Natural chelators in sea water: Detoxification of Zn2+ by brown algal polyphenols

We have examined growth responses of several species of marine phytoplankton, cultured with and without heavy metal stress, to supplements of polymeric polyphenols from the brown algae Ascophyllum nodosum (L.) Le Jol. and Fucus vesiculosus L. In the absence of additional heavy metals. supplements of up to 4000 μg. 1 of polyphenols had a small effect on initial growth rates for three of these microalgae and had no effect on maximum cell densities for four species. One very common, heavy metal-sensitive diatom, Skeletonema costatum (Grev.) Cl., showed significantly increasing maximum cell density in the cultures, with increasing addition of polyphenols to the medium. The toxicity of Zn²⁺ (0.5–2.0 mg·1 ¹) to cultures of the diatom Phaeodactylum tricornutum Bohlin was relieved by supplements (100–200 μg·1 ¹) of the brown algal polyphenols. Exudation of these polyphenols from brown seaweeds may contribute to the natural chelating capacity of inshore sea water.     

Effects of dissolved organic matter and ultraviolet radiation on the accrual, stoichiometry and algal taxonomy of stream periphyton

1. We investigated the effects of dissolved organic matter (DOM) and ultraviolet‐B (UVB) radiation on periphyton during a 30‐day experiment in grazer‐free, outdoor artificial streams. We established high [10–12 mg carbon (C) L⁻¹] and low (3–5 mg C L⁻¹) concentrations of DOM in artificial streams exposed to or shielded from ambient UVB radiation. Periphyton was sampled weekly for ash‐free dry mass (AFDM), chlorophyll (chl) a , algal biovolume, elemental composition [C, nitrogen (N) and phosphorus (P)], and algal taxonomic composition. 2. Regardless of the UVB environment, increased DOM concentration caused greater periphyton AFDM, chl a and total C content during the experiment. Increased DOM also significantly increased periphyton C : P and N : P (but not C : N) ratios throughout the experiment. Algal taxonomic composition was strongly affected by elevated stream DOM concentrations; some algal taxa increased and some decreased in biomass and prevalence in artificial streams receiving DOM additions. UVB removal, on the other hand, did not strongly affect periphyton biomass, elemental composition or algal taxonomic composition for most of the experiment. 3. Our results show strong effects of DOM concentration but few, if any, effects of UVB radiation on periphyton biomass, elemental composition and algal taxonomic composition. The effects of DOM may have resulted from its absorption of UVA radiation, or more likely, its provision of organic C and nutrients to microbial communities. The strong effects of DOM on periphyton biomass and elemental composition indicate that they potentially play a key role in food web dynamics and ecosystem processes in forested streams.     

Quantitative studies on brown algal phenols. II. Seasonal variation in polyphenol content of Ascophyllum nodosum (L.) Le Jol. and Fucus vesiculosus (L.)

The content of extractable polyphenols in the brown algae Ascophyllum nodosum (L.) Le Jol. and Fucus vesiculosus (L.) was measured at ≈28-day intervals for one year. Colorimetric methods based on the Folin-Denis, Brentamine, and vanillin-H₂SO₄ reactions were used to estimate relative contents of polyphenols, and these values were converted to absolute contents using the gravimetric method introduced earlier. Relatively little error was introduced by variations in the qualitative composition of the extracted polyphloroglucinols.There appeared to be a significant temporal correlation between polyphenol content and the reproductive state of the algae. The content of polyphenols in A. nodosum was at a minimum (≈9–10% of dry matter) during the period of maximum fruit body shedding (late May), and reached a maximum (≈12–14% of dry matter) during the ‘winter season’. In F. vesiculosus, the minimum (≈8–10% of dry matter) was one to two months later, just before the period of maximum fertility, and thereafter rose to a maximum (≈11–13% of dry matter) during the period of sterility. These results furthermore suggest that the bulk of the polyphenols are not readily accessible as reserve components, and indicate that modifications may be needed in the ‘chemical defense’ and ‘waste product’ hypotheses concerning the significance of brown algal polyphenols.     

Quantitative studies on brown algal phenols. I. Estimation of absolute polyphenol content of Ascophyllum nodosum (L.) Le Jol. and Fucus vesiculosus (L.)

