Evaluation of candidate probiotic strains for gilthead sea bream larvae (Sparus aurata) using an in vivo approach.

AIMS: The aim of this study was to evaluate the effect of six bacterial strains on gilthead sea bream larvae (Sparus aurata). METHODS AND RESULTS: Six bacterial strains isolated from well-performing live food cultures were identified by sequencing fragments of their 16s rDNA genome to the genus level as Cytophaga sp., Roseobacter sp., Ruergeria sp., Paracoccus sp., Aeromonas sp. and Shewanella sp. Survival rates of gilthead sea bream larvae transferred to seawater added these bacterial strains at concentrations of 6 +/- 0.3 x 10(5) bacteria ml(-1) were similar to those of larvae transferred to sterilized seawater and showed an average of 86% at 9 days after hatching, whereas, survival rates of larvae transferred to filtered seawater were lower (P < 0.05), and showed an average of 39%, 9 days after hatching. CONCLUSION: Several bacterial strains isolated from well-performing live food cultures showed a positive effect for sea bream larvae when compared with filtered seawater. SIGNIFICANCE AND IMPACT OF THE STUDY: The approach used in this study could be applied as an in vivo evaluation method of candidate probiotic strains used in the rearing of marine fish larvae.

Abundance, biomass and viability of bacteria in wastewaters: impact of treatment in horizontal subsurface flow constructed wetlands.

The aims of this project were to assess bacterial populations (abundance, biomass and viability) in the influents and effluents of four constructed wetlands, and to analyse the effect of such biological treatment on these bacterial characteristics. Using the BacLight probe it was possible to determine the total abundance, the proportion of intact vs. damaged cells, and the lengths, widths and biovolumes, of bacteria in each of the samples. The reduction in bacterial concentration was higher (67%) in the wetland used for secondary treatment than in those used for tertiary treatment (15-39%). The proportion of damaged cells was higher in the influent (i.e. settled sewage) of the wetland used for secondary treatment (78%) than in the influents of those wetlands used for tertiary treatment (45-70%). This suggested that the majority of bacteria in the settled sewage were dead or damaged, and that these were removed from the wastewaters more effectively than were undamaged cells during conventional secondary treatment (in this case, using rotating biological contactors or RBCs). In each wetland, the proportion of damaged cells was higher in the influent than in the effluent, suggesting that, as with RBCs, damaged bacteria were removed more effectively within the wetland than undamaged bacteria. The majority of bacteria leaving the constructed wetlands used for tertiary treatment, and 50% of those leaving the secondary treatment wetland, were physically intact and therefore probably viable. Although there was a decrease in the abundance of total bacteria with treatment, bacterial biomass did not necessarily decrease with the treatment.

Estimation of the viability of Vibrio cholerae 0139 by assessing cell membrane integrity.

Changes in the viability of Vibrio cholerae 0139 Bengal, estimated by cellular membrane integrity, in batch culture over 35 days, were investigated. Data indicated an initial period of rapid growth with up to 30% of bacterial mortality, followed by a period of slower growth, lower culturability but higher viability, from day 7 onwards. The size of viable bacteria significantly decreased during the incubation time, whilst the size of dead bacteria showed a less pronounced decrease. V. cholerae 0139 changed from a straight or curved rod shape to a spherical shape. This study shows that BacLight dyes are a fast and useful tool to examine health risk-associated bacteria, providing useful information about their viability and concentration.