Browsing by Subject "Toxin"

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    Control of the common carp through species-specific toxin delivery systems and biocontrol by bluegill sunfish
    (2018-03) Poole, Joshua
    The Common carp (Cyprinus carpio, or ‘carp’) is an invasive fish native to Eastern Europe and Asia and is one of the world’s most ecologically harmful species. It is known to cause issues with water clarity, increase nutrient levels, reduce aquatic vegetation, and impact waterfowl. There are many existing strategies to control carp, however, each have various issues. This has led to the search for more practical, sustainable, or broadly applicable control strategies. I investigated two emerging control strategies for carp: biocontrol of carp by bluegill sunfish, and selective toxin delivery systems. Biocontrol has been used successfully for decades in the agriculture industry; however, biocontrol for aquatic pest control is still rudimentary. Previous evidence has suggested that bluegill sunfish (Lepomis macrochirus) may be capable of controlling carp recruitment by consuming eggs and larvae of carp, however, this has never been tested in natural, whole-lakes. To test if bluegill were capable of limiting carp recruitment in natural lakes, I conducted a two-year experiment where carp were stocked into natural lakes, and bluegill were stocked in half of the lakes. The recruitment success of carp was assessed at various stages in first growing season of development: (1) the egg stage, (2) the post-larval juvenile stage, and (3) the end-of-season juvenile stage. The results indicate that bluegill predation had a major effect on the egg stage and the abundance of post-larval carp, but the abundance of end-of-season carp were affected by other processes (such as density-dependence). This is the first experiment to my knowledge that has conducted an experiment on biocontrol of a fish using multiple whole-lake manipulations. This may provide the most robust evidence to date that bicontrol of a fish is possible in natural systems. Next, I performed an analysis to examine lake characteristics that cause bluegill abundance to be low, and thus define conditions where bluegill density is too low to control carp through biocontrol. My model incorporated 12 lake and watershed variables that were used to explain variation in bluegill sunfish catch-per-unit-effort (CPUE). Of those variables, depth and water clarity had the largest effect. Specifically, bluegill abundance declined rapidly in lakes with maximum depths of less than 7 m, and a secchi disk depth less than 0.7 m. These conditions are indicative of lakes that winterkill, thus aeration may be a feasible way to stabilize bluegill populations in these systems. Last, I incorporated antimycin-a (ANT-A), a known fish toxicant, into a corn-based bait and conducted a series of experiments to determine its toxicity, leaching rate, and species-specificity. My results showed that ANT-A was lethal to carp at doses ≥ 4 mg/kg and that the amount of ANT-A that leached out of the bait in 72 h was not lethal to carp or bluegill (Lepomis macrochirus). Species-specificity trials were conducted in 227 L tanks, in which carp were stocked with three native species representing families that occur sympatrically with carp in my study region: the fathead minnow (Pimephales promelas), yellow perch (Perca flavescens) and bluegill. These trials showed high mortality of carp (46%) and fathead minnows (76%) but no significant mortality of perch or bluegill. Finally, a pond study, which used the same species composition except for fathead minnows, resulted in 37% morality among adult carp and no mortality among perch or bluegill. My results suggest that corn-based bait that contains ANT-A could be used to selectively control carp in ecosystems dominated by percids or centrarchids, such as lakes across the Great Plains ecoregion of North America, where carp are especially problematic.
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    Patulin degradation by yeast protein extract
    (2014-05) Folger, Brian Charles
    The mycotoxin patulin, produced by a number of fungi, most prominently Penicillium expansum, has proven problematic for the apple industry due to contamination of apple juice and apple cider. Presently, techniques to control patulin accumulation have proven increasingly ineffective due to the presence of antifungal resistant strains of mold, stability of patulin during thermal processing, and conflicting data on the efficacy of other treatments. However, fermented apple products such as hard ciders and apple cider vinegars are devoid of patulin. Fermentation with yeast resulted in complete degradation of patulin, possibly due to enzymatic degradation by yeast enzymes. Patulin has also been shown to be susceptible to adduct formation with free thiol containing molecules such as glutathione, which is naturally present in yeast cells. Limited studies have also looked at patulin adsorptivity onto the call walls of yeast. Degradation of patulin is, therefore, hypothesized to be caused by multiple mechanisms mainly caused by yeast proteins/enzymes.To assess the loss of patulin by protein extracted from yeast (Rhodosporidium kratochvilovae strain 62-121), patulin extraction methods were compared to determine the optimal method for patulin extraction from protein rich environments. The effect of boiling to halt any possible enzymatic degradation on total patulin loss was assessed by comparing patulin recovery to that of samples placed on ice after the assay. Yeast growth was optimized for the production of patulin-degrading protein extracts by surveying days of growth and subsequent storage at 4°C. Additionally, free thiol group reactivity with patulin was assessed upon incubation with protein extract, cysteine, and glutathione. Liquid chromatography and mass spectrometry (LC/MS) was used to detect patulin degradation products. Potential enzymatic activity was assessed by comparing the degradation activity of different protein extracts from yeast. Finally, patulin loss due to adsorption to inactivated yeast cell walls was determined. The use of acid and salt to precipitate the protein before patulin extraction resulted in the best patulin recovery from protein rich media, and an additional extraction following a modified AOAC method allowed for removal of excess salt without sacrificing patulin recovery. The use of boiling to denature the protein after the assay resulted in 10% higher patulin loss than when the samples were placed on ice, presumably due to adduct formation with thiol groups. Growing yeast for 6 days at room temperature was deemed adequate to obtain optimal patulin degradation; and subsequent incubation of the yeast at 4°C did not impair the patulin degradation activity. Yeast protein extracts were found to be inconsistent with respect to patulin degradation activity, nevertheless patulin degradation activity (up to 100% patulin) was observed in several batches. Patulin incubated with cysteine showed signs of free thiol blockage in both samples of protein extract and pure cysteine. Patulin incubated with glutathione was degraded at both pH 7 and 3.7, and one patulin-glutathione adduct (462 m/z) was identified via LC/MS. Lyophilized yeast cells demonstrated patulin adsorption capabilities after incubation at 30°C for 20 min. Observed results confirm that patulin can be degraded by the protein extract from yeast. The exact mechanism of patulin degradation by protein extracts remains unclear, yet it appears to be either enzymatic or chemical through thiol adduct formation. Our results indicated that the mechanism is a combination of the two. This research offers insight into possible patulin degradation mechanisms, and can give direction in applying this new method of patulin control in an industrial setting.