David Potesil

Analysis of Salicylic Acid in Willow Barks and Branches by an Electrochemical Method

An electrochemical method for measuring free salicylic acid (SA) was optimized and used to detect its content in barks and branches of thirteen Salix species. We utilized square wave voltammetry method in combination with pencil lead, the detection limit of which was 1.7 ng/ml of salicylic acid. The highest contents of free SA were observed in the bark of S. laponum (3.0 mg/g fr wt) and in the branches of S. purpurea, cv. Nana (2.1 mg/g fr wt) and S. planifolia (2.2 mg/g fr wt). The technique utilized for determination of SA in willow tissues has a much broader dynamic range and lower limit of detection in comparison to both linear sweep and cyclic voltammetry because of its efficient discrimination of capacitance current.

Ferrous iron oxidation by sulfur-oxidizing Acidithiobacillus ferrooxidans and analysis of the process at the levels of transcription and protein synthesis

In contrast to iron-oxidizing Acidithiobacillus ferrooxidans,A. ferrooxidans from a stationary phase elemental sulfur-oxidizing culture exhibited a lag phase in pyrite oxidation, which is similar to its behaviour during ferrous iron oxidation. The ability of elemental sulfur-oxidizing A. ferrooxidans to immediately oxidize ferrous iron or pyrite without a lag phase was only observed in bacteria obtained from growing cultures with elemental sulfur. However, these cultures that shifted to ferrous iron oxidation showed a low rate of ferrous iron oxidation while no growth was observed. Two-dimensional gel electrophoresis was used for a quantitative proteomic analysis of the adaptation process when bacteria were switched from elemental sulfur to ferrous iron. A comparison of total cell lysates revealed 39 proteins whose increase or decrease in abundance was related to this phenotypic switching. However, only a few proteins were closely related to iron and sulfur metabolism. Reverse-transcription quantitative PCR was used to further characterize the bacterial adaptation process. The expression profiles of selected genes primarily involved in the ferrous iron oxidation indicated that phenotypic switching is a complex process that includes the activation of genes encoding a membrane protein, maturation proteins, electron transport proteins and their regulators.

Comparative proteomic analysis of sulfur-oxidizing Acidithiobacillus ferrooxidans CCM 4253 cultures having lost the ability to couple anaerobic elemental sulfur oxidation with ferric iron reduction.

In extremely acidic environments, ferric iron can be a thermodynamically favorable electron acceptor during elemental sulfur oxidation by some Acidithiobacillus spp. under anoxic conditions. Quantitative 2D-PAGE proteomic analysis of a resting cell suspension of a sulfur-grown Acidithiobacillus ferrooxidans CCM 4253 subculture that had lost its iron-reducing activity revealed 147 protein spots that were downregulated relative to an iron-reducing resting cell suspension of the antecedent sulfur-oxidizing culture and 111 that were upregulated. Tandem mass spectrometric analysis of strongly downregulated spots identified several physiologically important proteins that apparently play roles in ferrous iron oxidation, including the outer membrane cytochrome Cyc2 and rusticyanin. Other strongly repressed proteins were associated with sulfur metabolism, including heterodisulfide reductase, thiosulfate:quinone oxidoreductase and sulfide:quinone reductase. Transcript-level analyses revealed additional downregulation of other respiratory genes. Components of the iron-oxidizing system thus apparently play central roles in anaerobic sulfur oxidation coupled with ferric iron reduction in the studied microbial strain.