Prokaryotic Growth, Metabolism, and Adaptation (2B) Practice Test

A researcher grows a neutrophilic bacterium in buffered media at 37°C with identical glucose and nitrogen sources but different pH values. After 6 hours, OD600 is measured.

Which condition best supports the observed growth pattern?

Table 1. Growth after 6 hours (pH vs OD600)

• pH 5.5: 0.10
• pH 6.5: 0.55
• pH 7.0: 0.85
• pH 8.0: 0.40

A gene expression study evaluates a knockout of ackA (acetate kinase), which converts acetyl phosphate to acetate while generating ATP (substrate-level phosphorylation). Wild-type and knockout strains are grown anaerobically at 37°C, pH 7.0 on 20 mM glucose. After 1 hour, extracellular acetate and culture ATP are measured.

Which conclusion is most supported by the experimental results?

Table 1. Measurements at 1 hour

• Wild-type: acetate 6.0 mM; ATP 2.2 mM
• $\Delta ackA$: acetate 1.5 mM; ATP 1.4 mM
• Wild-type + empty vector: acetate 5.8 mM; ATP 2.1 mM
• $\Delta ackA$ + complemented ackA: acetate 5.5 mM; ATP 2.0 mM