Volume recovery, surface properties and membrane integrity of Lactobacillus delbrueckii subsp bulgaricus dehydrated in the presence of trehalose or sucrose

TYMCZYSZYN E.; M. DEL ROSARIO DÍAZ; A. GÓMEZ-ZAVAGLIA; DISALVO E. A.

Rosario – Santa Fé

Congreso; XXXV REUNION ANUAL DE LA SOCIEDAD ARGENTINA DE BIOFÍSICA; 2006

Sociedad Argentina de Biofísica

In this work, dehydration of L. delbruecckii subsp bulgaricus has been evaluated and the effect of sucrose and trehalose as thermoprotectants has been investigated. The dehydration of L. bulgaricus has been analyzed at different levels. From one side, the lag time has been determined as a measure of the global damage produced during dehydration. On the other hand, the surface properties, cellular volume and membrane integrity have been investigated to get a deeper insight of specific targets of damage. Both trehalose and sucrose preserve microorganisms from damage, as measured by the lag time. This indicates that trehalose and sucrose considerably decreased the global damage produced by dehydration. The surface properties were analyzed by measuring: a) the z potential, b) cell volume, by light scattering and the haematocrit method, and c) membrane integrity with specific fluorescent probes (SYTO 9 and PI, and incorporation of DPH –fluorescence anisotropy-). Both trehalose and sucrose maintain the z potential and the cell volume close to the control (non-dried) after 10, 20 and 30 minutes dehydration. However, they could maintain the membrane integrity only when cells were dehydrated for short times (10 minutes). For larger times of dehydration, the membrane integrity could not be preserved (results obtained by fluorescence anisotropy and with SYTO 9 and PI were similar to the ones obtained for cells dehydrated in the absence of thermoprotectants). In summary, when the membrane damage is associated with maintenance of the z potential and the cellular volume, the cell is able to recover and grow. This occurs when trehalose and sucrose are used as thermoprotectants. On the contrary, the membrane damage produced by dehydration becomes irreversible only if it occurs together with a decrease in the absolute value of the z potential and with decay in the cellular volume. This happens when microorganisms are dehydrated in the absence of thermoprotectants. Hence, it can be concluded that the membrane damage is not a conclusive parameter to predict the ability to grow after dehydration. There are other structural parameters to be taken into account: z potential and cellular volume. This is the first time in which these two supramolecular parameters are correlated with cell viability, independently on the membrane damage. This result is of great importance because the use of kits determining viability based on the membrane integrity may be a source of false negative results.