Carbohydrate-Binding Protein MkC1qDC as an Effective Bacterial Agglutinin

C1q domain-containing (C1qDC) proteins are widespread in invertebrates and often perform immune functions by binding pathogens via carbohydrate components of pathogen-associated molecular patterns. The MkC1qDC protein from the hemolymph of the horse mussel Modiolus kurilensis has previously shown significant biomedical potential, including the ability to agglutinate marine bacteria. In this study, MkC1qDC protein was tested using 15 bacterial strains, 4 of which were standard terrestrial strains and theother 11 were isolated from marine organisms. The results showed agglutination by MkC1qDC protein of all tested species. Smaller and more numerous agglutination complexes were characteristic of the standard strains of Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis, and the marine bacteria Microbacterium spp. For all other species, large complexes measuring 10–50 μm in diameter were characteristic. Comparison of the agglutination complexes of all Gram-positive and Gram-negative strains in total did not reveal reliable differences, which demonstrates the broad effectiveness of MkC1qDC protein. To assess bacteriostatic activity, one representative culture from each of the four classes included in the study was selected: Pseudovibrio ascidiaceicola from the class Alphaproteobacteria; Acinetobacter johnsonii from the class Gammaproteobacteria; Lysinibacillus fusiformis from the class Bacilli; and Cutibacterium acnes from the class Actinomycetes. Bacteriostatic activity was observed against all four tested cultures, although the protein showed lower activity against L. fusiformis.These results indicate that MkC1qDC protein is an effective bacterial agglutinin valuable for biotechnological and biomedical applications.