Termicin

We identified the antifungal gene termicin in three species of Cryptocercus woodroaches. Cryptocercus represents the closest living cockroach lineage of termites, which suggests that the antifungal role of termicin evolved prior to the divergence of termites from other cockroaches. An analysis of Cryptocercus termicin and two β-1,3-glucanase genes (GNBP1 and GNBP2), which appear to work synergistically with termicin in termites, revealed evidence of selection in these proteins. We identified the signature of past selective sweeps within GNBP2 from Cryptocercus punctulatus and Cryptocercus wrighti. The signature of past selective sweeps was also found within termicin from Cryptocercus punctulatus and Cryptocercus darwini. Our analysis further suggests a phenotypically identical variant of GNBP2 was maintained within Cryptocercus punctulatus, Cryptocercus wrighti, and Cryptocercus darwini while synonymous sites diverged. Cryptocercus termicin and GNBP2 appear to have experienced similar selective pressure to that of their termite orthologues in Reticulitermes. This selective pressure may be a result of ubiquitous entomopathogenic fungal pathogens such as Metarhizium. This study further reveals the similarities between Cryptocercus woodroaches and termites.

Termites are often exposed to a variety of pathogens during their life cycle, which has led to the development of an innate immune system to resist these pathogens. Antimicrobial peptides (AMPs) play a crucial role in the innate immune system in insects. However, clear information on AMPs in termites has not been obtained. Therefore, exploring the function of AMPs in the subterranean termite Odontotermes formosanus (Shiraki) can lead to the development of novel termite control strategies that integrate RNA interference (RNAi) and pathogens. Here we first obtained two Oftermicins from O. formosanus and observed that the expression of these Oftermicin genes was significantly upregulated at the mRNA level after treatment with lipopolysaccharide (LPS) or Serratia marcescens Bizio (SM1). Interestingly, the expression of these Oftermicins increased not only in the donor termites but also in the recipient termites through transmission experiments. Bioassay experiments showed that the mortality of O. formosanus treated with SM1 after RNAi was significantly higher than that of other groups. In summary, dsOftermicins are important immunosuppressants for termite control and Oftermicins are optimal targets for termite control based on the combined use of RNAi and pathogens.

Background: Termicin is an antimicrobial peptide with six cysteines forming three disulfide bridges that was firstly isolated from the salivary glands and hemocytes of the termite Pseudacanthotermes spiniger. In contrast to many broad-spectrum antimicrobial peptides, termicin is most active against filamentous fungi. Although more than one hundred complementary DNAs (cDNAs) encoding termicin-like peptides have been reported to date, all these termicin-like peptides were obtained from Isoptera insects. Methods: The cDNA was cloned by combination of cDNA library construction kit and DNA sequencing. The polypeptide was purified by gel filtration and reversed-phase high performance liquid chromatography (RP-HPLC). Its amino acid sequence was determined by Edman degradation and mass spectrometry. Antimicrobial activity was tested against several bacterial and fungal strains. The minimum inhibitory concentration (MIC) was determined by microdilution tests. Results: A novel termicin-like peptide with primary structure ACDFQQCWVTCQRQYSINFISARCNGDSCVCTFRT was purified from extracts of the cockroach Eupolyphaga sinensis (Insecta: Blattodea). The cDNA encoding Es-termicin was cloned by cDNA library screening. This cDNA encoded a 60 amino acid precursor which included a 25 amino acid signal peptide. Amino acid sequence deduced from the cDNA matched well with the result of protein Edman degradation. Susceptibility test indicated that Es-termicin showed strong ability to kill fungi with a MIC of 25 μg/mL against Candida albicans ATCC 90028. It only showed limited potency to affect the growth of Gram-positive bacteria with a MIC of 200 μg/mL against Enterococcus faecalis ATCC 29212. It was inactive against gram-negative bacteria at the highest concentration tested (400 μg/mL). Es-termicin showed high sequence similarity with termicins from many species of termites (Insecta: Isoptera). Conclusions: This is the first report of a termicin-like peptide isolated from E. sinensis that belongs to the insect order Blattodea. Our results demonstrate the diversity of termicin-like peptides, as well as antimicrobial peptides in insects.