Tioman Island is one of many sources for underexplored actinobacterial diversity in Malaysia. Selective isolation, molecular profiling, 16S rRNA gene sequencing and phylogenetic analyses were carried out to highlight the diversity of the marine actinobacterial community in a sediment collected off Tioman Island. A high number of diverse actinobacteria were recovered using skim milk/HEPES pre-treatment on a mannitol-based medium. A total of 123 actinobacterial strains were isolated, including thirty obligate marine actinobacteria putatively identified as Salinispora spp. Molecular fingerprinting profiles obtained with a double digestion approach grouped the remaining non-Salinispora-like strains into 24 different clusters, with Streptomyces and Blastococcus as the major clusters. A total of 17 strains were identified as novel actinobacterial species within the genera Streptomyces (n = 6), Blastococcus (n = 5), Marinactinospora (n = 3), Nocardiopsis (n = 1), Agromyces (n = 1) and Nonomuraea (n = 1) based on 16S rRNA gene sequence analyses. Polyphasic data from three putative Marinactinospora spp. showed that the strains represent a new genus in the Nocardiopsaceae family. Crude extracts from the strains were also found to inhibit the growth of Gram-positive (Staphylococcus aureus, Bacillus subtilis) and Gram-negative (Providencia alcalifaciens) pathogens. Hierarchical clustering of the bioactivities of an active fraction revealed a unique profile, which is closely related that of fosfomycin.
A rare fungal endophyte, identified as Buergenerula spartinae (C28), was isolated from the roots of Cymbidium orchids and was characterised and evaluated for its antimicrobial activities. Bio-guided fractionation revealed 4 fractions from B. spartinae (C28) having antibacterial activities against at least one bacterial pathogen tested (Bacillus cereus and Staphylococcus aureus). However, inhibitory activities were absent against pathogenic fungi (Ganoderma boninense, Pythium ultimum and Fusarium solani). Fraction 2 and fraction 4 of B. spartinae (C28) exhibited potent antibacterial activities against S. aureus (MIC: 0.078 mg/mL) and B. cereus (MIC: 0.313 mg/mL), respectively. LCMS analysis revealed the presence of antibacterial agents and antibiotics in fraction 2 (benoxinate, pyropheophorbide A, (-)-ormosanine and N-undecylbenzenesulfonic acid) and fraction 4 (kaempferol 3-p-coumarate, 6-methoxy naphthalene acetic acid, levofuraltadone, hinokitiol glucoside, 3-α(S)-strictosidine, pyropheophorbide A, 5'-hydroxystreptomycin, kanzonol N and 3-butylidene-7-hydroxyphthalide), which may be responsible for the antibacterial activities observed. Most of the bioactive compounds profiled from the antibacterial fractions were discovered for the first time from endophytic isolates (i.e. from B. spartinae (C28)). Buergenerula spartinae (C28) from Cymbidium sp. is therefore, an untapped resource of bioactive compounds for potential applications in healthcare and commercial industries.