Immunogenic compositions and methods for eliciting an immune response against B. anthracis and other bacilli are provided that include immunogenic conjugates of a poly-&gamma-glutamic acid (&gammaPGA) polypeptide of B. anthracis, or of another Bacillus that expresses a &gammaPGA polypeptide. The &gammaPGA conjugates elicit an effective immune response against B. anthracis, or against another Bacillus, in mammalian hosts to which the conjugates are administered.