Physiological analysis of lactobacillus rhamnosus VTT E‐97800

Abstract

PurposeThis paper aims to describe the physiological analysis of L. rhamnosus VTT E‐97800 and its adaptive response to osmotic stress induced by trehalose.Design/methodology/approachCells of L. rhamnosus E800 in the stationary phase of growth were subjected to osmotic stress induced by trehalose treatments. The effects of osmotic stress on the viability of the study strain were determined by conducting flow cytometric analysis with carboxyfluorescein diacetate (cFDA) and propidium iodide (PI) and by observing the corresponding cells growth on MRS agar plates. Osmotic‐induced changes of esterase activity and membrane integrity were monitored. Ability to extrude intracellular accumulated cF (additional vitality marker) was taken into consideration.FindingsThe fluorescence‐based approach gave additional insights on osmotic induced changes of cellular events, which could not be explicitly assessed by culture techniques. Trehalose treatments caused a transient membrane permeabilization as revealed by a gradual decrease in esterase activity (a measure of enzyme activity and thus of viability) with increase in trehalose molarity. However, culturability on MRS agar was not significantly affected. Membrane integrity was maintained and there was an improvement in the ability of cells to extrude intracellular accumulated cF.Originality/valueThe paper provides a comparative study of the conventional culture techniques and the flow cytometric viability assessment which showed that esterase activity cannot be relied on to ascertain the culturability and viability status of an organism.