Amplification of DNA encoding entire type I polyketide synthase domains and linkers from streptomyces species

Exploiting the genome sequence of Streptomyces nodosus for enhanced antibiotic production

The genome of the amphotericin producer Streptomyces nodosus was sequenced. A single scaffold of 7,714,110 bp was obtained. Biosynthetic genes were identified for several natural products including polyketides, peptides, siderophores and terpenes. The majority of these clusters specified known compounds. Most were silent or expressed at low levels and unlikely to compete with amphotericin production. Biosynthesis of a skyllamycin analogue was activated by introducing expression plasmids containing either a gene for a LuxR transcriptional regulator or genes for synthesis of the acyl moiety of the lipopeptide. In an attempt to boost amphotericin production, genes for acyl CoA carboxylases, a phosphopantetheinyl transferase and the AmphRIV transcriptional activator were overexpressed, and the effects on yields were investigated. This study provides the groundwork for metabolic engineering of S. nodosus strains to produce high yields of amphotericin analogues.

Exploring the antagonistic producer Streptomyces MSI051: implications of polyketide synthase gene type II and a ubiquitous defense enzyme phospholipase A2 in the host sponge Dendrilla nigra

To explore the functional role of the antagonistic producer strain Streptomyces dendra sp. nov. MSI051 in the host sponge Dendrilla nigra, hypothetical factors including the antagonistic potential of MSI051 against biofilm bacteria and a ubiquitous defense enzyme phospholipase A2 (PLA2) in host sponge as well as in bacterial symbiont MSI051 were determined. The host sponge D. nigra and associated bacterial symbiont MSI051 contained high levels of PLA2. The host sponge showed PLA2 activity to the extent of 1032 U/L, with a specific activity of 2021 U/g, and strain MSI051 showed similar activity. The findings of the present study suggest that PLA2 in the sponge-associated bacteria might have an integrated functional role in the host defense system of marine sponges. This report may be the first on the role of PLA2 activity in sponge-associated bacteria. Isolate MSI051 was a potential antagonistic producer which showed a broad spectrum of antibacterial activity. Polyketide synthase gene type II in MSI051 ultimately evidenced the antagonistic potential. Antimicrobial activity was found to be positively skewed toward biofilm bacteria. This implies a functional role of MSI051 in the protection of host sponge against fouling processes.

In vitro antagonism of an actinobacterial Kitasatospora isolate against the plant pathogen Phytophthora citricola as elucidated with ultrahigh resolution mass spectrometry

Many soil microorganisms antagonistic to soil borne plant pathogens are well known for their ability to control diseases in situ. A variety of substances, like lytic enzymes, siderophores and antibiotics, produced by these organisms have the potential to protect roots against pathogens. Understanding the ecology and a functional assessment of antagonistic microbial communities in soil requires in-depth knowledge of the mechanisms involved in these interactions, a challenging task in complex systems if low-resolution methods are applied. We propose an information-rich strategy of general relevance, composed of adequate preconcentration in conjunction with ultrahigh resolution ion cyclotron resonance Fourier transform mass spectrometry (ICR-FT/MS) and nuclear magnetic resonance (NMR) spectroscopy to identify any bioactive substances in complex systems. This approach is demonstrated on the specific example of substance identification considered responsible for in vitro antagonism of an actinobacterial antagonist isolated from European beech (Fagus sylvatica) rhizosphere soil against the oomycetous root rot pathogen Phytophthora citricola. The isolate belonging to the genus Kitasatospora exhibited strong antibiosis against the oomycete in vitro. The bioactive substance was observed to exhibit a molar mass of 281.1699 g/mol in positive electrospray ionization mass spectra, and the high mass accuracy of the ICR-FT/MS measurements allowed a precise assignment of a molecular formula that was found identical to the macrolide polyketide cycloheximide C(15)H(23)NO(4)+H(+); its identity was then unequivocally confirmed by the information-rich atomic signature of proton NMR spectroscopy. In conclusion, the combination of the near orthogonal methods (pre)fractionation, ultrahigh-resolution ICR-FT mass spectrometry (yielding molecular and MS(n) fragment signatures) and nuclear magnetic resonance spectroscopy (providing atomic signatures) has been found capable of identifying a biocontrol active compound of Kitasatospora active against Phytophthora citricola expediently, quickly, and accurately. This straightforward approach is of general applicability to elucidate biocontrol mechanisms in any complex system with improved efficiency.