Chiang Mai Journal of Science

     Sri Lanka is an island nation with diverse ecosystems, including forests, wetlands, grasslands, and vast coasts. The country showcases a rich aquatic ecosystem that includes both coastal and inland waters. Freshwater habitats such as rivers, streams, marshes, and man-made reservoirs are the host for diverse fungal communities. However, documentation and identification of freshwater fungi in Sri Lanka have not yet been done as they face significant challenges, including unexplored taxa, misidentification, and hitherto reliance on morphological data, as well as limited funding, awareness, and expertise. This study aims to assess the limitations, potentials, and conservation efforts related to the identification of fungi in freshwater habitats in Sri Lanka. The assessment has revealed several potential opportunities for future research, including the exploration of novel fungal strains that are found in freshwater habitats, identification and classification of existing fungi, setting up and utilization of the freshwater fungal repository, access to reference databases, and identification of industrial applications.

     Sago pith waste (SPW) is an agricultural by-product from the sago starch extraction process. Using SPW supports the bio-circular green economy and sustainable agriculture. Although many bacterial culture media are commercially available, using SPW as a carbon source to develop culture media is considered an alternative way to save costs and limit the import of commercial media. This research aimed to develop culture media from SPW to culture the antagonistic rhizobacterium Streptomyces angustmyceticus NR8-2 and test the antifungal activity of the cell-free culture filtrate (CF) of S. angustmyceticus NR8-2 against Curvularia pseudobrachyspora, the pathogen of brown spot disease in dragon fruit. S. angustmyceticus NR8-2 was cultured on glucose yeast malt agar (GYMA) and glucose yeast malt broth (GYMB) as general media, modified sago pith waste yeast agar (SPYA), and sago pith waste yeast broth (SPYB); then, the bacterial growth was measured. S. angustmyceticus NR8-2 grew on SPYA similarly to on GYMA, and there was no morphological change when it was cultured on SPYA. S. angustmyceticus NR8-2 could also be cultured on both GYMB and modified SPYB, as indicated by spherical pellet development, but the biomass of S. angustmyceticus NR8-2 cultured on SPYB was significantly higher than that on GYMB (p<0.05). The biofilm formation of S. angustmyceticus NR8-2 on the surface of SPYB or GYMB displayed no significant difference in dry or fresh weight (p>0.05). The cell-free CF of S. angustmyceticus NR8-2 was collected and tested against the antifungal ability of C. pseudobrachyspora via agar well diffusion. Cell-free CFs from GYMB and SPYB effectively inhibited the growth of C. pseudobrachyspora with percentage inhibitions of 60.95 and 58.99%, respectively, with no statistical difference (p>0.05). The cell-wall-degrading enzyme activity of chitinase and β-1,3-glucanase showed no significant differences when S. angustmyceticus NR8-2 was cultured on GYMB and SPYB. Furthermore, the solid-state cultivation of S. angustmyceticus NR8-2 on SPW + yeast extract and SPW + dextrose + yeast extract showed bacterial populations of 2.56±1.38 × 108 and 3.38±1.89 × 108 CFU/g, significantly higher than when cultured on SPW alone. The results of our study show that SPW is a novel source for the development of novel media that can be used to culture antagonistic rhizobacterium S. angustmyceticus NR8-2.