Liudmila S. Shirokova

Adsorption of copper on Pseudomonas aureofaciens: protective role of surface exopolysaccharides.

Adsorption of copper on exopolysaccharide (EPS)-rich and (EPS)-poor soil rhizospheric Pseudomonas aureofaciens cells was studied as a function of pH and copper concentration at different exposure time in order to assess the effect of cell exopolysaccharides on parameters of adsorption equilibria. The surface properties of bacteria were investigated as a function of pH and ionic strength using potentiometric acid-base titration and electrophoresis that permitted the assessment of the excess surface proton concentration and zeta-potential of the cells, respectively. For adsorption experiments, wide range of Cu concentration was investigated (0.1-375 microM) in order to probe both weak and strong binding sites at the surface. Experimental results were successively fitted using a Linear Programming Model approach. The groups with pK(a) of 4.2-4.8 and from 5.2 to 7.2, tentatively assigned as carboxylates and phosphoryl respectively, are the most abundant at the surface and thus essentially contribute to the metal binding. The presence of exopolysaccharides on the surface decreases the amount of copper adsorbed on the bacterial cell wall apparently via screening the underlining functional groups of the cell wall. At the same time, dissolved EPS substances do not contribute to Cu binding in aqueous solution. Results of this study allow quantification of the role played by the surface EPS matrix as a protective barrier for metal adsorption on bacterial cell walls.

Diurnal variations of dissolved and colloidal organic carbon and trace metals in a boreal lake during summer bloom

This work describes variation of element concentration in surface water of a subarctic organic-rich lake during the diurnal cycle of photosynthesis. An unusually hot summer 2010 in European part of subarctic Russia produced elevated surface water temperature (28-30 °C) and caused massive cyanobacterial bloom. Diurnal variation of ~40 dissolved macro and trace elements and organic carbon were recorded in the humic Lake Svyatoe in the White Sea drainage basin. Two days continuous measurements with 3 h sampling steps at the surface (0.5 m) allowed tracing cyanobacterial activity via pH and O₂ measurement and revealed constant concentrations (within ±20-30%) of all major elements (Na, Mg, Cl, SO₄, K, Ca), organic and inorganic carbon and most trace elements (Li, B, Sc, Ti, Ni, Cu, Ga, As, Rb, Sr, Y, Zr, Mo, Sb, medium and heavy REEs, Hf, Pb, Th, U). The concentration of Mn demonstrated a factor of 3 decrease during the day following Mn adsorption onto cyanobacterial cells due to ~1 pH unit raise during the photosynthesis and Mn release during the night due to desorption from the cell surface. The role of Mn(II) photo-oxidation by reactive oxygen species could be also pronounced, although its contribution to Mn diurnal variation was much smaller than the adsorption at the cell surfaces. Similar pattern, but with much lesser variations (c.a., 10-20%), was recorded for Ba and Fe. On-site ultrafiltration technique allowed to distinguish between low molecular weight (LMW) complexes (<1 kDa) and high molecular weight (HMW) colloids (1 kDa-0.22 μm) and to assess their diurnal pattern. Colloidal Al and Fe were the highest during the night, when the contribution of HMW allochthonous colloids was maximal. Typical insoluble trivalent and tetravalent elements exhibited constant complexation (>80-90%) with HMW allochthonous organics, independent on the diel photosynthetic cycle. Finally, biologically-relevant metals (Cu, Co, Cr, V, and Ni) demonstrated significant variations of colloidal fractions (from 10 to 60%) not directly related to the photosynthesis. The majority of possible metal nutrients, being strongly associated with organic and organo-mineral colloids do not exhibit any measurable concentration variation during photosynthesis. The two types of element behavior during cyanobacterial bloom in the water column--constant concentration and sinusoidal variations--likely depend on element speciation in solution and their relative affinity to surfaces of aquatic microorganisms and complexation with authochthonous and allochthonous organic matter.

Heterotrophic bacterio‐plankton in thawed lakes of the northern part of Western Siberia controls the CO2 flux to the atmosphere

This work reports on results of bacterio‐plankton characterisation in thaw lakes of the northern part of Western Siberia via measurement the number of various groups of heterotrophic bacteria and the intensity of primary production/respiration in the water column. The eutrophic systems at the beginning of lake formation (permafrost thawing) are being replaced by essentially oligotrophic systems at the final, mature stage of the lake development (khasyrey). The CO2 flux from the lake surface to the atmosphere associated with microbial degradation of organic matter (107 ± 50 t C/km2/y) is at least one order of magnitude higher than the riverine organic carbon flux. The future climate evolution in this region, consisting in rising ground temperature and precipitation increase will bring about further acceleration of dissolved organic matter degradation in the water column and amplification of CO2 release to the atmosphere.

