Raymond L. Legge

Radical scavenging properties of polyamines

Abstract Di- and polyamines are effective scavengers of free radicals generated in a number of chemical and in vitro enzyme systems. Free radical production was quantified spectrophotometrically using nitroblue tetrazolium and cytochrome c or by electron spin resonance. Levels of superoxide radical formed either enzymatically with xanthine oxidase or chemically from riboflavin or pyrogallol were significantly inhibited by spermine, spermidine, putrescine and cadaverine at 10 and 50 mM. The more reactive hydroxyl radical generated by the Fenton reaction was also effectively scavenged by di- and polyamines. In addition, the production of superoxide radical by senescing microsomal membranes was inhibited by di- and polyamines, as was the superoxide-dependent conversion of 1- aminocyclopropane-1-carboxylic acid (ACC) to ethylene. The efficacy of polyamine-scavenging appears to be correlated with the extent of amination suggesting the involvement of amino groups. It is also apparent that some of the physiological effects of polyamines, in particular their propensity to inhibit lipid peroxidation and retard senescence, may be attributable to their radical-scavenging capability.

Recent developments in biodegradation of industrial pollutants by white rot fungi and their enzyme system

Increasing discharge and improper management of liquid and solid industrial wastes have created a great concern among industrialists and the scientific community over their economic treatment and safe disposal. White rot fungi (WRF) are versatile and robust organisms having enormous potential for oxidative bioremediation of a variety of toxic chemical pollutants due to high tolerance to toxic substances in the environment. WRF are capable of mineralizing a wide variety of toxic xenobiotics due to non-specific nature of their extracellular lignin mineralizing enzymes (LMEs). In recent years, a lot of work has been done on the development and optimization of bioremediation processes using WRF, with emphasis on the study of their enzyme systems involved in biodegradation of industrial pollutants. Many new strains have been identified and their LMEs isolated, purified and characterized. In this review, we have tried to cover the latest developments on enzyme systems of WRF, their low molecular mass mediators and their potential use for bioremediation of industrial pollutants.

Identifying fouling events in a membrane-based drinking water treatment process using principal component analysis of fluorescence excitation-emission matrices

The identification of key foulants and the provision of early warning of high fouling events for drinking water treatment membrane processes is crucial for the development of effective countermeasures to membrane fouling, such as pretreatment. Principal foulants include organic, colloidal and particulate matter present in the membrane feed water. In this research, principal component analysis (PCA) of fluorescence excitation-emission matrices (EEMs) was identified as a viable tool for monitoring the performance of pre-treatment stages (in this case biological filtration), as well as ultrafiltration (UF) and nanofiltration (NF) membrane systems. In addition, fluorescence EEM-based principal component (PC) score plots, generated using the fluorescence EEMs obtained after just 1hour of UF or NF operation, could be related to high fouling events likely caused by elevated levels of particulate/colloid-like material in the biofilter effluents. The fluorescence EEM-based PCA approach presented here is sensitive enough to be used at low organic carbon levels and has potential as an early detection method to identify high fouling events, allowing appropriate operational countermeasures to be taken.

Reversible and irreversible low-pressure membrane foulants in drinking water treatment: Identification by principal component analysis of fluorescence EEM and mitigation by biofiltration pretreatment

