Effects of seed morphology of Aspergillus niger (A. niger) AN151 on gluconic acid (GA) biosynthesis were investigated in 50-L fermenters. Online physiological parameters showed that the optimum seed morphology for GA biosynthesis was dispersed pattern rather than pellets which were widely used in industrial production. The highest overall yield of 1.051 +/- 0.012 (gg(-1)) was achieved using dispersed seed in shorter fermentation time (14.5h) with an initial glucose solution of 330 g L-1, and was 3.1% higher than the best reported data. And the average GA production rate under dispersed fermentation (21.0 +/- 0.9 gL(-1) h(-1)) was 73.6% and 39.1% higher than those with large and small pellets, respectively. The fermentation results showed that conversion of mycelial morphology from pellets to dispersed state had negligible impact on viscosity of fermentation broth at low biomass concentration (1.7 g L-1), while coefficient of volumetric oxygen transfer (k(L)a) improved more than 13%, suggesting that the promotion of oxygen transfer rate (OTR) between liquid medium and mycelia greatly increased GA production. Therefore, controlling the morphology of A. niger is an effective method for improving industrial GA production. (C) 2015 Elsevier Ltd. All rights reserved.