Isolation of Polyhydroxyalkanoate (PHA)-producing Azotobacter spp. from Crop Rhizospheres located in Lima, Peru

PHAs are polyesters found as internal granules in several microorganisms. Azotobacter is known for its ability to produce PHA. This study aimed to isolate Azotobacter from the rhizosphere of selected crops located in Lima and evaluate their PHA-producing potential. Nile Red medium was used for PHA detection, and Sudan Black B staining allowed microscopic observation. Biopolymer production and quantification were carried out in Burk’s medium, PHA minimal medium (PHAMM), and modified PHAMM. In Nile Red medium, 68.2% of strains produced PHA, with Azotobacter AzoLur20 exhibiting the highest production, 2.1 g/L of PHA at 96 hours in PHAMM. However, strain AzoLur19 showed higher productivity and stability, achieving 0.06 g/L*h of PHA. Additionally, Sudan Black B staining in Burk’s medium revealed larger Azotobacter cells with more defined granules. AzoLur19 was classified as Azotobacter chroococcum. In conclusion, Azotobacter species isolated from crops located in Lima can produce PHA with high yields, with A. chroococcum as the predominant species. Highlights: • A total of 22 Azotobacter strains were isolated, with A. chroococcum AzoLur19 identified as a promising PHA producer. • PHA accumulation was successfully screened using Nile Red and Sudan Black B staining methods. • AzoLur20 and AzoLur23 achieved high PHA yields, with up to 87.67% accumulation in Burk medium. • AzoLur19 strain reached the highest productivity (0.06 g/L·h) in both PHAMM and modified PHAMM media. • Modified PHAMM medium showed potential as an alternative for efficient PHA biosynthesis.