Bacterial behavior — term for swimming toward an attractant In microbial ecology, what is the correct term for directed movement of bacteria toward a higher concentration of a beneficial chemical attractant?

Introduction / Context:
Chemotaxis enables bacteria to sense chemical gradients and bias their random walks to locate nutrients or escape toxins. It is central to survival in changing environments and is mediated by chemoreceptors, signal transduction pathways, and flagellar motor control. Terms differentiate movement toward attractants versus away from repellents.

Given Data / Assumptions:

• Attractant concentration increases along the path of movement.
• Bacteria modulate “run” and “tumble” frequencies by altering flagellar rotation.
• Alternative taxis behaviors exist (photo-, magneto-, aero-), but the prompt specifies chemicals.

Concept / Approach:
Movement toward a desirable chemical gradient is defined as positive chemotaxis; movement away from harmful substances is negative chemotaxis. Phototaxis responds to light, magnetotaxis to magnetic fields, and aerotaxis to oxygen gradients. Therefore, the correct term directly follows from the sign of the response to a chemical cue.

Step-by-Step Solution:
Identify the stimulus type: chemical (not light, magnetic field, or oxygen specifically).Determine the direction: toward higher attractant concentration.Select “positive chemotaxis.”

Verification / Alternative check:
Capillary assays and microfluidic gradient chambers demonstrate accumulation of motile bacteria near attractants, confirming positive chemotaxis behavior experimentally.

Why Other Options Are Wrong:

• B: Negative chemotaxis is movement away from a chemical, not toward it.
• C: Phototaxis refers to light stimuli, not chemicals.
• D: Magnetotaxis aligns with geomagnetic fields via magnetosomes.
• E: Aerotaxis is movement along oxygen gradients, a subset distinct from generic chemotaxis to other chemicals.

Common Pitfalls:
Equating any directional movement with chemotaxis; the stimulus modality must match the term used.

Final Answer:
Positive chemotaxis