Association of an ice-nucleating pseudomonad with cultures of the marine dinoflagellate, Heterocapsa niei

The observations that terrestrial ice nuclei can have a biogenic origin and that certain bacteria can initiate freezing at exceptionally warm temperatures (−1.5°C) are now well documented. Less well understood are active ice nuclei (−2 to −5°C) found in sea water, marine fog and the marine atmosphere in general. Recently, the authors have isolated an ice nucleation-active (INA) bacterial strain (FB 1032) from cultures of the marine dinoflagellate, Heterocapsa niei. FB 1032 is halotolerant and phenotypically similar to Pseudomonas fluorescens biotype G, although it differs from biotype G strains in its bacteriophage sensitivity and expression of the INA phenotype. A search for the INA pseudomonad in sea water at La Jolla, California was unsuccessful, but several INA Erwinia sp. were isolated. The possible terrestrial origin of these INA bacteria is suggested

Microbial Production of Isoprene

Isoprene is a volatile hydrocarbon of unknown function, produced by certain bacteria, plants and animals, sometimes in huge amounts—the Earth’s forests are estimated to emit >500 x 106 tons of isoprene per year. With funding from this program we explored the biochemistry and regulation of isoprene formation in the model bacterial system, Bacillus subtilis, with the goals of explaining the biological rationale for isoprene biogenesis and constructing an isoprene-overproducing microbial system. Although the role for isoprene formation in B. subtilis is still uncertain, our current model for regulation of this hydrocarbon’s synthesis is that isoprene production in B. subtilis is controlled by a combination of i) rapid regulation of isoprene synthase activity and ii) supply of the substrate for isoprene synthase, dimethyallyl diphosphate (DMAPP). This model parallels our current thinking about the control of isoprene formation in plant chloroplasts. In this reporting period we have been working to test part ii) of this model; this work has produced new results using genetic and analytical approaches. For examples, we have developed an analytical method to resolve DMAPP and its isomer, isopentenyl diphosphate, from each other in bacteria and plants. We have also shown that the IPP isomerase (type 2) of B. subtilis is not the source of “isoprene synthase” activity, and discovered that B. subtilis releases C5 isoprenoid alcohols to the medium, suggesting that isoprene plus other C5 isoprenoids may be common by-products of metabolism. In addition, we have continued to work on our discovery that wild type B. subtilis strains form prolific biofilms, are normal components of plant root microflora, and are testing the idea that B. subtilis growing in biofilms uses isoprene to induce plant root exudation

A defined medium to investigate sliding motility in a Bacillus subtilis flagella-less mutant

BACKGROUND: We have recently shown that undomesticated strains of Bacillus subtilis can extensively colonize the surfaces of rich, semi-solid media, by a flagellum-independent mechanism and suggested that sliding motility is responsible for surface migration. Here we have used a flagella-less hag null mutant to examine and confirm sliding motility. RESULTS: Using a defined semi-solid medium we determined that a B. subtilis hag mutant colonized the surface in two stages, first as tendril-like clusters of cells followed by a profuse pellicle-like film. We determined the levels of macro- and micro-nutrients required for the tendril-to-film transition. Sufficient levels of each of the macronutrients, glycerol, Na-glutamate, and Na-phosphate, and inorganic nutrients, K(+), Mg(2+), Fe(2+ )and Mn(2+), were required for robust film formation. The K(+ )requirement was quantified in more detail, and the thresholds for complete tendril coverage (50 μM KCl) or film coverage (2–3 mM KCl) were determined. In addition, disruption of the genes for the higher affinity K(+ )transporter (KtrAB), but not the lower affinity K(+ )transporter (KtrCD), strongly inhibited the formation of both tendrils and films, and could be partially overcome by high levels of KCl. Examination of hag tendrils by confocal scanning laser microscopy revealed that tendrils are multicellular structures, but that the cells are not as highly organized as cells in wild-type B. subtilis pellicles. CONCLUSION: These results suggest that B. subtilis can use sliding motility to colonize surfaces, using a tendril-like growth mode when various macronutrients or micronutrients are limiting. If nutrients are balanced and sufficient, the surfaces between tendrils can be colonized by robust surface films. Sliding motility may represent a strategy for nutrient-deprived cells to colonize surfaces in natural environments, such as plant roots, and the media described here may be useful in investigations of this growth phenotype

Dynamical Constraints on the Formation of NGC 4472 and Its Globular Clusters

We present new radial velocities for 87 globular clusters around the elliptical galaxy NGC 4472, and combine these with our previously published data to create a data set of velocities for 144 globular clusters around NGC 4472. We utilize this data set to analyze the kinematics of the NGC 4472 globular cluster system. The new data confirms our previous discovery that the metal-poor clusters have significantly higher velocity dispersion than the metal-rich clusters in NGC 4472. We also find very little or no rotation in the more spatially concentrated metal-rich population, with a resulting upper limit for this population of (v/sigma)_{proj} < 0.34 at a 99% confidence level. The very small angular momentum in the metal-rich population requires efficient angular momentum transport during the formation of this population which is spatially concentrated and chemically enriched. Such angular momentum transfer can be provided by galaxy mergers, but has not been achieved in other extant models of elliptical galaxy formation that include dark matter halos. We also calculate the velocity dispersion as a function of radius, and show that it is consistent with roughly isotropic orbits for the clusters and the mass distribution of NGC 4472 inferred from X-ray observations of the hot gas around the galaxy.Comment: Accepted for publication in the Astronomical Journal, 27 pages, 4 figure

Science Frontiers In Galaxy Evolution: Deep-Wide Surveys

Astro2010: The Astronomy and Astrophysics Decadal Survey : Science White Papers no 79. Available online : http://www8.nationalacademies.org/astro2010/DetailFileDisplay.aspx?id=24