Bacterial Community and Culturable Actinomycete Diversity in Tropical Peat Swamp Forest Soils

Tropical peat swamp forests (TPSFs) are waterlogged, acidic ecosystems whose microbial communities remain poorly characterized, particularly members of the phylum Actinomycetota, which include many prolific producers of bioactive secondary metabolites. This study combined 16S rRNA gene amplicon sequencing and culture-dependent isolation to characterize bacterial community composition and actinomycete diversity in forest floor and wetland microhabitats of a Nong Chamrung peat swamp forest, Rayong, Thailand. Ten soil samples were investigated by 16S rRNA gene (V3–V4) amplicon sequencing to assess taxonomic composition and alpha and beta diversity. In parallel, actinomycetes were isolated using selective media and identified by 16S rRNA gene sequencing and phylogenetic analysis. Sequencing yielded 155,094 quality reads and 236 operational taxonomic units (OTUs) dominated by five phyla; Actinomycetota was significantly enriched in forest floor compared with wetland samples (LDA = 5.00, p = 0.017), while alpha diversity did not differ significantly between habitats and beta diversity showed a near-significant habitat trend. Amplicon sequencing identified Acidothermus and Mycobacterium as dominant Actinomycetota genera. In contrast, culture-dependent isolation recovered 53 strains representing eight genera, with Streptomyces accounting for 47.17% of the isolates despite its low relative abundance in the amplicon dataset. TPSF habitats harbor distinct actinomycete communities, and culture-dependent isolation reveals a substantial component—particularly Streptomyces—that is poorly represented by amplicon sequencing. This discrepancy highlights the complementary value of culture-independent and culture-dependent approaches and supports tropical peat swamp forest soils as a promising reservoir of culturable actinomycetes for further bioprospecting.