Contractile injection system and use thereof

A host selected from a eukaryote cell or a prokaryote cell comprising a Conserved Virulence cassette comprising structural operons selected from subtypes Ia, Ib, IIa, IIb, IIc, or IId, comprising Open Reading Frames (ORF) encoding a proteinaceous phage tail like syringe structure which functions as a delivery system of cargo, said Conserved Virulence Cassette being co-expressed with an Open Reading Frame controlled by a second promoter encoding a signal peptide and an effector cargo, said signal peptide comprising a packing motif that enables packing of said effector cargo into the syringe, said effector cargo being different from the cargo found in the natural contractile injection system of the Conserved Virulence Cassette and being of up to 300 kDa;

• wherein said packing motif has a covariance less than zero, said covariance being a function of a first vector and a second vector, said first vector comprising the amino acid hydrophilicities of each amino acid in said packing motif and said second vector comprising the electronic properties of each amino acid in said packing motif, said covariance having a lag of 2 for said first vector and for said second vector, wherein the Conserved Virulence cassette is expressed in the host.