Influence of Exogenous AHLs and Quorum Quenching AiiA Protein on the Production of Cellulase Enzyme in Marine Snow Associated Bacterium, Citrobacter freundii B1
Influence of Exogenous AHLs and Quorum Quenching AiiA Protein on the Production of Cellulase Enzyme in Marine Snow Associated Bacterium, Citrobacter freundii B1
Abdul Nabi Jatt1,2*
ABSTRACT
Quorum-sensing (QS) is a system by which microorganisms can monitor their own population density via small signalling molecules to communicate with each other. The sinking of marine snow aggregates is as an essential process for moving organic carbon source from the up-ward to down-ward in the ocean. Marine snow associated bacterial communities perform a crucial role in organic material degradation by producing extracellular hydrolytic enzymes and are considered as key components in global carbon cycle. The aim of this study was to screen marine snow associated bacterium, Citrobacter freundii B1 for the production of QS-signals particularly acyl-homoserine-lactones (AHLs) and their influence on the production of extracellular cellulase enzyme. Mainly, two different reporter strains such as Agrobacterium tumefaciens A136 and Chromobacterium violaceum CV026 were applied to confirm the production of signal molecules. The identification of signal molecules was achieved by GC-MS analysis. Intriguingly, GC-MS technique showed the presence of five different AHL-signal molecules (e.g., C-6, C-8, C-10, C-12, and C-14) produced by C. freundii B1. Moreover, extracellular cellulase enzyme (exoglucanase and endoglucanase) activity was highly induced in addition to exogenous AHLs. While, both exoglucanase and endoglucanase activities were radically decreased, when the growth medium was supplemented with quorum-quenching (QQ) AiiA protein. The present study, for the first time provides evidence that the QS system via AHL molecules involved in regulating the production of two different forms of an extracellular cellulase enzyme, i.e., exoglucanase and endoglucanase in marine snow associated bacterium C. freundii B1. Moreover, the present study has also reported five different AHL molecules (e.g., C-6, C-8, C-10, C-12, and C-14) produced by this bacterium.
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