble at the future division site. Protein monomers of FtsZ assemble into a ring-like structure at the center of a cell. Other components of the division apparatus then assemble at the FtsZ ring. This machinery is positioned so that division splits the cytoplasm and does not damage DNA in the process. As division occurs, the cytoplasm is cleaved in two, and in many bacteria, new cell wall is synthesized. The cell must copy its genetic material (DNA) and segregate these copies to opposite ends of the cell.

Slide 8: 

MinE localizes to a ring-like structure MinD accumulates alternately at the membrane periphery MinD ensures no FtsZ ring is assembled at either cell halves MinE at midcell prevents the MinD inhibitory activity MinE ring disassembles before completion of constriction DivIVA and MinD are localized to the cell poles FtsZ ring at midcell and recruitment of other cell division proteins DivIVA and MinD proteins then are recruited to the midcell Constriction is initiated constriction is completed, the FtsZ ring disassembles

Slide 9: 

In Caulobacter crescentus is mediated by MipZ, an inhibitor of FtsZ polymerization that forms a complex with the DNA-binding protein ParB at the chromosomal origin of replication, thus exploiting chromosome dynamics for its subcellular positioning

Slide 10: 

The MinCDE polar zone begins assembling at a cell pole and grows towards midcell (1–2 and 5–6). The MinE ring then assembles at the leading edge of the polar zone (3 and 7). The polar zone then disassembles, releasing MinC, MinD and MinE molecules, shrinking back to the pole, and finally releasing MinE from the E-ring (4–5 and 8–1). Because of the rapid oscillation, a zone of division inhibition (dark blue shading) is present near the two ends of the cell for a large portion of the cell cycle

Slide 12: 

Different types of cells or organelles and their use of FtsZ or alternative proteins for fission are shown. In euryarchaea and many bacteria, FtsZ (green) localizes to the inner side of the inner membrane as the Z ring. Crenarchaea and some bacteria lack FtsZ, so some other protein must localize as a ring at the site of division (yellow). In plastids and mitochondria, dynamin or dynamin-like protein rings (red) localize to the cytoplasmic face. These organelles also contain a dividing ring (blue) and, in the case of chloroplasts and some primitive mitochondria, an innermost ring of FtsZ (green). Most mitochondria, including those of fungi and animals, lack FtsZ and a detectable dividing ring, but still rely on dynamin on the cytosolic face for fission (red).

Slide 13: 

Staphylococcus aureus Cell wall synthesis occurs in Staphylococcus aureus, (green) Chromosome (blue) and cell membrane (red)

Slide 14: 

DNA replication/recombination/repair -- orangeCell division -- purpleTranscription -- light green, Protein synthesis -- pinkSignal transduction -- light blueMobility and chemotaxis -- dark blueCarbohydrate and amino acid metabolism -- dark greenunknown – yellow Functional categories of proteins are indicated by different colors: An expanded view of bacterial DNA replication . Proc. Natl. Acad. Sci. USA, 99(12): 8342-8347.2002 Bacterial replisome

Slide 15: 

In bacteria, the cell-division proteins all localize to a ring structure at the midpoint of the rod-shaped cells. The septal recruitment pathway in E. coli appears to be essentially linear, whereas septal recruitment in B. subtilis apparently occurs in two stages. This figure shows only the best-characterized members of the cell-division pathway in E. coli and B. subtilis (proteins depicted with the same shape and colour are homologous).

Slide 16: 

Thank you Good luck for exams

Fast & Cheap Bacteria Sex : 

Fast & Cheap Bacteria Sex

BActeria : 

BActeria 2 Domains Archea & Bacteria (eubacteria) Prokaryotes Cells with no true nucleus Successful & diverse 3.5-3.6 BYo 1/3 of earth’s biomass Asexual reproduction How do they persist given low genetic diversity & lack of mutation filtering system

3 Domains : 

3 Domains

Prokaryotes Who Are They?? : 

Prokaryotes Who Are They?? Germs, Bugs, Bacteria Disease The bad guys???

Bubonic Plague : 

Bubonic Plague

Food Poisoning : 

Food Poisoning

They Can Also… : 

They Can Also…

Photosynthesis : 

Photosynthesis

Fermentation : 

Fermentation

Nutrient Cycling : 

Nutrient Cycling

100,000++ spp : 

100,000++ spp Your body-1000 billion animal cells 10,000 billion bacteria cells

Diverse Niches : 

Diverse Niches Everywhere! Extreme temperatures High salt concentrations Acidic/ alkali conditions

Bacteria Live in Every Possible location on Earth! : 

Bacteria Live in Every Possible location on Earth! New Species of Ancient Bacteria Discovered 2 Miles Deep in Greenland Glacier

Dominate Life on Earth : 

Dominate Life on Earth

Prokaryotes : 

Prokaryotes Earliest life on earth (3.5-3.6 byo) Building blocks of life “Master Networkers” Symbiosis Genetic engineering Origin of aerobic & other respirations Origin of several types of photosynthesis Origin of cell wall

How Do They Do It??? : 

How Do They Do It???

