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. 1998 Oct;64(10):3740-7.
doi: 10.1128/AEM.64.10.3740-3747.1998.

Colonization of wheat roots by an exopolysaccharide-producing pantoea agglomerans strain and its effect on rhizosphere soil aggregation

N Amellal  1 , G Burtin, F Bartoli, T Heulin
Affiliations

Colonization of wheat roots by an exopolysaccharide-producing pantoea agglomerans strain and its effect on rhizosphere soil aggregation

N Amellal et al. Appl Environ Microbiol. 1998 Oct.

Abstract

The effect of bacterial secretion of an exopolysaccharide (EPS) on rhizosphere soil physical properties was investigated by inoculating strain NAS206, which was isolated from the rhizosphere of wheat (Triticum durum L.) growing in a Moroccan vertisol and was identified as Pantoea aglomerans. Phenotypic identification of this strain with the Biotype-100 system was confirmed by amplified ribosomal DNA restriction analysis. After inoculation of wheat seedlings with strain NAS206, colonization increased at the rhizoplane and in root-adhering soil (RAS) but not in bulk soil. Colonization further increased under relatively dry conditions (20% soil water content; matric potential, -0.55 MPa). By means of genetic fingerprinting using enterobacterial repetitive intergenic consensus PCR, we were able to verify that colonies counted as strain NAS206 on agar plates descended from inoculated strain NAS206. The intense colonization of the wheat rhizosphere by these EPS-producing bacteria was associated with significant soil aggregation, as shown by increased ratios of RAS dry mass to root tissue (RT) dry mass (RAS/RT) and the improved water stability of adhering soil aggregates. The maximum effect of strain NAS206 on both the RAS/RT ratio and aggregate stability was measured at 24% average soil water content (matric potential, -0.20 MPa). Inoculated strain NAS206 improved RAS macroporosity (pore diameter, 10 to 30 &mgr;m) compared to the noninoculated control, particularly when the soil was nearly water saturated (matric potential, -0.05 MPa). Our results suggest that P. agglomerans NAS206 can play an important role in the regulation of the water content (excess or deficit) of the rhizosphere of wheat by improving soil aggregation.

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Figures

FIG. 1
FIG. 1
Effect of inoculation with P. agglomerans NAS206 on wheat at various levels of soil water content. Values with different letters are significantly different at P < 0.05 by the Newman-Keuls test. Error bars show standard errors of mean values.
FIG. 2
FIG. 2
Cross effects of inoculation with P. agglomerans NAS206 and soil water content on the RAS/RT ratio (A) and the water stability of RAS (B). Values with different letters are significantly different at P < 0.05 by the Newman-Keuls test. Error bars show standard errors of mean values.
FIG. 3
FIG. 3
(A) Effect of bacterial inoculation and soil hydric treatment on the mercury pore volume of RAS and bulk soil aggregates. (B) Effect of inoculation with P. agglomerans NAS206 and soil hydric treatment on the cumulative mercury pore volume of RAS and bulk soil aggregates.
FIG. 3
FIG. 3
(A) Effect of bacterial inoculation and soil hydric treatment on the mercury pore volume of RAS and bulk soil aggregates. (B) Effect of inoculation with P. agglomerans NAS206 and soil hydric treatment on the cumulative mercury pore volume of RAS and bulk soil aggregates.
FIG. 4
FIG. 4
TEM of the wheat rhizosphere showing the ultrastructure of RAS at various magnifications. Panels: A, whole set of pores; B and C, intermicroaggregate porosity; D, clay domain porosity.
See this image and copyright information in PMC

References

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