Optimisation of initial cell concentration enhances freeze-drying tolerance of Pseudomonas chlororaphis.
The freeze-drying tolerance of Pseudomonas chlororaphis, an antifungal bacterium used as biocontrol agent was investigated. P. chlororaphis is freeze-drying sensitive and the viability drops more than 3 log units in the absence of protective freeze-drying medium. Of the freeze-drying media tested, lactose, sucrose, trehalose, glutamate, sucrose with glutamate, skimmed milk, and skimmed milk with trehalose, skimmed milk gave the lowest survival (0.6+/-0.2%) and sucrose the highest (6.4+/-1.2%). Cellular accumulation of sucrose from the freeze-drying medium and the protective effect of sucrose were dependent on sucrose concentration. The effect of initial cell concentration, from 1 x 10(7) to 5 x 10(10) CFU/ml, on survival after freeze-drying was studied for carbon starved cells with sucrose as freeze-drying medium. The highest freeze-drying survival values, 15-25%, were obtained for initial cell concentrations between 1 x 10(9) and 1 x 10(10) CFU/ml. For cell concentrations outside this window more than 10 times lower survival values were observed. P. chlororaphis was cultivated to induce stress response that could confer protection against freeze-drying inactivation. Carbon starvation and, to a lesser extent, heat treatment enhanced freeze-drying tolerance. By combining optimal cell concentration, optimal sucrose concentration and carbon starvation the survival after freeze-drying was 26+/-6%.
Palmfeldt
Johan
J
Department of Applied Microbiology, University of Lund, P.O. Box 124, SE-22 100 Lund, Sweden.
Rådström
Peter
P
Hahn-Hägerdal
Bärbel
B
D000818:Animals; D002244:Carbon / Q000378:metabolism; D003451:Cryoprotective Agents; D005612:Freeze Drying / Q000379:methods*; D018698:Glutamic Acid; D006358:Hot Temperature; D007785:Lactose; D008892:Milk; D011549:Pseudomonas / Q000254:growth & development* / Q000378:metabolism; D013395:Sucrose; D014199:Trehalose
D003451:Cryoprotective Agents; D018698:Glutamic Acid; D013395:Sucrose; D002244:Carbon; D014199:Trehalose; D007785:Lactose