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Bacterial Ecology Bacterial Ecology Definition - Relation between bacteria and non-living environment - Relation between bacteria and other living organisms - Relation between bacteria with each other Relation with non-living environment Bacteria plays roles as: Production Producers Degradation Degeneraters Consumers Relation with other living organisms (Symbiosis) Mutualism (Transient and resident microflora) Commensalism Parasitism Relation with each other (Symbiosis) Indifference Competition Antagonism Synergism Bacterial Genetics (Studying heritage variations in bacterial traits) Bacterial traits changes are due to: 1. Changes in environmental conditions 2. Changes in the genetic codes Changes in environmental conditions Brucella species are bacillus in 21 ○C and coccobacillus in 37 ○C Mycobacterium tuberculosis shows filamentous in 24 ○C when exposing glycerin. pneumococcus loses its capsule after some invitro culture. Staphylococcus aureus is not able to produce golden pigment in absence of oxygen. Salmonella species loses flagella when exposing phenol on culture. Adding calcium to Bacillus anthracis culture stops converting bacteria to spore form. Changes in bacterial traits Changes in the genetic codes 1- Intermicrobial exchange 2- Mutations (point mutations, insertions, deletions) Intermicrobial exchange Transformation (Capturing DNA from solution) Transduction (Phage-mediated) Conjugation (Bacterial Sex) Transformation Explored by F. Griffith (1928) using pneumococci The DNA released from a degenerated bacterium enters into another bacterium. There is no vector or mediation in this type of gene exchange. DNA-Mediated Transformation DNA-Mediated Transformation Intermicrobial exchanges by vectors Characteristics of genetic vectors must be capable of carrying a significant piece of donor DNA must be readily accepted by the host Plasmids – small, well characterized, easy to manipulate & can be transferred into appropriate host cells through transformation Bacteriophages – have the natural ability to inject their DNA into bacterial hosts through transduction 15 Transduction (madiated by phage) Microbe Library, American Society for Microbiology www.microbelibrary.org Lytic versus Lysogenic Generalized Transduction Generalized Transduction Transduction Specialized (Restricted): Transduction in which only certain donor genes can be transferred. Transduction (Restricted) Restricted Transduction (Lysogenic Phage) bio gal gal gal bio gal bio bio bio Transduction Significance – Common in Gram+ bacteria – Lysogenic (phage) conversion • e.g. Corynebacterium diptheriae toxin –Toxin derived from lysogenic phage Conjugation Definition: Gene transfer from a donor to a recipient by direct physical contact between cells Mating types in bacteria Donor F factor (Fertility factor) F (sex) pilus Recipient Lacks an F factor Donor Recipient Conjugation Significance Gram - bacteria Antibiotic resistance Gram + bacteria Production of adhesive material by donor cells Conjugation Conjugation: Sex or F Pilus Plasmids Plasmids Definition: Extrachromosomal genetic elements that are capable of autonomous replication (replicon) Plasmid Types: Congugative & Non-congugative Episome - a plasmid that can integrate into the chromosome Casmid – An integration of a plasmid and a bacteriophage Phenotypic effects Fertility (F factor) Bacteriocinogenic (or encoding some other toxins) Resistance (R factors) Structure of R Factors RTF Conjugative plasmid Transfer genes RTF R determinant Resistance genes R determinant Self-Transmissible R Plasmid Conjugation: F Plasmid Transfer Conjugation F+ and HFr cells F+ Hfr Integrated (Hfr) (High Frequency of Recombination) Hfr and F’ cells Hfr F’ Mechanism of Hfr x F- Crosses Hfr Hfr F- F- Hfr Hfr F- F- Mechanism of F’ x F- Crosses F’ F’ F- F’ F’ F- F’ F’ Transposable Genetic Elements Definition: Segments of DNA that are able to move from one location to another (across the genome or from one genome to another) Properties – “Random” movement • Transposase – Transposition may be accompanied by duplication Types of Transposable Genetic Elements Transposons (Tn)/ Insertion elements (IS) Definition: Elements that carry other genes in addition to those involved in transposition Nomenclature - Tn10, IS6110 Structure Composite Tns Importance Antibiotic resistance Epidemiology and evolutionary studies IS Resistance Gene(s) IS IS Resistance Gene(s) IS