ABSTRACT
In order to investigate the microbe-mineral interaction in the micro scale, spatial distribution and speciation of Cu and S in Halothiobacillus HT1 biofilm formed on a CuS surface was examined using synchrotron-based X-ray techniques. Confocal laser scanning microscope (CLSM) results indicated that Halothiobacillus HT1 biofilm formation gave rise to distinct chemical and redox gradients, leading to diverse niches in the biofilm. Live cells were distributed at the air-biofilm and membrane-biofilm interface. CuS was oxidized by Halothiobacillus HT1 biofilm, and copper penetrated into the biofilm. Sulfide was oxidized to cysteine (77.3%), sulfite (3.8%) and sulfonate (18.9%). Cu-cysteine-like species were involved in the copper homeostasis. These results significantly improve our understanding of the interfacial properties of the biofilm-mineral interface.
Subject(s)
Biofilms/drug effects , Copper/pharmacology , Halothiobacillus/cytology , Halothiobacillus/physiology , Synchrotrons , Halothiobacillus/drug effects , Microbial Viability/drug effects , Microscopy, Fluorescence , Sulfur/isolation & purification , X-Ray Absorption Spectroscopy , X-RaysABSTRACT
The disposal of low-level radioactive waste containing isotopes such as strontium by immobilization in cement paste has become common practice. However, the stability of cement paste in the environment may be impaired by sulfuric acid produced by sulfur-oxidizing bacteria. Since biodegradation rates in the environment of most radioactive waste burial sites are too low to be measured, determination of the degradation kinetics of cement paste is a difficult task. This study reports on the development of an accelerated biodegradation system for cement pastes in which the cement paste is exposed to a continuous culture of the sulfur-oxidizing bacterium Halothiobacillus neapolitanus. This system facilitated detection of the biodegradation processes in cement paste after as short a time as 15 days. A comparison of the durability of a cement paste blended with silica fume with that of unblended cement paste showed that the silica fume induced an increase in the leaching of Ca(+2) and Si and enhanced weight loss, indicating rapid deterioration in the structural integrity of the cement paste. The leaching of Sr(+2) from the silica fume amended cement paste was slightly reduced as compared with the non amended cement paste, indicating an increase in immobilization of strontium. Nevertheless, our findings do not support the use of silica fume as a suitable additive for immobilization of low-level radioactive waste.
Subject(s)
Halothiobacillus/drug effects , Halothiobacillus/metabolism , Silicon Dioxide/pharmacology , Strontium , Sulfur Compounds/metabolism , Biodegradation, Environmental , Biofilms , Microscopy, Electron, Scanning , Oxidation-Reduction , Sulfuric Acids/chemical synthesis , Sulfuric Acids/chemistry , Sulfuric Acids/pharmacologyABSTRACT
Sulfamate is an analogue of thiosulfate, and the sodium and potassium salts of sulfamic acid inhibited the chemolithoautotrophic growth on thiosulfate of Acidithiobacillus ferrooxidans and Halothiobacillus neapolitanus. The chemo-organotrophic growth of Paracoccus versutus on sucrose was similarly inhibited by sulfamate. Thiosulfate oxidation by suspensions of H. neapolitanus was, however, unaffected by sulfamate, showing that sulfamate did not directly affect thiosulfate uptake, activation or oxidation. Inhibition of P. versutus was not relieved by cysteine and methionine, indicating that sulfate uptake and sulfur amino acid biosynthesis were not directly affected by sulfamate. Sulfamate was not degraded by any of the bacteria, and so could not serve as an alternative to thiosulfate as an energy-yielding substrate. Sulfamate is also an analogue of ammonia and might act like hydrazine by inhibiting ammonium uptake or an essential enzyme activity.
