Bacteria reproduce through binary fission where they divide into two daughter cells after reaching a critical mass, involving nuclear and cytoplasmic division. Their rate of multiplication varies among species, with generation times ranging from 20 minutes for E. coli to 12-13 days for Mycobacterium leprae, although growth is eventually limited by nutrient depletion and toxic accumulation. Bacterial metabolism includes how they obtain carbon, reducing electrons, and energy, categorizing them into autotrophs, heterotrophs, lithotrophs, organotrophs, chemotrophs, and phototrophs.

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
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• 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
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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