Bacterial DNA is Dynamic : 

Bacterial DNA is Dynamic 2 forces act on bacterial DNA Selection for shorter length Favors DNA loss i.e. keep it simple Selection for gene function Drives acquisition of exogenous DNA

Bacteria DNA : 

Bacteria DNA Genophore Single double strand ring Very dynamic Smaller & less complex DNA Lower amounts of associated proteins Contains Information for essential functions

Bacteria Structure : 

Bacteria Structure

Bacteria Accessory DNA : 

Bacteria Accessory DNA Plasmid Smaller rings of DNA Contain fewer number of genes Codes for non vital functions “Accessory DNA” Specialized functions to accommodate environmental conditions Metabolism of unusual nutrients Adaptations to novel stimuli/ conditions Production of toxins Resistance to antibiotics Replicate independently

Plasmid DNA Good in a Pinch! : 

Plasmid DNA Good in a Pinch!

Bacteria Reproduction : 

Bacteria Reproduction Binary fission Fast, cheap Some bacteria once every 20 min Bacteria introduce vast amts of variation extensively w/in a few years Eukaryotes via mutation= MYS

Binary Fission : 

Binary Fission

Bacteria Sexual Reproduction : 

Bacteria Sexual Reproduction Sex is the Exchange genetic material from different individuals into a common cell Sex in bacteria occurs by uptake of exogenous DNA Horizontal gene transfer No gamete fusion or reproduction Alters existing genes

Increased Diversity : 

Increased Diversity Bacteria sex introduces variation in 2 ways Introduces novel gene sequences Alters existing genetic material

When do bacteria Have Sex : 

When do bacteria Have Sex Response to environmental stress Nutrient shortage Altered growing conditions Cell density (quorum sensing) Starvation

How Do Bacteria Have Sex? : 

How Do Bacteria Have Sex? Bacterial mechanisms for Introducing Variation Mutation Conjugation Transformation Transduction

Mutation : 

Mutation Error in DNA sequence Often occurs during replication of DNA Can be caused by a mutagen Ex. UV, Chemicals Can be deleterious or beneficial Rapid way to introduce diversity

Mutations are Relatively Common : 

Mutations are Relatively Common

Conjugation : 

Conjugation Process by which bacteria join to exchange genetic material Exchange plasmid DNA Uses conjugation pili Forms bridge between two bacterial cells

Bacteria Conjugation : 

Bacteria Conjugation

Bacteria Conjugation : 

Bacteria Conjugation

Transduction : 

Transduction Indirect exchange of DNA between individuals Utilizes a virus Bacteriophage Virus life cycle transfers bacteria DNA from one individual to another

Virus : 

Virus

How Does a Virus Work? : 

How Does a Virus Work?

Transformation : 

Transformation Direct exchange of DNA fragments Replaces homologous chromosome sequences Restores genes lost or degraded in populations Adds diversity Aids in repair of deleterious mutations Can occur intraspecifically & interspecifically Intraspecific transformation Increases changes in allele frequency more frequently than by mutation Bacteria analogue of Meiotic sex (recombination)

Transformation : 

Transformation

Cost of Transformation : 

Cost of Transformation Mechanics of DNA uptake requires energy Risk incorporating defective alleles What are the advantages….

Bacteria Species are Metapopulations : 

Bacteria Species are Metapopulations Bacteria form spatially distinct populations living under varied ecological conditions Ie distinct selection forces Can “lose” alleles that may be useful when conditions change Remember NS favors smaller genomes Transformation helps populations restore lost or degraded (mutated) alleles

“Superorganism” : 

“Superorganism” Can exchange w/ virtually any other bacteria “Essentially have access to a single gene pool & hence to the adaptive mechanism of the entire bacteria kingdom”

Bacteria : 

Bacteria

Epsilonproteobacteria : 

Epsilonproteobacteria Smallest of the five classes. Slender rods which can be straight, curved or helical.

Helicobacter pylori : 

Helicobacter pylori There are at least 23 species of Helicobacter isolated from humans, dogs, cats and other mammals. In some parts of the world 70-90% of the population is infected. Helicobacter pylori causes gastritis and peptic ulcer. Produces large amounts of urease and urea hydrolysis appears to be associated with its virulence.

