Catechin, a novel root exudate of Centaurea stoebe, exhibits pleiotropic effects on the soil microbial community and individual soil isolates, and undergoes chemical changes with numerous abiotic factors from soil

Allelopathy has been studied for (±)-catechin, a root exudate of spotted knapweed, as a plausible mechanism that facilitates knapweed invasion in North America. Phytotoxic effects are observed in invaded fields as well as greenhouse experiments when employing catechin or growing spotted knapweed, demonstrating similar effects on native plant species. However, many studies ignore the impact of catechin on microbial populations in soil. Understanding the impact of catechin on microbial processes will greatly aid our understanding of how spotted knapweed invasion can alter soil chemistry and biological processes. Chapter 2 will address the impact of soil and media parameters on catechin stability and extraction from soil. My results show catechin to be a highly reactive compound and that redox metals, the pH of the surrounding environment, and the aerobicity of the system can greatly alter catechin auto-oxidation rates. Chapter 3 expands on these findings by testing the impact of catechin-metal complexes on catechin phytotoxicity reported in the current literature. I demonstrate metals that lower the amount pure catechin in the system have differential effects on native plant species. I further reveal that conditions of increased environmental stress can further exacerbate this phytotoxic phenomenon. Chapter 4 addresses the impact of catechin on soil bacterial communities as well as individual bacterial populations. I confirm that catechin is not bacteriocidal, but instead should be categorized as bacteriostatic. In chapter 5, I extend the findings in chapter 4 to include a repressive effect to various bacterial genera but show that species capable of altering catechin stability can overcome this bacteriostatic effect. More importantly, I reveal that two simple organic acids were capable of restoring previously inhibited bacterial species. Chapter 6 focuses on the ability of catechin to prevent endospore formation, germination, and to alter cell morphology in many gram-positive endospore-forming bacteria commonly found in soil. The significance of this body of work is outlined in chapter 7 along with directions that future research might take to explore some of my more obscure findings

Alkaline iron(III) reduction by a novel alkaliphilic, halotolerant, \u3ci\u3eBacillus\u3c/i\u3e sp. isolated from salt flat sediments of Soap Lake

A halotolerant, alkaliphilic dissimilatory Fe(III)-reducing bacterium, strain SFB, was isolated from salt flat sediments collected from Soap Lake, WA. 16S ribosomal ribonucleic acid gene sequence analysis identified strain SFB as a novel Bacillus sp. most similar to Bacillus agaradhaerens (96.7% similarity). Strain SFB, a fermentative, facultative anaerobe, fermented various hexoses including glucose and fructose. The fructose fermentation products were lactate, acetate, and formate. Under fructose-fermenting conditions in a medium amended with Fe(III), Fe(II) accumulated concomitant with a stoichiometric decrease in lactate and an increase in acetate and CO2. Strain SFB was also capable of respiratory Fe(III) reduction with some unidentified component(s) of Luria broth as an electron donor. In addition to Fe(III), strain SFB could also utilize nitrate, fumarate, or O2 as alternative electron acceptors. Optimum growth was observed at 30°C and pH 9. Although the optimal salinity for growth was 0%, strain SFB could grow in a medium with up to 15% NaCl by mass. These studies describe a novel alkaliphilic, halotolerant organism capable of dissimilatory Fe(III) reduction under extreme conditions and demonstrate that Bacillus species can contribute to the microbial reduction of Fe(III) in environments at elevated pH and salinity, such as soda lakes

Alkaline iron(III) reduction by a novel alkaliphilic, halotolerant, \u3ci\u3eBacillus\u3c/i\u3e sp. isolated from salt flat sediments of Soap Lake

A halotolerant, alkaliphilic dissimilatory Fe(III)-reducing bacterium, strain SFB, was isolated from salt flat sediments collected from Soap Lake, WA. 16S ribosomal ribonucleic acid gene sequence analysis identified strain SFB as a novel Bacillus sp. most similar to Bacillus agaradhaerens (96.7% similarity). Strain SFB, a fermentative, facultative anaerobe, fermented various hexoses including glucose and fructose. The fructose fermentation products were lactate, acetate, and formate. Under fructose-fermenting conditions in a medium amended with Fe(III), Fe(II) accumulated concomitant with a stoichiometric decrease in lactate and an increase in acetate and CO2. Strain SFB was also capable of respiratory Fe(III) reduction with some unidentified component(s) of Luria broth as an electron donor. In addition to Fe(III), strain SFB could also utilize nitrate, fumarate, or O2 as alternative electron acceptors. Optimum growth was observed at 30°C and pH 9. Although the optimal salinity for growth was 0%, strain SFB could grow in a medium with up to 15% NaCl by mass. These studies describe a novel alkaliphilic, halotolerant organism capable of dissimilatory Fe(III) reduction under extreme conditions and demonstrate that Bacillus species can contribute to the microbial reduction of Fe(III) in environments at elevated pH and salinity, such as soda lakes

