Effects of La³⁺ on the competence of Escherichia coli as studied by microcalorimetry

Abstract

A series of microcalorimetric experiments were performed to investigate the effect of La³⁺ on the formation of the competent state of Escherichia coli HB101 by using a LKB-2277 BioActivity Monitor at 37°C. The thermogenic curves in the absence and in the presence of La³⁺ were obtained. Based on these curves, we calculated that the total heat effects (Q _T) and the maximal power (P _max) in the presence and absence of La³⁺. Our experiments indicate that the total heat effects in the presence of a low concentration of La³⁺ (≤ 100 µg/mL) are greater than those in the absence of La³⁺. Their trends are similar with respect to the increasing concentration of La³⁺. To the contrary, when the concentration of La³⁺ is greater than 100 µg/mL, the total heat effects decrease with the increasing concentration of La³⁺. Therefore, in the latter case, La³⁺ has inhibitory effects on the formation of competence. Our experimental results suggest that the La³⁺ ion in the environmental ecosystem can facilitate the formation of competence of E. coli HB101 and further stimulate the transfer of genetic materials between organisms.