Community Structure and Activity Dynamics of Nitrifying Bacteria in a Phosphate-Removing Biofilm

Abstract

The microbial community structure and activity dynamics of a phosphate-removing biofilm from a sequencing batch biofilm reactor were investigated with special focus on the nitrifying community. O 2 , NO 2 ؊ , and NO 3 ؊ profiles in the biofilm were measured with microsensors at various times during the nonaerated-aerated reactor cycle. In the aeration period, nitrification was oxygen limited and restricted to the first 200 m at the biofilm surface. Additionally, a delayed onset of nitrification after the start of the aeration was observed. Nitrate accumulating in the biofilm in this period was denitrified during the nonaeration period of the next reactor cycle. Fluorescence in situ hybridization (FISH) revealed three distinct ammonia-oxidizing populations, related to the Nitrosomonas europaea, Nitrosomonas oligotropha, and Nitrosomonas communis lineages. This was confirmed by analysis of the genes coding for 16S rRNA and for ammonia monooxygenase (amoA). Based upon these results, a new 16S rRNA-targeted oligonucleotide probe specific for the Nitrosomonas oligotropha lineage was designed. FISH analysis revealed that the first 100 m at the biofilm surface was dominated by members of the N. europaea and the N. oligotropha lineages, with a minor fraction related to N. communis. In deeper biofilm layers, exclusively members of the N. oligotropha lineage were found. This separation in space and a potential separation of activities in time are suggested as mechanisms that allow coexistence of the different ammonia-oxidizing populations. Nitrite-oxidizing bacteria belonged exclusively to the genus Nitrospira and could be assigned to a 16S rRNA sequence cluster also found in other sequencing batch systems.Modern biological treatment of wastewater involves not only C removal, but also elimination of the nutrients P and N (5,20). This requires the combined or sequential actions of various groups of microorganisms, such as heterotrophic bacteria, phosphate-accumulating organisms (PAO), and nitrifying and denitrifying bacteria. Consequently, purification plants and processes have become increasingly complex to satisfy the needs of the different microorganisms, usually in several reactor stages (5, 27). The integration of different functions in a single reactor would save reaction space and time and therefore is desirable from an economical point of view. However, difficulties often arise in establishing stable nitrification in such complex systems. Nitrifying bacteria (i.e., ammonia-oxidizing bacteria [AOB] and nitrite-oxidizing bacteria [NOB]) usually show low maximum growth rates, relatively low substrate affinities, and high sensitivity to toxic shocks or sudden pH changes (17,25,41). In the presence of organic matter, they can be easily outcompeted by heterotrophs for oxygen (56) and ammonia (19). Other problems to be solved are the inhibition of denitrification by the presence of oxygen (5) and the need for cyclic changes of oxic and anoxic (i.e., free of oxygen and nitrate) conditions for biological phosphate removal...

In Situ Characterization of Nitrospira -Like Nitrite-Oxidizing Bacteria Active in Wastewater Treatment Plants

“…In contrast to the aerobic incubation experiments, no uptake of organic or inorganic carbon sources by Nitrospira-like bacteria was observed in the absence of oxygen. However, combined FISH and microsensor measurements revealed that high numbers of Nitrospira-like bacterial cells can persist in biofilm zones with low oxygen pressure (17,36,41). The ability to switch from aerobic respiration to an anaerobic metabolism should be advantageous in such habitats.…”

16S rRNA and amoA-based phylogeny of 12 novel betaproteobacterial ammonia-oxidizing isolates: extension of the dataset and proposal of a new lineage within the nitrosomonads

“…During the past few years, the gene encoding the active site subunit of amoA has been exploited increasingly as a marker molecule for AOB diversity research in natural and engineered systems (Baribeau et al, 2000;Gieseke et al, 2001;Horz et al, 2000;Rotthauwe et al, 1997). Initially, amoA gene fragment sequences published previously of Nitrosospira spp.…”

Thermophilic biological nitrogen removal in industrial wastewater treatment

“…Nitrosomonas europaea, Nitrosomonas eutropha, Nitrosomonas halophila Juretschko et al (1998) NOLI 191 Nitrosomonas oligotropha lineage Gieseke et al (2001) Nso 1225 Ammonia oxidizing Beta-proteobacteria Mobarry et al (1996) Nso 190 Ammonia oxidizing Beta-proteobacteria Mobarry et al (1996) Neu 653 Nitrosomonads (halotolerant and obligatehalophilic) (applied with NEU653comp) Wagner et al (1995) NmV Nitrosoccus mobilis Juretschko et al (1998) Nsv 443 Nitrosospira, Nitrosolobus, Nitrosovibrio Mobarry et al (1996) Ntspa 712…”