Inhibitory Effects of Microalgal Biofilm on Vibrio parahaemolyticus

Microalgae are primary producers, the first trophic level in the food webs of aquatic ecosystems. Therefore, they have many potential applications in aquaculture. This study aimed to create autotrophic biofilms from microalgae strains belonging to the Nostocaceae, Protosiphonaceae, and Scenedesmaceae, isolated in Vietnam and to select a microalgal biofilm capable of inhibiting Vibrio parahaemolyticus. The microalgal biofilms were created by attaching the microalgal strains (cyanobacterium and green algae) to substrates (coconut fibre, sugarcane bagasse and cheesecloth). Additionally, the inhibitory effect of the microalgal biofilm on V. parahaemolyticus was evaluated based on the reduction proportion of V. parahaemolyticus cell numbers in an environment with the microalgal biofilm (co-culture method) compared to those in an environment without microalgal biofilm. The results showed that coconut fibre and cheesecloth had higher coverage density and biomass content of microalgae after 72 hours of biofilm formation than the sugarcane bagasse. We also found that microalgal biofilms formed by the combination of a cyanobacterial strain NK1111 with a green microalgal strain MBN1 or MHN122 reduced 76.2% - 99.8% of V. parahaemolyticus in 96 - 120 hours of co-culture. Meanwhile, microalgal biofilm formed by the strain NK1111 and a green microalgal strain MHB231 inhibited 91.8% of V. parahaemolyticus bacterium as early as 24 hours and inhibited 99.4% of this bacteria at 120 hours of co-culture. Therefore, the microalgal biofilms consisting of the strain NK1111 and the strain MHB231 on cheesecloth or coconut fibre substrate are highly appreciated for their potential application in shrimp farms in Vietnam.