Hydroxyl Radical Production from Irradiated Arctic Dissolved Organic Matter

The hydroxyl radical (OH·) plays an important role in the environmental chemistry and biogeochemistry of surface waters. OH· acts as a strong oxidant within the irradiated water column, and affects the bioavailability, cycling, and mineralization of dissolved organic matter (DOM), the speciation and redox state of important trace metals e.g., iron and copper, and the fate of persistent organic pollutants (POPs). The generation of this species from irradiated DOM may be especially important in Arctic surface waters during the boreal summer, which contains high levels of DOM and experiences continual solar irradiance. Here, we investigate the OH· produced from laser irradiated Arctic DOM isolated from Toolik Lake, AK (68°38′ N, 149°43′ W). We measured the wavelength dependence of OH· production for aqueous solutions of DOM and report that the greatest OH· production occurs at wavelengths less than 360 nm. OH· production rates ranged from 1.7 (±0.1)×10⁻⁷ M h⁻¹ to 6.4 (±0.2)×10⁻⁷ M h⁻¹, with the rate depending on both irradiation wavelength and to a lesser degree the method used to isolate the DOM matrix. These findings lead to a better understanding of the potentially important photo-oxidation processes that may impact DOM cycling in the Arctic.     

Acquisition of Fe from Various Natural Organic Matter Isolates by Aerobic Pseudomonad Bacteria

Iron (Fe) is an essential nutrient to most microorganisms. Aerobic microorganisms exhibit various strategies for acquiring Fe at near-neutral pH conditions, where Fe oxyhydroxides are insoluble. Although much research has focused on microbial acquisition of Fe from minerals, little is known about Fe acquisition from natural organic matter (NOM). Yet, in surface waters, soils and shallow sediments, Fe is often associated with natural organic matter (NOM), and this NOM-associated Fe could represent an important pool of Fe for microorganisms. Here, we investigated the growth of aerobic Pseudomonas mendocina on soil and surface water NOM samples containing Fe, under Fe-limited conditions. In the presence of NOM, bacteria grew to population sizes greater than in no-Fe-added controls, indicating that the bacteria were able to access Fe associated with NOM. Maximum population size correlated with the NOM-associated Fe concentration. In an additional experiment, Pseudomonas putida was able to acquire Fe from an NOM sample, demonstrating that this ability is not limited to P. mendocina. When Fe was added as 30 μ M FeEDTA plus NOM, together in the same reaction flasks, P. mendocina and P. putida growth was less than in the presence of 30 μM FeEDTA alone. The fact that Fe sources are not simply additive and that the presence of NOM inhibits growth in FeEDTA suggests that further study on the responses of bacteria to a combination of Fe sources is needed to understand the complexities of bacterial Fe acquisition in the subsurface.     

Labile and Recalcitrant Organic Matter Utilization by River Biofilm Under Increasing Water Temperature

Microbial biofilms in rivers contribute to the decomposition of the available organic matter which typically shows changes in composition and bioavailability due to their origin, seasonality, and watershed characteristics. In the context of global warming, enhanced biofilm organic matter decomposition would be expected but this effect could be specific when either a labile or a recalcitrant organic matter source would be available. A laboratory experiment was performed to mimic the effect of the predicted increase in river water temperature (+4?°C above an ambient temperature) on the microbial biofilm under differential organic matter sources. The biofilm microbial community responded to higher water temperature by increasing bacterial cell number, respiratory activity (electron transport system) and microbial extracellular enzymes (extracellular enzyme activity). At higher temperature, the phenol oxidase enzyme explained a large fraction of respiratory activity variation suggesting an enhanced microbial use of degradation products from humic substances. The decomposition of hemicellulose (β-xylosidase activity) seemed to be also favored by warmer conditions. However, at ambient temperature, the enzymes highly responsible for respiration activity variation were β-glucosidase and leu-aminopeptidase, suggesting an enhanced microbial use of polysaccharides and peptides degradation products. The addition of labile dissolved organic carbon (DOC; dipeptide plus cellobiose) caused a further augmentation of heterotrophic biomass and respiratory activity. The changes in the fluorescence index and the ratio Abs(250)/total DOC indicated that higher temperature accelerated the rates of DOC degradation. The experiment showed that the more bioavailable organic matter was rapidly cycled irrespective of higher temperature while degradation of recalcitrant substances was enhanced by warming. Thus, pulses of carbon at higher water temperature might have consequences for DOC processing.     

