Influence of substrate composition and flow rate on growth ofAzospirillum brasilenseCd in a co-culture with 3 sorghum rhizobacteria

Abstract

The ability of Azospirillum brasilense Cd to colonize the niche occupied by 3 bacterial strains previously isolated from sorghum rhizosphere was studied by means of the Biolog system. The isolates were identified by different methods as strains belonging to Pseudomonas putida, Stenotrophomonas maltophilia, and Klebsiella terrigena species. Several C sources, also chosen among the constituents of sorghum root exudates, were used to evaluate the metabolic profiles of Azospirillum and the sorghum rhizobacteria. Azospirillum brasilense Cd exploited the same class of C compounds as the sorghum rhizobacteria and overlapped in their niche requirements. Since structure and functioning of a microbial community are largely affected by the flow rate of nutrient supply, the competitive behavior of A. brasilense Cd was studied in a chemostat mixed culture under C-limited conditions using disodium succinate as C source. Only at high growth rates, i.e., when the C source was highly supplied, A. brasilense Cd appeared to be a good competitor and it became the dominant species, whereas at low growth rates, it was outnumbered by the other species. However, the coexistence of all the strains was always maintained, thus suggesting that interactions other than competition or a potential cross-feeding might occur within the mixed culture.

Structural and functional study in the rhizosphere of Oryza sativa L. plants growing under biotic and abiotic stress

“…Data from Biolog appear as an indirect analysis, as it has been related to modifications in exudation patterns (Lippi et al . ; Alisi et al . ; García‐Villaraco Velasco et al .…”

“…A better understanding of the relationships between microbial diversity and soil functions requires not only the use of more accurate assays for taxonomically and functionally characterizing DNA and RNA extracted from soil, but also high-resolution techniques with which to detect inactive and active microbial cells in the soil matrix (Nannipieri et al 2003). Data from Biolog appear as an indirect analysis, as it has been related to modifications in exudation patterns (Lippi et al 2004;Alisi et al 2005; Garc ıa-Villaraco Velasco et al 2009), and shifts in Biolog metabolic diversity patterns have been related to shifts in community composition (Schutter and Dick 2001;Crecchio et al 2004). Analysis of community-level catabolic profiling with RDA (Figs 4 and 5), indicated that sampling times and stress incidence were responsible of sample separation.…”