Xiancai Lu

Analysis of Genes and Proteins in Acidithiobacillus ferrooxidans During Growth and Attachment on Pyrite Under Different Conditions

Microbes are able to enhance the sulfide mineral decomposition, which lead to the formation of AMD. Attachment of bacterial cells to the mineral surface is an important process for pyrite oxidation by Acidithiobacillus ferrooxidans. The selective advantage of bacterial adhesion is considered to favor the surface localization of bacterial populations as nutritionally favorable. Environmental factors determine cell accumulation or dissociation of attachment. In our study, the amount of sessile cells increased rapidly during the initial stage of attachment on pyrite. Planktonic cells showed high activity leading to the accumulation of large colonies on the pyrite surface. We found three proteins to be up-regulated significantly. Additionally, by matching the sequences of the three proteins to the Pfam database, we found that they are related to adhesion, pili biosynthesis and movement. When we replaced pyrite with glass to provide an inert surface that abolished electrostatic forces, we found that cell attachment was maintained under nutrient-rich conditions but drastically reduced under conditions of limited nutrients or the presence of the inhibitor homoserinelactone. Our results are consistent with the idea that starvation may lead to inhibition of attachment by an unknown mechanism that allows bacteria to search for nutrient-rich habitats.

Tolerance and Biosorption of Heavy Metals by Cupriavidus metallidurans strain XXKD-1 Isolated from a Subsurface Laneway in the Qixiashan Pb-Zn Sulfide Minery in Eastern China

The heavy metal-resistant bacterial strain Cupriavidus metallidurans XXKD-1, was isolated from a 475 m subsurface laneway in the Qixiashan Pb-Zn mine, near Nanjing City in eastern China. The phylogenetic analysis based on the 16S rRNA gene sequence shows that the microorgamism has 99% similarity to C. metallidurans CH34. Minimal inhibitory concentrations (MICs) of metals for the bacterium were determined. The bacterial strain XXKD-1 exhibited high MIC values for various heavy metals and a large spectrum of antibiotic resistance. The order of toxicity of the metals to the bacterium was Cd2+ (1 mM) > Co2+ (2 mM) > Cr3+ (2.5 mM) > Ni2+ (3 mM) > Cu2+ (3.5 mM) > Mn2+ (6 mM) > Zn2+ (10 mM) in Tris minimal broth media. Metal bioaccumulation was determined during the course of growth. C. metallidurans strain XXKD-1 is a very efficient biosorbent. It can remove 74% Mn, 53% Cd, 52% Co, 48% Zn and 4% Cr in the cell walls and 4% Mn, 12% Cd, 11% Co, 9% Zn and 50% Cr in intracellular spaces during the active growth cycle (using initial heavy metal concentrations of 0.5 mM). However, it did not efficiently accumulate Cu and Ni, removing only 12% and 10% with total metal biosorption capacities of 3.8 mg/L (0.06 mM) and 3.1 mg/L (0.053 mM), respectively. Because C. metallidurans cells could grow in the presence of elevated concentrations of metals and present relatively high heavy metal biosorption capacities in aerobic conditions, this bacterium may have potential applications for the in-situ bioremediation of heavy metal-contaminated aqueous (or soil) systems in mine ecosystems.

Compensation phenomena found in Acidithiobacillus ferrooxidans after starvation stress

Acidithiobacillus ferrooxidans showed the compensate growth and oxidation after re‐feeding with sufficient ferrous materials after starvation. Compensatory phenomena were first detected in chemoautotrophic organisms. Starvation stress of Acidithiobacillus ferrooxidans was achieved via culturing in low concentrations of iron. During compensation, growth and ferrous oxidation took place faster than in controls. In addition, some genes related to ferrous oxidation (such as rus) and carbon assimilation (cbbR, csoS3) were expressed in different patterns in the low energy environments. Their expression patterns can account for this increased growth and oxidation. Other groups of genes (cspAB, feoAB, fur) were suppressed in response to starvation stress. The presence of pyrite and joint cold stress can render compensation nearly undetectable. This may be why the compensation phenomena observed under these conditions was not the same as that observed under single starvation stress conditions. Gene expression reflected a possible mechanism of tolerance to starvation in Acidithiobacillus ferrooxidans, which would allow the organism to adapt and survive in ferrous‐limited environments.