Radical S-Adenosylmethionine (SAM) Enzymes in Cofactor Biosynthesis: A Treasure Trove of Complex Organic Radical Rearrangement Reactions

In this minireview, we describe the radical S-adenosylmethionine enzymes involved in the biosynthesis of thiamin, menaquinone, molybdopterin, coenzyme F₄₂₀, and heme. Our focus is on the remarkably complex organic rearrangements involved, many of which have no precedent in organic or biological chemistry.     

Rates Of Enzymic Reactions In Predominantly Organic, Low Water Systems

This article makes a quantitative assessment of the activity of enzymes in predominantly organic reaction mixtures of very low water content (and thermodynamic water activity significantly less than 1). This is done by attempting to relate reaction rates to those in systems of higher water content, although several factors make fair comparison difficult. However, it seems that rates with lipases in low water systems can sometimes be at least as high as when the same amount of enzyme catalyses the same reaction in a more traditional system. Rates are usually higher when the catalyst is dispersed on a support, rather than with simple dried particles of enzymes. Rates per unit weight of catalyst are rather similar, even when the amount of active enzyme varies widely, suggesting that physical factors may be limiting. Little data is available for enzymes other than lipases.     

Organic Matter and Water Addition Enhance Soil Respiration in an Arid Region

Climate change is generally predicted to increase net primary production, which could lead to additional C input to soil. In arid central Asia, precipitation has increased and is predicted to increase further. To assess the combined effects of these changes on soil CO₂ efflux in arid land, a two factorial manipulation experiment in the shrubland of an arid region in northwest China was conducted. The experiment used a nested design with fresh organic matter and water as the two controlled parameters. It was found that both fresh organic matter and water enhanced soil respiration, and there was a synergistic effect of these two treatments on soil respiration increase. Water addition not only enhanced soil C emission, but also regulated soil C sequestration by fresh organic matter addition. The results indicated that the soil CO₂ flux of the shrubland is likely to increase with climate change, and precipitation played a dominant role in regulating soil C balance in the shrubland of an arid region.     

Escherichia coli Behavior in the Presence of Organic Matter Released by Algae Exposed to Water Treatment Chemicals

When exposed to oxidation, algae release dissolved organic matter with significant carbohydrate (52%) and biodegradable (55 to 74%) fractions. This study examined whether algal organic matter (AOM) added in drinking water can compromise water biological stability by supporting bacterial survival. Escherichia coli (1.3 × 10⁵ cells ml⁻¹) was inoculated in sterile dechlorinated tap water supplemented with various qualities of organic substrate, such as the organic matter coming from chlorinated algae, ozonated algae, and acetate (model molecule) to add 0.2 ± 0.1 mg of biodegradable dissolved organic carbon (BDOC) liter⁻¹. Despite equivalent levels of BDOC, E. coli behavior depended on the source of the added organic matter. The addition of AOM from chlorinated algae led to an E. coli growth equivalent to that in nonsupplemented tap water; the addition of AOM from ozonated algae allowed a 4- to 12-fold increase in E. coli proliferation compared to nonsupplemented tap water. Under our experimental conditions, 0.1 mg of algal BDOC was sufficient to support E. coli growth, whereas the 0.7 mg of BDOC liter⁻¹ initially present in drinking water and an additional 0.2 mg of BDOC acetate liter⁻¹ were not sufficient. Better maintenance of E. coli cultivability was also observed when AOM was added; cultivability was even increased after addition of AOM from ozonated algae. AOM, likely to be present in treatment plants during algal blooms, and thus potentially in the treated water may compromise water biological stability.     

