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Abstract:

Grazing in subalpine pasturelands located in watershed heads represents a potential risk in terms of fecal microbiological pollution of both soil and water. Hence, the role of pastoral practises on soils and aquifers quality needs to be evaluated.

The general goal of this work is to provide deeper knowledge on E. coli ecology in dairy alpine grassland soils and on controlling factors of E. coli in the environment. Microbiological analyses and molecular biology are carried out to evaluate the behaviour of E. coli populations in cow pats, soils and water (throughout the estimation of populational abundance and physiological status as well as genetic structure).

The rhizosphere soil (0-5 cm) is showed to be a permanent environmental reservoir of E. coli populations (104 cells g-1 dry soil) whatever the season or the pasture unit. This result raises the possibility that fecal E. coli could constitute a naturalized (sub)population, which is now part of the indigenous soil community of alpine pasture grasslands. In deeper soil layer below the root zone (5-25 cm), the abundance of E. coli is directly correlated to soil hydrodynamic as does the population genetic structure.

In water, E. coli populations are closely related to those from cow pats and from well-drained soils, connected to aquifers. Also, molecular markers have been elaborated to purchase E. coli physiological state. These results are discussed in terms of the indicator value of E. coli and of its behaviour in soils of pasture grasslands.

Key-words: Escherichia coli, fecal contamination, soil, watershed, hydrodynamic, reservoir, adaptation, genetic structure