Small-molecule, biologically active natural products continue to be our most rewarding source of, and inspiration for, new medicines. Sometimes we happen upon such molecules in minute quantities in unique, difficult-to-reach, and often fleeting environments, perhaps never to be discovered again. In these cases, determining the structure of a molecule-including assigning its relative and absolute configurations-is paramount, enabling one to understand its biological activity. Molecules that comprise stereochemically complex acyclic and conformationally flexible carbon chains make such a task extremely challenging. The baulamycins (A and B) serve as a contemporary example. Isolated in small quantities and shown to have promising antimicrobial activity, the structure of the conformationally flexible molecules was determined largely through J-based configurational analysis, but has been found to be incorrect. Our subsequent campaign to identify the true structures of the baulamycins has revealed a powerful method for the rapid structural elucidation of such molecules. Specifically, the prediction of nuclear magnetic resonance (NMR) parameters through density functional theory-combined with an efficient sequence of boron-based synthetic transformations, which allowed an encoded (labelled) mixture of natural-product diastereomers to be prepared-enabled us rapidly to pinpoint and synthesize the correct structures.
Manganese-oxidizing bacteria in the aquatic environment have been comprehensively investigated. However, little information is available about the distribution and biogeochemical significance of these bacteria in terrestrial soil environments. In this study, stratified soils were initially examined to investigate the community structure and diversity of manganese-oxidizing bacteria. Total 344 culturable bacterial isolates from all substrata exhibited Mn(II)-oxidizing activities at the range of 1 µM to 240 µM of the equivalent MnO2. The high Mn(II)-oxidizing isolates (>50 mM MnO2) were identified as the species of phyla Actinobacteria, Firmicutes and Proteobacteria. Seven novel Mn(II)-oxidizing bacterial genera (species), namely, Escherichia, Agromyces, Cellulomonas, Cupriavidus, Microbacterium, Ralstonia, and Variovorax, were revealed via comparative phylogenetic analysis. Moreover, an increase in the diversity of soil bacterial community was observed after the combined enrichment of Mn(II) and carbon-rich complex. The phylogenetic classification of the enriched bacteria represented by predominant denaturing gradient gel electrophoresis bands, was apparently similar to culturable Mn(II)-oxidizing bacteria. The experiments were further undertaken to investigate the properties of the Mn oxide aggregates formed by the bacterial isolates with high Mn(II)-oxidizing activity. Results showed that these bacteria were closely encrusted with their Mn oxides and formed regular microspherical aggregates under prolonged Mn(II) and carbon-rich medium enrichment for three weeks. The biotic oxidation of Mn(II) to Mn(III/IV) by these isolates was confirmed by kinetic examinations. X-ray diffraction assays showed the characteristic peaks of several Mn oxides and rhodochrosite from these aggregates. Leucoberbelin blue tests also verified the Mn(II)-oxidizing activity of these aggregates. These results demonstrated that Mn oxides were formed at certain amounts under the enrichment conditions, along with the formation of rhodochrosite in such aggregates. Therefore, this study provides insights into the structure and diversity of soil-borne bacterial communities in Mn(II)-oxidizing habitats and supports the contribution of soil-borne Mn(II)-oxidizing bacteria to Mn oxide mineralization in soils.
Capsicum annuum L., a fruit plant from tropical and subtropical regions, contains a range of essential nutrients and bioactive compounds which are known to exhibit a range of bioactivities including free radical scavenging (antioxidant), antimicrobial, antiviral, anti-inflammatory and anticancer. This review aims to give a comprehensive overview of the literature published on pharmacological behaviours of C. annuum L.
In this manuscript, we report that a bacterial multicopper oxidase (MCO266) catalyzes Mn(II) oxidation on the cell surface, resulting in the surface deposition of Mn(III) and Mn(IV) oxides and the gradual formation of bulky oxide aggregates. These aggregates serve as nucleation centers for the formation of Mn oxide micronodules and Mn-rich sediments. A soil-borne Escherichia coli with high Mn(II)-oxidizing activity formed Mn(III)/Mn(IV) oxide deposit layers and aggregates under laboratory culture conditions. We engineered MCO266 onto the cell surfaces of both an activity-negative recipient and wild-type strains. The results confirmed that MCO266 governs Mn(II) oxidation and initiates the formation of deposits and aggregates. By contrast, a cell-free substrate, heat-killed strains, and intracellularly expressed or purified MCO266 failed to catalyze Mn(II) oxidation. However, purified MCO266 exhibited Mn(II)-oxidizing activity when combined with cell outer membrane component (COMC) fractions in vitro. We demonstrated that Mn(II) oxidation and aggregate formation occurred through an oxygen-dependent biotic transformation process that requires a certain minimum Mn(II) concentration. We propose an approximate electron transfer pathway in which MCO266 transfers only one electron to convert Mn(II) to Mn(III) and then cooperates with other COMC electron transporters to transfer the other electron required to oxidize Mn(III) to Mn(IV).
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