Effect of the Mycorrhizosphere
on the Genotypic and Metabolic
Diversity of the Bacterial Communities Involved in
Mineral Weathering in a Forest Soil
S. Uroz,1* C. Calvaruso,2
M. P. Turpault,2 J. C. Pierrat,3
C. Mustin,4 and P. Frey-Klett1
INRA-UHP, Interactions Arbres Micro-organismes, UMR
1136, 54280 Champenoux, France.
Abstract
To date, several bacterial species
have been described as mineral-weathering agents which
improve plant nutrition and growth. However, the possible
relationships between mineral-weathering potential,
taxonomic identity, and metabolic ability have not
been investigated thus far. In this study, we characterized
a collection of 61 bacterial strains isolated from
Scleroderma citrinum mycorrhizae, the mycorrhizosphere,
and the adjacent bulk soil in an oak forest. The ability
of bacteria to weather biotite was assessed with a
new microplate bioassay that measures the pH and the
quantity of iron released from this mineral. We showed
that weathering bacteria occurred more frequently
in the vicinity of S. citrinum than in the
bulk soil. Moreover, the weathering efficacy of the
mycorrhizosphere bacterial isolates was significantly
greater than that of the bulk soil isolates. All the
bacterial isolates were identified by partial 16S
rRNA gene sequence analysis as members of the genera
Burkholderia, Collimonas, Pseudomonas, and
Sphingomonas, and their carbon metabolism
was characterized by the BIOLOG method. The most efficient
isolates belonged to the genera Burkholderia
and Collimonas. Multivariate analysis resulted
in identification of three metabolic groups, one of
which contained mainly bacterial isolates associated
with S. citrinum and exhibiting high mineral-weathering
potential. Therefore, our results support the hypothesis
that by its carbon metabolism this fungus selects
in the bulk soil reservoir a bacterial community with
high weathering potential, and they also address the
question of functional complementation between mycorrhizal
fungi and bacteria in the ectomycorrhizal complex
for the promotion of tree nutrition.
Keywords:Mycorrhizosphere,
Metabolic Diversity, Forest Soil, Scleroderma
citrinum, Burkholderia, Collimonas, Pseudomonas,Sphingomonas,
Organis farming.
