Yelloji Rao K. Mirajkar

Growth and attachment of Thiobacillus ferrooxidans during sulfide mineral leaching

The growth of Thiobacillus ferrooxidans, their attachment to sulfide minerals and detachment during bacterial leaching are discussed in this paper. Growth of the bacteria has been measured by cell count of the supernatants of the mineral suspensions while attachment to minerals and detachment were measured by periodic protein estimations for both the solid and liquid phases. Even in the absence of the nutrients, bacterial growth occurs and increases the available cell population during leaching; such growth was greater in sphalerite suspensions than in galena suspensions. The bacterial attachment studies suggest that more cells are attached onto galena mineral surface than to sphalerite surface. The mechanisms of bacterial attachment and detachment are discussed.

Crystal Growth of Hydroxyapatite In Vitro and Dental Calculus and Plaque Formation on Human Teeth In Vivo

Sodium polyvinylphosphonic acid (SPVPA) was synthesized using vinyl phosphonyl dichloride and azobisisobutyronitrile (AIBN) as a radical initiator. The homopolymer obtained was characterized by molecular weight, purity and impurities by using gel permeation chromatography and NMR. The pure polymer was used to assess the influence on crystal growth kinetics of hydroxyapatite (HAP) in vitro. Briefly, the experimental solution supersaturated with respect to hydroxyapatite (HAP) was prepared from stock solutions of CaCl2, K2HPO4, KH2PO4, and NaCl. The crystal growth was initiated by adding pure seeds of HAP at 37 °C. The precipitation kinetics was followed using a pH-stat and measuring calcium phosphate in the solution. The effect of the polymer on the crystal growth kinetics was assessed, and it was found that the polymer inhibited the growth at 10−5 M. The inhibitory effect of the polymer was related to its adsorption onto the growing crystals. The adsorption parameters were derived from an adsorption isotherm-yielding a K value of 1,950 m1/mM and the N value of 0.038 mM/m2. A topical application of 1% solution of the polymer onto teeth was effective in reducing calculus formation by 18% in rat model system. SPVPA was also very effective in reducing adsorption (>90%) of radiolabelled bacteria, Streptococcus mutans, and Actinomyces viscosus, onto saliva-coated hydroxyapatite beads and disks. The polymer was also tested in short-term human clinical studies and showed that 1% and 3% solutions significantly (P = 0.05) reduced bacterial plaque film on teeth by 21 to 36%, respectively. Collectively, the data indicated that the sodium polyvinylphosphonic acid has the potential to prevent soft and hard dental deposits on teeth.