The aim of this study was to isolate and identify Actinobacteria from Malaysia mangrove forest and screen them for production of antimicrobial secondary metabolites. Eighty-seven isolates were isolated from soil samples collected at 4 different sites. This is the first report to describe the isolation of Streptomyces, Mycobacterium, Leifsonia, Microbacterium, Sinomonas, Nocardia, Terrabacter, Streptacidiphilus, Micromonospora, Gordonia, and Nocardioides from mangrove in east coast of Malaysia. Of 87 isolates, at least 5 isolates are considered as putative novel taxa. Nine Streptomyces sp. isolates were producing potent antimicrobial secondary metabolites, indicating that Streptomyces isolates are providing high quality metabolites for drug discovery purposes. The discovery of a novel species, Streptomyces pluripotens sp. nov. MUSC 135T that produced potent secondary metabolites inhibiting the growth of MRSA, had provided promising metabolites for drug discovery research. The biosynthetic potential of 87 isolates was investigated by the detection of polyketide synthetase (PKS) and nonribosomal polyketide synthetase (NRPS) genes, the hallmarks of secondary metabolites production. Results showed that many isolates were positive for PKS-I (19.5%), PKS-II (42.5%), and NRPS (5.7%) genes, indicating that mangrove Actinobacteria have significant biosynthetic potential. Our results highlighted that mangrove environment represented a rich reservoir for isolation of Actinobacteria, which are potential sources for discovery of antimicrobial secondary metabolites.

and it showed a range of phylogenetic and chemotaxonomic properties consistent with those of the genus Streptomyces. The diamino acid of the cell-wall peptidoglycan was LL-diaminopimelic acid. The predominant menaquinones were MK-9(H 6 ), MK-9(H 4 ) and MK-9(H 8 ). Polar lipids detected were a lipid, an aminolipid, a phospholipid, phosphatidylinositol, phosphatidylethanolamine and two glycolipids. The predominant cellular fatty acids (.10.0 %) were anteiso-C 15 : 0 (20.8 %), iso-C 16 : 0 (18.0 %), iso-C 15 : 0 (12.2 %) and anteiso-C 17 : 0 (11.6 %). The whole-cell sugars were ribose, glucose and mannose.

Actinobacteria are one of the most important and efficient groups of natural metabolite producers. The genus Streptomyces have been recognized as prolific producers of useful natural compounds as they produced more than half of the naturally-occurring antibiotics isolated to-date and continue as the primary source of new bioactive compounds. Lately, Streptomyces groups isolated from different environments produced the same types of compound, possibly due to frequent genetic exchanges between species. As a result, there is a dramatic increase in demand to look for new compounds which have pharmacological properties from another group of Actinobacteria, known as rare actinobacteria; which is isolated from special environments such as mangrove. Recently, mangrove ecosystem is becoming a hot spot for studies of bioactivities and the discovery of natural products. Many novel compounds discovered from the novel rare actinobacteria have been proven as potential new drugs in medical and pharmaceutical industries such as antibiotics, antimicrobials, antibacterials, anticancer, and antifungals. This review article highlights the latest studies on the discovery of natural compounds from the novel mangrove rare actinobacteria and provides insight on the impact of these findings.

Mangrove is a complex ecosystem that contains diverse microbial communities, including rare actinobacteria with great potential to produce bioactive compounds. To date, bioactive compounds extracted from mangrove rare actinobacteria have demonstrated diverse biological activities. The discovery of three novel rare actinobacteria by polyphasic approach, namely MUSC 115, MUSC 117 and MUSC 78 from mangrove soils at Tanjung Lumpur, Peninsular Malaysia have led to the screening on antibacterial, anticancer and neuroprotective activities. A total of ten different panels of bacteria such as Methicillin-resistant (MRSA) ATCC 43300, ATCC 70069, NRBC 112582 and others were selected for antibacterial screening. Three different neuroprotective models (hypoxia, oxidative stress, dementia) were done using SHSY5Y neuronal cells while two human cancer cells lines, namely human colon cancer cell lines (HT-29) and human cervical carcinoma cell lines (Ca Ski) were utilized for anticancer activity. The result revealed that all extracts exhibited bacteriostatic effects on the bacteria tested. On the other hand, the neuroprotective studies demonstrated MUSC 115 extract exhibited significant neuroprotective properties in oxidative stress and dementia model while the extract of strain MUSC 78 was able to protect the SHSY5Y neuronal cells in hypoxia model. Furthermore, the extracts of MUSC 115 and MUSC 78 exhibited anticancer effect against Ca Ski cell line. The chemical analysis of the extracts through GC-MS revealed that the majority of the compounds present in all extracts are heterocyclic organic compound that could explain for the observed bioactivities. Therefore, the results obtained in this study suggested that rare actinobacteria discovered from mangrove environment could be potential sources of antibacterial, anticancer and neuroprotective agents.

Mumia flava gen. nov., sp. nov., an actinobacterium of the family Nocardioidaceae T formed a distinct clade in the family Nocardioidaceae and was most closely related to the members of the genera Nocardioides (16S rRNA gene sequence similarity, 91.9-95.1 %), Aeromicrobium (92.7-94.6 %), Marmoricola (92.5-93.1 %) and Kribbella (91.5-92.4 %). The cells of this strain were irregular coccoid to short rod shaped. The peptidoglycan contained LL-diaminopimelic acid as diagnostic diamino acid and the peptidoglycan type was A3c. The peptidoglycan cell wall contained LL-diaminopimelic acid, glycine, glutamic acid and alanine in a molar ratio of 1.5 : 0.9 : 1.0 : 1.5. The cell-wall sugars were galactose and rhamnose. The predominant menaquinone was MK-9(H 4 ). The polar lipids consisted of diphosphatidylglycerol, phosphatidylglycerol, phosphoglycolipid, glycolipid and four unknown phospholipids. The major cellular fatty acids were C 18 : 1 v9c (30.8 %), C 16 : 0 (24.1 %), and 10-methyl C 18 : 0 (13.9 %). The DNA G+C content was 72.0±0.1 mol%. On the basis of phylogenetic and phenotypic differences from members of the genera of the family Nocardioidaceae, a novel genus and species, Mumia flava gen. nov., sp. nov. are proposed.