G. Delgado

Biomineralization of carbonates by Halomonas eurihalina in solid and liquid media with different salinities : crystal formation sequence

Carbonate precipitation by 20 strains of the moderately halophilic species Halomonas eurihalina in both solid and liquid media was studied. The influence of salinity and temperature on the quantity and type of crystals precipitated was also investigated. Some strains of H. eurihalina formed crystals in all conditions tested. The mineral phases precipitated were magnesium calcite, aragonite and monohydrocalcite in variable proportions depending on various factors such as the type of growth medium employed and its salinity. Scanning electron microscopy and X-ray dispersive energy microanalysis were used to investigate the crystal formation sequence. The process of biolith formation was sequential. It started with chains or filaments of bacteria, giving way to discs which finally produced spherical forms of approximately 50 microns in diameter. We suggest a mechanism of carbonate crystal formation by H. eurihalina.

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 carbonates by Bacillus sp. isolated from saline soils

We studied carbonate precipitation by 26 moderately halophilic strains of Bacillus isolated from a saline soil, haplic Solonchac. They were cultured in both solid and liquid media with salt concentrations varying between 2.5% and 20% (w/v). Bacillus sp. formed mineral crystals in all the media tested, although the mineral precipitation diminished as salinity increased. The minerals that were precipitated included magnesium calcite, aragonite, monohydrocalcite, and dolomite, in varying proportions depending upon the growth medium used. We studied the morphology of the bioliths by means of scanning electron microscopy. We compared our results with those obtained using other taxonomic groups of moderately halophilic bacteria. We discuss possible mechanisms for formation of these biominerals and the probability of their formation in natural habitats.

Process of Carbonate Precipitation by Deleya halophila

Abstract. Scanning electron microscopy and X-ray dispersive energy microanalysis were used to investigate the formation of carbonate crystals by Deleya halophila. The formation of calcium carbonate crystals (polymorphous aragonite) by D. halophila is a sequential process that commences with a nucleus formed by the aggregation of a few calcified bacterial cells and the subsequent accumulation of more calcified cells and carbonate, which acts to weld the bacteria together. The process leads to the formation of spherical bioliths measuring approximately 50 μm in diameter. The mechanism of carbonate precipitation by D. halophila under our working conditions represents a process of induced biomineralization.

Precipitation of carbonates by Nesterenkonia halobia in liquid media.

We investigated the precipitation of carbonates by Nesterenkonia halobia in a liquid medium at different concentrations of salts and incubation times. N. halobia only produced crystals at salt concentrations of 2.5%, 7.5% and 15%. At 20% salt concentration no crystal formation was observed. Calcite, aragonite and dolomite were precipitated in different quantities, depending on the salinity of the medium and incubation time. Scanning and transmission electron microscopy, microanalysis and electron diffraction were all used to study in detail the morphology, composition and internal structure of the bioliths. We propose a mechanism for biolith formation involving both biological and inorganic processes.

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.

Biomineralization of Carbonates by Marinococcus albus and Marinococcus halophilus Isolated from the Salar de Atacama (Chile)

Abstract. We studied the precipitation of carbonates in 17 strains of moderately halophilic, Gram-positive cocci belonging to two species: Marinococcus halophilus and Marinococcus albus, isolated from the Salar de Atacama (Chile). They were cultivated in solid and liquid laboratory media for 42 days at salt concentrations (wt/vol) of 3%, 7.5%, 15%, and 20%. The bioliths precipitated were studied by X-ray diffraction and scanning electron microscopy. M. halophilus formed crystals at each of the salt concentrations, with a maximum number of strains capable of precipitating carbonates at 7.5% and 15% salt concentrations. M. albus did not precipitate at 20% and showed a maximum at 7.5%. This behavior is similar to that of other Gram-positive bacteria and differs from that found in Gram-negative bacteria. The bioliths precipitated were spherical, generally isolated, with a size of 10–100 μm, varying with salinity. They were of magnesium calcite (CO3 Ca1-x Mgx) with Mg content increasing with increasing salinity and Mg/Ca molar ratio of the culture medium. These results demonstrate the active role played by M. halophilus and M. albus in the precipitation of carbonates.

Precipitation of carbonates by Deleya halophila in liquid media: Pedological Implications in saline soils

We investigated the precipitation of carbonates by Deleya halophila in liquid culture media containing different concentrations of marine salt: 2.5%, 7.5%, 12.5%, and 20% (wt/vol). The microorganism was isolated from soils classified as haplic Solonchaks located in arid southeastern Spain. The mineral phases that were precipitated include aragonite, magnesium calcite, and monohydrocalcite in varying proportions depending on the salt concentration. In media containing 2.5% salt, the precipitate consisted of 100% aragonite; with 20% salt, the precipitate was 51% aragonite, 20% monohydrocalcite, and 29% magnesium calcite. Intermediate values were obtained with the middle two salt concentrations. The amount of magnesium in the formula for the precipitated magnesium calcites increased with salinity (0.16 atoms at 7.5% salt, 0.31 atoms at 12.5% salt, 0.32 atoms at 20% salt). The biomineralized formations gave rise to spherulites ranging in diameter from 20 to 500 μm depending on the salinity. The major morpholo...

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.