Poster: Salinity

Abs # 158: Effect of Salinity on the Uptake of Choline by Aphanothece halophytica

Presenter:	Incharoensakdi, Aran , iaran@sc.chula.ac.th
Authors	Incharoensakdi, Aran  (A)   Karnchanatat, Aphichart  (A)
Affiliations:	(A): Department of Biochemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand

The uptake of [¹⁴C]choline by a suspension of exponential-phase Aphanothece halophytica under various conditions has been studied. Salt stress was found to enhance the uptake of choline. The kinetics of choline transport followed the Michaelis-Menten relationship with apparent Km values of 272 and 286 mM, maximum rates of transport (Vmax) of 18 and 37 nmol/min/mg protein for unstressed and salt-stressed cells, respectively. Choline uptake under salt stress was significantly reduced in chloramphenicol-treated cells suggesting that the activation by salt stress occurred via an inducible transport system. This was corroborated by the existence of the periplasmic choline binding protein, whose content was higher in cells grown under salt- stress condition. Exogenously provided choline significantly increased the growth rate of cells grown under salt stress, although less efficiently than glycine betaine. The presence of 1 mM choline in the growth medium conferred tolerance to high salinity on A. halophytica with the maintenance of high growth up to 1.5 M NaCl. The uptake of choline was Na⁺-dependent, sensitive to various metabolic inhibitors as well as thiol-reactive agents. The results of competition studies suggested that N-methyl on one end of molecule and on the other end either an aldehyde, an alcohol or a neutral group were important features for substrate recognition.