Role of bacteria in marine barite precipitation: a case study using Mediterranean seawater.

Marine bacteria isolated from natural seawater were used to test their capacity to promote barite precipitation under laboratory conditions. Seawater samples were collected in the western and eastern Mediterranean at 250 m and 200 m depths, respectively, since marine barite formation is thought to occur in the upper water column. The results indicate that Pseudoalteromonas sp., Idiomarina sp. and Alteromonas sp. actually precipitate barite under experimental conditions. Barite precipitates show typical characteristics of microbial precipitation in terms of size, morphology and composition. Initially, a P-rich phase precipitates and subsequently evolves to barite crystals with low P contents. Under laboratory conditions barite formation correlates with extracellular polymeric substances (EPS) production. Barite precipitates are particularly abundant in cultures where EPS production is similarly abundant. Our results further support the idea that bacteria may provide appropriate microenvironments for mineral precipitation in the water column. Therefore, bacterial production in the past ocean should be considered when using Ba proxies for paleoproductivity reconstructions.

Consolidation of degraded ornamental porous limestone stone by calcium carbonate precipitation induced by the microbiota inhabiting the stone.

Although it has already been shown that calcareous stone can be consolidated by using a bacterially inoculated culture medium, a more user-friendly method is the in situ application of a sterile culture medium that is able to activate, among the microbial community of the stone, those bacteria with a potential for calcium carbonate precipitation. In order to test this new method for stone consolidation, non-sterilized decayed porous limestone was immersed in sterile nutritional media. Results were compared to those of the runs in which stone sterilized prior to the treatment was used. The effects of the microbial community on stone consolidation were determined by recording the evolution of the culture media chemistry. The treated stone was tested for mechanical resistance and porosity. Results demonstrate that the tested media were able to activate bacteria from the microbial community of the stone. As a consequence of the growth of these bacteria, an alkalinization occurred that resulted in calcium carbonate precipitation. The new precipitate was compatible with the substrate and consolidated the stone without pore plugging. Therefore, a good candidate to in situ consolidate decayed porous limestone is the application of a sterile culture medium with the characteristics specified in the present study.

Lanthanum fixation by Myxococcus xanthus: cellular location and extracellular polysaccharide observation.

Myxococcus xanthus is a soil bacterium of the myxobacteria group and is abundant in almost all soils. Its role in soil ecology is considered significant. One noteworthy characteristic of the bacterium is that it produces large quantities of extracellular polymeric substances (EPS). It is also known that its biomass has the capacity to fix heavy metals. Here it is reported that M. xanthus was able to accumulate 0.6 mmol of La per g of wet biomass and/or 0.99 mmol per g of dry biomass. Transmission Electron Microscopy (TEM) observation of M. xanthus cells treated with La showed that a substantial amount of this cation was fixed in the EPS and in the cell wall. Smaller amounts were also observed in the cytoplasm. Fixed La appeared as phosphate in all cellular locations. The results given here also show that the use of La enables TEM observation of the M. xanthus EPS as a dense fibrillar net surrounding the cells. This technique is relatively easy and prevents EPS collapse, which occurs frequently during the fixation and dehydration procedures commonly used in preparations for TEM observations. Since antibodies are no longer required, the La stain can be carried out without delaying bacterial cell cultivation or isolation. In addition, the presence of La in cell cytoplasm without cell degeneration suggests that this microorganism could be used as a model in the study of bacteria-lanthanide interactions.

Myxococcus xanthus biomass as biosorbent for lead.

This paper deals with lead biosorption by Myxococcus xanthus biomass in which dry biomass, accumulating up to 1.28 mmol of lead g(-1), is demonstrated to be a more efficient biosorbent than wet biomass. Dry biomass biosorption was found to be very rapid, reaching equilibrium after 5-10 min. Culture age, the initial lead concentration and pH affected this process, but temperature did not. Furthermore, by using sodium citrate as a desorbent agent, 92.17% of the biosorbed lead could be recovered. It was also established that the biosorbed lead is located on the cellular wall and within the characteristic extracellular polysaccharide of this micro-organism.

Extracellular bacterial mineralization within the context of geomicrobiology.

In the biosphere, bacteria can function as geochemical agents, promoting the dispersion, fractionation and/or concentration of matter. These processes, which are being more and more valued from the point of view of various scientific disciplines, have given rise to the field of geomicrobiology. At the same time, microbial processes resulting in the concentration of matter and thus inducing the formation of minerals, constitute an area of research of growing interest known as biomineralization. In this review a succinct summary of various aspects of both disciplines has been offered together with a more detailed review of those aspects related to extracellular bacterial mineralization. The significance of the role played by the metabolism of bacteria is discussed along with the results of recent research on the role of dead bacteria and bacterial remains that act as heterogeneous nuclei of crystallization. The role played by the membranes of bacteria has also been considered to be highly relevant, and a discussion concerning their possible value as models for both the study of more complex biomineralization processes as well as application in the field of biomimetic materials is put forward.

Comparative heavy metal biosorption study of brewery yeast and Myxococcus xanthus biomass.

The biosorption for La2+, Co2+, Mn2+, UO2(2+), Pb2+, Ag+, Zn2+, Cd2+ and Cr2+ by wet and dry biomass form Myxococcus xanthus obtained from laboratory cultures and Saccharomyces cerevisiae from the brewing industry has been studied. M. xanthus biomass was found to be the most efficient biosorbent for all of the metals assayed. However, due to the fact that S. cerevisiae is a low cost residual by-product from the brewing industry, and at the same time yields good levels of biosorption, it is considered in this work to be of great interest for use as a detoxifier of heavy metals contaminated waters. In addition, the use of sodium carbonate as a desorbent agent is discussed where it was possible to recover up to 94,53% of UO2(2+) by both M. xanthus and S. cerevisiae biomass.

Brewery yeast as a biosorbent for uranium.

Yeast cells are capable of carrying out biosorption with various heavy metals. The biomass deriving from Saccharomyces cerevisiae coming from brewing industries is a by-product that is possible to be used in the purification of water contaminated with these ions. In this paper we show that yeast biomass from one of the city's breweries can adsorb uranium efficiently, up to 2.4 mmol of this metal per gram of dry biomass. It can also be seen that the temperature (between 10 degrees and 37 degrees C) has no effect on the biosorption, while pH does have an influence, 4.5 being the best value. When the concentrations of uranium range between 0.1 and 0.5 mol l-1 the yeast dry biomass is capable of adsorbing between 84% and 98% of this metal in solution.