Revealing Actinobacterial Diversity Inhabiting Malaysian Beach Ridges Interspersed with Swales (BRIS) Soil : Insights from Culture-Dependent and Metagenomic Approaches

The discovery of novel antibiotics remains a pressing global challenge as many known microorganisms continue to yield compounds already present in existing drugs. To overcome this limitation, bioprospecting in underexplored and extreme environments using both culture-dependent and culture-independent strategies has become essential. In this study, we investigated the microbial diversity of Beach Ridges Interspersed with Swales (BRIS) soil from Setiu, Terengganu, Malaysia—an environment characterized by poor nutrient retention, low water-holding capacity, and acidity. A dual approach was employed: (i) culture-dependent isolation of actinomycetes using selective media, followed by morphological and 16S rRNA gene-based phylogenetic analysis, and (ii) culture-independent high-throughput sequencing of the 16S rRNA gene (Illumina MiSeq) to characterize the broader microbial community. Results from the selective isolation yielded 180 actinomycete isolates grouped into 69 colour-based categories, with 15 representatives identified by 16S rRNA sequencing as belonging predominantly to Streptomyces , alongside the rare genus Dermacoccus . In contrast, metagenomic analysis revealed a far richer microbial landscape comprising 4719 OTUs, 32 bacterial phyla, and 380 genera, including a high proportion of uncultured taxa. Notably, actinobacterial diversity was dominated by Acidothermus , whereas Streptomyces predominated in culture-dependent isolation, highlighting the complementary nature of both approaches. These findings confirm that BRIS soil harbours unique microbial communities shaped by its physicochemical conditions, with potential as a reservoir for rare actinomycetes and novel bioactive compounds. The study provides the first combined culture-dependent and metagenomic insight into BRIS soil microbiota and underscores its promise for future pharmaceutical and biotechnological exploration.