Insect immunity - Constitutive expression of a cysteine-rich antifungal and a linear antibacterial peptide in a termite insect

Two novel antimicrobial peptides, which we propose to name termicin and spi nigerin, have been isolated from the fungus-growing termite Pseudacanthoter mes spiniger (heterometabole insect, Isoptera). Termicin is a 36-amino acid residue antifungal peptide, with six cysteines arranged in a disulfide arr ay similar to that of insect defensins. In contrast to most insect defensin s, termicin is C-terminally amidated. Spinigerin consists of 25 amino acids and is devoid of cysteines. It is active against bacteria and fungi, Termi cin and spinigerin show no obvious sequence similarities with other peptide s. Termicin is constitutively present in hemocyte granules and in salivary glands. The presence of termicin and spinigerin in unchallenged termites co ntrasts with observations in evolutionary recent insects or insects undergo ing complete metamorphosis, in which antimicrobial peptides are induced in the fat body and released into the hemolymph after septic injury.