Lecture 5—Jan 17th: Organisms in their Environment (BES 108D) PDF

1 Lecture 5—Jan 17th BES 108D Organisms in their environment By Dr. Benazir Alam Copyright © 2025 Pearson Canada, Inc. 27 - 1  2 Topic:1 Prokaryotes: Bacteria and Archaea Chapter: 27...

1 Lecture 5—Jan 17th BES 108D Organisms in their environment By Dr. Benazir Alam Copyright © 2025 Pearson Canada, Inc. 27 - 1  2 Topic:1 Prokaryotes: Bacteria and Archaea Chapter: 27 Copyright © 2025 Pearson Canada, Inc. 27 - 2  Think Clostridium species make spores Why do you think Clostridium difficile infections in hospitals are of great concern? Copyright © 2025 Pearson Canada, Inc. 27 - 3  4 Endospores Bacillus anthracis, the bacterium that causes the disease anthrax in livestock and humans, produces endospores, that can remain dormant in soil for decades and become reactive upon inhalation or ingestion. Copyright © 2025 Pearson Canada, Inc. 27 - 4  Cell surface structure: Flagella (Salmonella typhimurium) Bacterial flagella are long, whip-like appendages that enable bacteria to move through their environment, a process known as motility. Flagella are rotating in a helical manner Copyright © 2025 Pearson Canada, Inc. 27 - 5 Motility In a heterogeneous environment, many bacteria exhibit taxis, the ability to move toward or away from a stimulus. Most motile bacteria propel themselves by flagella scattered about the surface or concentrated at one or both ends of the cell Chemotaxis is the movement toward or away from a chemical stimulus. Positive: Towards Negative: Away from a nutrients, oxygen or light toxic substance Copyright © 2025 Pearson Canada, Inc. 27 - 6 Internal Organization and DNA Prokaryotic genomes have less DNA than eukaryotic genomes and are associated with relatively fewer proteins Most of the genome consists of a single circular chromosome The chromosome is not surrounded by a membrane; it is located in the nucleoid region Some species of bacteria also have smaller circular DNA molecules called plasmids Copyright © 2025 Pearson Canada, Inc. 27 - 7 A Prokaryotic Chromosome and Plasmids Identify an additional plasmid visible in this micrograph? Copyright © 2025 Pearson Canada, Inc. 27 - 8 Internal Organization and DNA (3 of 3) There are some differences between prokaryotes and eukaryotes in DNA replication, transcription, and translation Smaller size of ribosomes (that are involved in protein translation) in prokaryotes allows antibiotics such as erythromycin (binds 23S ribosomal subunit) and tetracyclin (binds 30S ribosomal subunit) to inhibit translation and prevent bacterial growth without harming eukaryotic cells. Copyright © 2025 Pearson Canada, Inc. 27 - 9 Reproduction Prokaryotes reproduce quickly by binary fission and offspring are generally identical. A single prokaryotic cell divides into 2 cells, which then divide into 4, 8, 16, and so on. Many can divide every 1–3 hours; and some species in 20 minutes under ideal conditions Copyright © 2025 Pearson Canada, Inc. 27 - 10 Rapid Reproduction and Mutation Mutation rates during binary fission are low, but because of rapid reproduction, mutations can accumulate rapidly in a population The high diversity that results from mutations and rapid reproduction allows for rapid evolution Copyright © 2025 Pearson Canada, Inc. 27 - 11  12 At this rate, a single prokaryotic cell could give rise to a colony outweighing Earth in only two days—Why does it not happen? ✓The cells eventually exhaust their nutrient supply ✓Poison themselves with metabolic wastes ✓Face competition from other microorganisms ✓Consumed by other organisms/predators. Copyright © 2025 Pearson Canada, Inc. 27 - 12  13 Key features of prokaryotic biology: ❑They are small ❑They reproduce by binary fission ❑They have short generation times ❑Rapid reproduction gives rise to high mutation rates Copyright © 2025 Pearson Canada, Inc. 27 - 13 Genetic Diversity of Prokaryotes Three factors contribute to this genetic diversity: – Rapid reproduction that leads to accumulation of Mutation – Genetic recombination Copyright © 2025 Pearson Canada, Inc. 27 - 14 Genetic Recombination Genetic recombination, combining of DNA from two sources, contributes to diversity Prokaryotic DNA from different individuals can be brought together by transformation, transduction, and conjugation Movement of genes among individuals from different species is called horizontal gene transfer and from a parent to an offspring is called vertical gene transfer such as a binary fission. Copyright © 2025 Pearson Canada, Inc. 27 - 15  16 Vertical vs horizontal gene transfer Gene transfer between organisms that are not Parent Gene transfer from Parent to offspring and offspring Binary fission Copyright © 2025 Pearson Canada, Inc. 27 - 16  Transformation ❑ Transformation is the process by which a competent bacterium takes up free-floating plasmid DNA or small pieces of fragmented chromosomal DNA present in the Plasmid DNA environment from a dead or lysed bacteria. ❑ Once taken up by a competent bacteria, plasmid DNA can replicate independently. However, for DNA fragments to be integrated into the bacterium’s chromosome, the incoming DNA must be similar (or Dead