In bacterial population kinetics, “generation time” refers to what, and how is it commonly calculated from growth data?

Introduction / Context:
Generation time is a core metric of microbial growth, allowing comparisons across media, temperatures, and strains. It connects directly to doubling time during exponential growth and underlies calculations of specific growth rate.

Given Data / Assumptions:

• We consider the exponential phase where growth is balanced and rate is constant.
• Number of generations (n) over an interval (t) can be determined from counts or OD.
• Population doubling is the operational definition of one generation.

Concept / Approach:
By definition, generation time (g) is the time needed for the population to double. If a culture undergoes n doublings in time t, then g = t / n. Specific growth rate mu relates as mu = ln(2) / g, and the growth rate (generations per unit time) is 1 / g. These relationships are the foundation for plotting and interpreting growth curves.

Step-by-Step Solution:
State meaning: one generation equals one doubling. Use data to compute n (for example, from CFU or OD changes). Apply formula: g = t / n during exponential growth. Thus, both the definition and the formula are correct.

Verification / Alternative check:
When OD increases fourfold, that is two generations (since 2^2 = 4). If this took 40 minutes, g = 40/2 = 20 minutes, matching independent calculations using mu.

Why Other Options Are Wrong:

• Initial adjustment: That describes lag phase, not generation time.

Common Pitfalls:
Using non-exponential data (late log or early stationary) to compute g; this violates the assumption of constant rate.

Final Answer:
both (a) and (c).