With the increased use of membranes in drinking water treatment, fouling--particularly the hydraulically irreversible type--remains the main operating issue that hinders performance and increases operational costs. The main challenge in assessing fouling potential of feed water is to accurately detect and quantify feed water constituents responsible for membrane fouling. Utilizing fluorescence excitation-emission matrices (EEM), protein-like substances, humic and fulvic acids, and particulate/colloidal matter can be detected with high sensitivity in surface waters. The application of principal component analysis to fluorescence EEMs allowed estimation of the impact of surface water constituents on reversible and irreversible membrane fouling. This technique was applied to experimental data from a two year bench-scale study that included thirteen experiments investigating the fouling potential of Grand River water (Ontario, Canada) and the effect of biofiltration pre-treatment on the level of foulants during ultrafiltration (UF). Results showed that, although the content of protein-like substances in this membrane feed water (=biofiltered natural water) was much lower than commonly found in wastewater applications, the content of protein-like substances was still highly correlated with irreversible fouling of the UF membrane. In addition, there is evidence that protein-like substances and particulate/colloidal matter formed a combined fouling layer, which contributed to both reversible and irreversible fouling. It is suggested that fouling transitions from a reversible to an irreversible regime depending on feed composition and operating time. Direct biofiltration without prior coagulant addition reduced the protein-like content of the membrane feed water which in turn reduced the irreversible fouling potential for UF membranes. Biofilters also decreased reversible fouling, and for both types of fouling higher biofilter contact times were beneficial.

Superoxide radical production by microsomal membranes from senescing carnation flowers: an effect on membrane fluidity

Abstract The lipid fluidity of carnation microsomal membranes decreases during in vitro aging in a manner that correlates with enzymatic production of superoxide anion (O 2 − dot ) by the membranes. Levels of (O 2 − dot ) were determined from ESR spectra of the semiquinone formed when (O 2 − dot ) reacts with Tiron (1,2-dihydroxybenzene-3,5-disulfonic acid). Heat denaturation of the microsomes or addition of n -propyl gallate, a free radical scavenger, eliminated the Tiron radical signal and prevented the change in membrane fluidity. By contrast, the addition of xanthine/xanthine oxidase, a reputed (O 2 − dot )-generating system, accentuated the decrease in membrane fluidity and greatly increased the Tiron radical signal. Superoxide dismutase, an enzyme that catalyses the dismutation of (O 2 − dot ), reduced the amplitude of the Tiron radical signal. When Tiron was used as a scavenger of (O 2 − dot ), there was no change in membrane fluidity. The data collectively suggest that (O 2 − dot ) or highly reactive derivatives of (O 2 − dot ) induce membrane rigidification. In addition, microsomes from senescent flowers produce more (O 2 − dot ) than those from freshly cut flowers, suggesting that this reactive species of oxygen also contributes to membrane rigidification during natural senescence.

Comparative study of black-box and hybrid estimation methods in fed-batch fermentation

A neural network based softsensor is proposed for a PHB fed-batch fermentation process. The softsensor is designed to estimate the biomass concentration on-line. The design is based on the following model structures: 1. a feedforward neural network, 2. a RBFN (radial basis function neural network) and 3. hybrid models composed of either feedforward or RBFN neural network and the a priori known dilution term of the mass balance equations. The different designs are experimentally implemented and compared using Alcaligenes eutrophus as a model fed-batch system. Additionally, the possibility of directly inferring the substrate (glucose) concentration from the estimated biomass was investigated by assessing the variability of the corresponding yield coefficient. The combination of the neural network model and mechanistic differential equation provided the best results. Because of the variability in the yield coefficient, substrate concentration could not be inferred directly.

Ethylene formation from 1-aminocyclopropane-1-carboxylic acid by microsomal membranes from senescing carnation flowers

Isolated membranes from the petals of senescing carnation flowers (Dianthus caryophyllus L. cv. White-Sim) catalyze the conversion of 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene. A microsomal membrane fraction obtained by centrifugation at 131,000 g for 1 h proved to be more active than the membrane pellet isolated by centrifugation at 10,000 g for 20 min. The ethylene-producing activity of the microsomal membranes is oxygen-dependent, heat-denaturable, sensitive to n-propyl gallate, and saturable with ACC. Corresponding cytosol fractions from the petals are incapable of converting ACC to ethylene. Moreover, the addition of soluble fraction back to the membrane fraction strongly inhibits the ACC to ethylene conversion activity of the membranes. The efficiency with which isolated membranes convert ACC to ethylene is lower than that exhibited by intact flowers based on the relative yield of membranes per flower. This may be due to the presence of the endogenous soluble inhibitor of the reaction, for residual soluble fraction inevitably remains trapped in membrane vesicles isolated from a homogenate.

