Ingestion of the cycad toxins β-methylamino-L-alanine (BMAA) and azoxyglycosides is harmful to diverse organisms. However, some insects are specialized to feed on toxin-rich cycads with apparent immunity. Some cycad-feeding insects possess a common set of gut bacteria, which might play a role in detoxifying cycad toxins. Here, we investigated the composition of gut microbiota from a worldwide sample of cycadivorous insects and characterized the biosynthetic potential of bacteria isolated as putative keystone taxa. Cycadivorous insects shared a core gut microbiome consisting of six bacterial taxa, mainly belonging to the Proteobacteria, which we were able to isolate. To further investigate these potential keystone taxa from diverging lineages, we performed shotgun metagenomic sequencing of co-cultured bacterial sub-communities. We postulate and characterize four putative keystone bacteria from Serratia, Pantoea, and two different Stenotrophomonas lineages. The biosynthetic potential of these microorganisms includes a suite of biosynthetic gene clusters notably rich in siderophores and carotenoid-like aryl polyene pathways. Siderophore semi-untargeted metabolomics revealed a broad range of chemically related yet diverse iron-chelating metabolites, indicating a complex evolutionary landscape in which siderophores may have converged within the guts of cycadivorous insects. Among these, we provide evidence of the occurrence of an unprecedent desferrioxamine-like biosynthetic pathway that remains to be identified. These results provide a foundation for future investigations into how cycadivorous insects tolerate diets rich in azoxyglycosides, BMAA, and other cycad toxins, and highlight convergent evolution underlying chemical diversity.

Ingestion of the cycad toxins beta-methylamino-L-alanine (BMAA) and azoxyglycosides is harmful to diverse organisms. However, some insects are specialized to feed on toxin-rich cycads with apparent immunity. Some cycad-feeding insects possess a common set of gut bacteria, which might play a role in detoxifying cycad toxins. Here, we investigated the composition of gut microbiota from a worldwide sample of cycadivorous insects and characterized the biosynthetic potential of selected bacteria. Cycadivorous insects shared a core gut microbiome consisting of six bacterial taxa, mainly belonging to the Proteobacteria, which we were able to isolate. To further investigate selected taxa from diverging lineages, we performed shotgun metagenomic sequencing of co-cultured bacterial sub-communities. We characterized the biosynthetic potential of four bacteria from Serratia, Pantoea, and two different Stenotrophomonas lineages, and discovered a suite of biosynthetic gene clusters notably rich in siderophores. Siderophore semi-untargeted metabolomics revealed a broad range of chemically related yet diverse iron-chelating metabolites, including desferrioxamine B, suggesting the occurrence of an unprecedented desferrioxamine-like biosynthetic pathway that remains to be identified. These results provide a foundation for future investigations into how cycadivorous insects tolerate diets rich in azoxyglycosides, BMAA, and other cycad toxins, including a possible role for bacterial siderophores.

An analysis of the effect on the flow regime caused by reservoir operation is crucial to balancing the exploitation and protection of water resources. The long-term effect of this on the intraday scale and small storage capacity is considerable, but rarely analyzed. This study examines the world's largest dual-cascade hydro-junction, the Three Gorges Dam and Gezhouba Dam junction, as a case study, adopting eight indices to characterize the reservoir's inflow and outflow fluctuation. In doing this, we evaluate the alteration of the flow regime induced by an up-cascade reservoir and its alleviation caused by the down-cascade re-regulation. The results show: (1) an increment of the river flow fluctuation at the Three Gorges Dam, matched with hourly scale alleviation at the Gezhouba Dam; (2) a reduction (25.09 similar to 41.35%) in the quantitative indices of the river flow regime fluctuation; (3) perturbations on the power output. These findings provide references for developing methods to assess the re-regulation mechanisms in systems with upper- and lower-cascades.

