The aquaculture sector stands as the fastest-growing food production industry globally. Nutrition and diseases are two significant challenges that must be tackled to propel the industry forward. An intensive aquaculture system required aquafeed that enhances fish immunity and health to mitigate the stress effects induced by high density. Spirulina , a widely recognized microalga, has garnered attention as a nutritious feed for aquaculture due to its elevated protein content and valuable bioactive compounds. Besides, certain Spirulina species lacking a cell wall result in improved digestion and absorption. Spirulina also exhibit phycobiliproteins that possess various bioactives with health-related properties. These phycobiliproteins have gained attention and are commercially used in various sectors, including pharmaceuticals, cosmetics, food and beverages as well as animal feed . In aquaculture, phycocyanin, one of the phycobiliprotein has been shown to intensify the coloration in goldfish and improve the antioxidant status, immune response and disease resistance of Nile Tilapia ( Oreochromis niloticus). Yet, the current production of phycobiliprotein is insufficient to meet the growing market demand and fluctuations in production hampers its feasibility and sustainability.
To address these issues, this study was conducted to improve the growth, biomass and phycobiliprotein production in Spirulina sp. (UPMC-A0087) using an eco-friendly approach that involved utilising associated bacteria. Spirulina sp. was selected as the host for bacterial diversity and phycobiliprotein relationships as it is known to have higher phycobiliproteins than other blue-green microalgae . Thirteen bacteria were successfully isolated and each bacterium was co-cultured with the axenic Spirulina sp. The growth, biomass productivity and phycobiliprotein contents of axenic culture and bacteria co-culture were analyzed. Spirulina sp. co-culture with Bacillus cereus exhibited significantly higher specific growth rate and biomass productivity than other bacteria co-cultures. In terms of phycobiliproteins, co-culture with Aeromicrobium sp. showed significant higher phycocyanin (PC) , allophycocyanin (APC) and total phycobiliprotein contents than other bacteria cultures. Highest phycoerythrin (PE) content was found in xenic culture followed by co-culture with Achromobacter sp. This study illustrated that some bacterial species are associated with enhancing growth, biomass and phycobiliprotein production in microalgae . The findings hold promise for advancing the efficiency and sustainability of Spirulina -based aquafeeds, thereby supporting the goal of aquaculture industry to enhance nutritional quality and minimizing environmental impact.