Abstract
The water surface microlayer is still poorly explored, although it has been shown to contain a high density of metabolically active bacteria, often called bacterioneuston. Actinomycetes from the surface microlayer in the Trondheim fjord, Norway, have been isolated and characterized. A total of 217 isolates from two separate samples morphologically resembling the genus Streptomyces have been further investigated in this study. Antimicrobial assays showed that about 80% of the isolates exhibited antagonistic activity against non-filamentous fungus, Gram-negative, and Gram-positive bacteria. Based on the macroscopic analyses and inhibition patterns from the antimicrobial assays, the sub-grouping of isolates was performed. Partial 16S rDNAs from the candidates from each subgroup were sequenced and phylogenetic analysis performed. 7 isolates with identical 16S rDNA sequences were further studied for the presence of PKS type I genes. Sequencing and phylogenetic analysis of the PKS gene fragments revealed that horizontal gene transfer between closely related species might have taken place. Identification of unique PKS genes in these isolates implies that de-replication can not be performed based solely on the 16S rDNA sequences. The results obtained in this study suggest that streptomycetes from the neuston population may be an interesting source for discovery of new antimicrobial agents.
Highlights
Search for new biologically active microbial secondary metabolites is important in order to meet the increasing demand for new antibiotics
A number of antibiotic producers have been isolated from the marine environments [2, 3], and experimental data indicate that production of antibiotics could play an important role in the competitive relationship within the marine bacterial populations [4]
Bacteria morphologically similar to streptomycetes were isolated from surface microlayer collected at Steinvikholmen and in the Åsen fjord in the Trondheim fjord, Norway
Summary
Search for new biologically active microbial secondary metabolites is important in order to meet the increasing demand for new antibiotics. Actinomycetes, especially those belonging to the genus. Streptomyces bacteria were reported to produce ~70% of the currently characterized actinomycete natural products [1]. In an environment with high densities of metabolically active bacteria, competition is likely to be fierce, and properties such as production of antibiotics may give organisms an advantage. Antagonistic interactions among soil-living microorganisms are well documented, and are attributed to the production of antibiotics by certain bacteria and fungi in environments rich in organic material [5, 6]. The isolates were characterized using molecular taxonomy, assays for antimicrobial activity and presence of polyketide synthase genes
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