Seventy bacterial isolates from the rhizosphere of tomato were screened for antagonistic activity against the tomato foot and root rot-causing fungal pathogen Fusarium oxysporum f. sp. radicis-lycopersici. One isolate, strain PCL1391, appeared to be an efficient colonizer of tomato roots and an excellent biocontrol strain in an F. oxysporum/tomato test system. Strain PCL1391 was identified as Pseudomonas chlororaphis and further characterization showed that it produces a broad spectrum of antifungal factors (AFFs), including a hydrophobic compound, hydrogen cyanide, chitinase(s), and protease(s). Through mass spectrometry and nuclear magnetic resonance, the hydrophobic compound was identified as phenazine-1-carboxamide (PCN). We have studied the production and action of this AFF both in vitro and in vivo. Using a PCL1391 transposon mutant, with a lux reporter gene inserted in the phenazine biosynthetic operon (phz), we showed that this phenazine biosynthetic mutant was substantially decreased in both in vitro antifungal activity and biocontrol activity. Moreover, with the same mutant it was shown that the phz biosynthetic operon is expressed in the tomato rhizosphere. Comparison of the biocontrol activity of the PCN-producing strain PCL1391 with those of phenazine-1-carboxylic acid (PCA)-producing strains P. fluorescens 2-79 and P. aureofaciens 30-84 showed that the PCN-producing strain is able to suppress disease in the tomato/F. oxysporum system, whereas the PCA-producing strains are not. Comparison of in vitro antifungal activity of PCN and PCA showed that the antifungal activity of PCN was at least 10 times higher at neutral pH, suggesting that this may contribute to the superior biocontrol performance of strain PCL1391 in the tomato/F. oxysporum system.

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Monorden (1) and the novel resorcylic acid lactones pochonins A (2), B (4), C (6), D (7), and E (8) as well as tetrahydromonorden (5) and pseurotin A (22) were isolated from cultures of the clavicipitaceous hyphomycete Pochonia chlamydosporia var. catenulata strain P 0297. Fermentation of P 0297 in bromide-containing culture media led to a shift in secondary metabolite production and yielded monocillins III (3) and II (9) as major metabolites besides monorden (1) as well as the novel compounds pochonin F (10) and a monocillin II glycoside (11) as minor metabolites. Most of these compounds showed moderate activities in a cellular replication assay against Herpes Simplex Virus 1 (HSV1) and against the parasitic protozoan Eimeria tenella. In contrast to the structurally related zearalenone derivatives none of the metabolites of strain P 0297 were found to be active in a fluorescence polarization assay for determination of modulatory activities on the human estrogenic receptor ERbeta. Beta-zearalenol (17), but not zearalenone (15) and alpha-zearalenol (16), showed antiherpetic effects. We report the production, isolation, and structure elucidation of compounds 1-11 and their biological characterization.

Arbuscular-mycorrhizal fungi are obligate endosymbionts that colonize the roots of almost 80% of land plants. This paper describes the employment of a combined morphological and molecular approach to demonstrate that the cytoplasm of the arbuscular-mycorrhizal fungus Gigaspora margarita harbors a further bacterial endosymbiont. Intracytoplasmic bacterium-like organisms (BLOs) were detected ultrastructurally in its spores and germinating and symbiotic mycelia. Morphological observations with a fluorescent stain revealed about 250,000 live bacteria inside each spore. The sequence for the small-subunit rRNA gene obtained for the BLOs from the spores was compared with those for representatives of the eubacterial lineages. Molecular phylogenetic analysis unambiguously showed that the endosymbiont of G. margarita was an rRNA group II pseudomonad (genus Burkholderia). PCR assays with specifically designed oligonucleotides were used to check that the sequence came from the BLOs. Successful amplification was obtained when templates from both the spores and the symbiotic mycelia were used. A band of the expected length was also obtained from spores of a Scutellospora sp. No bands were given by the negative controls. These findings indicate that mycorrhizal systems can include plant, fungal, and bacterial cells.

The cinnabaramides A-G (1-7) were isolated from a terrestrial strain of Streptomyces as potent and selective inhibitors of the human 20S proteasome. Their chemical and biological properties resemble those of salinosporamide A, a recently identified lead compound from an obligate marine actinomycete, which is currently under development as an anticancer agent. Cinnabaramides F and G (6, 7) combine essential structural features of salinosporamide A and lactacystin and show about equal potency in vitro, with IC50 values in the 1 nM range. The properties and phylogenetic position of the producer organism, the production and isolation of compounds 1-7, their structure elucidation by MS and NMR, and their biological activities are reported. Additionally, an X-ray crystal structure was obtained from cinnabaramide A (1).