Polydopamine Polymerization in Anoxygenic Photosynthetic Organisms

Photosynthetic microorganisms represent attractive tools for the harvesting and the conversion of solar light in bioelectronic devices [1, 2]. The optimization of the interfaces of poorly conductive bacteria with electronic components can be achieved <i>via</i> biocompatible polymers that encapsulate the bacterial cells and allow the intimate contact between the outer cell membrane and the electron acceptor surface, required for an efficient electron transfer in biohybrid systems.<br/>The outer membrane of the metabolically active photosynthetic purple non sulfur bacterium <i>Rhodobacter (R.) sphaeroides </i>was coated with polydopamine (PDA), a bioinspired polymer produced by the self-polymerization of dopamine. Although the presence of oxygen is an essential requirement for dopamine polymerization [3], the PDA coting formation around the cell membrane occurred also in anaerobic condition.<br/>Laccases, enzymes belonging to multi-copper oxidases family, have been reported to oxidize a wide range of phenolic compounds and aromatic amines, including dopamine. Using laccase, the polymerization rate of the dopamine monomer was greatly increased, and the polymer film resulted more uniform compared to traditional self-polymerization and uncontrolled mechanism [4].<br/>Laccases have a wide taxonomic distribution in Nature but with few or little evidence of their presence in anaerobes, since these enzymes use oxygen as an electron acceptor [5]. Here we investigate the process of anaerobic polymerization of dopamine in the growth medium of <i>R. sphaeroides.</i><br/><br/>Similarly, laccase from <i>T. versicolor</i> was also used to improve dopamine polymerization around the photosynthetic organisms belonging to diatom microalgae, with the goal of wastewater treatment and their bioremediation.<br/><br/>[1] F. Milano, A. Punzi, R. Ragni, M. Trotta, G. M. Farinola, <i>Adv. Funct. Mater</i>., 29, 1805521, (2019)<br/>[2] a. M. Di Lauro, S. la Gatta, C. A. Bortolotti, V. Beni, V. Parkula, S. Drakopoulou, M. Giordani, M. Berto, F. Milano, T. Cramer, M. Murgia, A. Agostiano, G. M. Farinola, M. Trotta, F. Biscarini, <i>Adv. Electron. Mater.</i>, 6, 1900888, (2020)<br/>b. M. Di Lauro, G. Buscemi, M. Bianchi, et al., <i>MRS Advances</i> 5, 985–990 (2020)<br/>[3] H. Lee, S.M. Dellatore, W.M. Miller, P.B. Messersmith, <i>Science</i> 318(5849):426-30 (2007)<br/>[4] Q. Zhou, W. Wu, T. Xing, <i>RSC Adv.,</i> 12, 3763-3773 (2022)<br/>[5] F. Berini, M. Verce, L. Ausec, et al., <i>Appl Microbiol Biotechnol</i> 102, 2425–2439 (2018)