Methods for estimating the absolute polyphenol content of the brown algae Ascophyllum nodosum (L.) Le Jol. and Fucus vesiculosus (L.) have been developed and tested. Polyphenols were extracted almost quantitatively from Ascophyllum nodosum using aqueous acetone, whereas this procedure was somewhat less efficient with Fucus vesiculosus. Colorimetric methods based on the Folin-Denis reagent, Brentamine Fast Red 2G Salt, and vanillin-H₂SO₄ were applied to acetone-free extracts for determination of polyphenol content relative to suitable reference compounds. Gravimetric methods based on hide powder and on haemoglobin were employed to derive ‘estimation factors’ (EFs) which allow calculation of the absolute polyphenol content from the relative polyphenol content. The values calculated for absolute polyphenol content are considered to be reasonably accurate, despite imprecisions in the methods and despite often large standard deviations, and re-emphasize the potential physiological and ecological significance of brown algal polyphenols. Although the precise EFs calculated here are not valid for other brown algae, the methods are considered to be generally applicable to other Phaeophyceae.     

Distribution and functions of TonB-dependent transporters in marine bacteria and environments: implications for dissolved organic matter utilization

Background

Bacteria play critical roles in marine nutrient cycles by incorporating and redistributing dissolved organic matter (DOM) and inorganic nutrients in the ocean. TonB-dependent transporter (TBDT) proteins allow Gram-negative bacteria to take up scarce resources from nutrient-limiting environments as well as siderophores, heme, vitamin B12, and recently identified carbohydrates. Thus, the characterization of TBDT distribution and functions is essential to better understand the contribution TBDT to DOM assimilation and its consequences on nutrient cycling in the environment.

Methodology/Principal Findings

This study presents the distribution of encoded known and putative TBDT proteins in the genomes of microorganisms and from the Global Ocean Survey data. Using a Lek clustering algorithm and substrate specificities, the TBDT sequences were mainly classified into the following three groups: (1) DOM transporters; (2) Siderophores/Vitamins transporters; and (3) Heme/Hemophores/Iron(heme)-binding protein transporters. Diverse TBDTs were found in the genomes of oligotroph Citromicrobium bathyomarinum JL354 and Citromicrobium sp JLT1363 and were highly expressed in the stationary phase of bacterial growth. The results show that the Gammaproteobacteria and the Cytophaga-Flavobacterium-Bacteroides (CFB) group bacteria accounted for the majority of the TBDT gene pool in marine surface waters.

Conclusions/Significance

The results of this study confirm the ecological importance of TBDTs in DOM assimilation for bacteria in marine environments owing to a wide range of substrate utilization potential in the ubiquitous Gammaproteobacteria and CFB group bacteria.     

An automated colorimetric method for the determination of dissolved organic carbon in sea water by U.V. destruction

Summary A fast (30 samples/hour) and precise method is described, which can be used for both sea and fresh water in measuring dissolved organic carbon over a range of 0,1–10 mg C/liter. At this moment we are testing the efficiency of this D.O.C. analyser against flame ionization detection system.     

Impact of deforestation on solid and dissolved organic matter characteristics of tropical peat forests: implications for carbon release

This study compares the organic chemistry of peat beneath one of last remaining pristine tropical peat forests in Southeast Asia with a neighbouring peat dome that has been deforested, but not intentionally drained, in the Belait district of Brunei Darussalam, Borneo. We characterized the solid and dissolved organic matter collected from the two domes, through a combination of methods including elemental analysis, phenolic content and Fourier transform infrared spectroscopy (FTIR) investigation of solid peat, as well as optical characterisation (absorbance, fluorescence) of dissolved organic matter (DOM). The peat had a high content of lignin, consistent with its origin from the Shorea albida trees on the domes. Dissolved organic carbon (DOC) concentration in the pore water was significantly greater in the deforested site (79.9 ± 5.5 mg l^?1) than the pristine site (62.2 ± 2.2 mg l^?1). The dissolved organic matter was richer in nitrogen and phenolics in the deforested site. The optical properties (Fluorescence Index) indicated a modification of DOM cycling in the deforested site (enhanced decomposition of the peat and fresh litter). Comparison of the solid peat composition between the two sites also suggests effects of deforestation: sulphur, nitrogen and phenolic contents were higher in the deforested site. Taken together, these observations are consistent with peat enhanced decomposition in the deforested site, even without engineered drainage.     

Adsorption of dissolved organic matter to the inorganic filter substrate and its implications for C uptake measurements

Inorganic carbon uptake rates for glass fiber-filtered samples are higher than those for membrane-filtered samples because of adsorption of dissolved organic matter to the filter substrate. Experimentally derived values for adsorption onto filters were as follows (relative units): GF/F filter, 1, quartz filter, 1.1, GF/C filter, 0.6; GN-6 Gelman filter, 0.1; Nuclepore and Poretics filter, 0.0; Anodisc filter, 0.4 to 1.9.     