One-dimensional metric for tracking bacterial community divergence using sole carbon source utilization patterns.

Community level physiological profiling (CLPP) has become a popular method to characterize and track changes in heterotrophic bacterial communities. Although the CLPP method is a straight forward laboratory protocol which yields large amounts of functional information, the amount of data obtained can become overwhelming and often requires some type of multivariate analysis method for ordination and interpretation. Multivariate analysis can be challenging and requires a significant statistics background along with an understanding of the inferences and biases each multivariate analysis method incurs. This paper presents and evaluates a new approach to analyzing sole carbon source utilization data. A method is described which provides a one-dimensional metric derived from standard CLPP data (BIOLOG EcoPlate data). The one-dimensional community metric was derived using normalized Euclidean distances and shifts in the carbon source utilization patterns. The one-dimensional community metric did not provide all of the information of classical approaches such as principle component analysis (PCA) or guild grouping analysis; however, it was found to be more easily implemented and interpreted when analyzing the plate data. Validation of this approach is demonstrated using data acquired to track the divergence of bacterial communities in wetland mesocosm systems after an experimentally controlled disturbance. If the objective is to investigate community shifts over time the one-dimensional community divergence metric can be a useful tool.

Assessing the role of feed water constituents in irreversible membrane fouling of pilot-scale ultrafiltration drinking water treatment systems.

Fluorescence excitation-emission matrix (EEM) approach together with principal component analysis (PCA) was used for assessing hydraulically irreversible fouling of three pilot-scale ultrafiltration (UF) systems containing full-scale and bench-scale hollow fiber membrane modules in drinking water treatment. These systems were operated for at least three months with extensive cycles of permeation, combination of back-pulsing and scouring and chemical cleaning. The principal component (PC) scores generated from the PCA of the fluorescence EEMs were found to be related to humic substances (HS), protein-like and colloidal/particulate matter content. PC scores of HS- and protein-like matter of the UF feed water, when considered separately, showed reasonably good correlations with the rate of hydraulically irreversible fouling for long-term UF operations. In contrast, comparatively weaker correlations for PC scores of colloidal/particulate matter and the rate of hydraulically irreversible fouling were obtained for all UF systems. Since, individual correlations could not fully explain the evolution of the rate of irreversible fouling, multi-linear regression models were developed to relate the combined effect of HS-like, protein-like and colloidal/particulate matter PC scores to the rate of hydraulically irreversible fouling for each specific UF system. These multi-linear regression models revealed significant individual and combined contribution of HS- and protein-like matter to the rate of hydraulically irreversible fouling, with protein-like matter generally showing the greatest contribution. The contribution of colloidal/particulate matter to the rate of hydraulically irreversible fouling was not as significant. The addition of polyaluminum chloride, as coagulant, to UF feed appeared to have a positive impact in reducing hydraulically irreversible fouling by these constituents. The proposed approach has applications in quantifying the individual and synergistic contribution of major natural water constituents to the rate of hydraulically irreversible membrane fouling and shows potential for controlling UF irreversible fouling in the production of drinking water.

The scale-up of plant cell culture: Engineering considerations

The enormous versatility of plants has continued to provide the impetus for the development of plant tissue culture as a commercial production strategy for secondary metabolites. Unfortunately problems with slow growth rates and low products yields, which are generally non-growth associated and intracellular, have made plant cell culture-based processes, with a few exceptions, economically unrealistic. Recent developments in reactor design and control, elicitor technology, molecular biology, and consumer demand for natural products, are fuelling a renaissance in plant cell culture as a production strategy. In this review we address the engineering consequences of the unique characteristics of plant cells on the scale-up of plant cell culture.