Microbial growth analysis — A standard bacterial growth curve is most clearly obtained by plotting which variable against time?

Introduction:
The classic bacterial growth curve exhibits lag, exponential, stationary, and death phases. Representing data on appropriate axes is crucial for interpreting kinetics and estimating parameters such as specific growth rate.

Given Data / Assumptions:

• Well-mixed culture with periodic sampling.
• Cell counts or OD proportional to cell number within a usable range.
• Focus on visualizing exponential growth as a straight line.

Concept / Approach:
Plotting log(N) versus time linearizes exponential growth (N = N0 * exp(mu * t)), producing a straight line of slope mu / ln(10) on a base-10 semilog plot. This makes phase boundaries and rate estimation clearer than linear plots of N vs time.

Step-by-Step Solution:
1) Collect N(t) via plate counts or convert OD to cell numbers.2) Compute log10(N) at each time point.3) Plot log10(N) vs t; the exponential region is linear.4) Determine mu from slope: mu = slope * ln(10).

Verification / Alternative check:
Cross-validate with a linear plot of ln(N) vs time (natural log), which should also be linear in the exponential region with slope mu.

Why Other Options Are Wrong:

• (a) N vs time compresses the early exponential region; slope is not constant.
• (b) Spores are not the primary metric in standard vegetative growth curves.
• (d) Surviving cells vs time emphasizes death kinetics, not growth.
• (e) OD^2 lacks a general kinetic basis.

Common Pitfalls:
Using OD beyond linear range; failing to account for lag; mixing base-10 and natural logs inconsistently.

Final Answer:
Log of the number of cells versus time (semilog plot).