Effect of organic ligands and heterotrophic bacteria on wollastonite dissolution kinetics

Wollastonite (CaSiO3) dissolution rates were measured at 25°C in 0.01 M NaCl using a mixed-flow reactor as a function of pH (5 to 12) and concentration of forty organic ligands. Mostly stoichiometric dissolution was observed at these conditions. For seven ligands (acetate, citrate, EDTA, catechol, glutamic acid, 2,4-dihydroxybenzoic acid, glucuronic acid), batch adsorption experiments and electrokinetic measurements performed as a function of pH and ligand concentration confirmed the interaction of ligands with >CaOH2+ sites and allowed quantification of their adsorption constants. The effect of investigated ligands on wollastonite dissolution rate was modeled within the framework of the surface coordination approach taking into account the adsorption of ligands on dissolution-active sites and the molecular structure of the surface complexes they form. A positive correlation between surface adsorption constant and the stability constant of the corresponding reaction in homogeneous solution was observed. At neutral and weakly alkaline pH, the following total dissolved concentrations of ligands are necessary to double the rate of wollastonite dissolution: EDTA (10−4 M), phosphate (1.5 · 10−4 M), catechol (3 · 10−4 M), 8-hydroxyquinoline, gallic acid or adipate (5 · 10−4 M), 3,4-DHBA (7 · 10−4 M), PO3− (7.5 · 10−4 M), glutamate (0.002 M), citrate (0.003 M), malate or 2,4-DHBA (0.004 M), phthalate or succinate (0.005 M), tartrate (0.006 M), thioglycolate (0.008 M), aspartame (0.01 M), gluconate, ascorbate (> 0.01 M), malonate, diglycolate or lactate at pH 8.4 (0.02 M), formate or fumarate (0.05 M), oxalate (>0.05 M), bicarbonate (0.075 M), lactate at pH 5.6 (0.1 M), acetate (> 0.1 M), salicylate (0.15 M), humic acids (> 54 mg/L of dissolved organic carbon, DOC), gum xanthan (1.5-2.0 g/L). Sorbitol, mannitol, glucose, glucosamine, saccharose, fulvic acids and silica at pH ∼ 7 exhibit weakly inhibiting or no effect up to concentration of 0.1 M. The presence of the following ligands leads to a decrease of dissolution rates by a factor of 2: silica at pH 10.7 (2 · 10−4 M), glucuronic acid (0.001 M), algae exudates (30 mg/L DOC), mannit (0.02 M), urea (>0.05 M), pectin (>15 g/L), alginic acid (> 2 g/L). Overall, results of this study demonstrate that high concentrations (0.001-0.01 M) of organic ligands, whether they are originated from organic matter, enzymatic degradation or bacterial metabolic activity, are necessary to appreciably enhance wollastonite dissolution. This is further corroborated by batch experiments on live and dead cultures of soil bacteria Pseudomonas aureofaciens interaction with wollastonite. The release rates of both Ca and Si are only weakly affected by the presence of live or dead bacterial cells in inert electrolyte solution and in nutrient media: there is only ∼20 percent-increase of dissolution rate in experiments with live cultures compared to dead cultures. However, the reproducibility of rate measurements in ligand-free solutions at 7 ≤ pH ≤ 8 achieves ± 30 percent. Therefore, the effect of extracellular organic products on the weathering rate of Ca-bearing minerals is expected to be weak and the acceleration of “basic” silicate rocks dissolution in natural settings in the presence of soil bacteria is likely solely due to the pH decrease.

Western Siberia wetlands as indicator and regulator of climate change on the global scale

Western Siberia is a unique bog region. Siberian peatlands have been a major sink of atmospheric carbon since the last deglaciation and, on the other hand, in some epochs – like the present – they are the most powerful source of methane emission. About 104 Mha of Russian peatlands are located in Western Siberia, which consists almost completely of pristine peatland ecosystems. This paper considers the role of the Western Siberian peatlands in a global carbon balance and their possible influence on the formation of Earth’s climate.

