Cultivable diversity and plant growth-promoting traits of free-living bacteria from coffee soils under contrasting fertilization systems

Brazilian coffee production relies heavily on mineral fertilizers, particularly nitrogen-based inputs. However, the intensive use of these fertilizers is associated with nutrient losses, elevated production costs, and environmental impacts, highlighting the need for more sustainable alternatives. In this context, plant growth-promoting bacteria (PGPB) represent promising resources for improving nutrient use efficiency and reducing dependence on synthetic inputs. Nevertheless, the cultivable bacterial fraction associated with coffee soils remains poorly characterized under contrasting fertilization management systems. The objectives of this study were to isolate, identify, and characterize cultivable bacterial isolates recovered from Coffea arabica soils managed under conventional mineral fertilization (CMF) and organic fertilization, and to screen them for plant growth-promoting traits. Thirty-eight bacterial isolates were recovered and identified by Sanger sequencing of the 16S rRNA gene. Both fertilization systems shared dominant bacterial groups, although each management harbored exclusive bacterial genera. Eleven bacterial isolates from organic fertilization and nine from CMF exhibited growth in nitrogen-free semi-solid NFb medium. All isolates recovered from organic fertilization and several isolates from CMF solubilized tricalcium phosphate. Furthermore, no significant differences in indole-acetic acid production were observed among the bacterial isolates recovered from both fertilization systems. Overall, the cultivable bacterial fraction associated with both management systems exhibited considerable functional diversity and included multifunctional isolates with plant growth-promoting traits. These findings expand current knowledge of cultivable bacterial diversity in coffee soils and highlight the native microbiota as a promising source of candidate microorganisms for future microbial inoculants and microbial consortia adapted to sustainable coffee production.