Biofilm formation inhibition and dispersal of multi-species communities containing ammonia-oxidising bacteria

Abstract

Despite considerable research, the biofilm-forming capabilities of Nitrosomonas europaea are poorly understood for both mono and mixed-species communities. This study combined biofilm assays and molecular techniques to demonstrate that N . europaea makes very little biofilm on its own, and relies on the activity of associated heterotrophic bacteria to establish a biofilm. However, N . europaea has a vital role in the proliferation of mixed-species communities under carbon-limited conditions, such as in drinking water distribution systems, through the provision of organic carbon via ammonia oxidation. Results show that the addition of nitrification inhibitors to mixed-species nitrifying cultures under carbon-limited conditions disrupted biofilm formation and caused the dispersal of pre-formed biofilms. This dispersal effect was not observed when an organic carbon source, glucose, was included in the medium. Interestingly, inhibition of nitrification activity of these mixed-species biofilms in the presence of added glucose resulted in increased total biofilm formation compared to controls without the addition of nitrification inhibitors, or with only glucose added. This suggests that active AOB partially suppress or limit the overall growth of the heterotrophic bacteria. The experimental model developed here provides evidence that ammonia-oxidising bacteria (AOB) are involved in both the formation and maintenance of multi-species biofilm communities. The results demonstrate that the activity of the AOB not only support the growth and biofilm formation of heterotrophic bacteria by providing organic carbon, but also restrict and limit total biomass in mixed community systems.

Nitrifying biofilms deprived of organic carbon show higher functional resilience to increases in carbon supply

“…These two taxa likely dominated different biofilm niches, as shown by another study where N. europaea-lineage and N. oligotropha coexisted on the outer biofilm layer, whereas N. oligotropha dominated the deeper layers 51 . Moreover, N. europaea was reported to support heterotrophic growth and biofilm formation in the absence of external organic carbon 52 . Thus, the greater oxygen availability in R0 selected for different taxa as opposed to oxygen-limited R1.…”

Nitrite production by ammonia‐oxidizing bacteria mediates chloramine decay and resistance in a mixed‐species community

“…The medium contained final concentrations of 3.3 g l À1 (NH 4 ) 2 SO 4 , 5.85 g l À1 KH 2 PO 4 , 0.48 g l À1 NaH 2 PO 4 , 90 mg l À1 MgSO 4 , 22 µg l À1 CaCl 2 , 1.5 mg l À1 FeSO 4 /5 mg l À1 EDTA (a chelated iron mixture), 80 ng l À1 CuSO 4 and 400 µg l À1 Na 2 CO 3 , at a pH of 8.5. Nitrosomonas europaea (ATCC 19718) pure cultures or a commercial nitrifying culture (Bio-Culture; AquaSonic TM , Sydney, NSW, Australia), containing ammonia-oxidizing bacteria, nitrite-oxidizing bacteria and heterotrophic bacteria, were used in this study, expanding upon a modelling system described previously (Keshvardoust et al, 2019). This community and biofilm model was used as an experimental laboratory system to enable relatively rapid experiments, that incorporate the biochemical functionality of AOB coupled with the biofilm-forming ability of co-occurring species.…”

“…Accordingly, this study expands upon a previously published model using a mixed-species nitrifying community containing N. europaea and heterotrophic bacteria which varied in community composition in response to growth and culture ª 2020 The Authors. Microbial Biotechnology published by Society for Applied Microbiology and John Wiley & Sons Ltd, Microbial Biotechnology, 13, 1847-1859 conditions (Petrovich et al, 2017;Keshvardoust et al, 2019), to explore the potential contributions of AOB to biofilms and chloramine decay. This experimental microbial community was comprised of nearly 50% Nitrosomonasaceae (AOBs) and approximately 50% of heterotrophic bacteria when grown in nitrification medium.…”

“…Nitrite produced during nitritation can be readily and directly oxidized by chloramine, resulting in the formation of nitrate and the decomposition of chloramine into ammonia and free chloride (Vikesland et al ., 2001). Thus, the organic carbon and energy derived from the oxidation of ammonia produced via the decomposition of chloramine can be coupled with the reduction in chloramine concentration to allow for the proliferation of both nitrifying bacteria and heterotrophic microorganisms in surface‐attached mixed‐species biofilms (Petrovich et al ., 2017; Keshvardoust et al ., 2019).…”

“…To improve our understanding of the mechanisms of chloramine decay and microbial resistance to chloramination, a microbial model that addresses the ecological role of nitrifying and non‐nitrifying organisms, such as those found in chloramine‐treated drinking water systems will be invaluable to complement the chemical approaches that have been well‐studied. In this study, Pseudomonas aeruginosa was used to model a heterotrophic bacterium, while a mixed‐species community containing N. europaea and other bacteria was used to model mixed‐species nitrifying communities (Petrovich et al ., 2017; Keshvardoust et al ., 2019). Pseudomonas aeruginosa is a model biofilm‐forming organism that produces high amounts of alginate (Ochsner and Reiser, 1995; Whiteley et al ., 2001; Drenkard and Ausubel, 2002; Bazire et al ., 2005; Barraud et al ., 2006), that is known to associate with other organisms in mixed‐species biofilms (Riedel et al ., 2001) and can be found in drinking water (Shrivastava et al ., 2004).…”