Aerobic granulation of aggregating consortium X9 isolated from aerobic granules and role of cyclic di-GMP

•Aggregating consortium X9 was isolated from aerobic granules.•Proteins contents and cell surface hydrophobicity accelerate granulation.•Polysaccharide contents have little effects on granulation.•Cyclic-di-GMP reduced cell swarming motility for enhancing formation of mature granules. This study monitored the granulation process of an aggregating functional consortium X9 that was consisted of Pseudomonas putida X-1, Acinetobacter sp. X-2, Alcaligenes sp. X-3 and Comamonas testosteroni X-4 in shaken reactors. The growth curve of X9 was fit using logistic model as follows y=1.49/(1+21.3*exp(−0.33x)), the maximum specific cell growth rate for X9 was 0.33h−1. Initially X9 consumed polysaccharides (PS) and secreted proteins (PN) to trigger granulation. Then X9 grew in biomass and formed numerous micro-granules, driven by increasing hydrophobicity of cell membranes and of accumulated extracellular polymeric substances (EPS). In later stage the intracellular cyclic diguanylate (c-di-GMP) was at high levels for inhibiting bacteria swarming motility, thereby promotion formation of large aerobic granules. The findings reported herein advise the way to accelerate granule formation and to stabilize operation in aerobic granular reactors.