Plant–Microbe Interactions in Extreme Environments: Functional Adaptation of Bacterial Communities Associated with Hedysarum perrauderianum from Algerian Ecosystems

Abstract

Plant-associated microorganisms play a crucial role in ecosystem functioning by enhancing host adaptation to environmental constraints and contributing to soil restoration processes. This study investigates the functional diversity, stress tolerance, and phylogenetic relationships of bacterial communities associated with Hedysarum perrauderianum, an endemic Algerian legume growing in environmentally constrained habitats. Ten bacterial isolates recovered from root nodules were characterized using a polyphasic approach integrating morphological, physiological, biochemical, enzymatic, and molecular analyses. The isolates exhibited functional traits associated with plant–microbe interactions, including enzymatic activities involved in root colonization and nitrogen-related metabolism. Phenotypic profiling revealed considerable metabolic variability, particularly in carbohydrate assimilation patterns and amino acid utilization, with distinct nutritional preferences among isolates. All strains demonstrated adaptive capacities to abiotic stresses, including tolerance to elevated salinity (up to 1 M NaCl), acidic conditions (pH 4.5–5.5), and high concentrations of potentially toxic metals, particularly antimony, zinc, copper, and lead (MIC values reaching 1000 µg/ml), whereas sensitivity to mercury and cadmium was observed. Specific interactions with rhizobiophages further revealed ecological differentiation among bacterial isolates. Molecular characterization based on ARDRA and 16S rRNA gene sequencing assigned the isolates to three major phylogenetic groups within Gammaproteobacteria, corresponding to Enterobacter, Pantoea, and Pseudomonas. These findings demonstrate the ecological versatility of H. perrauderianum-associated bacteria and highlight their potential contribution to plant resilience in degraded and metal-affected ecosystems. The identified stress-adapted bacterial resources may provide valuable candidates for microbial-based approaches supporting ecosystem rehabilitation and sustainable land management.