Observations on particulate and dissolved organic matter in coral reef areas

Data are presented on the particulate and dissolved organic carbon at Eniwetok Atoll in the Pacific and of particulate organic carbon at South Caicos in the Caribbean. Some data from other locales are included for comparison. Proportionate increases are greater for the particulate matter released from off reefs than for the dissolved; in fact, the net flux of dissolved matter is sometimes negative. Particulate matter, in this case of the size and kinds retained on micro-filters, is dominated by fragments and amorphous material of mixed origins. Phytoplankton is sparse in such environments.     

Inhibitory effect of dissolved organic matter on triplet-induced oxidation of aquatic contaminants.

Excited triplet states of organic chromophores, in particular aromatic ketones, are capable of inducing oxidation of a variety of organic compounds. These reactions probably play an important role in the degradation of organic contaminants in sunlit natural waters. The effect of dissolved natural organic matter (DOM) on the oxidation rate of twenty-two aquatic organic contaminants, including phenols, anilines, phenylurea and s-triazine herbicides, and some pharmaceuticals, was investigated using photoexcited benzophenone-4-carboxylate (CBBP) as the oxidant. For about half of the studied compounds, a decrease in depletion rate was observed in the presence of Suwannee River fulvic acid, used as a reference DOM. Also, depletion rates decreased with increasing DOM concentration, as verified for five selected compounds. Such an inhibitory effect of DOM on oxidation is attributed to its antioxidant properties, whereby oxidation intermediates of the contaminants are supposed to be reduced back to their parent compounds. The presented screening study shows that DOM may be a relevant factor for inhibiting the oxidation of many organic contaminants in surface waters and possibly in engineered water treatment systems.     

Spectroscopic studies of bacteriorhodopsin fragments dissolved in organic solution.

Fourier transform infrared and UV fourth-derivative spectroscopies were used to study the secondary structure of bacteriorhodopsin and its chymotryptic and one of the sodium borohydride fragments dissolved in chloroform-methanol (1:1, v/v), 0.1 M LiClO4. The C1 fragment (helices C, D, E, F, and G) showed an alpha-helical content of about 53%, whereas C2 (helices A and B) had about 60%, and B2 (helices F and G) about 65% alpha-helix. The infrared main band indicated differences in alpha-helical properties between these fragments. These techniques were also used to obtain information on the interactions among helices. According to the results obtained from the hydrogen/deuterium exchange kinetics, about 40% of the amide protons of C2 are particularly protected against exchange, whereas for the C1 fragment this process is unexpectedly fast. UV fourth-derivative spectra of these samples were used to obtain information about the environment of Trp side chains. The results showed that the Trp residues of C2 are more shielded from the solvent than those of C1 or B2. The results of this work indicate that the specific interactions existing between the transmembrane segments induce different types of helical conformations in native bacteriorhodopsin.     

Growth response of Vibrio cholerae and other Vibrio spp. to cyanobacterial dissolved organic matter and temperature in brackish water

Environmental control of growth and persistence of vibrios in aquatic environments is poorly understood even though members of the genus Vibrio are globally important pathogens. To study how algal-derived organic matter and temperature influenced the abundance of different Vibrio spp., Baltic Sea microcosms inoculated with Vibrio cholerae, Vibrio vulnificus, Vibrio parahaemolyticus, Vibrio alginolyticus and native bacterioplankton, were exposed to different temperatures (12-25 degrees C) and amended with dissolved organic matter from Nodularia spumigena (0-4.2 mg C L(-1)). Vibrio abundance was monitored by culture-dependent and molecular methods. Results suggested that Vibrio populations entered a viable but nonculturable state during the incubations. Abundance of Vibrio spp. and total bacterioplankton were orders of magnitude higher in microcosms amended with organic matter compared with reference microcosms. Vibrio cholerae abundances ranged from 0.9 to 1.9 x 10(5) cells mL(-1) in treatments amended with 4.2 mg C L(-1). Vibrio cholerae abundance relative to total bacterioplankton and other Vibrio spp. also increased >10-fold. In addition, V. vulnificus abundance increased in mesocosms with the highest organic matter addition (0.9-1.8 x 10(4) cells mL(-1)). Temperature alone did not significantly affect abundances of total bacterioplankton, total Vibrio spp. or individual Vibrio populations. By contrast, cyanobacterial-derived organic matter represented an important factor regulating growth and abundance of V. cholerae and V. vulnificus in brackish waters.     

