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Item Assessment of Nannochloropsis gaditana growth and lipid accumulation with increased inorganic carbon delivery(2018-04) Pedersen, Todd C.; Gardner, Robert D.; Peyton, Brent M.Algal biomass refineries for sustainable transportation fuels, in particular biodiesel, will benefit from algal strain enhancements to improve biomass and lipid productivity. Specifically, the supply of inorganic carbon to microalgal cultures represents an area of great interest due to the potential for improved growth of microalgae and the possibility for incorporation with CO2 mitigation processes. Combinations of bicarbonate (HCO3−) salt addition and application of CO2 to control pH have shown compelling increases in growth rate and lipid productivity of fresh water algae. Here, focus was placed on the marine organism, Nannochloropsis gaditana, to investigate growth and lipid accumulation under various strategies of enhanced inorganic carbon supply. Three gas application strategies were investigated: continuous sparging of atmospheric air, continuous sparging of 5% CO2 during light hours until nitrogen depletion, and continuous sparging of atmospheric air supplemented with 5% CO2 for pH control between 8.0 and 8.3. These gas sparging schemes were combined with addition of low concentrations (5 mM) of sodium bicarbonate at inoculation and high concentration (50 mM) of sodium bicarbonate amendments just prior to nitrogen depletion. The optimum scenario observed for growth of N. gaditana under these inorganic carbon conditions was controlling pH with 5% CO2 on demand, which increased both growth rate and lipid accumulation. Fatty acid methyl esters were primarily comprised of C16:0 (palmitic) and C16:1 (palmitoleic) aliphatic chains. Additionally, the use of high concentration (50 mM) of bicarbonate amendments further improved lipid content (up to 48.6%) under nitrogen deplete conditions when paired with pH-controlled strategies.Item Effects of shear stress and substrate loading rate on pseudomonas aeruginosa biofilm thickness and density(1996-01) Peyton, Brent M.Thickness, roughness, and density data were obtained from monopopulation Pseudomonas aeruginosa biofilms grown in an annular reactor under different substrate loading rates and shear stresses. Biofilm thickness showed significant increases, up to approx. 30 μm, with increasing substrate loading rate. Shear stress had no significant effect on thickness. Biofilm roughness, as measured by the standard deviation of the thickness, increased with increasing thickness. Areal mass density significantly increased with substrate loading rate and was not significantly affected by shear stress. Substrate loading and shear stress did not significantly affect volumetric mass density. A numerical expression that describes changes volumetric density as a function of biofilm depth is presented.Item Biofilm surface positioning(1990) Lewandowski, Zbigniew; Walser, Gabriele Sabine; Larsen, R. W.; Peyton, Brent M.; Characklis, William G.Item Interactions between process waters, microbial biofilms, and metal substrata(1990) Characklis, William G.; Lee, Whonchee; Peyton, Brent M.; Lewandowski, ZbigniewItem A statistical analysis of the effect of substrate utilization and shear stress on the kinetics of biofilm detachment(1993-03) Peyton, Brent M.; Characklis, William G.One of the least understood processes affecting biofilm accumulation is detachment. Detachment is the removal of cells and cell products from an established biofilm and subsequent entrainment in the bulk liquid. The goal of this research was to determine the effects of shear stress and substrate loading rate on the rate of biofilm detachment. Monopopulation Pseudomonas aeruginosa and undefined mixed population biofilms were grown on glucose in a RotoTorque biofilm reactor. Three levels of shear stress and substrate loading rate were used to determine their effects on the rate of detachment. Suspended cell concentrations were monitored to determine detachment rates, while other variables were measured to determine their influence on the detachment rate. Results indicate that detachment rate is directly related to biofilm growth rate and that factors which limit growth rate will also limit detachment rate. No significant influence of shear on detachment rate was observed. A new kinetic expression that incorporates substrate utilization rate, yield, and biofilm thickness was compared to published detachment expressions and gives a better correlation of data obtained both in this research and from previous research projects, for both mono- and mixed-population biofilms.Item Fundamentals of Biofilm Processes(1988-08) Characklis, William G.; Larsen, R. W.; Peyton, Brent M.Item Kinetics of biofilm detachment(1992-11) Peyton, Brent M.; Characklis, William G.In predictive biofilm modeling, the detachment rate coefficient may be the most sensitive variable affecting both the predicted rate and the extent of biofilm accumulation. At steady state the detachment rate must be equal to the net growth rate in the biofilm. In systems where organic carbon is growth-limiting, the substrate carbon utilization rate determines the net biomass production rate and, therefore, the steady state biomass detachment rate. Detachment rates, first order with biofilm thickness, fit