Zeta potential of anoxygenic phototrophic bacteria and Ca adsorption at the cell surface: Possible implications for cell protection from CaCO3 precipitation in alkaline solutions

Electrophoretic mobility measurements and surface adsorption of Ca on living, inactivated, and heat-killed haloalkaliphilic Rhodovulum steppense, A-20s, and halophilic Rhodovulum sp., S-17-65 anoxygenic phototrophic bacteria (APB) cell surfaces were performed to determine the degree to which these bacteria metabolically control their surface potential equilibria. Zeta potential of both species was measured as a function of pH and ionic strength, calcium and bicarbonate concentrations. For both live APB in 0.1M NaCl, the zeta potential is close to zero at pH from 2.5 to 3 and decreases to -30 to -40 mV at pH of 5-8. In alkaline solutions, there is an unusual increase of zeta potential with a maximum value of -10 to -20 mV at a pH of 9-10.5. This increase of zeta potential in alkaline solutions is reduced by the presence of NaHCO(3) (up to 10 mM) and only slightly affected by the addition of equivalent amount of Ca. At the same time, for inactivated (exposure to NaN(3), a metabolic inhibitor) and heat-killed bacteria cells, the zeta potential was found to be stable (-30 to -60 mV, depending upon the ionic strength) between pH 5 and 11 without any increase in alkaline solutions. Adsorption of Ca ions on A-20s cells surface was more significant than that on S-17-65 cells and started at more acidic pHs, consistent with zeta potential measurements in the presence of 0.001-0.01 mol/L CaCl(2). Overall, these results indicate that APB can metabolically control their surface potential to electrostatically attract nutrients at alkaline pH, while rejecting/avoiding Ca ions to prevent CaCO(3) precipitation in the vicinity of cell surface and thus, cell incrustation.

West Siberian palsa peatlands: distribution, typology, cyclic development, present day climate-driven changes, seasonal hydrology and impact on CO2 cycle

Palsa peatlands occupy extensive areas in Western Siberia which is one of the most paludified flat lowlands of the world. Climatic changes in Western Siberia are more dramatic compared with other northern regions, and changes in palsa landscapes are more notable due to the severe continental climate here. The distribution, peculiarities and climate-indication capacities of West Siberian palsas are poorly known outside Russia. Thus, Western Siberia is one of the most interesting vast natural polygons for studying climate-driven changes in the landscapes. This paper aims to fill the gap in knowledge on West Siberian palsas and their capacity as a climate regulator. We present issues in distribution, typology and cyclic development of palsa peatlands and their actual climate-driven changes. We also analyse the role of palsas in the atmospheric cycle of CO2, and the hydrology of the palsa regions.

One of the possible mechanisms of thermokarst lakes drainage in West‐Siberian North

During the 2008 expedition carried out within the framework of the Russian–French network project CAR‐WET‐SIB, one of the possible mechanisms of drainage of thermokarst lakes in the north of Western Siberia was revealed. The discovered natural process is significantly amplified by climate warming and gains special urgency in this regard.

Decrease of concentration and colloidal fraction of organic carbon and trace elements in response to the anomalously hot summer 2010 in a humic boreal lake.

