Cross-feeding betweenThauera aminoaromaticaandRhodococcus pyridinivoransdrove quinoline biodegradation in a denitrifying bioreactor

Abstract

18The complex bacterial community is predominated by several taxa, such as 19 Thauera and Rhodococcus, in a quinoline-degrading denitrifying bioreactor. Yet it 20 remains unclear about how the interactions between the different bacteria mediate the 21 quinoline metabolism in denitrifying condition. In this study, we designed a 22 sequence-specific amplification to guide the isolation of the most predominant 23 bacteria and obtained four strains of Thauera aminoaromatica, the representative of 24 one key member in the bioreactor. Test on these isolates demonstrated that all of them 25 were unable to strive on quinoline but could efficiently degrade 2-hydroxyquinoline, 26 the hypothesized primary intermediate of quinoline catabolism, under nitrate-reducing 27 condition. However, another isolate, Rhodococcus pyridinivorans YF3, corresponding 28 to the second abundant taxon in the same bioreactor, was found to degrade quinoline 29 via 2-hydroxyquinoline. The end products and removal rate of quinoline by isolate 30 YF3 were largely varied with the quantity of available oxygen. Specifically, quinoline 31 could only be converted into 2-hydroxyquinoline without further transformation under 32the condition with insufficient oxygen, e.g. less than 0.5% initial oxygen in the vials. 33However, if were aerobically pre-cultured in the medium with quinoline the resting 34 cells of YF3 could anaerobically convert quinoline into 2-hydroxyquinoline. A 35 two-strain consortium constructed with isolates from Thauera (R2) and Rhodococcus 36 (YF3) demonstrated an efficient denitrifying degradation of quinoline. Thus, we 37 experimentally proved that the metabolism interaction based on the 38 2-hydroxyquinoline cross-feeding between two predominant bacteria constituted the 39 mainstream of quinoline degradation. This work sheds light on the understanding of 40 mechanism of quinoline removal in the denitrifying bioreactor. 41 42 Keywords：Quinoline-degrading bioreactor, 2-hydroxyquinoline, microbial 43 interaction, cross-feeding, oxygen, denitrification 44 45 Importance 46 We experimentally verified the most predominant Thauera sp. was indeed active 47 degrader for the intermediate metabolites and the second abundant taxon 48 Rhodococcus exerted, however, key function for opening the food box for a complex 49 quinoline-degrading community. An ecological guild composed of two isolates was 50 assembled, revealing the different roles of keystone organisms in the microbial 51community. This study, to our best knowledge, is the first report on the cross feeding 52 between the initial attacker with unprofitable catalysis of reluctant heterocyclic 53 compounds and the second bacterium which then completely degrade the compound 54 transformed by the first bacterium. These results could be a significant step forward 55 towards elucidation of microbial mechanism for quinoline denitrifying degradation. 56 57 Introduction 58Quinoline and its derivatives are typical N-heterocyclic compounds that occur 59 widely in coal tar, shale oil and creosote,...