Deinococci and Nonproteobacteria : 

Deinococci and Nonproteobacteria Aquifex and Thermotoga Aquifex belongs to the oldest branch of bacteria. It is a hyperthermophilic microaerophilic rod-shaped autotroph with a temperature optimum of 85 degrees. Thermotoga is also hyperthermophilic, but a chemoheterotroph. About 24% of its coding sequences are similar to archaeal genes.

Deinococcus : 

Deinococcus Deinococi are spherical rod-shaped and often associate in pairs or tetrads. Although they stain gram positive, their cell wall is layered and has an outer membrane like gram-negative bacteria. Almost all strains extraordinarily resistant to both desiccation and radiation.

Deinococcus : 

Deinococcus Can be isolated from many sources, but their natural habitat is not known. Their great resistance may be due to their ability to repair severely damaged chromosomes. Their genome consists of two circular chromosomes, a megaplasmid, and a small plasmid.

Photosynthetic bacteria : 

Photosynthetic bacteria These bacteria carry out oxygenic photosynthesis – they use water as an electron donor and generate oxygen. Bacteria use chlorophyll a.

Phylum Cyanobacteria : 

Phylum Cyanobacteria Are the largest and most diverse of photosynthetic bacteria. Their photosynthetic system closely resembles that of eucaryotes because they have chlorophyll a and photosystem II. Most cyanobacteria are obligate photolithotrophs, some can grow in the dark as chemoheterotrophs.

Cyanobacteria : 

Cyanobacteria Vary greatly in shape and appearance. May be unicellular, exist as colonies of many shapes or form filaments called trichomes. Cyanobacteria show diversity with respect to reproduction and employ a variety of mechanisms. Many filamentous cyanobacteria fix atmospheric nitrogen by means of special cells called heterocysts. Classification of cyanobacteria is still in an unsettled state.

Chlamydiae : 

Chlamydiae Obligate intracellular parasites that lack peptidoglycan in their cell walls. Not much larger than viruses, but have DNA and RNA, a plasma membrane, functioning ribosomes, metabolic pathways, reproduce by binary fission. Nonmotile, coccoids ranging in size from 0.2 – 1.5 um. Genomes are very small. Energy parasites – depend on hosts for ATP.

Chlamydia : 

Chlamydia Reproduce within the cytoplasmic vacuoles of host cells by a life cycle involving elementary bodies (EBs) and reticulate bodies (RBs). Chlamydia trachomatis causes trachoma. C. pneumoniae is a common cause of human pneumonia and there is indirect evidence that infections may be associated with development of arteriosclerosis.

Spirocheates : 

Spirocheates Ecologically diverse and grow in habitats ranging from mud to the human mouth. Chemoheterotrophic bacteria distinguished by their structure and mechanism of motility. Slender, long bacteria with a flexible helical shape. Unique pattern of motility is due to an unusual structure called the axial filament underlying an outer sheath or outer membrane. Treponema pallidum is a pathogen – causes syphilis

Bacteroidetes : 

Bacteroidetes Members of the Bacteroidetes are obligately anaerobic, chemoheterotrophic, nonsporing, motile or nonmotile rods of various shapes. Gliding motility is present in a diversity of bacteria. Cytophaga are active in the mineralisation of organic matter.

Gram Positive Bacteria : 

Gram Positive Bacteria Low G + C Strains High G + C Strains

Low G + C : 

Low G + C Class Mollicutes (The mycoplasmas) Bacteria lack cell walls and cannot synthesise peptidoglycan precursors. Pleomorphic Smallest bacteria capable of self-reproduction Require sterols for growth Usually facultative anaerobes

Mycoplasmas : 

Mycoplasmas Widespread In animals are associated with diseases of the respiratory and urogenital tracts. Cause many major diseases in livestock Mycoplasma genitalium- has one of the smallest genomes – 580 kilobases

Class Clostridia : 

Class Clostridia Largest genus is Clostridium and includes anaerobic bacteria that form endospores and do not carry out dissimilatory sulfate reduction. Have great practical impact, as they are anaerobic and form heat-resistant endospores. C. botulinum causes food poisoning. C. tetani causes tetanus.

Class Bacilli : 

Class Bacilli 2 orders – Bacillales Lactobacillales Genus Bacillus contains endospore-forming chemoheterotroph rods that are usually motile and flagellated. Bacillus subtilis has been sequenced – 4.2 million bp. Some members of the genus produce antibiotics. B. cereus can cause food poisoning. B. anthracis is the causative agent of anthrax. B. thuringiensis is an insecticide.

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