Abstract
The behaviour of a locally isolated diazotrophic consortium was investigated with the prospect of agricultural applications. A repeatable culture was obtained in a non-sterile bioreactor. Metagenomic analysis indicated Chryseobacterium ssp. and Flavobacterium ssp. were the dominant species, making up approximately 50% of the microbial community. The oxygen supply was varied and mass-transfer limited growth was attained under all experimental conditions. Negligible amounts of aqueous metabolites were formed, indicating a high selectivity towards biomass production. High oxygen availability resulted in decreased growth efficiencies i.e., the specific energy requirements for biomass synthesis. This was attributed to reduced electron transport chain efficiencies and nitrogenase protection mechanisms. Mass and energy balances indicated that sessile biomass with a high C:N served as a carbon sink. The most efficient growth was measured at an aeration feed composition of 21% oxygen and 79% nitrogen. The study presents one of the only known investigations of operational conditions on diazotrophic growth in a non-sterile bioreactor. In addition, it provides a strong foundation for the development of a Biological Nitrogen Fixation process with scaling potential.
Highlights
Population growth has been catalysed in the past decade by the rapid industrialisation of developing countries and technological advancements
This study aimed to investigate the behaviour of a non-sterile diazotrophic consortium with the prospect of utilising their nitrogen-fixing ability in agricultural applications
In the current study a locally obtained soil diazotrophic microbial culture was succesfully cultured in a non-sterile bench-scale bioreactor
Summary
Population growth has been catalysed in the past decade by the rapid industrialisation of developing countries and technological advancements. A 200% population increase with reference to 2011 is predicted to take place by 2050 [1] Due to this ever-expanding population, one of the main future challenges is food security [2]. To accommodate this surge in food demand, a concomitant exponential increase in food production—and fertilizer usage—is required [3]. In the late nineteenth century, a similar rise in food demand occurred which necessitated industrialised nitrogen fixation. This led to the invention of nitrogen-fixing processes in the early twentieth century [4]; the Haber-Bosch process (Equation (1)) for synthetic nitrogen production became the most prevalent in modern agriculture.
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