Effects of 2,4-dichlorophenoxyacetic acid on Rhizobium sp. membrane fluidity.

The effects of 1 mM 2,4-Dichlorophenoxyacetic acid on Rhizobium sp. in pure culture was studied. In a previous work it was demonstrated that this herbicide produces an alteration on the saturated to unsaturated phospholipid acyl chains ratio. In the present paper, it was found that this alteration produces a modification on the membrane fluidity in bacteria that had achieved the stationary phase. The same results were obtained when determinations were done in liposomes from sonicated lipids of treated bacteria, indicating that changes in phospholipid acyl chains may be the main cause of membrane fluidity alteration. In addition, it was determined that leucine transport as well as Ca(++)-ATPase activity (a membrane enzyme) was affected under the experimental conditions.