Chloroflexi bacterium (CFX2) Ca.Brocadia sinica (AMX2) Acetate Acetyl-CoA Acetate ALDH ALDH AK ACS NO,' NH,OH cetvl-p nrfA Vitamin B -Xylulose-5p Vitamin 812 Trp Phe His Lys Arg Vitamin B1 Vitamin B12 Trp Pha C02 otides.AAs.Saccharide .Ile Lys Leu Arg cetyl-CoA Acs Acetat degredati EP Acetaldehyde Vitamin B12 Leu Arg Trp Phe Tyr His TCA lle Lys Leu Arg Vitamin B7 NO NO:nxrA"NO NO, +NO2+N0+M20+M2 Ca.Jettenia ceni(AMX1) Rhodocyclaceae bacterium (PRO1) Fig 5.Proposed metabolic interactions among L coeni B sinica.Chloroflexi bocterium (CFX2)and Rhodocycloceoe bacterium (PRO1)in anammox consortia ertain amino acid synthetic pathways were up-regulated signifi. and B.sinica,and metabolic interactions within anammox conso y compard toduheu-uao that aco heterotrophs in ana d by atway.ALDH pathway and AckA-fp pathway but frst coss.Synthetic pathway and itamin B7 to other members of the ponses toacetate metabolic incudin minsacetate might promote Bvitamin synthe addition ko et al. tabolism and wth of all microbe sharing of B-vitamins or their Notes The authors declare no competing financial interests Acknowledgments 5.Conclusions In this study.discrepant responses of anammox certain amino acid synthetic pathways were up-regulated signifi- cantly in B. sinica, such as synthetic pathways of Lys and Arg. Therefore, acetate may enhance metabolic cross-feeding between B. sinica and heterotrophs. A more active, but costly, amino acid cross-feeding may result in more energy being saved for use in increasing the biomass (Guo et al., 2018). Besides, B-vitamin metabolic exchange between B. sinica and heterotrophs in anammox consortia could also be enhanced by acetate addition, helping to conserve energy by reducing metabolic energy costs. Synthetic pathway integrity and TPM values indicate that B. sinica and J. caeni may act as the main suppliers of vitamin B1 and vitamin B7 to other members of the community. B. sinica also had intact vitamin B12 synthetic pathways so that vitamin B12 might be supplied by B. sinica. As acetyl-CoA is precursor of vita￾mins, acetate might promote B-vitamin synthesis in B. sinica via up￾regulating synthesis of acetyl-CoA, and may facilitate the B-vitamin exchange process in the community (Krivoruchko et al., 2015). B￾vitamins are a large group of cofactors, which are essential for the metabolism and growth of all microbes (Jaehme and Slotboom, 2015). However, the cost of their synthesis is high. Therefore, sharing of B-vitamins or their precursors between community members may help to reduce metabolic energy costs, which may be accomplished via acetate addition (Romine et al., 2017). 5. Conclusions In this study, discrepant responses of anammox species J. caeni and B. sinica, and metabolic interactions within anammox consor￾tia, in response to acetate addition were investigated. According to COG functions analysis, B. sinica was more competitive than J. caeni when adding acetate. B. sinica exhibited superiority in metabolic activity and growth compared to J. caeni, due to the up-regulation of numerous genes that act on metabolic processes. Three acetate metabolic pathways were found in B. sinica, including acetyl-CoA pathway, ALDH pathway and AckA-Xfp pathway, but only the first two were observed in J. caeni. Discrepancies in the acetate meta￾bolic pathways and AMP-acs expression regulated by CRP, which exist between two anammox species, may result in different re￾sponses to acetate. Importantly, metabolic cross-feeding, including the nitrogen cycle, amino acid cross-feeding and B-vitamin meta￾bolic exchange were enhanced, especially between B. sinica and other heterotrophs, with acetate addition, contributing to a reduction in metabolic energy cost to the whole community, in addition to improving nitrogen removal rates of the anammox consortia. Notes The authors declare no competing financial interests. Acknowledgments The authors are grateful to the National Natural Science Foun￾dation of China (No. 51878008 and 91647211) for financial support. Fig. 5. Proposed metabolic interactions among J. caeni, B. sinica, Chloroflexi bacterium (CFX2) and Rhodocyclaceae bacterium (PRO1) in anammox consortia. Y. Feng et al. / Water Research 165 (2019) 114974 9