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Direct production of polyhydroxybutyrate and alginate from nitrogen-free waste/crude glycerol by Azotobacter vinelandii under atmospheric nitrogen conditions


 While biodiesel fuel is drawing attention as an environmentally friendly fuel, use of waste/crude glycerol, a byproduct of the fuel production process, has increasingly become an essential subject to be solved. Here we show the development of a low-cost fermentation technology using an atmospheric nitrogen-fixing bacterium to recycle waste/crude glycerol into functional biopolymers. Azotobacter vinelandii showed significant growth on tap water-diluted waste/crude glycerol without any pretreatment. Cell number of viable A. vinelandii increased over 1,000-fold under the optimal growth conditions. Most glycerol (~0.2%) in the waste/crude glycerol medium was completely depleted within 48 h of cultivation. The production of useful polymers, such as polyhydroxybutyrate and alginate, was also observed. Alginate productivity was increased 10-fold by blocking polyhydroxybutyrate synthesis pathway. Although there are few examples of using waste/crude glycerol directly as a carbon source for microbial fermentation, there are no reports on the use of waste/crude glycerol without adding nitrogen source. This study indicates that it is possible to develop a technology to produce industrially useful polymers from waste/crude glycerol by energy-saving and energy-efficient fermentation using atmospheric nitrogen-fixing A. vinelandii.