No abstract

Biogenic hydroxyapatite (bio-HA) has the potential for radionuclide capture and remediation of metalcontaminated environments. Biosynthesis of bio-HA was achieved via the phosphatase activity of a Serratia sp. supplemented with various concentrations of CaCl 2 and glycerol 2-phosphate (G2P) provided at pH 7.0 or 8.6. Presence of hydroxyapatite (HA) was confirmed in the samples by X-ray powder diffraction analysis. When provided with limiting (1 mM) G2P and excess (5 mM) Ca 2C at pH 8.6, monohydrocalcite was found. This, and bio-HA with less (1 mM) Ca 2C accumulated Eu(III) to »31% and 20% of the biomineral mass, respectively, as compared to 50% of the mineral mass accumulated by commercial HA. Optimally, with bio-HA made at initial pH 7.0 from 2 mM Ca 2C and 5 mM G2P, Eu(III) accumulated to »74% of the weight of bio-HA, which was equal to the mass of the HA mineral component of the biomaterial. The implications with respect to potential bio-HA-barrier development in situ or as a remediation strategy are discussed.

We have shown that the red cells found in the Red Rain (which fell on Kerala, India, in 2001) survive and grow after incubation for periods of up to two hours at 121 o C . Under these conditions daughter cells appear within the original mother cells and the number of cells in the samples increases with length of exposure to 121 o C. No such increase in cells occurs at room temperature, suggesting that the increase in daughter cells is brought about by exposure of the Red Rain cells to high temperatures. This is an independent confirmation of results reported earlier by two of the present authors, claiming that the cells can replicate under high pressure at temperatures upto 300 o C. The flourescence behaviour of the red cells is shown to be in remarkable correspondence with the extended red emission observed in the Red Rectagle planetary nebula and other galactic and extragalactic dust clouds, suggesting, though not proving an extraterrestrial origin.

Extraordinary claims have been made for the biological properties of the red rain cells of Kerala, including a suggestion that they lack DNA. We have investigated the fluorescence properties of red rain cells, and the solubility of the red pigment in a variety of solvents. Extraction of the pigment with DMSO allowed successful demonstration of DNA using DAPI staining. Cellular impermeability to staining reagents due to the red pigment is the likely explanation for the failure of previous efforts to demonstrate DNA in red rain cells.

Early studies on the coloured particles that fell as red rain over southern India identified them as unicellular eukaryotes such as members of the red algae or fungi; however, the results of the present investigation are not consistent with this designation. Using transmission electron microscopy, we have demonstrated significant differences in the ultrastructure when compared with representative species from these other groups. Most notably, the red rain cells show no evidence of typical eukaryotic internal structures such as mitochondria or endoplasmic reticulum. Furthermore, comparisons based on elemental composition using energy-dispersive X-ray analysis, as well as Raman spectral signatures demonstrate significant dissimilarities in their molecular composition. The identity and origins of the red rain cells remain an enigma; however, our findings are more consistent with an unidentified prokaryote, and thus suggest that previous attempts at their identification should be reappraised.