Isolation and Characterization of Heterotrophic Bacteria from Blue-Green Algae with Multiple Plant Growth Promoting Traits

Blue-green algae (BGA) are unique photosynthetic prokaryotes, which can survive and function under extreme conditions. BGA are associated with heterotrophic bacteria, which together play a distinct role in soil and plant development. Despite the high diversity of the heterotrophic bacteria associated with beneficial BGA, little is known about their potential ecological role. Thus, the present study aimed to obtain and identify BGA and their cultivable associated heterotrophic bacteria (AHB) as well as in vitro characterization of the obtained AHB isolates. Two nitrogen-fixing BGA were isolated from desert soil and identified as Anabaenopsis circularis strain AnHu and Nostoc sp. strain NoHu. Based on the colony morphology, 51 and 12 bacterial isolates were isolated from AnHu and NoHu, respectively, and screened for plant growth-promoting activities (PGPAs). Ten promising AHB isolates that displayed multifunctional ability were further identified using 16S rRNA gene sequence. The analysis revealed that the 6 and 4 identified AnHu- and NoHu-AHB isolates, were affiliated to 4 and 2 different phyla, respectively, indicating high diversity of cultivable AHB. The identified AHB isolates showed identical sequences with NCBI strains known for their functionality as plant growth promoters (PGPs) under harsh environmental conditions. Our results suggest that BGA-AHB are useful as an opulent source for PGPs in Egyptian agricultural arid soil.