Open AccessFunctional robustness and gene pools of a wastewater nitrification reactor: comparison of dispersed and intact biofilms when stressed by low oxygen and low pH
Author(s) -
Mao Yuejian,
Bakken Lars R.,
Zhao Liping,
Frostegård Åsa
Publication year - 2008
Publication title -
fems microbiology ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.377
H-Index - 155
eISSN - 1574-6941
pISSN - 0168-6496
DOI - 10.1111/j.1574-6941.2008.00532.x
Subject(s) - nitrification , biology , biofilm , anoxic waters , denitrifying bacteria , nitrosomonas , microbiology and biotechnology , denitrification , heterotroph , environmental chemistry , ammonia monooxygenase , wastewater , moving bed biofilm reactor , 16s ribosomal rna , bacteria , ecology , nitrite , nitrate , environmental engineering , archaea , nitrogen , chemistry , organic chemistry , genetics , engineering
The functional robustness of biofilms in a wastewater nitrification reactor, and the gene pools therein, were investigated. Nitrosomonas and Nitrosospira spp. were present in similar amounts (cloning‐sequencing of ammonia‐oxidizing bacteria 16S rRNA gene), and their estimated abundance (1.1 × 10 9 cells g −1 carrier material, based on amoA gene real‐time PCR) was sufficient to explain the observed nitrification rates. The biofilm also had a diverse community of heterotrophic denitrifying bacteria (cloning‐sequencing of nirK ). Anammox 16S rRNA genes were detected, but not archaeal amoA . Dispersed biofilms (DB) and intact biofilms (IB) were incubated in gas‐tight reactors at different pH levels (4.5 and 5.5 vs. 6.5) while monitoring O 2 depletion and concentrations of NO, N 2 O and N 2 in the headspace. Nitrification was severely reduced by suboptimal O 2 concentrations (10–100 μM) and low pH (IB was more acid tolerant than DB), but the N 2 O/NO 3 − product ratio of nitrification remained low (<10 −3 ). The NO 2 − concentrations during nitrification were generally 10 times higher in DB than in IB. Transient NO and N 2 O accumulation at the onset of denitrification was 10–10 3 times higher in DB than in IB (depending on the pH). The contrasting performance of DB and IB suggests that the biofilm structure, with anoxic/micro‐oxic zones, helps to stabilize functions during anoxic spells and low pH.