The role of quorum sensing signalling in EPS production and the assembly of a sludge community into aerobic granules

Abstract

Quorum sensing (QS) signalling has been extensively studied in single species populations. However, the ecological role of QS in complex, multi-species communities, particularly in the context of community assembly, has neither been experimentally explored nor theoretically addressed. Here, we performed a long-term bioreactor ecology study to address the links between QS, organization and composition of complex microbial communities. The conversion of floccular biomass to highly structured granules was found to be non-random, but strongly and positively correlated with N-acyl-homoserine-lactone (AHL)-mediated QS. Specific AHLs were elevated up to 100-fold and were strongly associated with the initiation of granulation. Similarly, the levels of particular AHLs decreased markedly during the granular disintegration phase. Metadata analysis indicated that granulation was accompanied by changes in extracellular polymeric substance (EPS) production and AHL add-back studies also resulted in increased EPS synthesis. In contrast to the commonly reported nanomolar to micromolar signal concentrations in pure culture laboratory systems, QS signalling in the granulation ecosystem occurred at picomolar to nanomolar concentrations of AHLs. Given that low concentrations of AHLs quantified in this study were sufficient to activate AHL bioreporters in situ in complex granular communities, AHL mediated QS may be a common feature in many natural and engineered ecosystems, where it coordinates community behaviour.

Diverse Profiles of AI-1 Type Quorum Sensing Molecules in Cultivable Bacteria from the Mangrove (Kandelia obovata) Rhizosphere Environment

“…The broad AHL spectrum suggests that the root microbial community has the capacity to synthesize multiple signals. This observation also corresponds with the profile of AHLs identified in the floccular sludge community (Tan et al, 2014). In addition, our results are consistent with a previous report that AHL-producing bacteria often produce long-chain rather than short-chain AHLs (Wagner-Dobler et al, 2005).…”

Gsy, a novel glucansucrase from Leuconostoc mesenteroides, mediates the formation of cell aggregates in response to oxidative stress

“…As EPSs had been shown to participate in biofilm formation3738 and cell adhesion39, we speculated that EPS synthesized by strain BD3749 might play critical roles in aggregate formation. This speculation was confirmed by the observation that cells cultivated in glucose medium failed to aggregate under the same conditions, indicating that the formation of aggregates was dependent on the EPS synthesized from sucrose.…”

A sustainable method for effective regulation of anaerobic granular sludge: Artificially increasing the concentration of signal molecules by cultivating a secreting strain

“…Previous studies have suggested that C4-HSL and AI-2 have positive effects on EPS production and promote the granulation of aerobic sludge (Ren et al, 2010;Tan et al, 2014;Xiong and Liu, 2010), while DSF inhibits the production of EPS and disperses bacterial aggregates (Deng et al, 2011;Tao et al, 2010). The specific roles of these signal molecules on anaerobic sludge granulation is still unknown.…”

“…To date, the types of signal molecules found in water and wastewater treatment systems include N-acyl-homoserine lactones (AHLs) in Gram negative bacteria, autoinducer-2 (AI-2) in interspecies communication, and diffusible signal factor (DSF) in intra-and interspecies bacteria (Feng et al, 2014;Shrout and Nerenberg, 2012). There are many papers demonstrating the positive effects of AHLs or AI-2 in aerobic sludge granulation (Li and Zhu, 2014;Ren et al, 2013Ren et al, , 2010Tan et al, 2014;Liu, 2012, 2010;Zhang et al, 2011) and increasing the efficiency of the granulating process by improving granular properties. AHLs add-back studies by Tan et al (2014) explained the promotion by AHLs in extracellular polymeric substance (EPS) synthesis and microbial aggregation.…”

“…There are many papers demonstrating the positive effects of AHLs or AI-2 in aerobic sludge granulation (Li and Zhu, 2014;Ren et al, 2013Ren et al, , 2010Tan et al, 2014;Liu, 2012, 2010;Zhang et al, 2011) and increasing the efficiency of the granulating process by improving granular properties. AHLs add-back studies by Tan et al (2014) explained the promotion by AHLs in extracellular polymeric substance (EPS) synthesis and microbial aggregation. Zhang et al (2011) speculated that the addition of boron would promote the formation of the precursor of AI-2, which resulted in accelerated aerobic granulation.…”