Surface geophysical exploration: developing noninvasive tools to monitor past leaks around Hanford's tank farms.

A characterization program has been developed at Hanford to image past leaks in and around the underground storage tank facilities. The program is based on electrical resistivity, a geophysical technique that maps the distribution of electrical properties of the subsurface. The method was shown to be immediately successful in open areas devoid of underground metallic infrastructure, due to the large contrast in material properties between the highly saline waste and the dry sandy host environment. The results in these areas, confirmed by a limited number of boreholes, demonstrate a tendency for the lateral extent of the underground waste plume to remain within the approximate footprint of the disposal facility. In infrastructure-rich areas, such as tank farms, the conventional application of electrical resistivity using small point-source surface electrodes initially presented a challenge for the resistivity method. The method was then adapted to directly use the buried infrastructure, specifically the steel-cased wells that surround the tanks, as "long" electrodes for both transmission of electrical current and measurements of voltage. Overcoming the drawbacks of the long electrode method has been the focus of our work over the past 7 years. The drawbacks include low vertical resolution and limited lateral coverage. The lateral coverage issue has been improved by supplementing the long electrodes with surface electrodes in areas devoid of infrastructure. The vertical resolution has been increased by developing borehole electrode arrays that can fit within the small-diameter drive casing of a direct push rig. The evolution of the program has led to some exceptional advances in the application of geophysical methods, including logistical deployment of the technology in hazardous areas, development of parallel processing resistivity inversion algorithms, and adapting the processing tools to accommodate electrodes of all shapes and locations. The program is accompanied by a full set of quality assurance procedures that cover the layout of sensors, measurement strategies, and software enhancements while insuring the integrity of stored data. The data have been shown to be useful in identifying previously unknown contaminant sources and defining the footprint of precipitation recharge barriers to retard the movement of existing contamination.

Haplo-insufficiency for different genes differentially reduces pathogenicity and virulence in a fungal phytopathogen.

The main determinant of pathogenicity in Ustilago maydis is the b-mating locus, where establishment of heterozygosity is sufficient to cause galls/tumors on maize plants. However, matings between haploids where one partner contains a mutation, in e.g., the smu1 gene, encoding a Ste20-like PAK kinase, often show reduced mating and pathogenicity compared to wild type. Here we show that similarly, diploids lacking one copy of smu1, are reduced in production of aerial hyphae, but do not show significantly-reduced virulence. Haplo-insufficiency was also observed for additional genes. UmPde1 is a cyclic phosphodiesterase involved in cAMP turnover as part of the cAMP-dependent PKA pathway. Hsl7 plays a role in cell length and in the filamentous response to low ammonium in haploid cells. Diploids deleted for one copy of either the pde1 or hsl7 genes had reduced or increased production of aerial hyphae, respectively, and both were severely impaired in virulence compared to wild type diploids. rho1 and pdc1 are two genes essential for cell viability in haploids. These genes also displayed haplo-insufficiency for pathogenesis. rho1/Δrho1 diploid cells were defective in pheromone production and detection, aerial hyphae induction, and were avirulent. In contrast, pdc1/Δpdc1 diploid cells only failed to produce tumors when applied to maize whorls. We predict the haplo-insufficiency of most of these signaling components is due to stoichiometric imbalance of the respective gene products with their interacting partners, thereby impairing virulence-induction mechanism(s). Further investigation of the bases for such haplo-insufficiency as well as of additional genes displaying this phenotype will provide important insights into fundamental aspects of development in this organism as well as inter-nuclear communication and genetic control.

Protection of Salmonella by ampicillin-resistant Escherichia coli in the presence of otherwise lethal drug concentrations.

