A. B. Campêlo and L. B. de Oliveira, “Occurrence and vertical distribution of Azotobacter and Beijerinckia in some soil profiles of the humid zone of Pernambuco”, PAB, vol. 4, no. 1, pp. 47–52, Apr. 2014, doi: 10.1590/S1678-3921.pab1969.v4.17776.