Bacterial reproduction & metabolism.pptx

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1. Bacterial reproduction & metabolism

2. Bacterial Cell Division Bacteria divide by cell division, i.e . by binary fission, cell division commences when bacterial cell reaches critical mass in its cellular constituents . Nuclear division followed by cytoplasmic division ™ Nuclear division: two strands of bacterial DNA separated and replicate to form new complementary strands. Two identical molecules of ds DNA are formed

3. ™ Cytoplasmic division: transverse septum grows across cell from cell membrane, cell wall materials deposited, two daughter cells get separated ™In few bacteria, daughter cells may remain partially attached even after cell division; so bacterial cells arranged in pair or in chain (e.g. streptococci) or in clusters (e.g. staphylococci).

4. Rate of Multiplication in Bacteria Generation time: time required for bacterium to give rise to two daughter cells under optimum condition Generation time for different bacteria: ™ Escherichia coli & most of other pathogenic bacteria : 20 min ™ Mycobacterium tuberculosis: 10–15 hours ™ Mycobacterium leprae : 12–13 days. Bacteria grow so rapidly, single bacterium can theoretically give rise to 1021 daughter cells in 24 hrs, does not happen in reality Bacterial multiplication arrested after few cell divisions due to exhaustion of nutrients & accumulation of toxic products

5. Bacterial Count Bacterial count expressed in terms of total count & viable count ™ Total count: total number of bacteria ( live or dead) in specimen, by counting bacteria under microscope using counting chamber ™ Viable count: number of living ( viable) cells in given specimen, obtained by technique called as pour plate method

6. Bacterial Growth Curve When bacterium is inoculated into suitable liquid culture medium & incubated , its growth follows definite course. When bacterial count of such culture is determined at different intervals and plotted in relation to time , bacterial growth curve is obtained comprising of four phases

7. Bacterial growth curve

8. Bacterial metabolism Process by which microbe obtains energy & nutrients (e.g. carbon) for its survival & reproduction Bacterial metabolism based on three principles: 1 . How bacteria obtain carbon for synthesizing cell mass ? „ Autotrophs : synthesize all their organic compounds by using atmospheric CO2 as their sole source of carbon „ Heterotrophs : They use reduced, preformed organic molecules as carbon sources

9. 2. How bacteria obtain reducing electrons used either in energy conservation or in biosynthetic reactions ? „ Lithotrophs : obtain reducing electrons from inorganic compounds „ Organotrophs : obtain reducing electrons from organic compounds. 3 . How bacteria obtain energy for living and growing? „ Chemotrophs : obtain energy from external chemical compounds „ Phototrophs : obtain energy from light

10. Chemoorganoheterotrophs group: Most of pathogenic bacteria Obtain energy , carbon, & reducing equivalents for biosynthetic reactions from organic compounds, e.g. Escherichia coli