Jesús Párraga

Biomineralization of carbonates by Halobacillus trueperi in solid and liquid media with different salinities.

We investigated the precipitation of carbonates by Halobacillus trueperi in both solid and liquid media at different salt concentrations and different magnesium/calcium ratios. H. trueperi precipitated at all assayed salt concentrations. When salt concentration increased, the quantity and the size of bioliths decreased and the time required increased. The precipitated minerals (determined by X-ray diffraction) were calcite, magnesium calcite and monohydrocalcite in variable proportions depending on the salinity and the physical state of the medium; the magnesium content of the magnesium calcites also varied with regard to the culture type. According to the saturation indices other minerals could also precipitate. Scanning electron microscopy showed that dominant morphologies of the bioliths were spherulitic with fibrous radiated interiors. We show that H. trueperi plays an active role in the precipitation of carbonates and we hypothesize about this process of biomineralization.

Precipitation of minerals by 22 species of moderately halophilic bacteria in artificial marine salts media: Influence of salt concentration

Precipitation of minerals was shown by 22 species of moderately halophilic bacteria in both solid and liquid artificial marine salts media at different concentration and different Mg2+-to-Ca2+ ratio. Precipitation of minerals was observed for all the bacteria used. When salt concentration increased, the quantity and the size of bioliths decreased, the time required for precipitation being increased. The precipitated minerals were calcite, magnesian calcite, aragonite, dolomite, monohydrocalcite, hydromagnesite and struvite in variable proportions, depending on the bacterial species, the salinity and the physical state of the medium; the Mg content of the magnesian calcite also varied according to the same parameters. The precipitated minerals do not correspond exactly to those which could be precipitated inorganically according to the saturation indices. Scanning electron microscopy showed that the formation of the bioliths is initiated by grouping of calcified cells and that the dominant final morphologies were spherulitic with fibrous radiated interiors. It was demonstrated that moderately halophilic bacteria play an active role in the precipitation of carbonates and we hypothesize about this process of biomineralization.

Precipitation of Carbonates by Bacteria from a Saline Soil, in Natural and Artificial Soil Extracts

The precipitation of carbonates by populations of bacteria from a saline soil cultivated in both solid and liquid culture media was studied. The soil was a Gley-Gypsic-Carbonated Solonchak from near an inland saltern in Granada, Spain. Two types of soil extract were prepared: 1:1 extract and saturation extract. The soil samples used for the bacteriological analysis were taken in situ from the A and C soil horizons. The culture media were made from (1) soil extract, (2) artificial soil solutions, and (3) artificial solutions of marine salts. The geochemical analysis of the solution was carried out using the program PHREEQC. Samples of purified bioliths were examined by X-ray diffraction and were observed with SEM. We found that the mineral precipitated from the natural and artificial soil extracts was calcite. Calcite was also found in the secondary accumulations of this soil. However in the media derived from marine salts, mixtures of calcite, magnesian calcite, and aragonite were precipitated, depending on the Mg2+ concentration, the [Mg]/[Ca] molar ratio, and the type of medium. The morphology of the minerals precipitated shows bacterial involvement in the process of pedogenic bioprecipitation. The precipitation studied could be regarded as a process of induced biomineralization.

Evolution of organic matter fractions after application of co-compost of sewage sludge with pruning waste to four Mediterranean agricultural soils. A soil microcosm experiment

The effect of co-compost application from sewage sludge and pruning waste, on quality and quantity of soil organic carbon (SOC) in four Mediterranean agricultural soils (South Spain), was studied in soil microcosm conditions. Control soil samples (no co-compost addition) and soils treated with co-composts to a rate equivalent of 140 Mg ha(-1) were incubated for 90 days at two temperatures: 5 and 35 degrees C. The significances of incubation temperature and the addition of co-compost, on the evolution of the different fractions of SOC, were studied using a 2(3) factorial design. The co-compost amendment increased the amounts of humic fractions: humic acids (HA) (1.9 times), fulvic acids (FA) (3.3 times), humin (1.5 times), as well as the free organic matter (1.4 times) and free lipids (21.8 times). Incubation of the soils enhanced its biological activity mainly in the amended soils and at 35 degrees C, leading to progressive SOC mineralization and humification, concomitant to the preferential accumulation of HA. The incubation results show large differences depending on temperature and soil types. This fact allows us to select suitable organic amendment for the soil when a rapid increase in nutrients through mineralization is preferred, or in cases intending the stabilization and preservation of the SOC through a process of humification. In soils with HA of more than 5 E(4)/E(6) ratio, the incubation temperature increased rates of mineralization and humification, whereas lower temperatures limited the extent of both processes. In these soils the addition of co-compost in spring or summer is the most recommendable. In soils with HA of lower E(4)/E(6) ratio (<5), the higher temperature favoured mineralization but not humification, whereas the low temperature maintained the SOC levels and even increased the HA/FA ratio. In these soils the moment of addition of organic amendment should be decided depending on the effect intended. On the other hand, the lower the SOC content in the original soil, the greater are the changes observed in the SOC after amendment with co-compost. The results suggest that proper recommendations for optimum organic matter evolution after soil amendment is possible after considering a small set of characteristics of soil and the corresponding soil organic matter fractions, in particular HA.

