Despite all these successes, bacterial expression is limited by the formation of inclusion
bodies or by the lack of adequate posttranslational modification. Prior endeavors
to express A. niger and Bacillus phytase in E. coli resulted in the formation of insoluble
aggregates [121,122]. A naturally competent Bacillus 168 strain was used for expressing
Bacillus phytase, in which a sequential optimization strategy was used to enhance
phytase production [123]. In addition, A. niger phytase has been successfully expressed
in the cytosolic fraction of E. coli in soluble form with the aid of folding modulators [87].