Metagenomic and functional analysis of hindgut microbiota of a wood-feeding higher termite

From the standpoints of both basic research and biotechnology, there is considerable interest in reaching a clearer understanding of the diversity of biological mechanisms employed during lignocellulose degradation. Globally, termites are an extremely successful group of wood-degrading organisms and are therefore important both for their roles in carbon turnover in the environment and as potential sources of biochemical catalysts for efforts aimed at converting wood into biofuels. Only recently have data supported any direct role for the symbiotic bacteria in the gut of the termite in cellulose and xylan hydrolysis. Here we use a metagenomic analysis of the bacterial community resident in the hindgut paunch of a wood-feeding 'higher' Nasutitermes species (which do not contain cellulose-fermenting protozoa) to show the presence of a large, diverse set of bacterial genes for cellulose and xylan hydrolysis. Many of these genes were expressed in vivo or had cellulase activity in vitro, and further analyses implicate spirochete and fibrobacter species in gut lignocellulose degradation. New insights into other important symbiotic functions including H2 metabolism, CO2-reductive acetogenesis and N2 fixation are also provided by this first system-wide gene analysis of a microbial community specialized towards plant lignocellulose degradation. Our results underscore how complex even a 1-microl environment can be.     

Techniques for making capillary microelectrodes

Résumé Nous décrivons un appareil facile à construire pour étirer des microélectrodes capillaires et une manière simple de remplir ceux-ci sous pression réduite.

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This work was supported by a research grant from the National Institute of Neurological Diseases and Blindness, U. S. Public Health Service.     

Discretizing light behaviour in linear and nonlinear waveguide lattices

Light propagating in linear and nonlinear waveguide lattices exhibits behaviour characteristic of that encountered in discrete systems. The diffraction properties of these systems can be engineered, which opens up new possibilities for controlling the flow of light that would have been otherwise impossible in the bulk: these effects can be exploited to achieve diffraction-free propagation and minimize the power requirements for nonlinear processes. In two-dimensional networks of waveguides, self-localized states--or discrete solitons--can travel along 'wire-like' paths and can be routed to any destination port. Such possibilities may be useful for photonic switching architectures.     

Protection of repetitive DNA borders from self-induced meiotic instability

DNA double strand breaks (DSBs) in repetitive sequences are a potent source of genomic instability, owing to the possibility of non-allelic homologous recombination (NAHR). Repetitive sequences are especially at risk during meiosis, when numerous programmed DSBs are introduced into the genome to initiate meiotic recombination. In the repetitive ribosomal DNA (rDNA) array of the budding yeast Saccharomyces cerevisiae, meiotic DSB formation is prevented in part through Sir2-dependent heterochromatin formation. Here we show that the edges of the rDNA array are exceptionally susceptible to meiotic DSBs, revealing an inherent heterogeneity in the rDNA array. We find that this localized DSB susceptibility necessitates a border-specific protection system consisting of the meiotic ATPase Pch2 and the origin recognition complex subunit Orc1. Upon disruption of these factors, DSB formation and recombination increased specifically in the outermost rDNA repeats, leading to NAHR and rDNA instability. Notably, the Sir2-dependent heterochromatin of the rDNA itself was responsible for the induction of DSBs at the rDNA borders in pch2Δ cells. Thus, although the activity of Sir2 globally prevents meiotic DSBs in the rDNA, it creates a highly permissive environment for DSB formation at the junctions between heterochromatin and euchromatin. Heterochromatinized repetitive DNA arrays are abundant in most eukaryotic genomes. Our data define the borders of such chromatin domains as distinct high-risk regions for meiotic NAHR, the protection of which may be a universal requirement to prevent meiotic genome rearrangements that are associated with genomic diseases and birth defects.