Phytotoxic Effects of (±)-Catechin In vitro, in Soil, and in the Field

BACKGROUND: Exploring the residence time of allelochemicals released by plants into different soils, episodic exposure of plants to allelochemicals, and the effects of allelochemicals in the field has the potential to improve our understanding of interactions among plants. METHODOLOGY/PRINCIPAL FINDINGS: We conducted experiments in India and the USA to understand the dynamics of soil concentrations and phytotoxicity of (+/-)-catechin, an allelopathic compound exuded from the roots of Centaurea maculosa, to other plants in vitro and in soil. Experiments with single and pulsed applications into soil were conducted in the field. Experimental application of (+/-)-catechin to soils always resulted in concentrations that were far lower than the amounts added but within the range of reported natural soil concentrations. Pulses replenished (+/-)-catechin levels in soils, but consistently at concentrations much lower than were applied, and even pulsed concentrations declined rapidly. Different natural soils varied substantially in the retention of (+/-)-catechin after application but consistent rapid decreases in concentrations over time suggested that applied experimental concentrations may overestimate concentrations necessary for phytotoxicity by over an order of magnitude. (+/-)-Catechin was not phytotoxic to Bambusa arundinacea in natural Indian soil in a single pulse, but soil concentrations at the time of planting seeds were either undetectable or very low. However, a single dose of (+/-)-catechin suppressed the growth of bamboo in sand, in soil mixed with organic matter, and Koeleria macrantha in soils from Montana and Romania, and in field applications at 40 microg l(-1). Multiple pulses of (+/-)-catechin were inhibitory at very low concentrations in Indian soil. CONCLUSIONS/SIGNIFICANCE: Our results demonstrate that (+/-)-catechin is highly dynamic in natural soils, but is phytotoxic well below natural concentrations measured in some soils and applied at low concentrations in the field. However, there is substantial conditionality in the effects of the allelochemical

Description of the novel perchlorate-reducing bacteria Dechlorobacter hydrogenophilus gen. nov., sp. nov. and Propionivibrio militaris, sp. nov.

Novel dissimilatory perchlorate-reducing bacteria (DPRB) were isolated from enrichments conducted under conditions different from those of all previously described DPRB. Strain LT-1T was enriched using medium buffered at pH 6.6 with 2-(N-morpholino)ethanesulfonic acid (MES) and had only 95% 16S rRNA gene identity with its closest relative, Azonexus caeni. Strain MPT was enriched in the cathodic chamber of a perchlorate-reducing bioelectrical reactor (BER) and together with an additional strain, CR (99% 16S rRNA gene identity), had 97% 16S rRNA gene identity with Propionivibrio limicola. The use of perchlorate and other electron acceptors distinguished strains MPT and CR from P. limicola physiologically. Strain LT-1T had differences in electron donor utilization and optimum growth temperatures from A. caeni. Strains LT-1T and MPT are the first DPRB to be described in the Betaproteobacteria outside of the Dechloromonas and Azospira genera. On the basis of phylogenetic and physiological features, strain LT-1T represents a novel genus in the Rhodocyclaceae; strain MPT represents a novel species within the genus Propionivibrio. The names Dechlorobacter hydrogenophilus gen. nov., sp. nov and Propionivibrio militaris sp. nov. are proposed

Shoot mass of <i>Bambusa arundinacea</i> seedlings exposed to different soil concentrations of (±)-catechin applied in multiple pulses.

<p>The x axis shows total measured concentrations of (±)-catechin below the bars and the applied concentrations in parentheses. Bars show 1 SE and shared letters indicate no significant difference among means as determined by ANOVA with treatment and pot as fixed variables and post-ANOVA Tukey tests; P<0.05.</p

Measured soil concentrations of (±)-catechin applied at 500 µg g⁻¹ to soils from western Montana (white bars) and eastern Romania (black bars) and measured over time after application.

<p>Error bars show 1 SE. ANOVA statistics are presented in the results.</p