Abstract
To date, different kinds of biosensing elements have been used effectively for environmental monitoring. Microbial cells seem to be well-suited for this task: they are cheap, adaptable to variable field conditions and give a measurable response to a broad number of chemicals. Among different pollutants, heavy metals are still a major problem for the environment. A reasonable starting point for the selection of a biorecognition element to develop a biosensor for metals could be that of a microorganism that exhibits good mechanisms to cope with metals. Pseudomonads are characterized by the secretion of siderophores (e.g., pyoverdine), low-molecular weight compounds that chelate Fe3+ during iron starvation. Pyoverdine is easily detected by colorimetric assay, and it is suitable for simple online measurements. In this work, in order to evaluate pyoverdine as a biorecognition element for metal detection, the influence of metal ions (Fe3+, Cu2+, Zn2+), but also of temperature, pH and nutrients, on microbial growth and pyoverdine regulation has been studied in P. fluorescens. Each of these variables has been shown to influence the synthesis of siderophore: for instance, the lower the temperature, the higher the production of pyoverdine. Moreover, the concentration of pyoverdine produced in the presence of metals has been compared with the maximum allowable concentrations indicated in international regulations (e.g., 98/83/EC), and a correlation that could be useful to build a colorimetric biosensor has been observed.
Highlights
Microorganisms are well-adapted to their own ecosystem, and the degree of their adaptability can be evaluated through different measurable parameters
CICP was not determined for zinc in the tested concentration range (0–46 μM). This last experiment has highlighted that P. fluorescens is well-suited to grow in the range of allowed concentrations of metals in water, and the correlation between the environmental quality standards and the CICP of Fe3+ and Cu2+ can be used to build a colorimetric biosensor, with the hopeful prospects of the in situ application of P. fluorescens pyoverdine. This introductory study has shown that pyoverdine production in P. fluorescens is influenced by the carbon source, temperature and the initial pH value
The microbial growth and pyoverdine production were higher when succinic acid was used instead of glucose as the carbon source, and the temperature was controlled at 15–20 °C
Summary
Microorganisms are well-adapted to their own ecosystem, and the degree of their adaptability can be evaluated through different measurable parameters (e.g., biomass growth, metabolism by-products, protein expression). When an environmental variable changes, the microorganisms react by altering their biochemical behavior One of these mechanisms can be used to build environmental biosensors: these are widely applicable devices that combine a biorecognition element with a signal transducer to obtain a new, on-site, analytical tool [1]. The pyoverdine of P. fluorescens was evaluated taking into account that factors other than iron limitation influence the production of siderophores in Pseudomonads [23], e.g., temperature, pH and the carbon source. The influence of these parameters and of different metal ions on growth and pyoverdine regulation was investigated. The pyoverdine production in the presence of metals was compared with the environmental quality standards established in international regulations (98/83/EC; WHO guidelines for drinking water quality)
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