The production of gluconic acid with respect to varying substrate concentrations in submerged (SmF), semisolid-state (SmSF), surface (SF), and solid-state surface (SSF) fermentations was analyzed. Under the various fermentation conditions the biomass and specific growth rate varied with different concentrations of glucose. The highest level of gluconic acid (106.5 g dm(-3)) with 94.7% yield was obtained under SSF conditions. In all cases the maximum degree of gluconic acid conversion was observed at on initial substrate concentration of 120 g dm(-3). The rate of glucose uptake increased on increasing the initial glucose concentration and glucose utilization was observed to be highest (89-94%) in the SmSF process and was comparable with the SSF and SF processes. The maximum rate of cell growth was obtained in all processes at an initial glucose concentration of 120g dm(-3). The gluconic acid production and change in pH were analyzed at varying time intervals and it was observed that the SmF and SmSF processes were completed within 6 days of incubation whereas the highest yield was observed after 12 days of incubation and continued thereafter in the SSF process. (C) 2003 Society of Chemical Industry.