homologous) to a region of the bacterium's chromosome. or lysed bacteria ❑ Competence can be either naturally occurring (in species like Streptococcus pneumoniae, Bacillus subtilis) Chromosomal or induced in the lab (by artificially manipulating the Competent DNA bacterium’s environment, such as through heat shock or bacteria electroporation). Fragmented ❑ A harmless strain of Streptococcus pneumoniae can be chromosomal transformed into pneumonia-causing cells if the cells are DNA exposed to DNA from a pathogenic strain Copyright © 2025 Pearson Canada, Inc. 27 - 17  Bacteriophage DNA Transduction Bacterial DNA Bacteriophage Transduction is the movement of genes between bacteria by bacteriophage (viruses that infect bacteria) A bacteriophage infects a bacterium and during the infection cycle, the virus can accidentally incorporate pieces of the bacterium’s DNA into its viral genome. Bacteria When the virus infects another bacterium, it injects the donor bacterium's DNA into the new host, which can then integrate this DNA into its own genome. Bacteriophage containing bacterial genes Copyright © 2025 Pearson Canada, Inc. 27 - 18 that can further infect other bacteria  Conjugation Conjugation is the process by which genetic material is unidirectionally transferred between two bacteria directly through a physical connection called a pilus. Chromosomal DNA Plasmid DNA Recipient Mating bridge Donor Donor Recipient Pilus/Mating bridge Copyright © 2025 Pearson Canada, Inc. 27 - 19 Conjugation A donor cell attaches to a recipient by a pilus, pulls it closer, and transfers DNA usually involved in antibiotic resistance or the ability to use new metabolites. A piece of DNA called the F or fertility factor is required for the production of pili. Cells containing the F plasmid/segment of DNA in the chromosome function as DNA donors during conjugation. Cells without the F factor function as DNA recipients during conjugation The F factor is transferable during conjugation Copyright © 2025 Pearson Canada, Inc. 27 - 20 How F factor is transferred during conjugation in E. coli Rolling circle replication Copyright © 2025 Pearson Canada, Inc. 27 - 21 R Plasmid R plasmids may carry resistance genes to upto 10 antibiotics Antibiotics kill sensitive bacteria, but not bacteria with specific R plasmids Many R plasmids, like F plasmids, have genes that encode pili and enable DNA transfer from one bacterial cell to another by conjugation Via natural selection, the fraction of bacteria with R plasmid increases rapidly in a population exposed to antibiotics Resistance genes can spread within and among bacterial species by horizontal gene transfer. Copyright © 2025 Pearson Canada, Inc. 27 - 22  The Role of Oxygen in Metabolism Prokaryotic metabolism varies with respect to O2 – Obligate aerobes require O2 for cellular respiration – Obligate anaerobes are poisoned by O2 and use fermentation or anaerobic respiration (by using nitrate, NO3- ions or sulphate, SO42- ions to accept electrons at the “downhill” end of electron transport chains) to generate ATP. – Facultative anaerobes can survive with or without O2 because they can switch between aerobic respiration and anaerobic respiration/fermentation depending on the presence or absence of O2 Copyright © 2025 Pearson Canada, Inc. 27 - 23  Metabolic Cooperation: Biofilms ❑ Metabolic cooperation refers to the interaction between different prokaryotic organisms or within a single prokaryotic community, where the exchange of metabolic products benefits the involved species. E.g. biofilms ❑ A biofilm is a complex community of microorganisms, primarily bacteria, embedded in a self-produced extracellular matrix often containing polysaccharides and proteins that form a slime layer or capsule. Pseudomonas aeruginosa forming a biofilm ❑ Channels in the biofilm allow nutrients to reach cells in the interior and wastes to be expelled. P. aeruginosa can ❑ Biofilms are difficult to treat with antibiotics: cause serious infections of human a. because of the extracellular matrix i.e. the capsule or slime layer skin, urinary tract, and make the entry of antibiotics difficult. lungs that are difficult b. Bacteria in a biofilm often exist in a state of slowed growth or to treat with antibiotics dormancy. Slow-growing or dormant bacteria are less susceptible to the action of antibiotics, as these drugs are less effective against non-dividing cells. This allows bacteria deep within the biofilm to survive even in the presence of antibiotics. c. The extracellular matrix of biofilms also helps bacteria evade detection and destruction by the immune Copyright system. © 2025 Pearson Canada, Inc. 27 - 24 Exploring Bacterial Diversity Copyright © 2025 Pearson Canada, Inc. 27 - 25 Exploring Bacterial Diversity - Cyanobacteria These gram-negative photoautotrophs are the only prokaryotes with plantlike, oxygen-generating photosynthesis. Cyanobacteria Copyright © 2025 Pearson Canada, Inc. 27 - 26 Exploring Bacterial Diversity – Gram-Positive Bacteria, a source of antibiotics Gram-positive bacteria Streptomyces is the source of many antibiotics such as tetracycline and erythromycin Copyright © 2025 Pearson Canada, Inc. 27 - 27