Tocopherol and Organic Free Radical Levels in Soybean Seeds during Natural and Accelerated Aging

Soybean seeds which had aged in long-term storage (“natural aging”) or by exposure to high temperature and humidity (“accelerated aging”) were analyzed for their tocopherol and organic free radical contents. Tocopherol levels remained unchanged during both types of aging. Three principal tocopherol homologues (α, γ, δ) were present in fairly constant proportions throughout. Organic free radical levels were also remarkably stable, presumably due to the relatively immobile environment of the dry seed. These results, taken in conjunction with previous data on the stability of unsaturated fatty acids in soybean seeds, indicate that it is improbable that lipid peroxidation need play a significant role during natural or accelerated aging in this species.     

Comparison of Soil Organic Matter in Created, Restored and Paired Natural Wetlands in North Carolina

Soil organic matter (SOM) content is a key indicator of soil quality and is correlated to a number of important soil processes that occur in wetlands such as respiration, denitrification, and phosphorus sorption. To better understand the differences in the SOM content of created (CW), restored (RW), and paired natural wetlands (NWs), 11 CW/RW-NW pairs were sampled in North Carolina. The site pairs spanned a range of hydrogeomorphic (HGM) subclasses common in the Coastal Plain. The following null hypotheses were tested: (1) SOM content of paired CW/RWs and NWs are similar; (2) SOM content of wetlands across different HGM subclasses is similar; and (3) interactions between wetland status (CW/RW vs. NW) and hydrogeomorphic subclass are similar. The first null hypothesis was rejected as CW/RWs had significantly lower mean SOM (11.8 ± 3.9%) than their paired NWs (28.98 ± 8.0%) on average and at 10 out of the 11 individual sites. The second and third null hypotheses were also rejected as CW/RWs and NWs in the non-riverine organic soil flat subclass had significantly higher mean SOM content (31.08 ± 14.2%) than the other three subclasses (8.18 ± 2.5, 11.18 ± 8.2, and 10.38 ± 4.2%). Individual sites within this fourth subclass also had significantly different SOM content. This indicated that it would be inappropriate to include the organic soil flat subclass with either the riverine or non-riverine mineral soil flat subclasses when considering restoration guidelines. These results also suggested that if there is a choice in mitigation options between restoration or creation, wetlands should be restored rather than created, especially those in the non-riverine organic soil flat subclass.     

Xiphinema americanum as Affected by Soil Organic Matter and Porosity

The effects of four soil types, soil porosity, particle size, and organic matter were tested on survival and migration of Xiphinema americanum. Survival and migration were significantly greater in silt loam than in clay loam and silty clay soils. Nematode numbers were significantly greater in softs planted with soybeans than in fallow softs. Nematode survival was greatest at the higher of two pore space levels in four softs. Migration of X. americanum through soft particle size fractions of 75-150, 150-250, 250-500, 500-700, and 700-1,000 μ was significantly greater in the middle three fractions, with the least occurring in the smallest fraction. Additions of muck to silt loam and loamy sand soils resulted in reductions in survival and migration of the nematode. The fulvic acid fraction of muck, extracted with sodium hydroxide, had a deleterious effect on nematode activity. I conclude that soils with small amounts of air-filled pore space, extremes in pore size, or high organic matter content are deleterious to the migration and survival of X. americanum, and that a naturally occurring toxin affecting this species may be present in native soft organic matter.     

Production of Urea by Bacterial Decomposition of Organic Matter Including Phytoplankton

A concentrated colony of Fragilaria crotonensis collected from the surface water of Lake Suwa, which is one of the typical eutrophic lakes in Japan, and organic matter contained in untreated surface water from the same lake were subjected to aerobic decomposition by bacteria in a dark room at a temperature of 20 ± 3 °C. An exponential increase of urea with time was recorded in both of the experiments. The apparent rate constants of urea production were calculated to be 0.083 day⁻¹ for decomposition of F. crotonensis and 0.051 day⁻¹ for decomposition of the organic matter contained in the untreated surface water. This study suggests that urea production by bacterial decomposition of organic matter, including phytoplankton, may be an important source of urea in natural waters under certain conditions.     

