Bioluminescent bacterial biosensors for the assessment of metal toxicity and bioavailability in soils.

A major factor governing the toxicity of heavy metals in soils is their bioavailability. Traditionally, sequential extraction procedures using different extractants followed by chemical analysis have been used for determining the biologically available fraction of metals in soils. Yet, the transfer of results obtained on non-biological systems to biological ones is certainly questionable. Therefore, bioluminescence-based bacterial biosensors have been developed using genetically engineered microorganisms, constructed by fusing transcriptionally active components of metal resistance mechanisms to lux genes from naturally bioluminescent bacteria like Vibrio fischeri for the assessment of metal toxicity and bioavailability in polluted soils. As compared to chemical methods, bacterial biosensors present certain advantages, such as selectivity, sensitivity, simplicity, and low cost. Despite certain inherent limitations, bacterial bioluminescent systems have proven their usefulness in soils under laboratory and field conditions. Finally, green fluorescent protein-based bacterial biosensors are also applicable for determining with high sensitivity the bioavailability of heavy metals in soil samples.

Climbing a ladder: a step-by-step approach to understanding the concept of agroecosystem health.

Population and individual health is linked to agroecosystem health. To comprehend the concept of agroecosystem health, one should climb a ladder consisting of several successive steps, each rung presenting a certain degree of instability (conceptual difficulty and uncertainty) in an advisable but not inevitable order. Here we suggest a ladder consisting of the following concepts: ecosystem, agroecosystem, biodiversity, sustainability, ecosystem health, and agroecosystem health. Although these concepts are to a certain extent well understood and grasped by scientists, politicians, natural resource managers, and environmentalists, some steps are still highly debatable, unclear, and present a considerable degree of reluctance to be defined and understood. Consequently, much empirical and theoretical effort must be made to construct solid conceptual ladders made up of such steps. In this enterprise, a traditional reductionistic approach confining interpretations to narrow scientific disciplines is unadvisable. Holistic, transdisciplinary approaches are required to reach the desired goal.