Precipitation of Carbonates and Phosphates by Bacteria in Extract Solutions from a Semi-arid Saline Soil. Influence of Ca2+ and Mg2+Concentrations and Mg2+/Ca2+ Molar Ratio in Biomineralization

We examine the ability of bacteria from a saline soil (Arenic-Gypsic-Hyposalic Solonchak) from the Santa-Pola marine saltern (Alicante, Spain) to precipitate carbonate and phosphate minerals. Solid culture media were prepared from natural soil extracts, from natural soil extracts amended with organic material in different proportions, and by modifying the Ca 2+ and Mg 2+ concentrations and the Mg 2+ /Ca 2 + molar ratio. A high percentage of moderately halophilic bacteria were able to form biominerals (calcite, magnesian calcite and/or struvite) in natural soil extracts with small amounts of added organic material and in ionically modified natural soil extracts. Light microscopy revealed three different types of bio-mineralization: colonies that precipitate carbonates, colonies that precipitate struvite, and colonies that precipitate both types of minerals. The precipitation of carbonates and struvite is not simultaneous, but successive. The concentration of Ca 2+ and the Mg 2+ /Ca 2 + molar ratio were more influential than the absolute amount of Mg 2+ on the precipitation of minerals. The higher the calcium concentrations are, the more carbonate-forming colonies there are and the fewer struvite-forming colonies. The bioliths precipitated were analyzed by Powder X-Ray Diffraction (PXRD) and Scanning Electron Microscope (SEM). In the magnesian calcites precipitated (Ca 1 − n Mg n CO 3 ), “n” (amount of magnesium that replaces calcium by formula) varied from 0.058 to 0.342. Struvite crystals are polyhedral and around 500 μm, while carbonate crystals are smaller (< 100 μm), spherical and usually in aggregates. The precipitation of minerals studied shows an active role of the bacteria, but the geochemical conditions are clearly influential. It may therefore be considered “induced biomineralization.” The results point out the possibility that in some soils the C, N, P, Ca and Mg cycles are coupled due to bacterial biomineralization.

Chemical, mineralogical and (micro)morphological study of coarse fragments in Mediterranean Red Soils

Abstract We studied the gravels derived from mica schists and micaceous quartzites of three Mediterranean Red Soils (Haploxeralf and Cryoboralf) from the Sierra Nevada (Andalusia, Spain) with emphasis on the following aspects: morphology (visual evidence of weathering, thin section description and scanning electron microscopy); composition (X-ray diffraction, extractable Fe, Al and Si, and electron microprobe analysis); and chemistry (pH, cation exchange capacity, specific surface area and organic carbon content). The gravels had undergone considerable modification during weathering in soil. A loss of the primary rock structure was detected, together with a decrease in compactness, an increase in roundness, color value and chroma. Neoformed kaolinite was present and relatively high contents of extractable forms of iron, aluminium and silica (citrate–dithionite and oxalate) were detected. From an analytical point of view, the surface properties (CEC and SSA) increased and the equilibrium pH decreased in the clasts which had undergone most weathering. The SEM study shows that the fabric changes from laminar schistose in the parent rock to other types in the gravels due to the weathering process. Electron microprobe analysis revealed the presence of phyllosilicates together with iron oxides in the illuvial infilling materials of fissures in the most altered clasts. These infillings affect the properties of the coarse fragments. The relationship detected between the properties of fine earth and those of the gravel fractions suggest that the coarse fragments have a significant influence on the properties of the soil.

