The Isolation Rate of Culturable Actinomycetes from Malaysian Borneo Forests and Their Activity Against Mammalian GSK-3β

Abstract

More than ten types of forests can be found in Sabah, Malaysian Borneo. Studies comparing culturable actinomycetes potential in this region are relatively scarce. This study described a preliminary statistical comparison of culturable actinomycetes isolation rates and their biological activity against mammalian glycogen synthase kinase-3 (GSK-3β). We isolated 1049 isolates using standard isolation media for actinomycetes (HVA, ISP4 and AIA) with distinctive morphologies from the main forest types in Sabah; primary, secondary, mangrove, and beach forests. Isolate prevalence analysis revealed that secondary forests had the highest soil-to-isolate ratio (1:11). Interestingly, Kruskal-Wallis analysis revealed no significant differences in the overall isolation rates of actinomycetes, including non-sporulating strains, between forest types (P-value=0.142). The crude extracts of these isolates were assayed against GSK-3β, and we identified 19 active isolates; nine from primary and nine from secondary forests (no significant mean difference (P-value=0.558), one from beach forests, and none from mangrove forests. Overall, despite the different sampling locations and soil types, the isolation rates of culturable actinomycetes in Sabah did not vary significantly. However, both primary and secondary forests yielded more actinomycetes isolates that were active against mammalian GSK-3β than mangrove and beach forests. Hence, secondary forests are an attractive alternative to primary forests for exploring bioactive compounds from culturable actinomycetes in Sabah.

GSK-3β inhibition with antiplasmodial activities from the extracts of actinomycetes isolated from Malaysian forest soil

“…Soil samples were collected from 2008-2010 from forests in Sabah, Malaysia, at 10-15 cm depth, mostly under leaf litter. As the soil microbial community adapts to specific micro-and macro-environments, different forest types were selected for soil sampling, as described previously (Mahmud et al, 2022a). Actinomycetes were isolated using the method previously described (Ho et al, 2009).…”

“…In this study, 514 actinomycetes strains were isolated from 144 soil samples. Subsequently, we identified nine actinomycetes extracts (MI4701, FA013, FH038, FH039(b), H17(1)-2, H17(2)-1, SA3H-1, SA8A-2 and SM0307) that showed differences in growth inhibition on yeasts at 37 °C compared to 28 °C, indicating selective Hs GSK-3β inhibition activity (Mahmud et al, 2022a) (Figure 1). In the presence of selective Hs GSK-3β inhibitor, Rog1 remains in phosphorylated form, and its accumulation causes yeast growth defects at 37 °C Since the activity of Hs GSK-3β at 28 °C is not vital for yeast survival, inhibition of Hs GSK-3β at this temperature exerted no or minimal yeast growth inhibition (Andoh et al, 2000).…”