Quorum sensing and quorum quenching abilities of selected bacteria isolated from antarctic / See-Too Wah Seng

See-Too, Wah Seng (2013) Quorum sensing and quorum quenching abilities of selected bacteria isolated from antarctic / See-Too Wah Seng. Masters thesis, University of Malaya.

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Abstract

Quorum sensing (QS) is a phenomenon which refers to bacterial cell-to-cell communication in a population manner. QS regulates diverse activities in bacteria. Bacteria that possess QS activity communicate through secreted signal molecules or autoinducer. The Gram-negative bacteria and archaeon use acyl homoserine lactones (AHLs) as a QS signal to achieve regulation through the luxI-luxR homolog system, wheareas Gram-positive bacteria use small peptides as autoinducers. Some of the Proteobacteria use quinolone compound as signaling molecules. Quorum quenching (QQ) on the other hand refers to interference of QS that inactivates the signaling molecules. Even though QS and QQ were extensively studied in mesophilic bacteria, much less studies were conducted on bacteria that live in extreme environments. So far, there is no reported studies on QS and QQ in Antarctic bacteria. This study aimed to isolate N-acyl homoserine lactone producing and degrading bacteria from soil samples that were collected at different sites in Antarctica. The present work had successfully isolated 36 bacteria which produced N-acyl homoserine lactone, and 22 bacteria which degraded a variety of N-acyl homoserine lactone or quinolone signaling molecules. A few bacterial isolates including Flavobacterium sp., Poloromonas sp., Simplicispira sp., Planococcus sp. and Psychrobacter sp. has not been reported to possess any QS or QQ activity. To the best of our knowledge, this thesis is the first report of QS and QQ activities in Antarctic bacteria. Other N-acyl homoserine lactone producing bacterial isolates were Pseudomonas sp., and Acinetobacter sp., and they were found to produce long chain AHLs including C12-HSL and 3-oxo-C15-HSL through the use of liquid chromatography mass spectrometry (LCMS). QQ activity was also found in the N-acyl homoserine lactone producing Pseudomonas sp., Acinetobacter sp., and in Gram-positive bacterial isolates, Bacillus sp. and Athrobacter sp. All the bacteria with QQ abilities degraded a different range of AHLs, confirmed through the use of rapid resolution liquid chromatography (RRLC). A few bacteria including Psychrobacteria, Planococcus and some of the Pseudomonas spp. were found to produce homoserine lactonase enzyme(s) that degraded the homoserine lactone ring of the signaling compound.

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