Characterization of bacterial symbionts of selected marine microalgae and evaluation of their microalgal growth-promoting attributes

Bacterial symbionts of marine microalgae may have beneficial attributes that could be used in the mass culture of microalgal live feeds for aquaculture. Gaining insight into the beneficial traits of marine microalgal symbionts is essential for the development of successful and sustainable hatchery operations in aquaculture. Hence, this study aimed to isolate, characterize, and evaluate growth-promoting traits of the bacterial symbionts on four microalgae species that are commonly utilized as live feed in aquaculture. A total of 23 bacterial symbionts were isolated from four selected microalgal cultures, and all were found to be Gram-negative. These isolates demonstrated promising biochemical and enzymatic activities, alongside remarkable tolerance to various abiotic stress conditions. Marinobacter was the most predominant cultivable bacterium associated with all microalgae. All the bacterial strains synthesized indole-3-acetic acid (IAA). Notably, Halomonas sp., from Navicula sp., produced 88.95 ± 0.40 µg mL−1 IAA, making it a potential candidate for enhancing microalgae growth. Several bacterial strains exhibited growth-promoting traits suggesting their potential role in sustained microalgal growth. This study highlights the strong symbiotic relationship between microalgae and their associated bacterial communities. The findings on bacterial symbionts of marine microalgae can be further explored for improving the productivity of microalgal culture systems.