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Quorum Sensing
Published in Vineet Kumar, Vinod Kumar Garg, Sunil Kumar, Jayanta Kumar Biswas, Omics for Environmental Engineering and Microbiology Systems, 2023
Archisman Bhunia, Kumar Narayan, Abhilasha Singh, Asmeeta Sircar, Nivedita Chatterjee
The regulatory gene expression in contrast to the changing density gradient was first observed in the form of luminescence in marine bacterium Vibrio fischeri in the early 1970s. Since then, it has been accepted as a model subject for exploring gene regulatory circuits in gram-negative Proteobacteria. In case of V. fischeri, quorum sensing is known to control the property of bioluminescence or the ability of the bacteria to produce light (Popham and Stevens, 2005). The two important genes involved in this phenomenon of regulatory stratagem are the following: luxI, which is responsible for encoding an AI synthase LuxI, and luxR, which encodes an AI-dependent activator gene LuxR; both are essential for luminescence. The LuxI synthesizes autoinducer molecules called N-acyl homoserine lactone (AHL) (3-oxo-hexanoyl-homoserine lactone). This AI accumulation on outstretching beyond a critical threshold concentration initiates the formation of LuxR-AHL complexes, resulting in the activation of the lux operon within the bacterial cytoplasm (Subramani and Jayaprakashvel, 2019).
Molecular Approaches Towards the Synthesis of Biosurfactants
Published in R.Z. Sayyed, Microbial Surfactants, 2022
Vidya Kothari, Arpana Jobanputra
Bio-surfactants are produced by bio-film producing bacteria. The bacterial communities are bio-film producers that are regulated by multiple signal processing (Peele et al. 2016). Bio-surfactants are exopolymers that can tolerate extreme PH and temperature conditions. These characterizes favours the bacteria to sustain under adverse conditions. A bacterium produces many kinds of molecules that allow bacteria to communicate population size. These molecules are generally regarded as auto inducer peptides that serve as signal carriers. Bio-surfactant producing quorum sensing regulatory bacteria use acyl carrier proteins and pass them onto the homoserine moiety. Quorum-sensing signalling may be extracellular or intracellular and is often mediated by N-acyl-homoserine lactone (AHL) concentration. Quorum sensing reveals the fact that bacteria have the capacity to access a number of other components, they can activate once the threshold number is reached. Acyl homoserine lactones are present mainly in Gram-negative bacteria and they control their own synthesis. Oligopeptide molecules are present mainly in Gram-Positive bacteria; their synthesis is dependent on ribosomes. It has been hypothesized that the production of auto inducing peptides and bio-film formation are interlinked (Peele et al. 2016).
Metabolism
Published in Volodymyr Ivanov, Environmental Microbiology for Engineers, 2020
Communication between bacterial cells, called quorum sensing, is used for the coordination of gene expression in the cells of a population. When the concentration of cells and produced signaling molecules are increased to some level due to cell aggregation, molecule (inducer) binds with the receptor in the cell are signaled and the transcription of certain genes -is activated, including those for inducer synthesis. Different molecules are used as signals of cell aggregation: peptides in Gram-positive bacteria; autoinducer AI-2 in both Gram-positive and Gram-negative bacteria; and acyl-homoserine lactones (AHL, Figure 3.6), the most common signaling molecules for Gram-negative bacteria. Quorum sensing signaling molecule: N-acyl homoserine lactone. R varies by chain lengths (4–18 carbon atoms) and some other minor chemical changes.
Eichhornia crassipes root biomass to reduce antibiotic resistance dissemination and enhance biogas production of anaerobic membrane bioreactor
Published in Environmental Technology, 2022
Hadi Fakhri, Duygu Nur Arabaci, Suleyman Ovez, Sevcan Aydin
The TMP profiles of C1, C2 and EC reactors were observed and analysed to deduce the potential impact of E. crassipes on biofouling and biofilm formation (Figure 2b). The reactors were operated until a predetermined value of total biofouling, 25 kPa, which for C1, C2 and EC reactors lasted 16,12 and 12 days respectively (Table 1). While the TMP of C1 increased at a steady rate throughout the operational period, C2 and EC reactors both showed rapid increase which slowed down upon reaching ca. 200 kPa. The faster rate of increase of the TMP values observed in the C2 and EC reactors can be attributed to the impact of antibiotics on the microorganism community, the increased extracellular polymeric substances (EPS) production caused by the stress induced by antibiotics as a self-defense mechanism. The stimulatory effects of sub-MIC concentrations of antibiotics have previously been reported, with effects ranging from initiating biofilm formation through altering concentrations of signal molecules to enhance synthesis of polysaccharide components of extracellular polymer matrix [21]. Increased secretion of EPS notes the acceleration of biofilm formation and biofouling, which in turn causes rapid TMP increase. The EC reactor showed increased TMP compared to C1 reactor and exhibited a similar behaviour as C2 reactor. While TMP profile is similar, a significant difference was observed in biogas production and microbial communities. This shift may be attributed to E. crassipes biomass providing an additional surface for the microorganisms to attach to and proliferate, combined with the adsorption of antibiotics in its environment, leading to a more suitable environment for beneficial microorganisms. Quorum quenching by antibiotics may also be inhibited through the E. crassipes biomass’ adsorption of antibiotics, leading to a higher rate of membrane biofouling. ERY has been previously reported to inhibit N-acyl-homoserine Lactone (AHL) synthesis, which is a molecule involved in quorum sensing [22], and ERY removal in particular has been increased in the presence of E. crassipes.