Isolation, distribution and evaluation of cytotoxic and antioxidant activity of cultivable actinobacteria from the Oman Sea sediments

Screening bioactive natural products from bacteria is a determinative step in the drug discovery programs. The present study aim to isolate actinobacteria from the Oman Sea sediments for determining the effects of different culture media and treatments on the yield of the isolation process, and measure the DPPH radical scavenging and Artemia cytotoxic activity of culture extracts of the actinobacterial isolates. A total of 290 actinobacterial isolates were collected from 14 sediment samples. Heat treatment(40.68%) and M4 medium(29.31%) exhibited the maximum isolation rates of actinobacteria. Streptomyces isolates were dominantly distributed in all of the investigated stations according to 16 S rRNA gene sequencing. The distribution pattern of Streptomyces followed a depth-dependent frequency trend, whereas the members of rare genera including Micromonospora, Nocardia Actinoplanes, Nocardiopsis, Saccharopolyspora and Crossiella were distributed in deeper stations. Approximately,25% of the examined isolates could scavenge 90% of 10^–4 mol/L DPPH solutions at 1 250 μg/mL final concentration of their ethyl acetate culture extracts. Furthermore, the most potent extracts could scavenge DPPH radicals with IC50 ranges from 356.8 to 566.4 μg/mL. Brine shrimp cytotoxicity tests showed that 38.88% of the examined culture extracts exhibited LC50 lower than 1 000 μg/mL against the Artemia cells. Moreover, the most potent culture extracts exhibited LC50 range from 335.4 to 534.4 μg/mL. Phylogenetic analysis by 16 S rRNA gene sequence revealed that the OS 005, OS 263 and OS 157 closely related to Streptomyces djakartensis, Streptomyces olivaceus and Nocardiopsis dassonvillei respectively. These results suggested the widespread distribution of the antioxidant and cytotoxic producing actinobacteria in the Oman Sea sediments, which could be considered as promising candidates for the discovery of microbial bioactive compounds.

Antioxidant and antifungal activities of two spices of mangrove plant extract

Objective:To evaluate the antifungal and the radical scavenging capacity related to antioxidant potential of ethanol and water extracts of leaves of Rhizophora mucronata(R.mucronata)and Avicennia marina(A.marina)mangrove plant species against five postharvest pathogenic bacteria.Methods:In vitro assessment of antioxidant and antifungal activities was evaluated in this present study for both aqueous and ethanol extracts prepared from leaves of A.marina and R.mucronata.The antioxidant activities of these mangroves were evaluated by using reducing power and 1,1-diphenyl-2-picrylhydrazyl assays with butylated hydroxytoluene and L-(+)-ascorbic acid as standards.Results:The result showed that the antioxidant activities of all extracts increased with increasing concentration of extracts.However,the ethanol extracts of both species showed the highest antioxidant activities.Antimicrobial tests were then carried out by the disk diffusion method.The ethanol extracts of both species showed antifungal activities on Penicillium purpurogenum,Penicillium chrysogenum,Penicillium notatum,Aspergillus niger,Alternaria alternata and Penicillium italicum.However,none of the water extracts exhibited antifungal activity on the studied fungi.Among all the pathogens,tested Aspergillus flavus was the most resistant fungi.Different concentrations of extracts from A.marina and R.mucronata showed different amounts of control against tested fungal strains.Conclusions:This study indicated that mangrove species has natural antioxidant and antifungal properties.