Mercury absorption by Pseudomonas fluorescens BM07 grown at two different temperatures.

Pseudomonas fluorescens BM07 was characterized as a producer of cold-induced biopolymer by decreasing the temperature down to as low as 10 degrees C. It was previously shown that the synthesis of BM07 biopolymer was inhibited at 30 degrees C. The present study was conducted to investigate the biosorption of mercury (Hg2+) ions on the BM07 cells grown on M1 minimal medium at two temperatures (10 degrees C and 30 degrees C). The effects of various factors including pH, contact time, initial concentration of metal and cell biomass on the biosorption yield were also studied. Study of the effect of pH on mercury removal indicated that the metal biosorption increased with increasing pH from 3.0 to 7.0. The optimum adsorption pH value was found to be 7.0. Our results showed that, at optimum pH, BM07 cells were able to uptake the mercury up to 102 and 60 mg Hg2+/g dry biomass for 10 degrees C and 30 degrees C grown cells respectively. The removal capacity of cells increased when the cell biomass concentrations increased. The maximum removal efficiency was obtained when cells concentration was 0.83 mg dry biomass/ml for both conditions. The initial metal ion concentration significantly influenced the equilibrium metal uptake and adsorption yield. The equilibrium data were analyzed using Langmuir adsorption model. The qmax was 62.9 and 82.25 mg Hg2+/g dry biomass for cells grown at 30 degrees C and 10 degrees C respectively. The results suggest that, the existence of residual cold-induced biopolymer on the external surface of cells may play an important role in biosorption efficiency, as P. fluorescens BM07 cells which were grown at 10 degrees C under similar conditions showed higher efficiency to biosorbe mercury than non-polymer producing cells grown at 30 degrees C.

Defining the plant disulfide proteome.

There is considerable interest in redox regulation and new targets for thioredoxin and glutaredoxin are now being identified. It would be of great benefit to the field to have a list of all possible candidates for redox regulation--that is all disulfide proteins in plant. We developed a simple and very powerful method for identifying proteins with disulfide bonds in vivo. In this method, free thiols in proteins are fully blocked by alkylation, following which disulfide cysteines are converted to sulfhydryl groups by reduction. Finally, proteins with sulfhydryls are isolated by thiol affinity chromatography. Our method is unique in that membrane proteins as well as water-soluble proteins are examined for their disulfide nature. By applying this method to Arabidopsis thaliana we identified 65 putative disulfide proteins, including 20 that had not previously been demonstrated to be regulated by redox state. The newly identified, possibly redox-regulated proteins include: violaxanthin de-epoxidase, two oxygen-evolving enhancer proteins, carbonic anhydrase, photosystem I reaction center subunit N, photosystem I subunit III, S-adenosyl-L-methionine carboxyl methyltransferase, guanylate kinase, and bacterial mutT homolog. Possible functions of disulfide bonding in these proteins are discussed.