Plant growth-promoting traits of Rhizophora mangle-associated bacteria and their effects on tomato (Solanum lycopersicum)

Mangrove ecosystems harbor a remarkable microbial diversity that plays essential roles in nutrient recycling and transformation, contributing to soil fertility and quality. However, the exploration of this microbiota as a source of plant growth-promoting bacteria (PGPB) remains at an early stage. In this study, bacterial strains associated with the rhizosphere of <i>Rhizophora mangle</i> from Colombian Pacific mangroves were characterized and their effects on <i>Solanum lycopersicum</i> var. <i>cerasiforme</i> were evaluated. Strains were isolated using nitrogen-free media and identified through 16S rRNA gene sequencing. Key plant growth-promoting (PGP) functions were assessed, including biological nitrogen fixation (confirmed by the presence of the <i>nifH</i> gene), indole-3-acetic acid (IAA) production, siderophore synthesis, and phosphate and potassium solubilization. All isolates fixed nitrogen and produced IAA; 50 % synthesized siderophores, 72 % solubilized potassium, and 90.9 % solubilized phosphate. A factorial analysis of mixed data (FAMD) was used to select four functionally promising strains: <i>Raoultella terrigena</i> RFN53, <i>Klebsiella variicola</i> RFN55, <i>Cellulosimicrobium</i> sp. RFN73, and <i>Klebsiella</i> sp. RFN75, which were evaluated in independent paired greenhouse trials. Inoculation with <i>Cellulosimicrobium</i> sp. RFN73, as well as the combinations RFN53+RFN55 and RFN73+RFN75, significantly enhanced plant growth, increasing plant height, leaf area, and biomass accumulation (<i>p</i> < 0.05) compared to the control. These findings highlight the potential of <i>R. mangle</i>-associated bacteria as biofertilizers and underscore the importance of including safety assessments and detailed functional characterization to ensure their responsible use in sustainable agricultural systems.