New probiotic candidates for mussels

In New Zealand the culture of Greenshell mussels (Perna canaliculus) has an annual value of US$145 million, 65% of the total value of aquaculture products. This means it is big business and there has been a relatively recent switch from relying on natural settlement of the mussels to hatchery production. However, as with all intensive farming systems pathogens have taken their toll, especially at the larval stage, and from isolation procedures V. splendidus and V. coralliilyticus/neptunius have been found to be the primary causative agents. In the past antibiotics were used to treat disease outbreaks but due to the risks now associated with them, probiotics have been the preferred method of treatment. The authors mention that previously, two probiotics have been isolated and put to use with marked improvements in larval survival, but that few field studies have been conducted under industry conditions. Therefore, they aim to study the effects of two novel probiotic strains under such commercial conditions.

P. canaliculus larvae were inoculated with the probiotics Alteromonas macleodii 0444 and Neptunomonas sp. 0536 everyday from the day of hatching. On the third day larvae were challenged with pathogenic Vibrio sp. DO1 and V. splendidus bacteria. Pathogen doses were of concentrations previously known to cause infection and a higher concentration condition was also included to determine to extent of the benefit afforded by the probiotics. Samples were also taken daily from the rearing water and the larval population to examine the levels of probiotic and pathogenic bacteria within each.

Results showed that both probiotics increased larval survival when administered before the pathogen challenge. Also, both were effective at the lower and higher concentrations of pathogens, as 35.8 % survival increased to 66.1% at the minimum concentration and at the higher concentration survival went from 13.5% to 50.1% (average values). This is evidence that these probiotics can provide larvae with protection against pathogens during the early larval stage (when most mortality occurs) and when added to the results from control larvae and those only treated with probiotics we can conclude that they also benefit the general health and survival of larvae, as the control survival of 67.4% increased to 78.5% when probiotics were added alone. These results were reproduced in all but one case (0444 vs. V. splendidus) which is encouraging; but perhaps most exciting was the finding that Neptunomonas sp. 0536 seemed to not only inhibit colonisation by the vibrios tested, but also by many naturally occurring vibrio strains. This suggests potential wider applications for this relatively newly discovered genus and demonstrates the need to find new and more effective probiotic bacteria, as they are obviously out there.

I was quite impressed by this paper as it seemed comprehensive and well thought out in all aspects. The authors obviously recognise the need for new strains of probiotics to combat the ever changing strains of pathogen present in the environment; not only to save costs during manufacture but also to reduce the harmful bacteria present in seafood which could cause human illness, as many vibrios do.

A review of: Kesarcodi-Watson, A., Kaspar, H., Lategan, M. J. and Gibson, L. (2010) Alteromonas macleodii 0444 and Neptunomonas sp. 0536, two novel probiotics for hatchery-reared Greenshell™ mussel larvae, Perna canaliculus. Aquaculture, 309, 49-55