Eikelboom's morphotype 0803 in activated sludge belongs to the genus Caldilinea in the phylum Chloroflexi

Abstract

Micromanipulated filamentous bacteria from bulking and foaming activated sludge morphologically identified as Eikelboom type 0803 were shown to be affiliated to the genus Caldilinea within the phylum Chloroflexi. Specific FISH probes were designed for their in situ detection and quantification in seven Danish wastewater treatment plants with biological nutrient removal. The survey applied all species-specific probes for Chloroflexi of relevance in activated sludge treatment plants as well as the phylum-specific probes. Type 0803 filaments constituted around 20% of the total Chloroflexi population. In four of the treatment plants, type 0803 and type 0092 co-occurred and were the dominating fraction of the Chloroflexi population. In the other plants, most Chloroflexi could not be identified beyond the phylum level, suggesting a yet far larger diversity. On average, for all plants, the total Chloroflexi population constituted 12% of the entire microbial population and seems to play an important structural role in the sludge floc formation. Ecophysiological characterization of type 0803 showed their potential role in macromolecule conversion as evident by high levels of exoenzyme expression. Acetate was not consumed. Glucose was consumed with oxygen, nitrite and nitrite as electron acceptors, suggesting that type 0803 may be a denitrifier. Their surfaces were hydrophobic, explaining their occasional occurrence in foaming incidents.

Genomic and in situ investigations of the novel uncultured Chloroflexi associated with 0092 morphotype filamentous bulking in activated sludge

“…The potential for aerobic respiration Cfx-K genome annotation confirmed the potential for aerobic respiration (Supplementary Table S5; Figure 4). Although only few of the described Cfx-K-related species (of the classes Anaerolineae, Caldilineae and Ardenticatenia) are able to utilize oxygen as an electron acceptor (see Supplementary Table S4), aerobic uptake of substrates is a common feature of members of this phylum in full-scale activated sludge systems (Kragelund et al, 2007(Kragelund et al, , 2011 and was also confirmed in situ for the B45 phylotype in this study (see later). Figure 4 Metabolic model for members of the B45 phylotype in activated sludge.…”

“…Whether or not B45 members directly contribute to the hydrolysis of complex carbon sources remains to be demonstrated. The aerobic utilization of complex organic material has been demonstrated for other members of the Chloroflexi in nutrient removal systems (Miura et al, 2007;Kragelund et al, 2011). Nitrite and nitrous oxide may both serve as alternate electron acceptors for the strain with the Cfx-K genome.…”

“…Neither polyphosphate nor lipid storage has been detected in B45 by standard in situ histochemical staining methods (Speirs et al, 2009). Phylum-level in situ investigations of the Chloroflexi in activated sludge biomass suggest they have a role in degradation of complex polymers and display a preference for sugar utilization (Kragelund et al, 2007(Kragelund et al, , 2011. Whether this holds true for B45 phylotype members remains to be determined.…”

“…The relatively high observed abundances of these groups indicates that they are likely the most important filamentous organisms in these systems (Mielczarek et al, 2012;McIlroy et al, 2015b) and they simply must make a substantial contribution to the bulk nutrient transformations observed. Although the ecophysiology of the 'Candidatus Microthrix parvicella' and P2CN44 phylotypes has been described (Kragelund et al, 2011;McIlroy et al, 2013), minimal ecological and physiological information is available for members of the B45 phylotype.…”

“…These phylotypes (classified with the MiDAS taxonomy 1.20; McIlroy et al, 2015b) include 'Kouleothrix' spp. (Eikelboom type 1851;Beer et al, 2002;Kohno et al, 2002), B45 (type 0092; Speirs et al, 2009), P2CN44 (type 0803; Kragelund et al, 2011) and 'Candidatus Sarcinathrix' spp. (type 0914; Speirs et al, 2011).…”