Enterobacter and Pseudomonas: two dominant players in the rhizosphere phosphate-solubilizing bacterial communities of forage grasses adapted to alkaline-sodic soils of the flooding pampa

Abstract

Cultivable phosphate solubilizing bacteria (PSB) communities associated to native (Sporobolus indicus) and exotic (Panicum coloratum) forage grasses adapted to alkaline-sodic soils of the flooding pampa were analyzed. PSB represented 2–14% of cultivable rhizobacteria and Box-PCR fingerprinting revealed a high genetic diversity in both rhizospheres. Taxonomic identification by MALDI-TOF showed that PSB populations of P. coloratum and S. indicus rhizospheres are dominated by the phylum Proteobacteria (92,51% and 96,60% respectively) and to a lesser extent (< 10%), by the phyla Actinobacteria and Firmicutes. At the genus level, both PSB populations were dominated by Enterobacter and Pseudomonas. Siderophore production, nitrogen fixation and indoleacetic acid production were detected in a variety of PSB genera of both plant species. A higher proportion of siderophore and IAA producers were associated to P. coloratum than S. indicus, probably reflecting a greater dependence of the exotic species on rhizospheric microorganisms to satisfy its nutritional requirements in soils of the flooding pampa. This study contributes to the knowledge of the taxonomic and functional diversity of PSB that can be cultivated in environments that have not been explored yet, such as alkaline-sodic soils that impose nutritional limitations for plant growth. Likewise, the results obtained on the PSB community of both plant species constitute valuable information and a starting point to advance in the development of efficient biofertilizers for forage grasses adapted to alkaline-sodic environments and thus reduce the environmental impact of chemical fertilizers.