Lecture 4 Dr. Dalia M. Mohsen Prof. of Microbiology

Reproduction in Prokaryotes Reproduction in Prokaryotes Types of reproduction are -  Binary fission (Bacteria)  Budding (yeasts)  Conidiospores (moulds and yeasts)  Fragmentation of filaments (molds) Dr. Dalia M. Mohsen Prof. of Microbiology

Binary Fission

Dr. Dalia M. Mohsen Prof. of Microbiology Budding Seen in yeast cells, and few bacterial species

Dr. Dalia M. Mohsen Prof. of Microbiology Conidiospores Produce chains of Conidiospores carried externally at the tip of the filaments

Dr. Dalia M. Mohsen Prof. of Microbiology Generation time Time required for the cell to divide (and its population to double. Depends on – Type of bacteria – Environmental conditions, like temperature Average generation time is 1 to 3 hrs. – Can vary from 20 min to 24 hrs

Dr. Dalia M. Mohsen Prof. of Microbiology Phases of Growth 4 Phases 4 Phases 1. Lag Phase 2. Log Phase 3. Stationary Phase 4. Death Phase

Dr. Dalia M. Mohsen Prof. of Microbiology Period of little or no cell division Bacteria are first introduced into an environment or media Bacteria are “checking out” their surroundings Undergo intense metabolic activity, synthesis of enzymes and various molecules There is increase in cells sizes but no increase in the cells number Last for few minutes to hours or several days

Dr. Dalia M. Mohsen Prof. of Microbiology Log Phase Log Phase Rapid cell growth rate (exponential growth) Cellular reproduction is most active population doubles every generation time Generation time is constant – on graph is seen as a straight line microbes are sensitive to adverse conditions – antibiotics – anti-microbial agents – Elevated temperature – Starvation – Change in pH

Dr. Dalia M. Mohsen Prof. of Microbiology Stationary Phase Growth rate slows, the number of microbial death balances the number of new cells produced. Death rate = growth rate Cells begin to encounter environmental stress – lack of nutrients – lack of water – not enough space – metabolic wastes – oxygen – pH Endospores would form now at the end of this stage

Dr. Dalia M. Mohsen Prof. of Microbiology Death Phase Death Phase

Dr. Dalia M. Mohsen Prof. of Microbiology

Enumeration of Bacteria Enumeration of Bacteria

Dr. Dalia M. Mohsen Prof. of Microbiology Estimation of microbial counts by indirect method – Turbidity – Metabolic activity – Dry weight

Dr. Dalia M. Mohsen Prof. of Microbiology Perform serial dilutions of a sample Direct Measurements of Microbial Growth

Dr. Dalia M. Mohsen Prof. of Microbiology Inoculate Petri plates from serial dilutions Plate Count Figure 6.16

Dr. Dalia M. Mohsen Prof. of Microbiology After incubation, count colonies on plates that have colonies (CFUs) Plate Count

Dr. Dalia M. Mohsen Prof. of Microbiology Pour and spread plate method

Dr. Dalia M. Mohsen Prof. of Microbiology Filtration

Dr. Dalia M. Mohsen Prof. of Microbiology Multiple tube MPN test Count positive tubes and compare to statistical MPN table. Figure 6.18b Most probable number method

Dr. Dalia M. Mohsen Prof. of Microbiology Direct Microscopic Count Figure 6.19

Dr. Dalia M. Mohsen Prof. of Microbiology Turbidity Estimating Bacterial Numbers by Indirect Methods

Dr. Dalia M. Mohsen Prof. of Microbiology Metabolic activity – amount of certain metabolic product is in direct proportion with the number of bacteria. Ex. – an acid or CO 2 Dry weight – good method for measuring filamentous organisms. Ex. - Fungus is removed from medium – extraneous material removed – dried in a desiccator - weighed

Dr. Dalia M. Mohsen Prof. of Microbiology