the experimental data well, but are not predictive since the coefficients must be determined experimentally.Item Iron sulfides and sulfur species produced at hematite surfaces in the presence of sulfate-reducing bacteria(2001-01) Neal, Andrew L.; Techkarnjanaruk, Somkiet; Dohnalkova, Alice; McMready, D.; Peyton, Brent M.; Geesey, Gill G.In the presence of sulfate-reducing bacteria (desulfovibrio desulfuricans) hematite (a-Fe2O3) dissolution is affected potentially by a combination of enzymatic (hydrogenase) reduction and hydrogen sulfide oxidation. As a consequence, ferrous ions are free to react with excess H2S to form insoluble ferrous sulfides. X-ray photoelectron spectra indicate binding energies similar to ferrous sulfides having pyrrhotite-like structures (Fe2p3/2 708.4 eV; S2p3/2 161.5 eV). Other sulfur species identified at the surface include sulfate, sulfite and polysulfides. Thin film X-ray diffraction identifies a limited number of peaks, the principal one of which may be assigned to the hexagonal pyrrhotite (102) peak (d = 2.09 Å; 22 = 43.22°), at the hematite surface within 3 months exposure to sulfate-reducing bacteria (SRB). High-resolution transmission electron microscopy identifies the presence of a hexagonal structure associated with observed crystallites. Although none of the analytical techniques employed provide unequivocal evidence as to the nature of the ferrous sulfide formed in the presence of SRB at hematite surfaces, we conclude from the available evidence that a pyrrhotite stoichiometry and structure is the best description of the sulfides we observe. Such ferrous sulfide production is inconsistent with previous reports in which mackinawite and greigite were products of biological sulfate reduction (Rickard 1969a; Herbert et al., 1998: Benning et al., 1999). The apparent differences in stoichiometry may be related to sulfide activity as the mineral surface, controlled in part by H2S autooxidation in the presence of iron oxides. Due to the relative stability of pyrrhotite at low temperatures, ferrous sulfide dissolution is likely to be reduced compared to the more commonly observed products of SRB activity. Additionally, biogenic pyrrhotite formation will also have implications for geomagnetic field behavior of sediments.Item A review of spectroscopic methods for characterizing microbial transformations of minerals(2002-10) Geesey, Gill G.; Neal, Andrew L.; Suci, Peter A.; Peyton, Brent M.Over the past decade, advances in surface-sensitive spectroscopic techniques have provided the opportunity to identify many new microbiologically mediated biogeochemical processes. Although a number of surface spectroscopic techniques require samples to be dehydrated, which precludes real-time measurement of biotransformations and generate solid phase artifacts, some now offer the opportunity to either isolate a hydrated sample within an ultrahigh vacuum during analysis or utilize sources of radiation that efficiently penetrate hydrated specimens. Other nondestructive surface spectroscopic techniques permit determination of the influence of microbiological processes on the kinetics and thermodynamics of geochemical reactions. The ability to perform surface chemical analyses at micrometer and nanometer scales has led to the realization that bacterial cell surfaces are active sites of mineral nucleation and propagation, resulting in the formation of both stable and transient small-scale surface chemical heterogeneities. Some surface spectroscopic instrumentation is now being modified for use in the field to permit researchers to evaluate mineral biotransformations under in situ conditions. Surface spectroscopic techniques are thus offering a variety of opportunities to yield new information on the way in which microorganisms have influenced geochemical processes on Earth over the last 4 billion years.Item Assessment of lead toxicity to desulfovibrio desulfuricans g20: influence of components of lactate c medium(2001-08) Sani, Rajesh K.; Geesey, Gill G.; Peyton, Brent M.The bioavailability and toxicity of lead (Pb) to Desulfovibrio desulfuricans G20 is greatly influenced by aqueous phase chemical composition. Apparent Pb toxicity is reduced by precipitation and complexation with chemicals found in standard growth media for sulfate-reducing bacteria (SRB). To determine the influence of medium composition on observed Pb toxicity, a new medium was developed to more accurately assess the toxicity of Pb to Desulfovibrio desulfuricans. The new medium, metal toxicity medium (MTM), eliminates abiotic Pb precipitation and minimizes formation of Pb complexes in solution. Significant growth of Desulfovibrio desulfuricans was observed on MTM in the absence of Pb, while no measurable growth was observed at 3 mg/1 Pb as PbCl2. For comparison, in Lactate C medium (Burlage et al., 1998) abiotic Pb precipitation was apparent, and the specific growth rate at 100 mg/1 Pb was only reduced by 8.1% compared to the Pb-free control. Toxicity was measured in terms of longer lag times and slower growth rates (including no growth) as compared to Pb-free controls. This report describes the effects of specific medium components on Pb toxicity to Desulfovibrio desulfuricans and provides a better baseline for comparison of natural and industrial waters for observing heavy metal toxicity on SRB.