There is a constant research into new feed substitutes in the aquaculture industry in order to find solutions for diseases caused by microbes, and the rapid development of antibiotic resistance makes it challenging to find new substances to control the health of a stock. Many marine bacteria produce active metabolites that represent new promising sources for antimicrobial compounds, and species of the genera Pseudoalteromonas, Phaeobacter, Ruegeria and Vibrio are in particular of interest for sources of probiotics in aquaculture. However, there is a lack of understanding how the bioactive compounds could affect the eukaryotic host organisms, and the toxicity to the animals needs to be assessed before they can be considered as useful treatments and feed substitutes.
This study has examined the effects of bacteria and their bioactive compounds (see Table) on two model organisms – Artemia sp. and Caenorhabditis elegans. The authors analysed examined several bacterial strains, among which were V. coralliilyticus and E. coli that were used as positive and negative killing control (respectively). Live bacterial cultures were added to Artemia nauplii and C. elegans, and only Artemia nauplii were exposed to the pure compounds additionally. Results showed that on or both model organisms showed reduced survival in the presence of strains from Pseudoalteromonas sp., species of the families Photobacteriaceaea and Vibrionaceaea and of the class Actinobacter, however in contrast, the bacterial strains of the Roseobacter clade, producing broad-spectrum antibiotics TDA, generally had no negative effect on the organisms, which confirms their suitability as sources for probiotics in aquaculture.
In my opinion, this study contributed to better understanding of the different antimicrobial compounds produced by bacteria and their effects on eukaryotic organisms. The authors assessed the effects of different compounds produced by different strains very neatly, and the results give very important insights into the toxicity of the compounds on model organisms. The crustacean tested here could be an important indicator for the effects of the compounds on other commercially important crustacean farmed in the aquaculture industry. However, since some differences between the nematode and the crustaceans were found, it would be important to assess the influences of these compounds to other farmed animals in different taxonomic groups such as fish or shellfish before using these antimicrobial compounds safely. Moreover, studies should be conducted to test the interactions of the strains with the host organisms in general, so that the metabolites could be identified as the cause of death with a higher certainty.
Neu et al. (2014). Toxicity of Bioactive and Probiotic Marine Bacteria and Their Secondary Metabolites in Artemia sp. and Caenorhabditis elegans as Eukaryotic Model Organisms. Applied and Environmental Microbiology , Vol. 80(1), pp. 146-153