N’DRI Ahou Roseline^{1, 2,}, ALUI Konan Alphonse³, KOKORA Aya Philomène^{1, 2}, ANGORATCHI Marius Ebaley Yves-Magloire^{1, 2}, ANGOUA Amanahan Mauricette Prisca², TOURE Kakoumani Lama Ruth^{1, 2}, COULIBALY Yele Fatoumata^{1, 2}, KARAMOKO Detto^{1, 2}, MOROH Jean-Luc Aboya^{1, 2}

In the context of declining soil fertility associated with agricultural intensification in Côte d’Ivoire, the use of plant growth promoting rhizobacteria (PGPR) represents a sustainable alternative to nitrogen-based inputs. This study assessed the atmospheric nitrogen-fixing potential of cultivable bacteria isolated from rhizospheric soils and roots (endophytes) collected along a gradient of anthropization. A total of sixty-five (65) samples were collected from anthropized areas (maize and cassava fields) and low-anthropized areas (Banco Forest, Haut Bandama Reserve, and Lataha). Following isolation on nutrient agar and Pseudomonas Agar, 234 isolates were purified (78.63% rhizospheric; 21.37% endophytic). Nitrogen-fixing capacity was screened in vitro using nitrogen-free peptone water, with colorimetric quantification of ammonia production. Cultivable bacterial densities were generally higher in soils than in roots and tended to increase in low-anthropized sites. Among the isolates, 96.15% produced ammonia, with 14 isolates showing high performance after 72 h of incubation. The concentrations produced by these bacteria ranged from 18.60 x 10^-3 to 11.05 x 10^-3 mg/ml. Three sporulating isolates were selected and identified using the API 50 CHB system as Bacillus cereus (88.6%), Bacillus coagulans (70.5%), and Brevibacillus laterosporus (83%). Ammonia assimilation increased linearly with bacterial abundance, and strain-specific efficiency differed significantly, with Brevibacillus laterosporus exhibiting the highest performance. These results highlight the potential of sporulating bacilli as promising biofertilizer candidates.

Plant growth–promoting rhizobacteria, biological nitrogen fixation, ammonia, Bacillus, anthropization gradient