Diversity of Streptomyces spp. from mangrove forest of Sarawak (Malaysia) and screening of their antioxidant and cytotoxic activities

Abstract

Streptomycetes have been the center of attraction within scientific community owing to their capability to produce various bioactive compounds, for instance, with different antimicrobial, anticancer, and antioxidant properties. The search for novel Streptomyces spp. from underexplored area such as mangrove environment has been gaining attention since these microorganisms could produce pharmaceutically important metabolites. The aim of this study is to discover the diversity of Streptomyces spp. from mangrove in Sarawak and their bioactive potentials - in relation to antioxidant and cytotoxic activities. A total of 88 Streptomyces isolates were successfully recovered from the mangrove soil in Kuching, state of Sarawak, Malaysia. Phylogenetic analysis of all the isolates and their closely related type strains using 16S rRNA gene sequences resulted in 7 major clades in the phylogenetic tree reconstructed based on neighbour-joining algorithm. Of the 88 isolates, 18 isolates could be considered as potentially novel species according to the 16S rRNA gene sequence and phylogenetic analyses. Preliminary bioactivity screening conducted on the potential novel Streptomyces isolates revealed significant antioxidant activity and notable cytotoxic effect against tested colon cancer cell lines (HCT-116, HT-29, Caco-2, and SW480), with greater cytotoxicity towards SW480 and HT-29 cells. This study highlighted that the Sarawak mangrove environment is a rich reservoir containing streptomycetes that could produce novel secondary metabolites with antioxidant and cytotoxic activities.

Figure 1

Neighbour-joining phylogenetic tree based on 16S rRNA gene sequences showing the relationship between the 88 Streptomyces sp. isolates and their closely related type strains. Bootstrap value based on 1000 resampled datasets are shown at branch nodes. Bar, 0.005 substitutions per site.

Figure 2

Neighbour-joining phylogenetic tree based on 16S rRNA gene sequences showing relationship between 18 potentially novel Streptomyces sp. and their closely related type strains. Bootstrap value based on 1000 resampled datasets are shown at branch nodes. Bar, 0.002 substitutions per site.

Figure 3

ABTS radical scavenging activity of extracts from potentially novel Streptomyces sp. isolates. Symbol (*) indicates p < 0.05 significant difference between the extract and control (without extract).

Figure 4

Metal chelating activity of extracts from potentially novel Streptomyces sp. isolates. Symbol (*) indicates p < 0.05 significant difference between the extract and control (without extract).

Figure 5

SOD-like activity of extracts from potentially novel Streptomyces sp. isolates. Symbol (*) indicates p < 0.05 significant difference between the extract and control (without extract).

Figure 6

Correlation between total phenolic content and antioxidant capacity of 18 Streptomyces methanolic extracts. The relationship was observed in three different antioxidant assays: (A) ABTS, (B) SOD, and (C) metal chelating.

Figure 7

Cytotoxic activity of extracts from potentially novel Streptomyces isolates against colon cancer cell lines. The measurement of cell viability was done using MTT assay and the concentration of extract was 400 µg/mL. The graphs show cytotoxicity effect of the extracts against: (A) HCT-116, (B) Caco-2, (C) SW480, and (D) HT-29. All data are expressed as mean ± standard deviation and significance level are set as 0.05. Symbol (*) indicates p < 0.05 significant difference between the cells treated with extract and control (without extract).