Rates of Drying and Survival of Rhizobium meliloti Strains During Storage at Different Relative Humidities

Abstract

An investigation was made of the survival of six strains of Rhizobium meliloti filtered on membrane filters and held in atmospheres of controlled relative humidities (RH) of from 0 to 100% at 30°C in the presence of air. The rate of water loss in the desiccator was determined by the humidity-controlling solution used. Drying was accelerated by a mild evacuation of the desiccator during the drying step. Survival rates of R. meliloti strains were much higher after slow drying to 0% RH than immediately after rapid drying. Fast drying (drying period less than 3.4 h) was shown to adversely affect the tolerance to storage at all RH values tested (no survival after 2 to 5 days of storage). When survival during storage was measurable (after slow drying), the optimum RH values for storage were 43% for strains A145 and Wu498, 22 to 43% for strains RCR2011, Wu499, and Arl6, and 83% for strain RCR2004. The most favorable drying periods were 8, 9.2, 14.2, and 50.1 h for the subsequent storage of strain RCR2011 at RH values of 0, 22, 43, and 83%, respectively. The damaging effects of rapid drying on the tolerance of strain RCR2011 to storage at different RH values could be prevented either by rehydration and subsequent slow redrying or incomplete rapid drying followed by slow drying. It is suggested that R. meliloti strains are susceptible to desiccation stresses. However, the quantitative differences among strains appear to be large enough to permit selection with regard to tolerance to desiccation and storage in dried states. survival of semidried microorganisms. Can.

Factors affecting the survival ofBradyrhizobiumapplied in liquid cultures to soya bean [Glycine max(L.) Merr.] seeds

“…To my knowledge, this is the first report of the effects of RH on survival of rhizobia on legume seeds. In spite of the reports by Mary et al (1985Mary et al ( , 1994, the magnitude of the effects reported here was not anticipated. Apparently, hydration of the dry seed coat results in a much more favourable environment for the applied bacteria.…”

“…The most comprehensive survey involved only analysis of cell damage, not survival (Bushby and Marshall 1977b). Other reports indicate substantial differences in survival among strains of B. japonicum and Sinorhizobium meliloti applied to membrane filters (Mary et al 1985(Mary et al , 1994. It should be possible to significantly improve survival of inoculant bacteria on soya bean seeds just by selecting strains for tolerance to desiccation.…”

“…Survival of B. japonicum on glass beads was about the same at 0% RH vs 75% RH (Cliquet and Catroux 1994). In contrast, Mary et al (1985Mary et al ( , 1994 have reported substantial positive effects of increased RH on survival of rhizobia on membrane filters (composition not specified), although discerning quantitative differences is difficult because of a graphical presentation of results.…”

“…The studies with salt addition to the medium were conducted without humidity control and over a period spanning summer into winter months. It was noted that there were very large declines in survival over time in spite of similar initial CFU and trehalose levels ( (Cliquet and Catroux 1994;Mary et al 1985Mary et al , 1986Mary et al , 1994, the seasonal changes were suspected of being because of seasonal lowering of laboratory RH. Although laboratory RH in the winter months was not accurately measured, it was definitely below 25% and probably below 20%, based on comparative survival results.…”

Production and survival during storage of spray‐dried Bradyrhizobium japonicum cell concentrates

“…Experiments on the effects of RHs on survival during storage showed that the driest environments led to the greatest survival rates. These results confirm previous works (Mary et al 1985;Mugnier and Jung 1985;Mary et al 1986). The harmful effects of temperature on survival of Rhizobiaceae in the dried state currently described in the literature (Kremer and Peterson 1983;Juwarkar and Rewari 1988;Pesenti-Barili et al 1991) were also observed in this study although satisfactory survival rates were obtained during storage at 3% RH.…”