Microbial population dynamics and proteomics in membrane bioreactors with enzymatic quorum quenching

Abstract

Quorum sensing gives rise to biofilm formation on the membrane surface, which in turn causes a loss of water permeability in membrane bioreactors (MBRs) for wastewater treatment. Enzymatic quorum quenching was reported to successfully inhibit the formation of biofilm in MBRs through the decomposition of signal molecules, N-acyl homoserine lactones (AHLs). The aim of this study was to elucidate the mechanisms of quorum quenching in more detail in terms of microbial population dynamics and proteomics. Microbial communities in MBRs with and without a quorum quenching enzyme (acylase) were analyzed using pyrosequencing and compared with each other. In the quorum quenching MBR, the rate of transmembrane pressure (TMP) rise-up was delayed substantially, and the proportion of quorum sensing bacteria with AHL-like autoinducers (such as Enterobacter, Pseudomonas, and Acinetobacter) also decreased in the entire microbial community of mature biofilm in comparison to that in the control MBR. These factors were attributed to the lower production of extracellular polymeric substances (EPS), which are known to play a key role in the formation of biofilm. Proteomic analysis using the Enterobacter cancerogenus strain ATCC 35316 demonstrates the possible depression of protein expression related to microbial attachments to solid surfaces (outer membrane protein, flagellin) and the agglomeration of microorganisms (ATP synthase beta subunit) with the enzymatic quorum quenching. It has been argued that changes in the microbial population, EPS and proteins via enzymatic quorum quenching could inhibit the formation of biofilm, resulting in less biofouling in the quorum quenching MBR.

Membrane biofouling retardation and improved sludge characteristics using quorum quenching bacteria in submerged membrane bioreactor

“…Similar approach was attempted by Kim et al [21] using pre-isolated strain [16] and found significant reduction in the development of communities responsible for sensing mechanism. Kim et al [19], incorporated Rhodococcus sp.…”

Regulating exopolysaccharide gene wcaF allows control of Escherichia coli biofilm formation

“…Excessive growth of biofilms and associated EPS would also greatly limit the diffusion of substrates and nutrients to the cells 19,20 . Consequently, the cells in the inner layers of biofilm would become less active.…”

“…cyclic di-guanosine monophosphate (c-di-GMP)) that regulate biofilm development 26–28 , and peptide that reduces stress responsive guanosine pentaphosphate (ppGpp) concentration 29 . Other biological methods also include quorum quenching that interrupts autoinducer-mediated quorum sensing 20,30 and controlling the production of adhesive proteins such as csgA which could inhibit initial attachment of the bacteria 12 .…”

Quorum Quenching Mediated Approaches for Control of Membrane Biofouling

“…The robust biofilms are needed for treatment of wastewater by trickling filters, granular sludge and moving bed biofilm reactors 6, 80. However, deposition of biofilms and associated extracellular polysaccharides (EPS) on membrane surfaces decreases filtration flux and causes permeability loss 81, 82. The non-degraded organic matters, microbial flocs and SMP are also considered as potential foulants 83, 84, but the formation of biofilms on membrane surfaces is the major contributor in membrane biofouling and is the main obstacle restricting the development of MBR technology for advanced wastewater treatment.…”

“…In addition to this, several studies have linked presence of AHLs with biofilm formation and addressed the problem of membrane biofouling in MBRs 82, 89, 92. The chromatographic analysis of MBR sludge using HPLC technique has identified the presence of several AHLs molecules.…”