De Zoete, Amber Yasemin ShirinBrink, Hendrik GideonBeukes, Joshua CornelusVan Rooyen, Ignatius LeopoldusNicol, Willie2022-10-072022-10-072021-11-15de Zoete, A.Y.S.; Brink, H.G.; Beukes, J.C.; van Rooyen, I.L.; Nicol, W. Diazotrophic Behaviour in a Non-Sterile Bioreactor: The Effect of O2-Availability. Processes 2021, 9, 2039. https://DOI.org/10.3390/pr9112039.2227-9717 (online)10.3390/pr9112039https://repository.up.ac.za/handle/2263/87599The 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.en© 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license.DiazotrophsBio-fertilizerNitrogen fixationATP down-regulationArticle