A mutant of B. megaterium resistant to bacteriophage infection was isolated successfully. The the mutant, free and alginate encapsulated B. megaterium cells were studied for their  efficiency in solublizing phosphate in vitro (in liquid cultures) and in vivo (as biofertilizers for wheat plants)
In pure liquid cultures no depressive effect for phages was detected on the efficiency of B. megaterium neither in encapsulated state nor in phage resistant mutant form. Whereas, B. megaterium (free cells) inhibited completely in the liquid cultures due to presence of bacteriophages.
In wheat plants inoculated with either mutant resistant to phage or encapsulated cells of B. megaterium significant increases in plant dry and fresh weight /plant as well as plant P% and  count of phosphate solublizing bacteria in rhizosphere soil, were recorded comparing to plants treated with the free cells. Presence of phages reduced numbers of P- solublizing bacteria in rhizosphere soil and significantly reduced dry, fresh weight /plant and plant P% in plants which received free cells comparing to plants treated with free cells in absence of phages. In wheat plants treated with either mutant resistant to phage or encapsulated cells, phages had no significant on the studied measurements.