Effect of N-acyl homoserine lactones (AHLs) quorum sensing signal molecules on Enterococcus faecalis biofilm formation

Surfaces submerged in seawater are colonized by various microorganisms, resulting in the formation of heterogenic marine biofilms. This work aims to evaluate the biofilm formation by Cobetia marina alex and doing a comparative study between this promising strain with the two bacterial strains isolated previously from the Mediterranean seawater, Alexandria, Egypt. Three strains; Cobetia marina alex, Pseudoalteromonas sp. alex, and Pseudoalteromonas prydzensis alex were screened for biofilm formation using the crystal violet (CV) quantification method in a single culture. The values of biofilm formed were OD600= 3.0, 2.7, and 2.6, respectively leading to their selection for further evaluation. However, factors affecting biofilm formation by C. marina alex were investigated. Biofilm formation was evaluated in single and multispecies consortia. Synergistic and antagonistic interactions proved in this work lead to the belief that these bacteria have the capability to produce some interesting signal molecules N-acyl Homoserine Lactones (AHLs)

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Use of Sinorhizobium meliloti as an Indicator for Specific Detection of Long-Chain N-Acyl Homoserine Lactones

Applied and Environmental Microbiology ◽

10.1128/aem.70.6.3715-3723.2004 ◽

2004 ◽

Vol 70 (6) ◽

pp. 3715-3723 ◽

Cited By ~ 47

Author(s):

Inmaculada Llamas ◽

Neela Keshavan ◽

Juan E. GonzÃ¯Â¿Â½lez

Keyword(s):

Quorum Sensing ◽

Sinorhizobium Meliloti ◽

Paracoccus Denitrificans ◽

Indicator Strain ◽

Signal Molecules ◽

Specific Detection ◽

Homoserine Lactones ◽

Sensing Systems ◽

Acyl Homoserine Lactones ◽

Long Chain

ABSTRACT Population-density-dependent gene expression in gram-negative bacteria involves the production of signal molecules characterized as N-acyl homoserine lactones (AHLs). The synthesis of AHLs by numerous microorganisms has been identified by using biosensor strains based on the Agrobacterium tumefaciens and Chromobacterium violaceum quorum-sensing systems. The symbiotic nitrogen-fixing bacterium Sinorhizobium meliloti is rapidly becoming a model organism for the study of quorum sensing. This organism harbors at least three different quorum-sensing systems (Sin, Mel, and Tra), which play a role in its symbiotic relationship with its host plant, alfalfa. The Sin system is distinguished among them for the production of long-chain AHLs, including C18-HL, the longest AHL reported so far. In this work, we show that construction of a sinI::lacZ transcriptional fusion results in a strain that detects long-chain AHLs with exquisite sensitivity. Overexpression of the SinR regulator protein from a vector promoter increases its sensitivity without loss of specificity. We also show that the resulting indicator strain can recognize long-chain AHLs produced by unrelated bacteria such as Paracoccus denitrificans and Rhodobacter capsulatus. This S. meliloti indicator strain should serve as a tool for the specific detection of long-chain AHLs in new systems.

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