Discovery of novel rare actinobacteria isolated from mangrove environments in the east coast of Peninsular Malaysia

Mangrove forest is a complex ecology and it refers to a group of tropical trees and shrubs that grows in the intertidal zone. It contains various microorganisms including rare actinobacteria that can produce bioactive compounds with interesting bioactivities. The goals of this research were to describe the taxonomic status of novel rare actinobacteria and to screen their bioactivity for antibacterial, neuroprotective and cytotoxic properties. Three rare actinobacteria strains namely MUSC 115T, MUSC 117T and MUSC 78T were successfully isolated from mangrove sediments, collected from Tanjung Lumpur river, Peninsular Malaysia. Characterization using polyphasic approach showed that strains MUSC 115T and MUSC 117T have many differences with other species of the genus Microbacterium and Sinomonas, respectively. Combined phylogenetic, genotypic, chemotaxonomic, and phenotypic analyses proved that strain MUSC 115T represent a novel species, Microbacterium mangrovi sp. nov., while strain MUSC 117T represent a novel species namely Sinomonas humi sp. nov. Meanwhile, strain MUSC 78T was also characterized by polyphasic approach and results showed that it was different from other genera of the family Intrasporangiaceae. Thus, it can be described as a novel genus, Monashia gen. nov., the type species of which is Monashia flava sp. nov. The successfully characterization of the novel strains have led to the screening of bioactivities on antibacterial, neuroprotective and anticancer properties. The crude extract from all novel strains were prepared using solvent extraction method. Antibacterial screening of the crude extracts demonstrated inhibitory effects against 10 bacteria tested including Methicillin-resistant Staphylococcus aureus (MRSA) ATCC 43300, ATCC 70069, ATCC 33591, ATCC BAA-44, Acinetobacter calcoaceticus NBRC 13006, Bacillus subtilis ATCC 31098, Pseudomonas aeruginosa NBRC 112582, Salmonella typhi ATCC 19430, Vibrio parahaemolyticus VP103, and Escherichia coli ATCC 25922. On the other hand, the neuroprotective studies revealed that Microbacterium mangrovi MUSC 115T extract exhibited significant neuroprotective activity in oxidative stress and dementia model. Meanwhile, the extract of strain Monashia flava MUSC 78T was able to protect the SHSY5Y neuronal cells in hypoxia model. Furthermore, the extracts of Microbacterium mangrovi MUSC 115T and Monashia flava MUSC 78T exhibited anticancer effect against Ca Ski cell line. Based on the findings of this study, mangrove environment is a potentially rich source for the discovery of novel rare actinobacteria with interesting bioactivities for the new drugs development