Microbial synthesis of poly- γ -glutamic acid ( γ -PGA) with fulvic acid powder, the waste from yeast molasses fermentation [post]

Yazhou Li, Jianghan Wang, Na Liu, Luxin Ke, Xiuyun Zhao, Gaofu Qi
2020 unpublished
Background: Molasses is a wildly used feedstock for fermentation, but it also poses a severe wastewater-disposal problem worldwide. Recently, the wastewater from yeast molasses fermentation is being processed into fulvic acid (FA) powder as a fertilizer for crops, but it consequently induces a problem of soil acidification after being directly applied into soil. In this study, the low-cost FA powder was bioconverted into a value-added product of γ-PGA by a glutamate independent producer of
more » ... lus velezensis GJ11.Results: FA power could partially substitute the high-cost substrates such as sodium glutamate and citrate sodium for producing γ-PGA. With FA powder in the fermentation medium, the amount of sodium glutamate and citrate sodium used for producing γ-PGA were both decreased around one third. Moreover, FA powder could completely substitute Mg2+, Mn2+, Ca2+ and Fe3+ in the fermentation medium for producing γ-PGA. In the optimized medium with FA powder, the γ-PGA was produced at 42.55 g/L with a productivity of 1.15 g/(L·h), while only 2.87 g/L was produced in the medium without FA powder. Hydrolyzed γ-PGA could trigger induced systemic resistance (ISR), e.g. H2O2 accumulation and callose deposition, against the pathogen's infection in plants. Further investigations found the ISR triggered by γ-PGA hydrolysates was dependent on the ethylene (ET) signalling and nonexpressor of pathogenesis-related proteins 1 (NPR1). Conclusions: To our knowledge, this is the first report to use the industry waste, FA powder, as a sustainable substrate for microbial synthesis of γ-PGA. This bioprocess can not only develop a new way to use FA powder as a cheap feedstock for producing γ-PGA, but also help to reduce pollution from the wastewater of yeast molasses fermentation.
doi:10.21203/rs.3.rs-48414/v2 fatcat:gamyjdezfrdhlk6x6pjong7nnq