BACKGROUNDMorphology and size of biofilms of Pichia pastoris under different culture conditions are key to understanding growth physiology in solid-state fermentation (SSF) and differences relative to submerged fermentation (SmF). Two microscopic techniques were used to contrast these phenomena, comparing SSF on polyurethane foam and SmF, with three concentrations of glycerol as carbon source. Growth parameters such as specific growth rate, maintenance energy, and substrate consumption were also evaluated. RESULTSHigher specific growth rate and maximum growth were obtained in SSF at every glycerol concentration compared with that obtained in SmF. Maintenance energy was higher (33%) in SmF and was related to lower biomass production (66%) than that obtained in SSF. Besides, in SmF, as substrate concentration increased, oxygen availability decreased; such differences in oxygenation could explain differences in biofilm formation. Scanning electron microscopy revealed that P. pastoris produced a compact multilayered biofilm embedded in SSF when compared with SmF, where smaller aggregates were scarcely observed by confocal microscopy. CONCLUSIONThis is the first work where growth parameters of P. pastoris in SSF and SmF are related to biofilm observations, which will help to improve SSF systems for P. pastoris production and its industrial application. (c) 2017 Society of Chemical Industry