Jeffrey T. Richards

Hypobaric biology: Arabidopsis gene expression at low atmospheric pressure.

As a step in developing an understanding of plant adaptation to low atmospheric pressures, we have identified genes central to the initial response of Arabidopsis to hypobaria. Exposure of plants to an atmosphere of 10 kPa compared with the sea-level pressure of 101 kPa resulted in the significant differential expression of more than 200 genes between the two treatments. Less than one-half of the genes induced by hypobaria are similarly affected by hypoxia, suggesting that response to hypobaria is unique and is more complex than an adaptation to the reduced partial pressure of oxygen inherent to hypobaric environments. In addition, the suites of genes induced by hypobaria confirm that water movement is a paramount issue at low atmospheric pressures, because many of gene products intersect abscisic acid-related, drought-induced pathways. A motivational constituent of these experiments is the need to address the National Aeronautics and Space Administrations plans to include plants as integral components of advanced life support systems. The design of bioregenerative life support systems seeks to maximize productivity within structures engineered to minimize mass and resource consumption. Currently, there are severe limitations to producing Earth-orbital, lunar, or Martian plant growth facilities that contain Earth-normal atmospheric pressures within light, transparent structures. However, some engineering limitations can be offset by growing plants in reduced atmospheric pressures. Characterization of the hypobaric response can therefore provide data to guide systems engineering development for bioregenerative life support, as well as lead to fundamental insights into aspects of desiccation metabolism and the means by which plants monitor water relations.

Laser-induced fluorescence spectroscopy of dark- and light-adapted bean (Phaseolus vulgaris L.) and wheat (Triticum aestivum L.) plants grown under three irradiance levels and subjected to fluctuating lighting conditions

Abstract Fluorescence spectral characteristics associated with growth under different irradiance levels, and during rapidly changing lighting conditions, were measured on healthy bean (Phaseolus vulgaris L.) and wheat (Triticum aestivum L.) plants using a laser-induced fluorescence spectroscopy (LIFS) system. The LIFS system was designed as a prototype of a handheld field remote sensing system and used a tripled Nd:YAG laser to produce ultraviolet (UV) excitation photons at 355 nm. Dark-adapted canopies of the bean and wheat plants grown under 150, 300, or 450 μmol m−2 s−1 of photosynthetically active radiation (PAR) exhibited LIFS spectra with higher relative fluorescence intensities than emissions from light-adapted plants at all three light levels. Blue/red and blue/far-red leaf fluorescence ratios for both bean and wheat plants increased dramatically as PAR increased, but red/far-red ratios decreased as PAR increased. Light-adapted plants grown under the three light levels were then subjected to several rapidly changing lighting conditions. Plants were exposed sequentially to 150, 300, and 650 μmol m−2 s−1 PAR from metal halide lamps, followed by a fourth light treatment of 650 μmol m−2 s−1 PAR from a mixture of metal halide and tungsten–halogen lamps. The tungsten–halogen lamps added significant amounts of near-infrared (NIR) irradiation to the background light environment provided by the metal halide lamps. Results indicated that both bean and wheat canopies generally exhibited stable blue, green, red, and far-red fluorescence emissions when plants were exposed to 150, 300, and 650 μmol m−2 s−1 PAR from the metal halide lamps. In contrast, when bean and wheat plants were exposed to the NIR-enriched light supplied by the tungsten–halogen lamps, blue and green fluorescence remained stable, but red and far-red fluorescence increased dramatically immediately after exposure to the NIR photons. However, the increased levels of red and far-red fluorescence observed after exposure to NIR light decreased quickly (within 55 s) and returned to “baseline” levels observed at the start of the rapidly changing light experiments. Results indicate that handheld LIFS instruments can be used for remote sensing of plant canopies under a diversity of lighting conditions including full darkness, dawn and dusk lighting environments, and under rapidly changing light environments similar to those encountered on partly cloudy days.

Super-elevated CO2 interferes with stomatal response to ABA and night closure in soybean (Glycine max).