Study of biomineral formation by bacteria from soil solution equilibria

Abstract The role of bacteria in mineral neoformation in a saline soil was studied. In this soil, authigenic precipitation of gypsum and calcite takes place. Bacteria isolated from the soil were cultivated ‘in vitro’ in solid and liquid media prepared from soil solutions (1: 1 extract). Precipitation of calcite spherulites of between 20 and 50 μm diameter and of other bioliths was observed. From soil solutions (1 : 1 extract and saturation extract) activity coefficients and the states of reaction for 18 minerals were calculated using the SOLMINEQ 88 program. Calcite, dolomite, gypsum and aragonite were in equilibrium with the saturation extract while in the 1:1 extract no mineral phases in equilibrium were present. Therefore, bacteria must play an active role in calcite precipitation in this saline soil.

Multivariate analysis in the quantitative evaluation of soils for reforestation in the Sierra Nevada (southern Spain)

Soil characteristics that most strongly influence the outcome of the evaluation of soils for reforestation were determined with multivariate analysis. R-mode factor analysis was used to relate results of the soil survey with those of the soil evaluation. We studied the area of the Sierra Nevada mountains in southern Spain. Soil variables were measured in 163 soil profiles, collected in a survey of the two soil environments of the Sierra Nevada: the calcareous and silicic zones. Four factor analyses showed that sand, clay, gravel and organic carbon content, and pH were the most useful soil characteristics in evaluating site keys that affect tree and shrub growth (nutrient availability, rooting space and soil water availability). In the calcareous zone, hue, value and chroma color, and pH, were easily determined soil characteristics that established and classified the suitability of forest sites. In the silicic zone, hue, value and chroma, and altitude were the characteristics found most useful in evaluating forest sites.

Carbonate and Phosphate Precipitation by Saline Soil Bacteria in a Monitored Culture Medium

Carbonate and phosphate precipitation by bacteria isolated from a saline soil was studied in vitro in a liquid culture medium over 45 days. Physicochemical parameters of this medium were continuously monitored using both selective electrodes (continuous monitoring, CM) and individual measurements by other techniques on days 5, 10, 15, 20, 25, 35 and 45 (discontinuous monitoring, DM). In DM, the precipitated minerals were studied (XRD and SEM-EDX) and the saturation index of the mineral phases was analyzed (PHREEQC program). Using the CM and DM data it was possible to distinguish several temporary stages in which both the medium and the mineralogy changed: 1) 0 to 10 days: pH reaches 8.4; significant loss of Mg2+ (incorporated into the bacterial biomass) and Ca2+ (through mineral precipitation); formation of crystals, although not in sufficient quantity to be studied until day 10. 2) 10 to 25 days: pH decreases but remains above 8; appreciable loss of Mg2+ and Ca2+ due to formation of spherical carbonate bioliths with traces of phosphates occluded within these carbonates. 3) After 25 days: biomineralization slow down; pH returns to initial values and struvite is formed (idiomorphic prismatic crystals). These trends are in agreement with the findings of other workers, although with some peculiarities regarding stages and types of mineral precipitated. In some cases the struvite contained small quantities of K and Ca, possibly because these are intermediate mineral species between typic-struvite, K-struvite and Ca-struvite. The bacteria-mediated precipitation of carbonates of Ca and/or Mg and phosphates (struvite) by the bacteria from a saline soil is demonstrated. However, struvite was not found in the soils of origin of the bacteria, possibly because it is a metastable mineral in most soils.

Impact of spent coffee grounds as organic amendment on soil fertility and lettuce growth in two Mediterranean agricultural soils

ABSTRACT The use of spent coffee grounds (SCG) as organic amendment is a triple solution: a reuse of this bio-residue (6 millions of tons per year), an increase in soil organic carbon (SCG contain 82% of carbohydrates and 13% of proteins) and a decrease in CO2 emissions into the atmosphere. Thus, we investigate the effect of SCG on soil and plants in an in vitro assay. The variables considered were SCG dose (2.5 and 10%), two agricultural soils (Calcisol and Luvisol), and four cultivation times (15, 30, 45 and 60 days). The chemical and physicochemical soil properties, SEM images and growth parameters were analyzed. The highest dose of SCG increased organic carbon, total N and available K and P by 286%, 188%, 45%, and 9%, respectively, while decreasing lettuce growth by 233% compared to control. The SEM study revealed that SCG particles are incorporated into soil aggregates and microorganisms grow over them, which is also corroborated by a 10-times increase of soil respiration rate. The behavior of both soils differs for some SCG effects. In conclusion, SCG have a great potential to increase soil fertility and further investigations are needed in order to improve the use of SCG as amendment.