Geosmin and 2-methylisoborneol (MIB) outbreaks in tropical water bodies, such as Southeast Asia, by actinomycetes have not yet been elucidated in detail. Six Streptomyces isolates from lowland environments in Malaysia were selected and evaluated for their odor production under different temperatures. The gene responsible for the production of geosmin, geoA, was detected in all isolates, while only two isolates harbored tpc, which is responsible for 2-MIB production. This result suggested that geosmin and 2-MIB synthesis pathway genes already existed in the environment in the Tropics of Southeast Asia. Furthermore, our isolates produced musty odor compounds at 30°C, and differences were observed in musty odor production between various temperatures. This result indicated the potential for odor episodes in water bodies of the tropical countries of Southeast Asia throughout the year due to the mean annual ambient temperature of 27°C in the lowlands.
Musty odor production by actinomycetes is usually related to the presence of geosmin and 2-methylisoborneol (2-MIB), which are synthesized by enzymes encoded by the geoA and tpc genes, respectively. Streptomyces spp. strain S10, which was isolated from a water reservoir in Malaysia, has the ability to produce geosmin when cultivated in a basal salt (BS) solid medium, but no 2-MIB production occurred during growth in BS medium. Strain S10 could produce higher levels of geosmin when the phosphate concentration was limited to 0.05 mg/L, with a yield of 17.53 ± 3.12 ✕ 105 ng/L, compared with growth in BS medium. Interestingly, 2-MIB production was suddenly detected when the nitrate concentration was limited to 1.0 mg/L, with a yield of 1.4 ± 0.11 ✕ 105 ng/L. Therefore, it was concluded that phosphate- and nitrate-limiting conditions could induce the initial production of geosmin and 2-MIB by strain S10. Furthermore, a positive amplicon of geoA was detected in strain S10, but no tpc amplicon was detected by PCR analysis. Draft genome sequence analysis showed that one open reading frame (ORF) contained a conserved motif of geosmin synthase with 95% identity with geoA in Streptomyces coelicolor A3 (2). In the case of the tpc genes, it was found that one ORF showed 23% identity to the known tpc gene in S. coelicolor A3(2), but strain S10 lacked one motif in the N-terminus.
A comparative analysis of metabolites from different parts of Curcuma aeruginosa, i.e. leaves, stems, adventitious
roots and rhizomes was performed by GC-MS/MS coupled with multivariate statistical analysis. The GC-MS/MS analysis
confirmed the occurrence of 26 metabolites belonged to terpenoids in almost all the samples. The Principal Component
Analysis (PCA) indicated that there was a clear distinction between rhizomes and other plant parts, i.e. stems, leaves,
and adventitious roots that could be explained by relatively higher contents of terpenoids including curzerene, alphafarnesen, furanocoumarin, velleral, germacrone cineole, borneol, beta- and gamma- elemene and methenolone. The
results of Hierarchical Clustering Analyses (HCA) corresponded with the PCA results where many terpenoids found
abundantly high in rhizome were clustered together. This was supported by the Pearson correlation analysis that
showed a significantly good relationship between those terpenoids. The adventitious roots demonstrated the strongest
antioxidant activity as compared to the other plant parts which could be attributed to its highest Total Phenolic
Contents (TPC). Total phenolic contents of all the plant parts were positively correlated with their antioxidant activities
which indicate that phenolic compounds may play a role in the overall antioxidant activities of the plants. The results
of the study highlighted the potential of this underexploited Curcuma species which could serve as a new source of
important phytochemicals and natural antioxidant that could be incorporated in functional foods and nutraceuticals.
In addition, chemical and biological evidence shown in the present work has rationalised the different uses of various
plant parts of C. aeruginosa.