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 Relation with non-living environment Bacteria plays roles as:  Production Producers  Degradation Degeneraters Consumers

Relation with other living organisms (Symbiosis) Relation with other living organisms (Symbiosis) Mutualism (Transient and resident microflora) Commensalism Parasitism

Relation with each other (Symbiosis) Indifference Competition Antagonism Synergism

Bacterial traits changes are due to: 1. Changes in environmental conditions 2. Changes in the genetic codes Bacterial Genetics (Studying heritage variations in bacterial traits)

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)

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. Transformation

DNA-Mediated Transformation

Intermicrobial exchanges by vectors

15 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

Transduction (madiated by phage)

Microbe Library, American Society for Microbiology

Lytic versus Lysogenic

Generalized Transduction

Transduction Specialized (Restricted): Transduction in which only certain donor genes can be transferred.

Transduction (Restricted)

Restricted Transduction (Lysogenic Phage) gal bio gal bio gal bio gal bio gal

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 Donor Recipient  Recipient Lacks an F factor

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 Tn 9 Tn 21 Tn 10 Tn 8 RTF R determinant  Resistance genes

Self-Transmissible R Plasmid

Conjugation: F Plasmid Transfer

Conjugation

F + and HFr cells Integrated (Hfr) (High Frequency of Recombination) F+F+ Hfr

Hfr and F’ cells Hfr F’

Mechanism of Hfr x F - Crosses HfrF-F- F-F- F-F- F-F-

Mechanism of F’ x F - Crosses 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 Resistance Gene(s)