Soil bacteria that utilize inositol hexaphosphate (IHP) were isolated from a range of soils using defined selection media. An analysis of 200 randomly selected isolates indicated that less than 0.5% of the culturable population of soil bacteria were capable of using IHP as a sole source of C and P. From a further 238 isolates obtained from enrichment culture, four unique organisms (identified by randomly amplified polymorphic DNA-polymerase chain reaction) were selected and characterized for their ability to specifically utilize IHP. These four organisms were putatively identified as either fluorescent Pseudomonas spp. (P. putida CCAR53 and CCAR59) or nonfluorescent Pseudomonas spp. (P. mendocina CCAR31 and CCAR60) as determined by partial DNA sequence analysis of 16S rRNA genes. The fluorescent Pseudomonas strains exhibited marked phytase activity and liberated up to 81% of the phosphate from IHP either in the absence or presence of arabinose as an additional C source. The nonfluorescent strains also exhibited an ability to liberate Pi from IHP but were effective only in the presence of added arabinose. Strains CCAR59 and CCAR60 could effectively utilize either Na-IHP or Ca-IHP at pH 7.0, whereas only strain CCAR59 could grow and utilize these substrates at pH 5.0.
