Image: Michele Jo via Wikimedia Commons
The brine shrimp, Artemia salina, is a small crustacean, about one and a half centimetres long, with three eyes and eleven pairs of legs. The species is an important feed for aquaculture fish. With the increase in fish farming, the demand for brine shrimp as fish feed is growing.
Large scale shrimp cultivation, however, increases the risk of infection from Vibrio parahaemolyticus. This bacterium causes vibriosis, an acute pancreatic necrosis disease, leading to large scale shrimp mortality. Moreover, the infection can be transmitted from shrimps to humans.
At present, to reduce Vibrio infection, antibiotics are used. This poses environmental risks.
Abigail Fernandes and her mentor, Renitta Jobby, from the Amity University, Mumbai decided to try using probiotic lactic acid bacteria for reducing Vibrio infection. Probiotic bacteria are known to protect against disease and to promote growth. This, of course, is dependent on the probiotic strain used and the type of metabolites produced by them. The results need to be statistically analysed. The duo collaborated with other researchers in Amity itself as well as th NMIMS University, Mumbai, Municipal Corporation of Greater Mumbai, Dadar, and Goa University, to test their hypothesis.
The researchers tested five probiotic bacterial strains in different concentrations on brine shrimp and then challenged the shrimp with Vibrio parahaemolyticus.
Shrimps that were exposed to the probiotic strains, Limosilactobacillus fermentum or Lactiplantibacillus plantarum, survived better when they were also exposed to Vibrio, though all five strains seemed to work.
Interestingly, the survival of shrimps exposed to these two probiotic bacteria was marginally lower in the absence of Vibrio.
Would it be better if the shrimps were treated earlier when they are in cyst form? The researchers checked.
Brine shrimp cysts exposed to Vibrio did not hatch and develop further. But when the cysts were treated with the five probiotic strains, there was no statistically significant change in the hatching rate of the cysts compared to normal development of cysts.
Would pre-treating brine shrimp cysts with probiotics provide immunity against Vibrio infection?
The emergence and survival rate of the pre-treated shrimps was much better than found in the untreated control.
But how do these probiotics work? The researchers investigated.
Vibrio parahaemolyticus produces a protein which stunts the growth and viability of brine shrimp. Akhil Nair and Vinothkannan Ravichandran at Amity University stepped in to use molecular docking to analyse the interaction between metabolites produced by the probiotics and the pathogenic proteins. They found that lactic acid had a strong binding affinity with these proteins. This suggests that the metabolites from the probiotics may be conferring resistance to Vibrio infection.
Among the five probiotics, Limosilactobacillus fermentum and Lactiplantibacillus plantarum showed better protection. Fish feed producers who cultivate brine shrimp can now start using these bacteria as a protective measure against Vibrio infections.
Marine Biology Research (2023)
DOI: 10.1080/17451000.2023.2235590
Reported by M. S. Shivakumar
Periyar University, Salem
*This report was written during the 4th online workshop organised by Current Science.
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