Single cyanobacteria@silica porous microcapsules via a sol–gel layer by layer for heavy-metal remediation

Heavy-metal removal from industrial wastewater is a major issue. The use of microbial biosorbent is a low cost, sustainable, and efficient way for water cleaning, but the living organisms are limited by their sensitivity and fragility and subjected to water contamination by other relevant bacteria. In order to improve the use of the powerful photosynthetic prokaryote, this work focused on the development of a new protection method of cyanobacterial strains of the genus Synechococcus sp. PCC7002 by a multiple coating including an external layer made of silica. This surfacing was performed using the layer-by-layer method and different polyelectrolytes. Polydiallyldimethylammonium chloride, a cationic polymer is used as a link between the cell wall and silica shell, while polystyrene sulfonate is inserted to play a protective role against ultraviolet light irradiation. This study discloses the synthesis of a highly efficient hybrid material and the excellent protection brought by the silica material. First of all, the layers, in particular four layers, deposited around single cells offer a strong protection against very harmful UV-C light irradiation while maintaining high viability and the same bioadsorption capacity for heavy-metal ions in solution. The long-term viability of this living material and its successful use for copper and lead sequestration, confirms the possibility of exploiting encapsulated cyanobacteria to improve current biotechnologies for wastewater purification. [Figure not available: see fulltext.]