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.

Black gill disease in Litopenaeus vannamei made by various agents

Melanization of shrimp gills is a general symptom in shrimp black bill diseases(sBG);therefore,the cause is not immediately apparent.This study aimed to determine the primary and secondary agents associated with a black gill outbreak in the Delvar complex in the Bushehr Province of Iran.During July and August of 2020,450 healthy and affected shrimps were collected based on brown to black gill color from three farms of the Bushehr Province in Iran.Characterization of pathogens was performed by gross signs,wet mounts,microbiological tests,histopathology methods,and sequencing of molecular markers.The mean weight and length of infected shrimps was significantly(P<0.05)lower than the healthy shrimps.The histological examination of sBG indicated the adhesion of secondary lamellae,accumulation of hemocyte cells at the end of the secondary lamellae,and necrosis of epithelial cells with pyknosis and karyorrhexis.According to our results,Aspergillus sydowii as a primary agent correlates with sBG disease in Litopenaeus vannamei from Iran,and other biotic factors,including bacterial(Vibrio owensii and V.parahaemolyticus)probably are secondary agents associated with sBG disease.