Actinomycete bacteria produce a wide variety of secondary metabolites with diverse biological activities, some of which have been developed for human medicine. Rare actinomycetes are promising sources in search for new drugs, and their potential for producing biologically active molecules is poorly studied. In this work, we have investigated the diversity of actinomycetes in the shallow water sediments of the Trondheim fjord (Norway). Due to the use of different selective isolation methods, an unexpected variety of actinomycete genera was isolated. Although the predominant genera were clearly Streptomyces and Micromonospora, representatives of Actinocorallia, Actinomadura, Knoellia, Glycomyces, Nocardia, Nocardiopsis, Nonomuraea, Pseudonocardia, Rhodococcus and Streptosporangium genera were isolated as well. To our knowledge, this is the first report describing isolation of Knoellia and Glycomyces species from the marine environment. 35 selected actinomycete isolates were characterized by 16S rDNA sequencing, and were shown to represent strains from 11 different genera. In addition, these isolates were tested for antimicrobial activity and the presence of polyketide synthase and non-ribosomal peptide synthetase genes. This study confirms the significant biodiversity of actinobacteria in the Norwegian marine habitats, and their potential for producing biologically active compounds.

Recently, it was shown that a cellulose-negative mutant (Cell) ofAcetobacterxylinum ATCC 23769 carried an insertion of an indigenous transposable element (IS1031A) about 500 bp upstream of the bcs operon, required for cellulose synthesis. Here we show that Cell can be complemented by wild-type DNA covering the insertion point. Nucleotide sequencing of this region revealed the presence of two open reading frames, ORF1 and ORF2. ORF2, which is disrupted by the IS1031A insertion in Cell, potentially encodes the complementing function. ORF1 encodes a protein (CMCax) with significant homology to previously described endoglucanases. A cloned DNA fragment containing ORF1 expressed a carboxymethyl cellulose-hydrolyzing activity in Escherichia coli. In A. xylinum, CMCax is secreted into the culture growth medium. The CMCax mature protein consists of 322 amino acids and has a molecular mass of 35.6 kDa.

Twenty-seven marine sediment-and sponge-derived actinomycetes with a preference for or dependence on seawater for growth were classified at the genus level using molecular taxonomy. Their potential to produce bioactive secondary metabolites was analyzed by PCR screening for genes involved in polyketide and nonribosomal peptide antibiotic synthesis. Using microwell cultures, conditions for the production of antibacterial and antifungal compounds were identified for 15 of the 27 isolates subjected to this screening. Nine of the 15 active extracts were also active against multiresistant Gram-positive bacterial and/or fungal indicator organisms, including vancomycin-resistant Enterococcus faecium and multidrug-resistant Candida albicans. Activityguided fractionation of fermentation extracts of isolate TFS65-07, showing strong antibacterial activity and classified as a Nocardiopsis species, allowed the identification and purification of the active compound. Structure elucidation revealed this compound to be a new thiopeptide antibiotic with a rare aminoacetone moiety. The in vitro antibacterial activity of this thiopeptide, designated TP-1161, against a panel of bacterial strains was determined.

Abstract:The marine environment represents a largely untapped source for isolation of new microorganisms with potential to produce biologically active secondary metabolites. Among such microorganisms, Gram-positive actinomycete bacteria are of special interest, since they are known to produce chemically diverse compounds with a wide range of biological activities. We have set out to isolate and characterize actinomycete bacteria from the sediments in one of the largest Norwegian fjords, the Trondheim fjord, with respect to diversity and antibiotic-producing potential. Approximately 3,200 actinomycete bacteria were isolated using four different agar media from the sediment samples collected at different locations and depths (4.5 to 450 m). Grouping of the isolates first according to the morphology followed by characterization of isolates chosen as group representatives by molecular taxonomy revealed that Micromonospora was the dominating actinomycete genus isolated from the sediments. The deep water sediments contained a higher relative amount of Micromonospora compared to the shallow water samples. Nine percent of the isolates clearly required sea water for normal growth, suggesting that these strains represent obligate marine organisms. Extensive screening of the extracts from all collected isolates for antibacterial and antifungal activities revealed strong antibiotic-producing potential among them. The latter implies that actinomycetes from marine sediments in Norwegian fjords can be potential sources for the discovery of novel anti-infective agents.

BE-14106 is a macrocyclic lactam with an acyl side chain previously identified in a marine-derived Streptomyces sp. The gene cluster for BE-14106 biosynthesis was cloned from a Streptomyces strain newly isolated from marine sediments collected in the Trondheimsfjord (Norway). Bioinformatics and experimental analyses of the genes in the cluster suggested an unusual mechanism for assembly of the molecule. Biosynthesis of the aminoacyl starter apparently involves the concerted action of a distinct polyketide synthase (PKS) system and several enzymes that activate and process an amino acid. The resulting starter unit is loaded onto a second PKS complex, which completes the synthesis of the macrolactam ring. Gene inactivation experiments, enzyme assays with heterologously expressed proteins, and feeding studies supported the proposed model for the biosynthesis and provided new insights into the assembly of macrolactams with acyl side chain.