Outer membrane vesicles (OMVs) have been identified in a wide range of bacteria, yet little is known of their biogenesis. It has been proposed that OMVs can act as long-range toxin delivery vectors and as a novel stress response. We have found that the formation of OMVs in the Gram-negative opportunistic pathogen
Serratia marcescens
is thermoregulated, with a significant amount of OMVs produced at 22 or 30°C and negligible quantities formed at 37°C under laboratory conditions. Inactivation of the synthesis of the enterobacterial common antigen (ECA) resulted in a hypervesiculation phenotype, supporting the hypothesis that OMVs are produced in response to stress. We demonstrate that the phenotype can be reversed to wild-type (WT) levels upon the loss of the Rcs phosphorelay response regulator RcsB, but not RcsA, suggesting a role for the Rcs phosphorelay in the production of OMVs. MS fingerprinting of the OMVs provided evidence of cargo selection within wild-type cells, suggesting a possible role for
Serratia
OMVs in toxin delivery. In addition, OMV-associated cargo proved toxic upon injection into the haemocoel of
Galleria mellonella
larvae. These experiments demonstrate that OMVs are the result of a regulated process in
Serratia
and suggest that OMVs could play a role in virulence.
Lyophilized cells of Bacillus popilliae were protected from moisture when suspended in pellets of tung oil polymer which were then coated with paraffin wax. The survival of the protected cells at various levels of relative humidity (RH) and under various storage conditions was determined. During 6 months of storage, moisture appeared to have little effect on survival of the cells when the RH level was 22% or less; but, at higher RH levels, survival declined upon storage. Viable cells were recovered when pellets were stored for 3 months at 33% RH, 2 months at 42% RH, 1 month at 50% RH, and 4 days in distilled water. Under field conditions, some cells survived at least 1 week of storage.
Lyophilized cells of
Bacillus popilliae
were protected from moisture when suspended in pellets of tung oil polymer which were then coated with paraffin wax. The survival of the protected cells at various levels of relative humidity (RH) and under various storage conditions was determined. During 6 months of storage, moisture appeared to have little effect on survival of the cells when the RH level was 22% or less; but, at higher RH levels, survival declined upon storage. Viable cells were recovered when pellets were stored for 3 months at 33% RH, 2 months at 42% RH, 1 month at 50% RH, and 4 days in distilled water. Under field conditions, some cells survived at least 1 week of storage.
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