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Degradation of alkanes is a widespread phenomenon in nature, and numerous microorganisms, both prokaryotic and eukaryotic, capable of utilizing these substrates as a carbon and energy source have been isolated and characterized. In this review, we summarize recent advances in the understanding of bacterial metabolism of long-chain n-alkanes. Bacterial strategies for accessing these highly hydrophobic substrates are presented, along with systems for their enzymatic degradation and conversion into products of potential industrial value. We further summarize the current knowledge on the regulation of bacterial long-chain n-alkane metabolism and survey progress in understanding bacterial pathways for utilization of n-alkanes under anaerobic conditions.

A complete set of genes responsible for the biosynthesis of the antifungal polyene antibiotic nystatin in S. noursei ATCC 11455 has been cloned and analyzed. This represents the first example of the complete DNA sequence analysis of a polyene antibiotic biosynthetic gene cluster. Manipulation of the genes identified within the cluster may potentially lead to the generation of novel polyketides and yield improvements in the production strains.

Acinetobacter sp. strain DSM 17874 is capable of utilizing n-alkanes with chain lengths ranging from that of decane (C 10 H 22 ) to that of tetracontane (C 40 H 82 ) as a sole carbon source. Two genes encoding AlkB-type alkane hydroxylase homologues, designated alkMa and alkMb, have been shown to be involved in the degradation of n-alkanes with chain lengths of from 10 to 20 C atoms in this strain. Here, we describe a novel high-throughput screening method and the screening of a transposon mutant library to identify genes involved in the degradation of n-alkanes with C chain lengths longer than 20, which are solid at 30°C, the optimal growth temperature for Acinetobacter sp. strain DSM 17874. A library consisting of approximately 6,800 Acinetobacter sp. strain DSM 17874 transposon mutants was constructed and screened for mutants unable to grow on dotriacontane (C 32 H 66 ) while simultaneously showing wild-type growth characteristics on shorter-chain nalkanes. For 23 such mutants isolated, the genes inactivated by transposon insertion were identified. Targeted inactivation and complementation studies of one of these genes, designated almA and encoding a putative flavin-binding monooxygenase, confirmed its involvement in the strain's metabolism of long-chain n-alkanes. To our knowledge, almA represents the first cloned gene shown to be involved in the bacterial degradation of long-chain n-alkanes of 32 C's and longer. Genes encoding AlmA homologues were also identified in other long-chain n-alkane-degrading Acinetobacter strains.

Fungal infections represent a serious problem for patients with immune systems compromized either by HIV infection, or administration of immunosuppressive drugs during cancer therapy and organ transplantation. High dissemination and proliferation rates of many pathogenic fungi along with their insusceptibility to common antimicrobial drugs urge implementation of efficient and reliable antifungal therapy. Up to date, polyene macrolide antibiotics proved to be the most effective antifungal agents due to their potent fungicidal activity, broad spectrum, and relatively low frequency of resistance among the fungal pathogens. However, polyene macrolides are rather toxic, causing such serious side effects as renal failure, hypokalemia and thrombophlebitis, especially upon intravenous administration. Current views on the biosynthesis of polyene macrolides, their mode of action and structure-function relationship, as well as strategies used to overcome the toxicity problem are discussed in this review. In addition, some of the new potential applications for polyene macrolides in therapy of prion diseases, HIV infection and cancer are highlighted.

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.

Over the past 15 years the biosynthetic gene clusters for numerous bioactive polyketides have been intensively studied and recently this work has been extended to the antifungal polyene macrolides. These compounds consist of large macrolactone rings that have a characteristic series of conjugated double bonds, as well as an exocyclic carboxyl group and an unusual mycosamine sugar. The biosynthetic gene clusters for nystatin, pimaricin, amphotericin and candicidin have been investigated in detail. These clusters contain the largest modular polyketide synthase genes reported to date. This body of work also provides insights into the enzymes catalysing the unusual post-polyketide modifications, and the genes regulating antibiotic biosynthesis. The sequences also provide clues about the evolutionary origins of polyene biosynthetic genes. Successful genetic manipulation of the producing organisms leading to production of polyene analogues indicates good prospects for generating improved antifungal compounds via genetic engineering.