Fig. 5.

Sensitivity of P. putida F1 to nicotinic acid and cytosine measured by quantitative capillary assays. (a) Chemotactic responses to various concentrations of nicotinic acid compared to the response to 50 mM cytosine (the previously determined peak attractant concentration; Liu et al., 2009). Response to the positive control attractant 0.2 % Casamino acids (CAA) is also shown. The mean number of cells that accumulated in capillaries containing buffer only was subtracted from each dataset (590±140 cells). (b) Response to 50 mM nicotinic acid (attractant in the capillary) in competition capillary assays in which 50 mM cytosine (competitor) was present or absent in both the capillary and cell suspension as indicated. Cultures were grown in MSB containing 5 mM nicotinic acid and results represent the mean±sem of at least three independent experiments (nine or more capillaries in total), except the cytosine data in (a) (two independent experiments, six capillaries in total).