Assessment of bacterial and structural dynamics in aerobic granular biofilms

Abstract

Aerobic granular sludge (AGS) is based on self-granulated flocs forming mobile biofilms with a gel-like consistence. Bacterial and structural dynamics from flocs to granules were followed in anaerobic-aerobic sequencing batch reactors (SBR) fed with synthetic wastewater, namely a bubble column (BC-SBR) operated under wash-out conditions for fast granulation, and two stirred-tank enrichments of Accumulibacter (PAO-SBR) and Competibacter (GAO-SBR) operated at steady-state. In the BC-SBR, granules formed within 2 weeks by swelling of Zoogloea colonies around flocs, developing subsequently smooth zoogloeal biofilms. However, Zoogloea predominance (37–79%) led to deteriorated nutrient removal during the first months of reactor operation. Upon maturation, improved nitrification (80–100%), nitrogen removal (43–83%), and high but unstable dephosphatation (75–100%) were obtained. Proliferation of dense clusters of nitrifiers, Accumulibacter, and Competibacter from granule cores outwards resulted in heterogeneous bioaggregates, inside which only low abundance Zoogloea (<5%) were detected in biofilm interstices. The presence of different extracellular glycoconjugates detected by fluorescence lectin-binding analysis showed the complex nature of the intracellular matrix of these granules. In the PAO-SBR, granulation occurred within two months with abundant and active Accumulibacter populations (56 ± 10%) that were selected under full anaerobic uptake of volatile fatty acids and that aggregated as dense clusters within heterogeneous granules. Flocs self-granulated in the GAO-SBR after 480 days during a period of over-aeration caused by biofilm growth on the oxygen sensor. Granules were dominated by heterogeneous clusters of Competibacter (37 ± 11%). Zoogloea were never abundant in biomass of both PAO- and GAO-SBRs. This study showed that Zoogloea, Accumulibacter, and Competibacter affiliates can form granules, and that the granulation mechanisms rely on the dominant population involved.

Embedding and slicing of intact in situ collected marine snow

“…FITC-ConA and Alexa647-ConA also successfully stained the aggregate matrix at concentrations as low as 100 lg/mL (Figs. 4d, 7), which was expected as lectin stains have been explored in considerable depth for staining EPS in biofilms (Neu et al 2001;Strathmann et al 2002), river snow (Neu 2000;B€ ockelmann et al 2002), and sludge aggregates (McSwain et al 2005;Weissbrodt et al 2013). Compared to Alcian Blue, FITC-ConA/Alexa647-ConA covered similar areas of the aggregate matrix but stained slightly distinctive features.…”

Microbial Population Dynamics and Ecosystem Functions of Anoxic/Aerobic Granular Sludge in Sequencing Batch Reactors Operated at Different Organic Loading Rates

“…Most studies investigate the effects of operational parameters by analyzing the community composition in samples obtained at a single sampling date during steady-state operation (e.g., Ebrahimi et al, 2010; Gonzalez-Gil and Holliger, 2011; Cydzik-Kwiatkowska, 2015). Only a few reports assess the temporal variation of the microbiome (Li et al, 2008; Weissbrodt et al, 2013; Lv et al, 2014). However, steady-state process performance does not necessitate stable microbial community composition: long-term studies of full-scale activated sludge treatment plants revealed strong variation in the bacterial population and a gradual succession away from initial conditions (Wells et al, 2011; Fredriksson, 2013; Kim et al, 2013).…”

Critical review on biofilm methods

“…Identification of the EPS carbohydrates could be approached using fluorescence lectinbinding analysis (FLBA) which detects glycoconjugates and their distribution within the biofilm (Figure 10(C), and S1) (Marchal et al, 2011;Neu & Lawrence, 2014bTuronova et al, 2016;Zippel & Neu, 2011). Characterization of EPS carbohydrate using FLBA depends on the specificity of the lectins used (Weissbrodt et al, 2013;Zhang et al, 2015a). Conventional fluorescence-labeled probes detected with fluorescence correlation spectroscopy (FCS) for the overall structure of the biofilm could be also employed to assess the viscosity and porosity of the biofilm (Peulen & Wilkinson, 2011).…”