Imaging Mass Spectrometry of a Coral Microbe Interaction with Fungi

Fungal infections are increasing worldwide, including in the aquatic environment. Microbiota that coexist with marine life can provide protection against fungal infections by secretion of metabolites with antifungal properties. Our laboratory has developed mass spectrometric methodologies with the goal of improving our functional understanding of microbial metabolites and guiding the discovery process of anti-infective agents from natural sources. GA40, a Bacillus amyloliquefaciens strain isolated from an octocoral in Panama, displayed antifungal activity against various terrestrial and marine fungal strains. Using matrix-assisted laser desorption/ionization-imaging mass spectrometry (MALDI-IMS), the molecular species produced by this microbe were visualized in a side-by-side interaction with two representative fungal strains, Aspergillus fumigatus and Aspergillus niger. The visualization was performed directly on the agar without the need for extraction. By evaluating the spatial distributions, relative intensities and m/z values of GA40 secreted metabolites in the fungal interactions and singly grown control colonies, we obtained insight into the antifungal activity of secreted metabolites. Annotation of GA40 metabolites observed in MALDI-IMS was facilitated by MS/MS networking analysis, a mass spectrometric technique that clusters metabolites with similar MS/MS fragmentation patterns. This analysis established that the predominant GA40 metabolites belong to the iturin family. In a fungal inhibition assay of A. fumigatus, the GA40 iturin metabolites were found to be responsible for the antifungal properties of this Bacillus strain.     

A bipolar integrated continuous-time filter with optimized dynamicrange

In the design of integrated continuous-time filters it is often difficult to choose a proper integrator circuit because the relative merits of the different possibilities are little known. A thorough analysis of all the possible circuits is necessary. In this work, the design and an accurate analysis of the noise and distortion properties of one type of integrator, based on a tunable bipolar transconductor, are given. The analysis is used to optimize the dynamic range, and the results are verified by simulation and measurement. A fifth-order low-pass filter design and implementation are presented to illustrate the usefulness of the designed integrator