Induction of natural competence by different chitin sources. Different chitin sources and chitin derivatives were tested for their ability to induce natural competence in V. cholerae A1552. Lanes 1 and 2: chitosan; lanes 3 and 4: chitin flakes; lanes 5 and 6: chitin powder; lanes 7 and 8: crab-shell fragments (approx. 1 cm2). The medium was not changed at the time of donor DNA (2 ug LacZ-Kan gDNA) addition for all odd lanes but for all even lanes. Average of four independent experiments.