We present faint galaxy counts from deep VRI images obtained with the Keck Telescope. These images reach R similar to 27 in median seeing FWHM similar to 0 ''.5-0 ''.6, and we detect a integrated galaxy number density of 7 x 10(5) deg(-2), equivalent to 3 x 10(10) galaxies in the observable universe. In addition we present median galaxy colors as a function of magnitude; bluing trends are visible in all colors to R similar to 24.5. Fainter than R similar to 24.5, however, the typical V - R color becomes redder again, V - I remains constant, and R - I becomes yet bluer. These trends are consistent with the VRI count slopes, implying a decrease in the V slope at the faintest levels, which our data support. Taking advantage of our good seeing we also present median half-light radii for faint galaxies; these show a steady decline at fainter magnitudes, leading to an intrinsic half-light radius of similar to 0 ''.2 for a typical R similar to 26 galaxy. Irrespective of the redshift distribution, the extremely high galaxy surface densities and their small intrinsic sizes are consistent with a scenario in which the majority of the very faint field population are dwarf galaxies or subgalactic units.

We have combined deep starcount data with Galaxy model predictions to investigate how effectively such measurements probe the faint end of the halo luminosity function, We have tested a number of star/galaxy classification techniques using images taken in 0.5 arcsec seeing with LRIS on the Keek telescope, and we iind that different combinations of these techniques can produce variations of 10% in the inferred starcounts at R = 22.5 and 30% at R = 24.5 mag. The decreasing average angular size of galaxies with fainter magnitude effectively limits ground-based work to R < 25.5 mag. The higher angular resolution provided by HST allows one to probe at least 2 mag fainter, but the small field size is a significant limitation, In either case, our models show that the contribution from halo subdwarfs is effectively limited to colours of (R-1)<1.0. with the redder stars being members of the Galactic disk, The apparent increase in number density for M(V) > 10 in the derived luminosity function is a result of contributions from disk stars at fainter absolute magnitudes and does not provide evidence for an upturn in the halo subdwarf mass function. Indeed, starcount data alone are not an effective method of probing the shape of the halo luminosity function close to the hydrogen-burning limit, Finally, we examine how the Hubble Deep Field observations can be used to constrain the contribution of various stellar components to die dark-matter halo. (C) 1996 American Astronomical Society.

We present deep galaxy counts and half-light radii from F160W (lambda(c) = 1.6 mu m) images obtained with the Near-Infrared Camera and Multiobject Spectrograph on the Hubble Space Telescope. Nearly 9 arcmin(2) have been imaged with camera 3, with 3 sigma depths ranging from H = 24.3 to 25.5 in a 0." 6 diameter aperture. The slope of the counts fainter than H = 20 is 0.31, and the integrated surface density to H less than or equal to 24.75 is 4 x 10(5) galaxies deg(-2). The half-light radii of the galaxies decline steeply with apparent magnitude. At H = 24, we are limited by both the delivered FWHM and the detection threshold of the images.

We present the results of a survey which utilizes the NICMOS Camera 3 Parallel grism and imaging observations of random fields. We have identified 33 H alpha emission-line galaxies at 0.75 < z < 1.9. The inferred co-moving number, density of these objects is 3.3 x 10(-4) h(50)(3), Mpc(-3), very similar to that of the bright Lyman break objects at z similar to 3. The mean star formation rate of these galaxies 21 M. yr(-1) for H-0 = 50km/s/Mpc. Using this sample, we derived the H alpha luminosity function (LF) at z = 1.3. The integrated H alpha luminosity density at z similar to 1.3 is 1.64 x 10(40) h(50) erg s(-1) Mpc(-3), approximately 14 times greater than the local value reported by Gallego et al. (1995). The volume averaged star formation rate at 1.3 +/- 0.5 is 0.13 M. yr(-1) Mpc(-3) without correction for extinction. The SFR derived at similar to 6500 Angstrom is a factor of 3 higher than that deduced from 2800 Angstrom continua. We believe that this difference is largely due to dust extinction. The implied total extinction at 2800 Angstrom is in the range of 2 - 4 magnitude. However, the precise determination of the total extinction is sensitive to the model assumptions.

