Encrypted antimicrobial peptides from proteins present in the plasma of the millipede Rhinocricus sp.

Millipedes are among the most diverse and abundant arthropods in terrestrial environments. However, little is known about their innate immune response against invading pathogenic microorganisms, which is very intriguing considering that the evolutionary success of millipedes is largely due to this complex and primitive defense system, since it allowed them to colonize a wide variety of microhabitats characterized by their high microbial proliferation. Accordingly, the aim of the present work was to determine the presence of antimicrobial peptides in the hemolymph of the millipede Rhinocricus sp. In total, four native peptides with potent antimicrobial activity against different microorganisms, lack of cytotoxicity against Vero cells and lack of hemolytic effects against human erythrocytes were isolated and named RP40-16, RP40-19, RP40-20/1 and RP40-20/2. The analysis with bioinformatics tools suggested that these peptides may be encrypted in large proteins present in the plasma: Hemocyanin and thioester-containing protein. Considering these results, it can be said that millipede hemolymph represents a promising source of molecules with potential for the development of non-conventional antibiotics. Therefore, in order to have a clearer notion of the biotechnological potential and the role of these peptides in the innate immune response of Rhinocricus sp., future studies should focus on elucidating their mechanisms of action, as well as additional biological properties.

Sarconesin II, a New Antimicrobial Peptide Isolated from Sarconesiopsis magellanica Excretions and Secretions.

Antibiotic resistance is at dangerous levels and increasing worldwide. The search for new antimicrobial drugs to counteract this problem is a priority for health institutions and organizations, both globally and in individual countries. Sarconesiopsis magellanica blowfly larval excretions and secretions (ES) are an important source for isolating antimicrobial peptides (AMPs). This study aims to identify and characterize a new S. magellanica AMP. RP-HPLC was used to fractionate ES, using C18 columns, and their antimicrobial activity was evaluated. The peptide sequence of the fraction collected at 43.7 min was determined by mass spectrometry (MS). Fluorescence and electronic microscopy were used to evaluate the mechanism of action. Toxicity was tested on HeLa cells and human erythrocytes; physicochemical properties were evaluated. The molecule in the ES was characterized as sarconesin II and it showed activity against Gram-negative (Escherichia coli MG1655, Pseudomonas aeruginosa ATCC 27853, P. aeruginosa PA14) and Gram-positive (Staphylococcus aureus ATCC 29213, Micrococcus luteus A270) bacteria. The lowest minimum inhibitory concentration obtained was 1.9 µM for M. luteus A270; the AMP had no toxicity in any cells tested here and its action in bacterial membrane and DNA was confirmed. Sarconesin II was documented as a conserved domain of the ATP synthase protein belonging to the Fli-1 superfamily. The data reported here indicated that peptides could be alternative therapeutic candidates for use in infections against Gram-negative and Gram-positive bacteria and eventually as a new resource of compounds for combating multidrug-resistant bacteria.