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Cowpea Vigna unguiculata [L.] Walp. is the main subsistence crop of the semi-arid region and a low-cost protein source, especially for poorer populations. The production of this crop in the Northeast is low clue to the lack of agricultural inputs, among them, nitrogen fertilizer. Plant-growth promoting bacteria (BGPB) are being studied to maximize N-2 fixation, provide nutrients such as P or phytohormones and inhibit diseases. The objectives of this study were to verify the viability of co- inoculation of cowpea seeds with Paenibacillus, Brevibacillus and/or Bacillus together with Bradyrhizobium on cowpea; characterize the strains for the production of indol acetic acid (IAA) and phosphate solubilization, as well as to evaluate the synergism among microorganisms as an alternative to optimize biological nitrogen fixation. The experiments were conducted in a laboratory and a greenhouse of the Agronomic Institute of Pernambuco (IPA), with cowpea cu. "IPA - 206" and the strains Bacillus sp. - 449, 450, 451, 461 and ANBE 31, B. cereus - 440, B. subtilis - 438, 441, 454, 455 and 459, B. pumilus 444, 445 and 448, B. megaterium - 462 and Brevibacillus brevis - 447, Paenibacillus brasilensis -24, 172 and 177, P. graminis - 04.21 MC, MC 22:13 and 60,106 BR, P. polymyxa - S21 and P. durus - RBN4. No capacity to produce IAA or solubilize phosphate was observed in the microorganisms. Synergism was observed between the strains of Bacillus v. (449) and Bacillus pumilus (444) co-inoculated with Bradyrhizobium on cowpea.