Bioresorbable silicon electronics technology offers unprecedented opportunities to deploy advanced implantable monitoring systems that eliminate risks, cost and discomfort associated with surgical extraction. Applications include post-operative monitoring and transient physiologic recording after percutaneous or minimally invasive placement of vascular, cardiac, orthopedic, neural or other devices. We present an embodiment of these materials in both passive and actively addressed arrays of bioresorbable silicon electrodes with multiplexing capabilities, that record in vivo electrophysiological signals from the cortical surface and the subgaleal space. The devices detect normal physiologic and epileptiform activity, both in acute and chronic recordings. Comparative studies show sensor performance comparable to standard clinical systems and reduced tissue reactivity relative to conventional clinical electrocorticography (ECoG) electrodes. This technology offers general applicability in neural interfaces, with additional potential utility in treatment of disorders where transient monitoring and modulation of physiologic function, implant integrity and tissue recovery or regeneration are required.

Articles you may be interested inThe electronic structure changes and the origin of the enhanced optical properties in N-doped anatase TiO2-A theoretical revisitWe present first-principles density-functional calculations for the electronic properties of nitrogen͑N͒-doped as well as carbon͑C͒-doped titanium dioxide ͑TiO 2 ͒. We find that the bands originating from N ͑C͒ 2p states appear in the band gap of TiO 2 , but the mixing of N ͑C͒ with O 2p states is too weak to produce a significant band-gap narrowing. Our results are consistent with several recent experimental data of N-doped TiO 2 , where the absorption of visible light is due to isolated N 2p states above the valence-band maximum of TiO 2 rather than due to a band-gap narrowing.

The asbABCDEF gene cluster from Bacillus anthracis is responsible for biosynthesis of petrobactin, a catecholate siderophore that functions in both iron acquisition and virulence in a murine model of anthrax. We initiated studies to determine the biosynthetic details of petrobactin assembly based on mutational analysis of the asb operon, identification of accumulated intermediates, and addition of exogenous siderophores to asb mutant strains. As a starting point, in-frame deletions of each of the genes in the asb locus (asbABCDEF) were constructed. The individual mutations resulted in complete abrogation of petrobactin biosynthesis when strains were grown on iron-depleted medium. However, in vitro analysis showed that each asb mutant grew to a very limited extent as vegetative cells in iron-depleted medium. In contrast, none of the B. anthracis asb mutant strains were able to outgrow from spores under the same culture conditions. Provision of exogenous petrobactin was able to rescue the growth defect in each asb mutant strain. Taken together, these data provide compelling evidence that AsbA performs the penultimate step in the biosynthesis of petrobactin, involving condensation of 3,4-dihydroxybenzoyl spermidine with citrate to form 3,4-dihydroxybenzoyl spermidinyl citrate. As a final step, the data reveal that AsbB catalyzes condensation of a second molecule of 3,4-dihydroxybenzoyl spermidine with 3,4-dihydroxybenzoyl spermidinyl citrate to form the mature siderophore. This work sets the stage for detailed biochemical studies with this unique acyl carrier protein-dependent, nonribosomal peptide synthetase-independent biosynthetic system.

The glycolipid antibiotic rhamnolipid B isolated from Pseudomonas aeruginosa strain B5 was evaluated for in vitro antifungal activity and in vivo control against phytophthora blight and anthracnose under glasshouse conditions. Rhamnolipid B showed antifungal activity against Cercospora kikuchii, Cladosporium cucumerinum, Colletotrichum orbiculare, Cylindrocarpon destructans, Magnaporthe grisea and Phytophthora capsici. Microscopic observation revealed that the high level of antifungal activity (10 mg ml À1 ) against P capsici was mainly due to a lytic effect on zoospores. Zoospore lysis began in the presence of 10 mg ml À1 of rhamnolipid B and most of the zoospores were collapsed at 25 mg ml À1 . Rhamnolipid B showed inhibitory activity against the germination of zoospores and hyphal growth of P capsici at concentrations of 50 mg ml À1 . Spore germination of the anthracnose plant pathogen C orbiculare was also inhibited in the presence of 50 mg ml À1 of rhamnolipid B, although hyphal growth was not affected at this concentration. In the glasshouse, the ef®cacy of rhamnolipid B against phytophthora blight was similar to that of metalaxyl on pepper plants when treated just before inoculation with P capsici. Treatment with either at 500 mg ml À1 completely protected pepper plants from phytophthora blight. Rhamnolipid B also suppressed the development of C orbiculare infection on leaves of cucumber plants.

