True about corynebacterium diptheria includes all of the following except :
Deep invasion is not seen
Elek’s test is done for toxigenicity
Metachromatic granules are seen
Toxigenicity is mediated by chromosomal change
“Corynebacteriophage beta carries the structural gene (tox + ) encoding diptheria toxin and a family of closely related corynebacteriophage are responsible for toxigenic conversion of tox – C.diptheria to tox + phenotype.”

Elek’s gel precipitation test is in vitro test for toxin detection.