The Roles of Rhodococcus Ruber in Denitrification with Quinoline as the Electron Donor

Abstract

Denitrification is an important step in domestic wastewater treatment, but providing bioavailable electron donors is an expense.  However, some industrial wastewaters contain organic compounds that could be a no-cost electron donor.  Wastewater containing quinoline is one of special examples, although it used to trouble people as its recalcitrant characteristic.  In this work, quinoline was used as an electron donor to drive denitrification through bioaugmentation with Rhodococcus ruber, which is able to biodegrade quinoline.  When quinoline-acclimated biomass (QAB) was used for denitrification, addition of R. ruber accelerated biodegradation of quinoline and its first mono-oxygenation intermediate (2-hydroxyquinoline), and this also accelerated denitrification, by which quinoline become a new resource as electron donor to drive denitrification.  R. ruber was not active in denitrification, but its biodegradation of quinoline and 2-hydroxyquinoline supplied intermediates that other bacteria used to respire nitrate.  In contrast, glucose-acclimated biomass (GAB) could not achieve effective denitrification with quinoline, with or without R. ruber added.  Analysis by high-throughout sequencing showed that genera Ignavibacterium, Ferruginibacter, Limnobacter, and Denitrosoma were important for quinoline biodegradation with denitrification in QAB.  In summary, bioaugmented R. ruber and endogenous bacterial strains had complementary roles when biodegrading quinoline to enhance denitrification.  The significance of this study is to arouse people to use recalcitrant industrial wastewater as electron donor to drive denitrification.

Keywords: Quinoline, denitrification, Rhodococcus ruber, electron donor.