Studies have shown stomatal conductance (g(s)) of plants exposed to super-elevated CO2 (>5000micromol mol(-1)) increases in several species, in contrast to a decrease of g(s) caused by moderate CO2 enrichment. We conducted a series of experiments to determine whether super-elevated CO2 alters stomatal development and/or interferes with stomatal closure in soybean (Glycine max). Plants were grown at nominal ambient (400), elevated (1200) and super-elevated (10,000micromol mol(-1)) CO2 in controlled environmental chambers. Stomatal density of the plant leaf was examined by a scanning electron microscope (SEM), while the stomatal response to the application of exogenous abscisic acid (ABA), a phytohormone associated with water stress and stomatal control, was investigated in intact growing plants by measuring the g(s) of abaxial leaf surfaces using a steady-state porometer. Relative to the control (400micromol mol(-1) CO2) plants, daytime stomatal conductance (g(s,day)) of the plants grown under 1200 and 10,000micromol mol(-1) CO2 was reduced by 38% and 15%, respectively. Dark period stomatal conductance (g(s,night)) was unaffected by growing under 1200mumol mol(-1) CO2) but dramatically increased under 10,000micromol mol(-1) CO2. Stomatal density increased by 10% in the leaves of 10,000micromol mol(-1) CO2-grown plants, which in part contributed to the higher g(s,night) values. Elevating [CO2] to 1200micromol mol(-1) enhanced ABA-induced stomatal closure, but further increasing CO2 to 10,000micromol mol(-1) significantly reduced ABA-induced stomatal closure. These results demonstrated that stomatal response to ABA is CO2 dependent. Hence, a stomatal failure to effectively respond to an ABA signal and to close at night under extremely high CO2 may increase plants susceptibility to other abiotic stresses.

Heat Melt Compaction as an Effective Treatment for Eliminating Microorganisms from Solid Waste

One of the technologies being tested at Ames Research Center as part of the logistics and repurposing project is heat melt compaction (HMC) of solid waste to reduce volume, remove water and render a biologically stable and safe product. Studies at Kennedy Space Center have focused on the efficacy of the heat melt compaction process for killing microorganisms in waste and specific compacter operation protocols, i.e., time and temperature required to achieve a sterile, stable product. The work. reported here includes a controlled study to examine the survival and potential re-growth of specific microorganisms over a 6-month period of storage after heating and compaction. Before heating and compaction, ersatz solid wastes were inoculated with Bacillus amyloliquefaciens and Rhodotorula mucilaginosa, previously isolated from recovered space shuttle mission food and packaging waste. Compacted HMC tiles were sampled for microbiological analysis at time points between 0 and 180 days of storage in a controlled environment chamber. In addition, biological indicator strips containing spores of Bacillus atrophaeus and Geobacillus stearothermophilus were imbedded in trash to assess the efficacy of the HMC process to achieve sterilization. Analysis of several tiles compacted at 180deg C for times of 40 minutes to over 2 hours detected organisms in all tile samples with the exception of one exposed to 180deg C for approximately 2 hours. Neither of the inoculated organisms was recovered, and the biological indicator strips were negative for growth in all tiles indicating at least local sterilization of tile areas. The findings suggest that minimum time/temperature combination is required for complete sterilization. Microbial analysis of tiles processed at lower temperatures from 130deg C-150deg C at varying times will be discussed, as well as analysis of the bacteria and fungi present on the compactor hardware as a result of exposure to the waste and the surrounding environment. The two organisms inoculated into the waste were among those isolated and identified from the HMC surfaces indicating the possibility of cross contamination.

Characterization of Volume F trash from four recent STS missions: weights, categorization, water content

accounted for 50% of the total trash and 69% of the total water for the four missions; drink items were 16% of total weight and 16% water; food wastes were 22% of total weight and 15% of the water; office waste and plastic film were 2% and 11% of the total waste and did not contain any water. The results can be used by NASA to determine requirements and criteria for Waste Management Systems on future missions.

UV LED as a Light Source for Photocatalytic Oxidation of Trace Organic Contaminants

-2 , and LED-13 mW cm -2 was 80, 91, and 95.5%, while their corresponding mineralization efficiency was 28.2, 44.3, and 76.2%, respectively. These results suggest that the LED-reactor is less efficient in oxidizing ethanol compared to the FL-reactor at the same irradiance level, but increasing radiant flux greatly enhances the PCO efficiency. The lower POC efficiency in the LED than the FL reactor is likely attributable to the uneven radiation of the LED module over the non-transparent photocatalyst (Silica Titania Composite); consequently, some of the catalyst received less than the average radiant flux. Strategies for addressing the challenges associated with the light distribution and heat management were also explored.

