Spontaneous Assembly of Exopolymers from Phytoplankton

Phytoplankton exopolymeric sub stances (EPS) con trib ute sig nif i cantly to the dis solved or ganic car bon (DOC) pool in the ocean, play ing cru cial roles in the sur face ocean car bon cy cle.Re cent stud ies have dem on strated that ~10% of ma rine DOC can self-as sem ble as microgels through elec tro static Ca bonds pro vid ing hotspots of en riched mi cro bial sub strate.How ever, the ques tion whether EPS can self-as sem ble and the for ma tion mech a nisms for EPS microgels have not been ex am ined.Here we re port that EPS from three rep re sen ta tive phytoplankton spe cies, Synechococcus, Emiliania huxleyi, and Skeletonema costatum can spon ta ne ously self as sem ble in ar ti fi cial sea wa ter (ASW), form ing mi cro scopic gels of ~ 3 -4 mm in di am e ter.Dif fer ent from the ma rine DOC poly mers as sem bly, these EPS sam ples can self-as sem ble in Ca 2+ -free ASW.Fur ther ex per i ments from flu o res cence en hance ment and chem i cal com po si tion anal y sis con firmed the ex is tence of fair amounts of hy dro pho bic do mains in these EPS sam ples.These re sults sug gest that hy dro pho bic in ter ac tions play a key role in the assembly of EPS from these three species of marine phytoplankton.