Optimization of cultural conditions for Labyrinthula species isolated from mangrove leaves

Labyrinthulids which are marine osmoheterotrophic, straminipilan protists under Labyrinthulomycetes, thrive in brackish waters and mangrove-rich areas. Despite their long history and widespread occurrence in marine and terrestrial environments, this group of organisms is less studied compared to their closely-related organisms such as thraustochytrids, and so far less is known about their optimum growth conditions in laboratory setups. Although the labyrinthulid group is important ecologically, our understanding of their true culturable diversity, isolation, and long-term viability remains poorly documented. Thus, three labyrinthulid strains (AK1, DV1, and DV2) were studied here for culture optimization, mode of growth and prolonged cell viability (at least 14 d) by using customized agar media. Optimal temperature (35°C) and pH conditions (pH 6.0-7.0) were best for their growth specifically on media with 6% glucose concentration and 60% salinity (parts per thousand). Broth medium with carabao grass extract was suitable in keeping the isolates viable for more than 14 d but their growth in extract-based media was not significantly different from those grown on base medium, Glucose-Yeast Extract-Peptone agar (GPYA). Although it is not well understood what defense mechanism this organism needs to provide them longer viability in the environment, this study gives insights on their preferred culturable conditions.