The effect of nanoparticles on soil and rhizosphere bacteria and plant growth in lettuce seedlings.

Nanomaterials are increasingly being considered for use in agricultural applications, where they have been suggested for a range of uses including fertilizer and pesticide applications. Among nanomaterial applications, agricultural use has a particularly high likelihood of introducing significant quantities of nanomaterials to the environment. The focus of this work was on conducting preliminary experiments examining how nanomaterials might influence rhizosphere bacteria, and in turn influence plant growth. For this work, buttercrunch lettuce seeds were grown in the presence of suspensions of three different nanoparticles. Two of the studied nanomaterials, amine-modified polystyrene nanospheres and titanium dioxide nanoparticles, caused significant decreases in both rhizosphere bacterial counts and plant root and stem growth. In contrast, sulfate-modified polystyrene nanospheres actually increased rhizosphere bacterial counts, but had no significant impact on growth. Only the amine-modified polystyrene nanospheres were found to attach to root surfaces, suggesting that nanomaterial attachment to root surfaces is not a requirement for hindered plant growth. It was hypothesized that attachment of amine-modified polystyrene and TiO2 nanomaterials to bacteria themselves could be changing the bacteria surface properties, and ultimately reducing bacterial affinity for root surfaces.

The impact of antibacterial handsoap constituents on the dynamics of triclosan dissolution from dry sand.

Triclosan has been widely used as an antibacterial agent in consumer and industrial products, and large quantities continue to be discharged to natural waters annually. The focus of this work was on studying the dynamics of triclosan dissolution following evaporative drying. Warm weather can cause the water in intermittent streams or the unsaturated zone to evaporate, causing nonvolatile compounds to form solid precipitates. Because dissolution of precipitates is a relatively slow process, the dynamics of dissolution following evaporation may play an important role in controlling the release of contaminants to the environment. The specific purpose of the work was to explore the effects of surfactant co-contaminants from an industrial antibiotic handsoap on the dissolution dynamics of triclosan. The work used a fiber optic-based optical cell to conduct stirred-batch dissolution experiments for sands coated with different mass loadings of triclosan. Results show that the presence of surfactants from the hand soap not only increase the apparent equilibrium solubility, but also increase the rate of approach to equilibrium. A model describing the dissolution process was developed, and was found to be consistent with experimental data. Results of the work suggest that even small solubility enhancement by surfactant co-contaminants may have a significant impact on dissolution dynamics. Because waters containing significant quantities of triclosan are also among those most likely to contain surfactant co-contaminants, it is likely that the release of triclosan to the environment following evaporation may be faster in many cases than would be predicted from experiments based on pure triclosan.

Microbial surface thermodynamics and applications.

Microbial surface thermodynamics is the reflection of microbial physicochemical and biological characteristics and it bridges micro-scale structures with macro-scale biological functions. Microbial surface thermodynamics is theoretically based on colloid surface thermodynamics using the classical theory of colloidal stability, Derjauin-Landau-Verwey-Overbeek (DLVO) theory. An extended DLVO theory is applied to for the hydration forces not considered in the classical DLVO theory. Herein, a review of current application of microbial surface thermodynamic theory is presented. Microbial surface thermodynamic theory is the fundamental theory in interpreting microbial hydrophilicity or hydrophobicity, microbial attachment, and microbial biofilm development.

Equilibrium and kinetic adsorption of bacteria on alluvial sand and surface thermodynamic interpretation.

Equilibrium and kinetic adsorption of Escherichia coli HB 101, E. coli JM 109, Pseudomonas fluorescens, Pseudomonas putida and Pseudomonas sp. on alluvial sand from the Canadian River alluvium (Norman, OK) was investigated through column experiments. Equilibrium adsorption of these five bacterial strains followed the Freundlich expression and was a function of zero energy points, an indication of the zero energy buffer zone. Among the microorganisms studied, P. putida had the greatest equilibrium adsorption (162.4 x 10(8) cell/g sediment with a microbial injectate concentration of 10(8) cell/ml), followed by Pseudomonas sp. (127.9 x 10(8) cell/g sediment), E. coli HB 101 (62.8 x 10(8) cell/g sediment), E. coli JM 109 (58.4 x 10(8) cell/g sediment), and P. fluorescens (42.6 x 10(8) cell/g sediment). The first-order kinetic adsorption rate coefficient was an exponential function of the total interaction free energy between the bacteria and sediment evaluated at the primary minimum, Delta G(132)(TOT) (PM). E. coli HB 101 had the greatest kinetic adsorption rate coefficient on the sediment (5.10 h(-1)), followed by E. coli JM 109 (4.52 h(-1)), P. fluorescens (2.12 h(-1)), P. putida (2.04 h(-1)), and Pseudomonas sp. (1.34 h(-1)).

Microbial surface thermodynamics and interactions in aqueous media.

Microbial surface thermodynamics and interactions in aqueous media were investigated for seven typical rod-shaped bacterial strains of Enterobacteriaceae, Pseudomonadaceas, and Bacillaceae, which included Escherichia coli HB101, Escherichia coli JM109, Pseudomonas fluorescens, Pseudomonas putida, Pseudomonas aeruginosa, Pseudomonas sp., and Bacillus subtilis. All the microorganisms studied exhibited a monopolar and predominant hydrophilic surface and a negative Delta G132tot, total free energy of interactions between microbes (1) and silica gel or Canadian River Alluvium (CRA) (2) immersed in water (3) at the equilibrium distance, which accounted for their attachment on the medium surface. The microbial attachment was proportional to the corresponding Delta G132tot values. Among the microorganisms studied, B. subtilis had the most attachment on both silica gel and CRA because it had the smallest Delta G132tot values (-17.14kT for silica gel and -21.84kT for CRA). The origins of Lifshitz-van der Waals, Lewis acid/base, and electrostatic interactions were discussed and related to experimental observations.

Bioaerosol Concentration at an Outdoor Composting Center.

Compost centers are one of many environments that produce airborne microorganisms. The objective of this study was to compare the bacterial, fungal, and acti-nomycete concentrations at the Norman, OK, compost center to background concentration of these same microorganisms. For this comparison, a modified Andersen Microbial Sampler was used. Sampling was performed at three sites at the outdoor compost center and at two background sites. The concentration of each microorganism was measured as total colony forming units per cubic meter (CFU/m3). The predominantly downwind compost center site had a 10-fold increase in all the microorganisms in comparison with the other sites (p < 0.05). The median concentrations (95% confidence interval) of total viable bacteria, Gram-negative bacteria, fungi, and actinomycetes at this site were 5059 (CI95= 4952-9600) CFU/m3, 2023 (CI95= 2586-6806) CFU/m3, 972 (CI95= 964-1943) CFU/m3, and 2159 (CI95= 1755-4190) CFU/m3, respectively.