Ebio 3400 1st Edition Lecture 15Outline of Last Lecture I. GeneticsOutline of Current Lecture II. Phage replicationIII. Bacteriophages life cycles (2)IV. Back to Bacterial GeneticsV. BacteriaCurrent LectureI. Bacteriophage ReplicationAll viruses require a host cell for reproduction.a. Thus, they all face the same needs for host infection:i. Host recognition and attachmentii. Genome entryiii. Assembly of virionsiv. Exit and transmissionBacteriophages Attach to Host Cells Contact and attachment are mediated by cell-surface receptors.- Proteins that are specific to the host species and which bind to a specific viral component.- Bacterial cell receptors are normally used for important functions for the host cell.- Example: sugar uptakePhage Reproduction within Host Cells Most bacteriophages (phages) inject only their genome into a cell through the cell envelope.- The phage capsid remains outside, attached to the cell surface. - It is termed a “ghost.”II. Bacteriophages life cycles (2)1. Lytic cycle2. Bacteriophage quickly replicates, killing host cellThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.2. Lysogenic cycle- Bacteriophage is quiescent.- Integrates into cell chromosome, as a prophage- Can reactivate to become lytic The “decision” between the two cycles is dictated by environmental cues- In general, events that threaten host cell survival trigger a lytic burstConsequences of lysogenic cycle: lysis and lysogenyCalls are immune to further infection by that phageCan lead to specialized transductionCan cause lysogenic conversion: viral genes that change the phenotype of the host cell e.g some phage have genes for toxin production and can convert a non-pathogenic bacterium to a pathogenic one  Phages use host cell machinery to synthesize capsids They then assemble progeny phages Exit from cell- Lysis- Make enzyme that breaks down cell wall- Host cell bursts to release progeny phage- Slow release- Filamentous phages can extrude individual progeny through cell envelope- Host cells grow slowly but do not die Generalized transduction results from the lytic cycle. Chromosome is digested into smallpieces - some of which can end up being packaged in virus particlesProphage = the lysogenic phage incorporated into the bacterial chromosome…III. Back to Bacterial GeneticsTransduction:Transfer of host DNA via bacteriophage2 types: Specialized & Generalized TransductionSpecialized results from lysogeny followed by the lytic cycle- Specialized transduction by a temperate phage. Results from the lysogenic cycle… Specific pieces of DNA (near insertion sites) are transferred- Insertion of Lambda into a specific spot the bacterial chromosome- Genetic recombination and transfer within cells- 1) Transposition - Transposons - discovered by Barbara McClintock - working withMaize (they were later found to be very common in prokaryotes…)- Can be found on plasmids, chromosomes and phage so also can be involved in transformation, transduction and conjugation- 2) Recombination at sites of homology - crossing over- Movement of DNA within cellse.g.Transposons - discovered by Barbara McClintock - working with Maize (they were later found to be very common in prokaryotes- Summary: Transposition involves small segments of DNA (transposons, "jumping genes") that can move around chromosomes, plasmids or even viruses.Insertion sequences are very simple and typically contain genes for transposase and inverted repeats on either end. Simplest kind of transposase Transposons are more complex and may contain a number of genes that confer e.g. antibiotic resistance and/or toxin production. Carry other genes as well important for medicine and microbiotransfer by one of two mechanisms:- Replicative or nonreplicative transpositionIV. BacteriaA profound common feature of bacteria is their central apparatus for gene expression, including:a. RNA polymerase, ribosomal RNAs, and translation factorsThis underlies the selective activity of antibioticsMost bacterial cells possess cell walls made of peptidoglycan. b. Another target for antibioticsA phylum is a group of bacteria sharing a common ancestor that diverged early from other bacteria, based on small-subunit rRNA (SSU rRNA) sequence.Well-studied CULTURED bacterial phyla include:c. Deep-branching thermophilesd. Cyanobacteriae. Gram-positive bacteriaf. Proteobacteriag. Deep-branching Gram-negative bacteriah. Spirochetesi. Chlamydiae, Planctomycetes, andVerrumicrobiaDeep Branching Thermophiles The bacteria that appear to have diverged the earliest from ancestral archaea and eukaryotes are called “deep-branching”- Include extremophiles that share physiology and habitat with archaea Show the fastest doubling rates of all cells, as well as high rates of mutation- Which may have accelerated their molecular clocks- May appear to have diverged earlier than they in fact did- Aquificae and Thermotoga- Genomes show extensive transfer of archaeal genes- The most extreme bacterial hyperthermophiles- • Aquifex spp. are H2 oxidizers and fix CO2 by running the TCA cycle backwards. One of the only hyperthermophilic aerobes - - Use of H2 by so many deeply branching thermophiles suggests H2 was very common on the early earth- SomeThermotoga live near submarine hydrothermal vents, have a protein sheath (“toga”)- Phylum Deinococcus-ThermusDeinococcusradiodurans- Not thermophilic- Resists extremely high doses of radiation, and desiccation- Has thick cell wall and S-layer- Has several copies of chromosome per cell and is very efficient at DNA repair…- Chloroflexi- Photoheterotrophic; moderately thermophilic- Green nonsulfur bacteria- Forms filamentous mats in association with thermophilic cyanobacteria- Cyanobacteria are the only oxygenic phototrophic prokaryotes- Contain chlorophyll and accessory pigments- Many fix N2 in specialized cells called heterocysts- Chloroplasts are ancient cyanobacteria- Single-celled cyanobacteria include Synechococcus and Prochlorococcus.- Most abundant phototrophs in oceans- Some genera are filamentous:- Oscillatoria- Nostoc- Anabaena- Forms spores called akinetes- Cyanobacteria play key roles in many ecosystems.- Environmental change may cause the colonial cyanobacteria Trichodesmium to form giant blooms- In addition, cyanobacteria share many kinds of