Wheat native endophytic bacteria isolated from Mediterranean and Atlantic agroecosystems: identification, functional profiling and seedling bioassays

Abstract

Wheat (Triticum aestivum) cultivation is increasingly challenged by climate change, scarcity of natural resources and dependence on synthetic fertilizers. Plant growth-promoting bacteria (PGPB) represent a promising, sustainable approach to increase crop resilience and enhance resource-use efficiency. However, most studies have primarily focused on PGPB isolated from specific geographical regions and predominantly from the rhizosphere, thereby limiting the exploration of microbial diversity that may harbor novel strains with distinct functional traits and enhanced biostimulant potential. Thus, this study explored wheat-native endophytic bacteria isolated across different agroecosystems in the Mediterranean and Atlantic region, integrating taxonomy, broad multi-trait assessment for functional profiling and seedling bioassays to explore PGPBs with potential for improvement of wheat resilience. A total of 181 isolates belonged to the families Pseudomonadaceae, Bacillaceae and Paenibacillaceae, from which 66 representatives were selected for downstream analysis. Most isolates exhibited relevant plant growth-promoting traits, including indole compounds production (95.5%), 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity (100%), siderophore production (100%), and phosphate solubilization (62%). In addition, many isolates demonstrated tolerance to salinity and PEG-induced osmotic stress. Interestingly, substantial variability was observed among strains in the magnitude of these functional traits. Several isolates significantly enhanced wheat germination and early seedling growth, with Pseudomonas tritici (B254) increasing total biomass by 35.2%. In contrast, Bacillus pumilus (B393) and Pseudomonas sp. (B451) showed inhibitory and suppressive effects on germination and seedling development. These findings reveal a wide range of functional diversity among wheat endophytic bacteria and highlight promising native strains for the development of bioinoculants to improve wheat performance.