Review on Transforming TiO 2 into a Visible-Light- Responsive Catalyst for Water and Air Purification

Photocatalytic oxidation (PCO) of organic contaminants is a promising air and water quality management technique which offers energy and cost savings compared to thermal catalytic oxidation (TCO). The most widely used photocatalyst, anatase TiO2, has a wide band gap (3.2 eV) requiring UV photons to activate it. Solar radiation consists of ~4-6% UV and 45% visible light at the Earth’s surface. Therefore, catalysts capable of utilizing these visible photons need to be developed to make PCO approaches more efficient, economical, and safe. Many approaches have been taken to make TiO2 visible-light-active (VLA) with varied degrees of success. Strategies attempted thus far fall into three categories based on their electrochemical mechanisms: 1) photosensitizing TiO2 with Dyes; 2) altering the band gap of TiO2; and 3) coupling TiO2 with a narrow band gap semiconductor. There are diverse technical approaches to implement each of these strategies. This paper presents a brief review of these approaches and their outcomes in terms of the photocatalytic activity and photonic efficiency of the resulting products under visible light. Although resulting visible-light-responsive (VLR) photocatalysts show promise, there is very few comparative studies on the performance of unmodified TiO2 under UV and the modified TiO2 under visible light. It was found that the UV-induced catalytic activity of unmodified TiO2 is much greater than the visible-light-induced catalytic activity of the VLR catalyst at the current state of technology. Furthermore, VLR-catalysts have much lower quantum efficiency than UV-catalysts. This stresses the need for continuing research in this area.

Microbial Characterization of Space Solid Wastes Treated with a Heat Melt Compactor

The purpose of the project has been to characterize and determine the fate of microorganisms in space-generated solid wastes before and after processing by candidate solid waste processing. For FY11, the Heat Melt Compactor (HMC) was the candidate technology that was assessed. Five HMC product disks were produced at ARC from either simulated space-generated trash or from actual space trash. The actual space trash was the STS 130 Volume F compartment wet waste. Conventional microbiological methods were used to detect and enumerate microorganisms in heat melt compaction (HMC) product disks and in surface swab samples of the HMC hardware before and after operation. In addition, biological indicators were added to the STS trash prior to compaction to determine if these spore-forming bacteria could survive the HMC processing conditions, i.e., high temperature (160 ϒC) over a long duration (3 hrs). The HMC disk surfaces were sanitized with 70% alcohol prior to obtaining the core saples to ensure that surface dwelling microbes did not contaminate the HMC product disk interior. Microbiological assays were run before and after sanitization and found that sanitization greatly reduced, but did not eliminate, the number of identified isolates. To characterize the interior of the disks, ten 1.25 cm diameter core samples were aseptically obtained from each disk. These were run through the microbial characterization analyses. Low counts of bacteria, on the order of 5 to 50 viable cells per core, were found, indicating that the HMC operating conditions might not be sufficient for absolute sterilization of the waste. However, the direct counts were 6 to 8 orders of magnitude greater, demonstrating that the vast majority of microbes present in the wastes were dead or non-cultivable. An additional indication that the HMC processing conditons were sterilizing the wastes were results from commercial spore test strips that had been added to the wastes prior to HMC operation. Nearly all could be recovered from the HMC disks post-operation and all were showed negative growth when run through the manufacturer’s protocol, meaning that the 1 x 10 6 or so spores impregnated into the strips were dead. Control test strips, i.e., not exposed to the HMC conditions, were all strongly positive. One area of concern is that the identities of isolates from the cultivable counts included several human pathogens, namely Staphylococcus aureus.

Silica-Titania Composite (STC)'s Performance in the Photocatalytic Oxidation of Polar VOCs

The objective of this paper is to determine the performance of a Silica-Titania Composite (STC) in the photocatalytic oxidation (PCO) of polar VOCs for potential applications in trace contaminant control within space habitats such as the ISS and CEV Orion. Tests were carried out in a bench scale STC-packed annular reactor under continuous illumination by either a UV-C germicidal lamp(lambda (sub max) = 254 nm) or UV-A fluorescent BLB (lambda(sub max) = 365 nm) for the removal of ethanol (a predominant polar VOC in the ISS cabin). The STCs performance was evaluated in terms of the ethanol mineralization rate, mineralization efficiency, and the extent of its oxidation intermediate (acetaldehyde) formation in response to the type of light source (photon energy and photon flux) and relative humidity (RH) implemented. Results demonstrated that acetaldehyde was the only quantifiable intermediate in the effluent under UV illumination, but was not found in the dark adsorption experiments. The mineralization rate increased with an increase in photon energy (UV-C greater than UV-A), even though both lamps were adjusted to emit the same incident photon flux, and also increased with increasing photon flux. However, photonic efficiency decreased as the photon flux increased. More importantly, a higher photon flux gave rise to a lower effluent acetaldehyde concentration. The effect of RH on PCO was complex and intriguing because it affected both physical adsorption and photocatalytic oxidation. In general, increasing RH caused a decrease in adsorption capacity for ethanol and reduced the mineralization efficiency with a concomitant higher acetaldehyde evolution rate. The effect of RH was less profound than that of photon flux.