Microbial systems have become the preferred testing grounds for experimental work on the evolution of traits that benefit other group members. This work, based on conceptual and theoretical models of frequency-dependent selection within populations, has proven fruitful in terms of understanding the dynamics of group beneficial or 'public goods' traits within species. Here, we expand the scope of microbial work on the evolution of group-beneficial traits to the case of multi-species communities, particularly those that affect human health. We examined whether beta-lactamase-producing Escherichia coli could protect ampicillin-sensitive cohorts of other species, particularly species that could cause human disease. Both beta-lactamase-secreting E. coli and, surprisingly, those engineered to retain it, allowed for survival of a large number of ampicillin-sensitive cohorts of Salmonella enterica serovar Typhimurium, including both laboratory and clinical isolates. The Salmonella survivors, however, remained sensitive to ampicillin when re-plated onto solid medium and there was no evidence of gene transfer. Salmonella survival did not even require direct physical contact with the resistant E. coli. The observed phenomenon appears to involve increased release of beta-lactamase from the E. coli when present with S. enterica. Significantly, these findings imply that resistant E. coli, that are not themselves pathogenic, may be exploited, even when they are normally selfish with respect to other E. coli. Thus, Salmonella can gain protection against antibiotics from E. coli without gene transfer, a phenomenon not previously known. As a consequence, antibiotic-resistant E. coli can play a decisive role in the survival of a species that causes disease and may thereby interfere with successful treatment.

Physiological and growth responses of C3 and C4 plants to reduced temperature when grown at low CO2 of the last ice age.

During the last ice age, CO2 concentration ([CO2]) was 180-200 micromol/mol compared with the modern value of 380 micromol/mol, and global temperatures were approximately 8 degrees C cooler. Relatively little is known about the responses of C3 and C4 species to long-term exposure to glacial conditions. Here Abutilon theophrasti Medik. (C3) and Amaranthus retroflexus L. (C4) were grown at 200 micromol/mol CO2 with current (30/24 degrees C) and glacial (22/16 degrees C) temperatures for 22 d. Overall, the C4 species exhibited a large growth advantage over the C3 species at low [CO2]. However, this advantage was reduced at low temperature, where the C4 species produced 5 x the total mass of the C3 species versus 14 x at the high temperature. This difference was due to a reduction in C4 growth at low temperature, since the C3 species exhibited similar growth between temperatures. Physiological differences between temperatures were not detected for either species, although photorespiration/net photosynthesis was reduced in the C3 species grown at low temperature, suggesting evidence of improved carbon balance at this treatment. This system suggests that C4 species had a growth advantage over C3 species during low [CO2] of the last ice age, although concurrent reductions in temperatures may have reduced this advantage.

Photosynthetic responses of loblolly pine (Pinus taeda) needles to experimental reduction in sink demand.

Sink strength in loblolly pine (Pinus taeda L.) was experimentally manipulated on two sun-exposed branches on each of two neighboring trees by excising the emerging terminal cohort (second flush of 1996) during a period of rapid needle expansion. In addition, export of photosynthate was restricted on one of these branches from each tree by removal of bark and phloem just below the second flush of 1995. Treatment-induced changes in needle biochemistry were measured in 3-month-old (first flush of 1996) and 1-year-old (final flush of 1995) needles collected 1, 5 and 8 days after treatment. In 3-month-old needles, sugar concentration increased by 24% one day after leader excision, and increased by 86% on Day 8 after leader excision and girdling. Starch concentration increased by 33% in 3-month-old needles on Day 1 after leader excision, and by 400% in 1-year-old needles on Day 8 after leader excision and girdling. Physiological changes in 3-month-old and 1-year-old needles were measured by open-flow gas exchange and chlorophyll fluorescence on Day 8 after leader excision and girdling. Light- and CO(2)-saturated net photosynthesis decreased following treatment in both 3-month-old and 1-year-old needles (23 and 17%, respectively). Maximum rate of carboxylation (V(cmax)) decreased by 25% in 3-month-old needles and by 31% in 1-year-old needles in response to leader excision and girdling. The combined treatment resulted in a 38% decrease in maximum rate of electron transport (J(max)) in 3-month-old needles and a 37% decrease in J(max) in 1-year-old needles. Before leader excision and girdling, 2% oxygen in air stimulated photosynthesis by 17 to 19%, but this stimulation was only 3 to 4% at 9 days after treatment. These physiological responses indicate that experimentally lowered sink strength resulted in rapid feedback inhibition of leaf-level photosynthetic capacity in loblolly pine.