Agriculture Reference
In-Depth Information
Chapter 5
A RE R HIZOBIUM AND S OIL E NZYME
A CTIVITIES G OOD I NDICATORS OF
H EAVY M ETAL S OIL C ONTAMINATION ?
S.I.A. Pereira 1 , I.V. Castro 2 and E. Figueira 1
1 Centre for Cell Biology, Department of Biology, Campus Santiago,
3810-193 AVEIRO, Portugal
2 Departamento de Ecologia, Recursos Naturais e Ambiente,
EFN-INRB, Av. da República 2780-159 OEIRAS, Portugal
A BSTRACT
The widespread pollution of soils is an increasing urgent problem because of its
contribution to environmental deterioration on a global basis. Several toxic compounds,
such as heavy metals, often contaminate soils. The main sources of heavy metal pollution
are mining, industries and application of metal-containing pesticides, fertilizers and
sewage sludge. In recent decades there has been increasing concern with heavy metal, not
only because of their toxicity to animals, plants and microorganisms, but also because
they are highly toxic, mutagenic and/or carcinogenic to humans.
Due to their small size, which provides a large contact area that can interact with the
surrounding environment, microorganisms are the first biota showing the impact of toxic
compounds. Microorganisms being in intimate contact with the soil environment are
considered to be the best indicators of soil pollution. In general, they are very sensitive to
low concentrations of contaminants and provide a rapid response to soil perturbation.
Rhizobium spp. are ubiquitous gram-negative soil bacteria that have a profound
scientific and agronomic significance due to their ability to establish nitrogen-fixing
symbiosis with legumes, which is of major importance to the maintenance of soil fertility.
There is increasing evidence of the adverse effects of heavy metals on soil microbial
processes, including on soil enzymatic activities. Soil enzymes are the driving force
behind all the biochemical transformations occurring in the soil. Enzymes catalyse all
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