土壤溶解性有机质及其表面反应性的研究进展

溶解性有机质(DOM)是土壤溶液中的一个重要的组成部分,在土壤化学和生物过程中起着十分重要的作用。虽然DOM在天然有机质中所占的比例并不高,但它将土壤中的矿物质、有机质联系在一起,并能调控环境污染物的迁移转化与归宿,因此国内外学者都很重视溶解性有机质对土壤环境中污染物环境行为影响的研究。综述了DOM的分类和分离技术,DOM的结构及其表征方法,DOM的表面反应性以及对有机污染物、重金属在土壤中吸附、迁移的影响等,并提出了有待于进一步研究的一些问题。     

Physicochemical and spectroscopic characteristics of dissolved organic matter extracted from municipal solid waste (MSW) and their influence on the landfill biological stability

For the purpose of evaluating the stability of municipal solid waste (MSW) excavated from a landfill, dissolved organic matter was extracted and characterized by physicochemical and spectroscopic methods. Results showed that dissolved organic carbon concentration, ratio of dissolved organic carbon to dissolved organic nitrogen, and specific ultraviolet absorbance at 254 nm were in the range of 0.383-3.502 g kg⁻¹, 0.388-3.693 and 2.700-4.629 L mg⁻¹ m⁻¹, respectively, indicating the stability of MSW. Results obtained from Fourier transform infrared spectra have demonstrated that the stability of excavated MSW was characterized by disappearance of some easily biodegradable compounds; and the 1635/1406 ratio varied from 0.979 to 1.840 and was higher than that of the matured compost. The excitation-emission matrix spectra have shown that the principal components in excavated MSW comprised humic substances and the MSW was stable by the presence of a peak with wavelength pair of ∼280/420 nm.     

溶解性有机质对土壤中有机污染物环境行为的影响

土壤中溶解性有机质(DOM)是生物活性和物理化学反应活性都很活跃的有机组分,主要通过疏水吸附、分配、氢键、电荷转移、共价键、范德华力等多种作用与有机污染物结合,提高溶液中有机污染物的溶解度,改变土壤中有机污染物的吸附-解吸、迁移-转化等环境行为．DOM对有机污染物的吸附-解吸、迁移-转化过程的影响有双重性：一方面,DOM与有机污染物在土壤表面的共吸附可增加土壤对有机污染物的吸附容量,促进有机污染物在土壤中的吸持;另一方面,DOM对有机污染物的增溶作用,有利于土壤中有机污染物的解吸,提高移动性．作为光敏剂,DOM能提高土壤中有机物的光解反应速率．在一定条件下,DOM也可影响土壤中有机污染物的水解过程．DOM对土壤中有机污染物环境行为的影响与DOM和有机污染物的性质及其相互作用的介质条件密切相关．     

Role of ultraviolet-B radiation on bacterioplankton and the availability of dissolved organic matter

Attenuation of ultraviolet (UV)-radiation into the water column is highly correlated with the concentration of the dissolved organic matter (DOM). Thus UV penetrates deeper into marine waters than into freshwater systems. DOM is efficiently cleaved by solar surface radiation levels consuming more oxygen than bacterial metabolism. This photolytically cleaved DOM exhibits higher absorbance ratios (250/365 nm) than untreated DOM. Natural bacterioplankton reach higher abundance if inoculated in previously solar-exposed DOM than in untreated DOM; during bacterial growth the absorbance ratio declines steadily indicating the utilization of the photolytically cleaved DOM. On the other hand, bacterioplankton are greatly reduced in their activity if exposed to surface solar radiation levels. Photoenzymatic repair of DNA induced by UV-A radiation, however, leads to an efficient recovery of bacterial activity once the UV-B stress is released. Turbulent mixing of the upper layers of the water column leads to a continuous alteration of the UV exposure regime. Close to the surface, bacteria and DOM are exposed to high levels of UV-B leading to a reduction in bacterial activity and to photolysis of DOM. Once mixed into deeper layers where UV-B is attenuated, but sufficient UV-A is remaining to allow photoenzymatic repair, the photolytically cleaved DOM is efficiently taken up by bacterioplankton leading to even higher bacterial activity than prior to the exposure. Thus, the overall effect of UV on bacterioplankton is actually an enhancement of bacterial activity despite their lack of protective pigments.     

森林生态系统DOM的来源、特性及流动

可溶性有机物质（Dissolved Organic Matter)是森林生态系统主要的可移动碳库及重要的养分库。系统综述了森林生态系统DOM的来源,组成,性质,季节动态;DOM释放与存留机制及影响因素,森林生态系统DOM的流动及干扰对DOM动态影响等,已有研究表明DOM的森林生态系统C、N、P循环,成土作用,污染物迁移等方面起着重要作用。今后森林生态系统DOM的研究应集中于以几方面：（1）确定森林生态系统中DOM源和汇;（2）评价森林水文条件对DOM释放与存留的调节作用;（3）探讨全球气候变化对森林生态系统DOM的影响;（4）可溶性有机氮（Dissolved Organic Nitrogen),可溶性有机磷（Dissolved Organic Phosphorus)动态与可溶性有碳（Dissolved Organic Carbon）动态的差别。