Diversity Of Cultivable Actinobacteria In The South Atlantic Sediments And Polyphasic Taxonomic

The marine environment represents a largely untapped source for isolation of newmicroorganisms with potential to produce biologically active secondary metabolites.Among such microorganisms, Gram-positive actinobacteria is of special interest,since they are known to produce chemically diverse compounds with a wide range ofbiological activities. We have set out to isolate and characterize actinomycete bacteriafrom14sediment samples collected from South Atlantic Ocean.A total of321actinobacteria were recoverd using different kinds of pre-treatments and selectivemedia. The isolates can be assigned to7orders,16families and24genera. There are18putative novel species, among which4strains share the highest16S rRNA genesequence similarity of bellow97%with other type strains,11strains share97%-98%and the other3strains share98%-98.5%. Grouping of the isolates according to themorphology firstly and followed by characterization of isolates chosen as grouprepresentatives by molecular taxonomy, it revealed that Dietzia (20.56%),Brachybacterium (14.33%), Microbacterium (13.08%), Kocuria (11.53%) andStreptomyces (10.28%) were the dominating actinomycete genura isolated from thesediments.Using the degenerate oligonucleotide primers, some representative strains werescreened for genes encoding type I and type II polyketide synthases and nonribosomalpeptide synthases by polymerase chain reaction. Antimicrobial activity wasdetermined by observing bacterial growth inhibition. The effect of each pre-treatmentand each selective medium was assessed and the method of dispersion and differentialcentrifugation (DDC) was better than the others. As for the selective media, Humicacid-vitamin (HV) was the best. The deep-sea environments of South Atlantic Oceanharbour highly diverse actinobacterial communities, many of which appear to be novel candidate species. The actinobacteria with antimicrobial activity could be apromising source for antimicrobial bioactive agents.Taxonomy of four novel candidate species relied on polyphasic combinations ofphenotypic, chemotaxonomic and genotypic characteristics. Three of the four strainsbelonged to the genus Nesterenkonia and the other one belonged to the genusBrachybacterium.