We present results from our analysis of F160W NICMOS Parallel images. These data cover similar to 9 so. arcminutes and reach 3 sigma depths of H= 24.3 - 25.5 in a 0.6 " diameter aperture with integration times of 2,000 to 13,000 seconds. We derive the first deep H band galaxy counts. The slope of the counts for H< 20 is 0.31, consistent with various K-band measurements from the Keck telescopes. The measured number counts vs, magnitude relation is reasonably well fitted with no-evolution models with a low Omega value. The half-light radii of the galaxies declines steeply with apparent magnitude and reaches the NIC3 resolution limit at H=23.5. Deep ground-based VRI imaging of one NICMOS held has revealed an extremely red galaxy with R-H = 6 and H of 18.8. Our analyses of the grism data show that we can reach 3 sigma flux limits of of 1 x 10(-16) to 2 x 10(-17) ergs/sec/cm(2) for integration times of 2,000 to 21,000 seconds. We have detected a total of 33 emission line galaxies. The comoving number density is similar to 2 x 10(-4)Mpc(-3) The detected emission lines are probably H-alpha 6563 Angstrom. Thus, the derived star formation rates, without extinction correction, are 10 - 163M. per year for galaxies at redshifts between 0.7 and 1.9.

We present a luminosity function for H alpha emission from galaxies at redshifts between 0.7 and 1.9 based on slitless spectroscopy with the near-infrared camera and multiobject spectrometer on the Hubble Space Telescope. The luminosity function is well fit by a Schechter function over the range 6 x 10(41) < L (H alpha) < 2 x 10(43) ergs s(-1) with L* = 7 x 10(42) ergs s(-1) and phi* = 1.7 x 10(-3) Mpc(-3) for H-0 = 50 km s(-1) Mpc(-1) and q(0) = 0.5. We derive a volume-averaged star formation rate at z = 1.3 +/- 0.5 of 0.13 M. yr(-1) Mpc(-3) without correction for extinction. The star formation rate that we derive at similar to 6500 Angstrom is a factor of 3 higher than that deduced from 2800 Angstrom continua. If this difference is caused entirely by reddening, the extinction correction at 2800 Angstrom is quite significant. The precise magnitude of the total extinction correction at rest-frame UV wavelengths (e.g., 2800 and 1500 Angstrom) is sensitive to the relative spatial distribution of the stars, gas, and dust, as well as to the extinction law. In the extreme case of a homogeneous foreground dust screen and a Milky Way or LMC extinction law, we derive a total extinction at 2800 Angstrom of 2.1 mag, or a factor of 7 correction to the UV luminosity density. If we use the Calzetti reddening curve, which was derived for the model in which stars, gas, and dust are well mixed and nebular gas suffers more extinction than stars, our estimate of A(2800) is increased by more than 1 mag.

We present the first results of a survey of random fields with the slitless G141 (lambda(c) = 1.5 mu m, Delta lambda = 0.8 mu m) grism on the near-IR camera and multiobject spectrometer (NICMOS) on board the Hubble Space Telescope (HST). Approximately 64 arcmin(2) have been observed at intermediate and high Galactic latitudes. The 3 sigma limiting line and continuum fluxes in each field vary from 7.5 x 10(-17) to 1 x 10-17 ergs cm(-2) s(-1) and from H = 20 to 22, respectively. Our median and area-weighted 3 sigma limiting line fluxes within a 4 pixel aperture are nearly identical at 4.1 x 10(-17) ergs cm(-2) s(-1) and are 60% deeper than the deepest narrowband imaging surveys from the ground. We have identified 33 emission-line objects and derive their observed wavelengths, fluxes, and equivalent widths. We argue that the most likely line identification is Ho! and that the redshift range probed is from 0.75 to 1.9. The 2 sigma rest-frame equivalent width Limits range from 9 to 130 Angstrom, with an average of 40 Angstrom. The survey probes an effective comoving volume of 10(5) h(50)(-3) Mpc(3) for q(0) = 0.5. Our derived comoving number density of emission-line galaxies in the range 0.7 < z < 1.9 is 3.3 x 10(-4) h(50)(3) Mpc(-3), very similar to that of the bright Lyman break objects at z similar to 3. The objects with detected emission lines have a median F160W magnitude of 20.4 (Vega scale) and a median Ka luminosity of 2.7 x 10(42) ergs s(-1). The implied star formation rates range from 1 to 324 M-circle dot yr(-1), with an average [N II] lambda lambda 6583, 6548 corrected rate of 21 M-circle dot yr(-1) for H-0 = 50 km s(-1) Mpc and q(0) = 0.5 (34 M-circle dot yr(-1) for q(0) = 0.1).