Petrobactin, a virulence-associated siderophore produced by Bacillus anthracis, chelates ferric iron through the rare 3,4-isomer of dihydroxybenzoic acid (3,4-DHBA). Most catechol siderophores, including bacillibactin and enterobactin, use 2,3-DHBA as a biosynthetic subunit. Significantly, siderocalin, a factor involved in human innate immunity, sequesters ferric siderophores bearing the more typical 2,3-DHBA moiety, thereby impeding uptake of iron by the pathogenic bacterial cell. In contrast, the unusual 3,4-DHBA component of petrobactin renders the siderocalin system incapable of obstructing bacterial iron uptake. Although recent genetic and biochemical studies have revealed selected early steps in petrobactin biosynthesis, the origin of 3,4-DHBA as well as the function of the protein encoded by the final gene in the B. anthracis siderophore biosynthetic (asb) operon, asbF (BA1986), has remained unclear. In this study we demonstrate that 3,4-DHBA is produced through conversion of the common bacterial metabolite 3-dehydroshikimate (3-DHS) by AsbF-a 3-DHS dehydratase. Elucidation of the cocrystal structure of AsbF with 3,4-DHBA, in conjunction with a series of biochemical studies, supports a mechanism in which an enolate intermediate is formed through the action of this 3-DHS dehydratase metalloenzyme. Structural and functional parallels are evident between AsbF and other enzymes within the xylose isomerase TIM-barrel family. Overall, these data indicate that microbial species shown to possess homologs of AsbF may, like B. anthracis, also rely on production of the unique 3,4-DHBA metabolite to achieve full viability in the environment or virulence within the host.AsbF structure ͉ dehydratase ͉ siderophore ͉ virulence factor S iderophore production in pathogenic bacteria has gained considerable attention because of its crucial function in essential iron uptake by many microbes and the relevance of siderophore-associated proteins as molecular markers of various infectious agents (1). In Bacillus anthracis, the causative agent of anthrax, 2 siderophores, petrobactin and bacillibactin (Fig. 1A), play a significant role during iron acquisition (2-4), but only petrobactin is absolutely essential for full virulence within a mammalian host (5). This siderophore was initially discovered from the Gram-negative marine bacterium Marinobacter hydrocarbonoclasticus, whose genome bears a biosynthetic gene cluster homologous to the B. anthracis asb operon (2). Recent genetic and chemical analysis suggests that petrobactin biosynthesis may also be a prerequisite for virulence in related Bacillus species (6). These studies highlight the importance of elucidating the mechanisms of siderophore production in pathogenic microbes as a target for abrogating infection by organisms like B. anthracis, a rapidly virulent microbe with proven potential as a bioterrorism agent. Based on these factors, we have initiated studies to investigate key biosynthetic enzymes for petrobactin assembly in efforts to establish new antimicrobial targets t...

Diversity of actinomycetes and their antifungal activities against some plant pathogenic fungi were examined in various vegetative soils from 14 different sites in the western part of Korea. Actinomycete counts ranged from 1.17 x 10(6) to 4.20 x 10(6) cfu x g(-1) dried soil. A total of 1510 actinomycetes were isolated from the soil samples. Streptomyces was predominant in soils with a pH range of 5.1-6.5, 9.1-13.0% moisture, and 9.1-11.0% organic matter. Most Micromonospora, Dactylosporangium, and Streptosporangium were distributed in soils with pH 4.0-5.0, 2.0-9.0% moisture, and 4.0-7.0% organic matter. Actinomadura and nocardioform actinomycetes were abundant in soils with pH 4.0-5.0 and 13.1-20.0% moisture and with 9.1-11.0 and 4.0-7.0% organic matter, respectively. Populations of Streptomyces were predominant in all the soils, but were highest in grassland and lowest in mountain-forest soils. Micromonospora was most abundant in pepper-field soil and nocardioform actinomycetes were highest in rice paddy field soil. Dactylosporangium was predominant in lake-mud sediments and pepper-field soil, Streptosporangium in lake-mud sediments, and Actinomadura in mountain-forest soil. Antifungal actinomycetes were abundant in orchard soil and lake mud. More than 50% of antifungal isolates from most soils were classified as genus Streptomyces. Actinomycete isolates that showed strong antifungal activity against Alternaria mali, Colletotrichum gloeosporioides, Fusarium oxysporum f.sp. cucumerinum, and Rhizoctonia solani were predominant in pepper-field soils, whereas those against Magnaporthe grisea and Phytophthora capsici were abundant in radish-field soils.

Recently, iron acquisition and, more specifically, enzymes involved in siderophore biosynthesis have become attractive targets for discovery of new antibiotics. Accordingly, targeted inhibition of the biosynthesis of petrobactin, a virulence-associated siderophore encoded by the asb locus in Bacillus anthracis, may hold promise as a potential therapy against anthrax. This study describes the biochemical characterization of AsbC, the first reported 3,4-dihydroxybenzoic acid-AMP ligase, and a key component in the biosynthesis of DHB-spermidine (DHB-SP), the first isolable intermediate in petrobactin biosynthesis. AsbC catalyzes adenylation to the corresponding AMP ester of the unusual precursor 3,4-dihydroxybenzoate, in addition to benzoate substrates bearing hydrogen bond-donating substituents at the para and meta positions on the phenyl ring. In a second reaction, AsbC catalyzes transfer of the activated starter unit to AsbD, an aryl carrier protein similar to acyl and peptidyl carrier proteins that function in fatty acid, polyketide, and nonribosomal peptide biosynthesis. A third protein, AsbE, is shown to be responsible for condensation of 3,4-dihydroxybenzoyl-AsbD with spermidine, providing the DHB-spermidine arms that are linked to citrate for assembly of petrobactin. On the basis of the selective substrate profile of AsbC, a nonhydrolyzable analogue of 3,4-DHB-AMP was synthesized and shown to effectively inhibit AsbC function in vitro.

Background: asbABCDEF mediates petrobactin production and facilitates anthrax virulence. Results: Purified AsbA-E proteins reconstituted petrobactin assembly in vitro. The crystal structure and enzymatic studies of AsbB highlight its function and role in the siderophore pathway. Conclusion: AsbB characterization demonstrated reaction flexibility and substrate positions in the binding pocket. Significance: Siderophore synthetases represent promising antimicrobial targets, and characterization of these versatile enzymes enables creation of novel compounds.