Biomineralization of Platinum by <i>Escherichia coli</i>

The widespread use of platinum in many industrial applications has led to its release into the environment at elevated concentrations with potential adverse effects on human and environmental health. However, the nature of interactions between mobile platinum complexes and the biotic components of the environment, which are increasingly being exposed to platinum, is poorly studied. The aim of this study was to assess the impact of Pt(IV)-chloride on the growth and activity of the well-characterized bacteria Escherichia coli. Bacterial survival and viability in the presence of different concentrations of Pt(IV)-chloride were assessed in liquid culture, while platinum retention was assessed using experimentation with sand-filled columns with the residual platinum concentration measured by atomic absorption spectroscopy. Bacterial biomineralization of platinum was studied with scanning electron microscopy. The results showed that E. coli tolerated PtCl4 at concentrations of up to 10,000 &#181;M over 21 days and remained viable after 112 days of incubation with PtCl4 at 10,000 &#181;M in sand columns. Overall, 74 wt.% and 50 wt.% of platinum was mineralized in E. coli and blank sand columns, respectively. The results of this study confirm that E. coli is capable of biomineralizing platinum. The results confirm that the interaction of platinum with bacteria is not limited to known metal-resistant bacterial species

Bio-harvesting and pyrolysis of the microalgae Botryococcus braunii

The microalgae Botryococcus braunii is widely recognized as a potentially important biofuel-feedstock whose commercial exploitation is limited by difficulties with its cultivation and harvesting. In this study, two B. braunii strains, Kossou-4 and Overjuyo-3 were successfully cultured at a 500 l-scale for 60-days. Harvesting by bio-flocculation with Aspergillus fumigatus at an optimum ratio of 1:40 of fungus to microalgal culture resulted in up to 98% recovery of biomass in the two strains. Ultimate analysis (C, N, H, S, ash, high heating value) and pyrolysis (analytical and preparative pyrolysis and GC–MS assays) showed that co-harvesting with fungi did not cause any impairment of the feedstock value of the microalgal biomass. This work represents the first report on the successful culturing and harvesting of these strains at a 500 l-scale using bio-flocculation. The use of A. fumigatus represents an efficient and economical method for the harvest of B. braunii for biofuel production

Biological role in the transformation of platinum-group mineral grains

Platinum-group elements are strategically important metals. Finding new deposits is becoming increasingly difficult owing to our limited understanding of the processes that affect their mobility in surface environments. Microorganisms have been shown to promote the mobility of metals around ore deposits. Here we show that microorganisms influence the mobility of platinum-group elements in mineral grains collected from Brazil, Australia and Colombia. Scanning electron microscopy showed biofilms covering the platinum-group mineral grains. The biofilms contained abundant platinum-group element nanoparticles and microcrystalline aggregates, and were dominated by Proteobacteria, many of which were closely related to known metal-resistant species. Some platinum-group mineral grains contained carbon, nitrogen, sulfur, selenium and iodine, suggesting the grains may be biogenic in origin. Molecular analyses show that Brazilian platinum–palladium grains hosted specific bacterial communities, which were different in composition from communities associated with gold grains, or communities in surrounding soils and sediments. Nano-phase metallic platinum accumulated when a metallophillic bacterium was incubated with a percolating platinum-containing medium, suggesting that biofilms can cause the precipitation of mobile platinum complexes. We conclude that biofilms are capable of forming or transforming platinum-group mineral grains, and may play an important role for platinum-group element dispersion and re-concentration in surface environments