Effects of Added Organic Matter and Water on Soil Carbon Sequestration in an Arid Region

It is generally predicted that global warming will stimulate primary production and lead to more carbon (C) inputs to soil. However, many studies have found that soil C does not necessarily increase with increased plant litter input. Precipitation has increased in arid central Asia, and is predicted to increase more, so we tested the effects of adding fresh organic matter (FOM) and water on soil C sequestration in an arid region in northwest China. The results suggested that added FOM quickly decomposed and had minor effects on the soil organic carbon (SOC) pool to a depth of 30 cm. Both FOM and water addition had significant effects on the soil microbial biomass. The soil microbial biomass increased with added FOM, reached a maximum, and then declined as the FOM decomposed. The FOM had a more significant stimulating effect on microbial biomass with water addition. Under the soil moisture ranges used in this experiment (21.0%–29.7%), FOM input was more important than water addition in the soil C mineralization process. We concluded that short-term FOM input into the belowground soil and water addition do not affect the SOC pool in shrubland in an arid region.     

Growth of Ferrobacillus ferrooxidans on Organic Matter

Following a brief adaptation period to glucose, Ferrobacillus ferrooxidans was grown on glucose, mannitol, several other sugars, and a few amino acids in the absence of an oxidizable iron source. Prolonged growth on an organic substrate free from iron rendered the organism obligately organotrophic. The growth rate of the bacterium was greater in heterotrophic culture; the doubling time was approximately 4.5 hr on glucose. The bacterium retained its acidophilic properties during adaptation and growth on glucose and would not grow in neutral or slightly alkaline media. Addition of p-aminobenzoic acid was necessary for abundant growth of the cells on glucose. Of the eight strains of Fe(++)-oxidizing bacteria studied, only two strains grew on glucose in a nondialyzed system. The results of manometric studies are discussed with regard to metabolic efficiency of organic matter in this organism.     

Using Satellite Remote Sensing to Estimate the Colored Dissolved Organic Matter Absorption Coefficient in Lakes

Given the importance of colored dissolved organic matter (CDOM) for the structure and function of lake ecosystems, a method that could estimate the amount of CDOM in lake waters over large geographic areas would be highly desirable. Satellite remote sensing has the potential to resolve this problem. We carried out model simulations to evaluate the suitability of different satellite sensors (Landsat, IKONOS, and the Advanced land Imager [ALI]) to map the amount of CDOM in concentration ranges that occur in boreal lakes of the Nordic countries. The results showed that the 8-bit radiometric resolution of Landsat 7 is not adequate when absorption by CDOM at 420 nm is higher than 3 m⁻¹. On the other hand, the 16-bit radiometric resolution of ALI, a prototype of the next generation of Landsat, is suitable for mapping CDOM in a wider range of concentrations. An ALI image of southern Finland was acquired on 14, July 2002 and in situ measurements were carried out in 15 lakes (18 stations). The results showed that there is a high correlation (R² = 0.84) between the 565 nm/660 nm ALI band ratio and the CDOM absorption coefficient in lakes. Analysis of 245 lakes in the acquired satellite image showed a normal distribution of CDOM concentration among the lakes. However, the size distribution of lakes was highly skewed toward small lakes, resulting in the CDOM concentration per unit lake area being skewed toward high values. We showed that remote sensing enables synoptic monitoring of the CDOM concentration in a large number of lakes and thus enables scaling up to the level of large ecosystems and biomes.     

Bioremediation of Chlorate or Perchlorate Contaminated Water Using Permeable Barriers Containing Vegetable Oil

A scale model of an in situ permeable barrier, formed by injecting vegetable oil onto laboratory soil columns, was used to remove chlorate and perchlorate from flowing groundwater. The hypothesis that trapped oil would serve as a substrate enabling native microorganisms to reduce chlorate or perchlorate to chloride as water flowed through the oil-rich zone had merit. Approximately 96% of the 0.2 mM chlorate and 99% of the 0.2 mM perchlorate present in the water was removed as water was pumped through columns containing vegetable oil barriers. The product formed was chloride. When nitrate at 1.4 mM was added to the water, both nitrate and chlorate were removed. High concentrations of chlorate or perchlorate can be treated; 24 mM chlorate and 6 mM perchlorate were completely reduced to chloride during microcosm incubations. Microorganisms capable of reducing perchlorate are plentiful in the environment. Received: 19 December 2001 / Accepted: 25 January 2002