Evaluation of alginate-encapsulated Azotobacter chroococcum as a phage-resistant and an effective inoculum

The efficiency of free and alginate-encapsulated Azotobacter chroococcum in fixing nitrogen and their susceptibility to bacteriophages were studied in pure liquid cultures (in vitro) and under cultivated soil conditions (in vivo). Bacteriophages of A. chroococcum were isolated and were found to be common in soil of the Experimental Farm of Fac. Agric., Minia Univ., Egypt. In pure liquid cultures, the immobilized cells exhibited much higher nitrogenase activity (about 57 fold) than the free ones. The encapsulation system offered high protection to A. chroococcum against their phages. No nitrogenase activity was detected for the free cells in presence of phages. Uner cultivated soil conditions, inoculation of maize plants (Zea mays, cv. GIZA 2) with immobilized A. chroococcum, markedly increased rhizosphere and rhizoplane Azotobacter population, significantly increased plant N% as well as dry weight/plant, compared to those inoculated with free cells. In free cells inoculated-plants, bacteriophages had a marked depressive effect on rhizosphere and rhizoplane Azotobacter population, significantly reduced plant N% and dry weight/plant, as compared to plants inoculated with free cells in absence of phages. In plants inoculated with immobilized cells, no significant effect for presence of phages was detected in plant N% and dry weight/plant, whereas, a slight reduction in rhizosphere and rhizoplane _{Azotobacter population} was observed.