Analysis of the methylation of total cellular protein by mass spectrometry revealed that methylated proteins accounted for ~2/3 (1,158/1,750) and ~1/3 (591/1,766) of the identified proteins in the wild type and the mutant strains, respectively, indicating that there is extensive protein methylation in S. islandicus and that aKMT is a major protein methyltransferase in this organism.