The colloidal distribution and size fractionation of organic carbon (OC), major elements and trace elements (TE) were studied in a seasonally stratified, organic-rich boreal lake, Lake Svyatoe, located in the European subarctic zone (NW Russia, Arkhangelsk region). This study took place over the course of 4 years in both winter and summer periods using an in situ dialysis technique (1 kDa, 10 kDa and 50 kDa) and traditional frontal filtration and ultrafiltration (5, 0.22 and 0.025 μm). We observed a systematic difference in dissolved elements and colloidal fractions between summer and winter periods with the highest proportion of organic and organo-ferric colloids (1 kDa-0.22 μm) observed during winter periods. The anomalously hot summer of 2010 in European Russia produced surface water temperatures of approximately 30°C, which were 10° above the usual summer temperatures and brought about crucial changes in element speciation and size fractionation. In August 2010, the concentration of dissolved organic carbon (DOC) decreased by more than 30% compared to normal period, while the relative proportion of organic colloids decreased from 70-80% to only 20-30% over the full depth of the water column. Similarly, the proportion of colloidal Fe decreased from 90-98% in most summers and winters to approximately 60-70% in August 2010. During this hot summer, measurable and significant (>30% compared to other periods) decreases in the colloidal fractions of Ca, Mg, Sr, Ba, Al, Ti, Ni, As, V, Co, Y, all rare earth elements (REEs), Zr, Hf, Th and U were also observed. In addition, dissolved (<0.22 μm) TE concentrations decreased by a factor of 2 to 6 compared to previously investigated periods. The three processes most likely responsible for such a crucial change in element biogeochemistry with elevated water temperature are 1) massive phytoplankton bloom, 2) enhanced mineralization (respiration) of allochthonous dissolved organic matter by heterotrophic aerobic bacterioplankton and 3) photo-degradation of DOM and photo-chemical liberation of organic-bound TE. While the first process may have caused significant decreases in the total dissolved concentration of micronutrients (a factor of 2 to 5 for Cr, Mn, Fe, Ni, Cu, Zn and Cd and a factor of >100 for Co), the second and third factors could have brought about the decrease of allochthonous DOC concentration as well as the concentration and proportion of organic and organo-mineral colloidal forms of non-essential low-soluble trace elements present in the form of organic colloids (Al, Y, Ti, Zr, Hf, Th, Pb, all REEs). It can be hypothesized that climate warming in high latitudes capable of significantly raising surface water temperatures will produce a decrease in the colloidal fraction of most trace elements and, as a result, an increase in the most labile low molecular weight LMW(<1 kDa) fraction.

Moss and Peat Leachate Degradability by Heterotrophic Bacteria: The Fate of Organic Carbon and Trace Metals

ABSTRACT The respiration of dissolved organic matter (DOM) by aerobic heterotrophic bacterioplankton in boreal surface waters is one of the major factors that regulate CO2 exchange of lakes and rivers with the atmosphere in arctic and subarctic zones. The DOM that originates from topsoil leaching and vegetation degradation is brought to the lakes by surface flow and is subjected to coagulation and degradation by heterotrophic bacteria, which are well-established processes in the majority of boreal aquatic settings. The behavior of colloids and organic complexes of trace metals during this process is virtually unknown. In this work, we studied the interaction of two model heterotrophic bacteria, soil Pseudomonas aureofaciens and aquatic Pseudomonas reactans, with peat and Sphagnum moss leachates from the permafrost region under controlled laboratory conditions in nutrient-free media. The moss leachate was the better substrate for bacterial survival, with P. reactans exhibiting an order of magnitude higher live cell number compared with P. aureofaciens. In eight-day experiments, we analyzed organic carbon and ∼40 major and trace elements (TEs) during heterotrophic bacteria growth. The total net decrease in the concentration of dissolved organic carbon (DOC) was similar for both bacteria and ranged from 30 mg gwet−1 to ≤10 mg gwet−1 during 8 days for the moss and peat leachate, respectively. Despite significant evolutions of pH, DOC, dissolved inorganic carbon (DIC), and cell number, most major (Mg, K, and Ca) and TEs remained nearly constant (within ±30% of the control). Only Fe, Al, P, Zn, Mn, Co, and Ba and to a much lesser extent Cd, Pb, Rare Earth Elements (REEs), U, Ti, and Zr were affected (p < 0.05) by the presence of bacteria relative to the control and exhibited slight to moderate decreases during the experiment. Adsorption onto bacterial surfaces produced fast initial removal of Al, Mn, and Ba and to a lesser degree Cd, Pb, REEs, and U. Intracellular metabolic assimilation mostly affected P, Zn, and Co and progressively decreased their concentrations. Finally, coagulation as individual Fe/Al hydroxides due to DOM removal or pH change could also affect elements that were precipitated with organomineral colloids (Ti and Zr). The degrees of major and TE susceptibility to bacterial activity based on concentration changes during the experiment in both substrates ranged over three orders of magnitude from mg L−1 to µg L−1 and followed the order DOC >> P >> Ba > Zn ≥ Fe ≥ Al > Mn > Cu ≥ Sr > Zr ≥ Ti > Ni ≥ Co > REEs ≥ U > Hf∼Th, which reflected the abundance of the elements in the two substrates. Generally, the soil exopolysaccharide producing bacterium P. aureofaciens in the peat leachate had the greatest impact of the four combinations investigated in this study (two bacteria with two substrates). Under ongoing environmental changes in the boreal zone, the autochthonous processes of bacterioplankton activity are able to decrease the concentrations of a very limited number of TEs, including mainly Fe and several macro- (P) and micro- (Zn, Mn, and Ba) nutrients.