Chlamydomonas reinhardtii-derived mytichitin-CB/hispidalin chimera efficiently inhibits the growth of bacteria by disrupting their membrane integrity

The antimicrobial peptides Mytichitin-CB and Hispidalin were isolated from Mytilus coruscus and Benincasa hispida, respectively. Our previous studies showed that Mytichitin-CB, when expressed in Chlamydomonas reinhardtii, inhibits the bacterial growth with moderate efficiency. Naturally isolated or Pichia pastoris-expressed Hispidalin also exerts moderate efficiency for inhibiting the growth of bacteria. Here, we expressed a chimeric peptide composed of Mytichitin-CB and Hispidalin that we named as MCH in C. reinhardtii. MCH was stably expressed and its yield accounted for 0.18% of total soluble proteins of the host cells. C. reinhardtii-derived MCH inhibited the growth of both Gram-positive and Gram-negative bacteria by disrupting their cell membrane integrity. Its minimal inhibitory concentration (MIC) were ranged between 20 and 40 μg/mL, demonstrating that MCH is more potent for inhibiting the bacterial growth than individual microalgae-expressed Mytichitin-CB and yeast-expressed Hispidalin. Of more importance, MCH was temperature- and pH-tolerant, protease-resistant and exhibited low hemolytic activity against rat erythrocytes and low cytotoxicity to human embryonic kidney 293 (HEK 293) and Madin-Darby bovine kidney (MDBK) cells. Therefore, we conclude that C. reinhardtii-derived chimeric peptide MCH has a great potential for being developed to replace traditional antibiotics in the future.