Promoting substrates uptake and curdlan synthesis of Agrobacterium sp. by attenuating the exopolysaccharide encapsulation

Abstract

During curdlan production by Agrobacterium sp., the secreted exopolysaccharide (EPS) gradually encapsulated Agrobacterium sp., accompanied by cell aggregation, resulted in inhibited substrate uptake and curdlan synthesis. To relieve the EPS encapsulation effect, the shake-flask culture medium was quantitatively supplemented with 2 % to 10 % endo-β-1,3-glucanase (BGN), while obtaining curdlan with a decreased weight-average molecular weight ranging from 18.99 × 104 Da to 3.20 × 104 Da. In a 7-L bioreactor, the 4 % BGN supplement substantially attenuated the EPS encapsulation, resulting in increased glucose consumption and curdlan yield to 66.41 g/L and 34.53 g/L after fermentation of 108 h, which improved 43 % and 67 %, respectively compared with the control. The disruption of EPS encapsulation with BGN treatment accelerated the regeneration of ATP and UTP, resulting in sufficient uridine diphosphate glucose for curdlan synthesis. The upregulation of related genes at the transcription level reveals that the respiratory metabolic intensity, the energy regeneration efficiency, and the curdlan synthetase activity were enhanced. This study presents a simple and novel strategy of relieving the effects of EPS encapsulation on the metabolism of Agrobacterium sp. for the high-yield and value-added production of curdlan, which could be potentially applied in producing other EPSs.