Effect of salt on EPS production by halotolerant bacteria for aerobic granular sludge treatment

Extracellular polymeric substances (EPS) are overproduced by some microbes as a response to stress. The diverse composition of microbial EPS confers unique properties to these biopolymers, which find application in the food industry (e.g., thickening agents) or in the wastewater treatment (e.g., flocculants). The aerobic granular sludge (AGS) process is a promising biotechnology which relies on EPS-producing bacteria for granule formation and stability. One of the current challenges is to use the AGS process to treat high salinity wastewater. Bioaugmentation with EPS-producing halotolerant bacteria can be used as strategy to increase the robustness of AGS to high salinity. The aim of the present study was to retrieve halotolerant EPS producers from wastewater and to investigate EPS production at varying salt levels. Bacteria were isolated from brine wastewater collected in a fish canning plant. Ten isolates were compared for biofilm production (potential EPS producers) using different carbon sources and NaCl concentration (0 to 40 g L-1). Four isolates were selected for EPS production, in a medium with salt concentration up to 40 g NaCl L-1 and using saline wastewater from a fish canning plant. The EPS content in proteins, humic acids and carbohydrates was quantified. The four most promising EPS producing bacteria belonged to the Kocuria (isolate A1), Psychrobacter (isolate H3) and Acinetobacter (isolates H4 and CX1) genera. Isolate A1 was the best biofilm producer, forming more biofilm compared to the other isolates with acetate (10 g L-1) and 20 or 40 g L-1 of NaCl. In the presence of the highest salt concentration (40 g NaCl L-1), isolate A1 produced more EPS, containing a higher percentage of carbohydrates in its composition. These EPS producers are being assessed for bioaugmentation of an AGS process treating high salinity wastewater.