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Fungal secondary metabolites (SM) are bioactive compounds that are important in fungal ecology and, moreover, both harmful and useful in human endeavors (e.g., as toxins and pharmaceuticals). Recently a nuclear heterocomplex termed the Velvet complex, characterized in the model ascomycete Aspergillus nidulans, was found to be critical for SM production. Deletion of two members of the Velvet complex, laeA and veA, results in near loss of SM and defective sexual spore production in A. nidulans and other species. Using a multicopy-suppressor genetics approach, we have isolated an Aspergillus nidulans gene named rsmA (remediation of secondary metabolism) based upon its ability to remediate secondary metabolism in ⌬laeA and ⌬veA backgrounds. Overexpression of rsmA (OE::rsmA) restores production of sterigmatocystin (ST) (a carcinogenic SM) via transcriptional activation of ST biosynthetic genes. However, defects in sexual reproduction in either ⌬laeA or ⌬veA strains cannot be overcome by OE::rsmA. An intact Velvet complex coupled with an OE::rsmA allele increases SM many fold over the wild-type level, but loss of rsmA does not decrease SM. RsmA encodes a putative bZIP basic leucine zipper-type transcription factor.Secondary metabolites are biologically active compounds that are diverse in structure and often possess either pharmacological or toxic properties. To customize and control the biosynthesis of these natural products, we must understand how secondary metabolites (SM) are regulated. In fungi, SM production is controlled by global transcription factors encoded by genes unlinked to the SM biosynthetic gene clusters. Such genes regulate multiple physiological processes and generally respond to environmental cues such as pH, temperature, and nutrition (27,45). Regulation of many clustered genes is also largely dependent on pathway-specific transcription (18,22,42) and signal transduction pathways that link secondary metabolism with sporulation (13).LaeA is a global regulator of SM in the aspergilli. LaeA, a putative methyltransferase, was first identified in Aspergillus nidulans (5), A. fumigatus (6), and, subsequently, A. flavus (25). Overexpression (OE) of laeA increases the production of multiple metabolites in the aspergilli, whereas deletion of laeA silences expression of SM genes (1,5,8,20). LaeA is thus used as a genomic mining tool, providing a novel method for identifying new SM through microarray and chemical analyses (8,20,34). Moreover, deletion of laeA in A. fumigatus decreases the virulence of this human pathogen (4, 6); similarly, A. flavus laeA deletants are also reduced in virulence on host seed (1, 25). LaeA homologs are also found in other filamentous fungi such as Penicillium chrysogenum and Fusarium fujikuroi, where they control SM, pigmentation, sporulation, and virulence (29,43).Another important SM regulatory protein identified in A. nidulans is encoded by veA, otherwise known as velvet. VeA is a light-dependent regulator governing both development and SM production in several aspergilli (A...

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This study demonstrated that sodium ascorbate could function as signal modulator and virulence inhibitor in Ps. aeruginosa.

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Subtelomeric secondary metabolite (SM) gene clusters are frequently surrounded by DNA repeats and transposon-like elements. The A. nidulans penicillin cluster, 30 kb from the telomere of chromosome VI, is bordered by such elements. Deletions of penicillin telomere proximal and distal border regions resulted in decreased penicillin production. A 3.7 kb distal region called PbIa, consisting of the putative transposable element DNA-2, was examined further where its replacement by a pyrG marker presented a similar phenotype as loss of the global SM regulator LaeA, resulting in a decrease in penicillin gene expression and product formation. In contrast, placement of the pyrG marker on either side of PbIa had no effect on penicillin synthesis. A requirement for PbIa in penicillin production was also apparent in a histone deacetylase mutant, ΔhdaA, enhanced for penicillin production. Trans complementation of the PbIa element near and within the terrequinone A cluster on chromosome V did not restore penicillin biosynthesis or increase production of terrequinone A. Taken together, this data provides evidence for transposon involvement in SM cluster regulation.

The spread of multidrug-resistant Pseudomonas aeruginosa isolates constitutes a serious clinical challenge. Bacterial efflux machinery is a crucial mechanism of resistance among P. aeruginosa. Efflux inhibitors such as phenylalanine arginyl β-naphthylamide (PAβN) promote the bacterial susceptibility to antimicrobial agents. The pathogenesis of P. aeruginosa is coordinated via quorum sensing (QS). This study aims to find out the impact of efflux pump inhibitor, PAβN, on QS and virulence attributes in clinical isolates of P. aeruginosa. P. aeruginosa isolates were purified from urine and wound samples, and the antimicrobial susceptibility was carried out by disc diffusion method. The multidrug-resistant and the virulent isolates U16, U21, W19 and W23 were selected. PAβN enhanced their susceptibility to most antimicrobial agents. PAβN reduced QS signalling molecules N-3-oxo-dodecanoyl-l-homoserine lactone and N-butyryl-l-homoserine lactone without affecting bacterial viability. Moreover, PAβN eliminated their virulence factors such as elastase, protease, pyocyanin and bacterial motility. At the transcription level, PAβN significantly (P<0.01) diminished the relative expression of QS cascade (lasI, lasR, rhlI, rhlR, pqsA and pqsR) and QS regulated-type II secretory genes lasB (elastase) and toxA (exotoxin A) compared to the control untreated isolates U16 and U21. In addition, PAβN eliminated the relative expression of pelA (exopolysaccharides) in U16 and U21 isolates. Hence, P. aeruginosa-tested isolates became hypo-virulent upon using PAβN. PAβN significantly blocked the QS circuit and inhibited the virulence factors expressed by clinical isolates of P. aeruginosa. PAβN could be a prime substrate for development of QS inhibitors and prevention of P. aeruginosa pathogenicity.