Mathematical Modeling of the Quorum Sensing in Vibrio harveyi / Modelado Matemático de la Detección de Quórum en Vibrio harveyi

Abstract One of the most used bacteria in the Quorum Sensing (QS) experimental works is the Vibrio harveyi, which is used as reporter bacteria to detect the Autoinducers-2 (AI-2) activity of other bacteria. Nevertheless, the description of its QS mechanism by the mathematical modeling is an approach still unexploited. For biological systems, it is necessary to consider the high variability of the experimental data, thus identifiability and parametric reliability analyses must be performed before a model could be used. The following work describes a methodology for parameter fitting and parametric identifiability analysis in a model that describes the dynamics of AI-2 in V. harveyi bacteria. Identifiability analyses showed that all parameters are identifiable, but parametric dependency analyses showed two linearly dependent parameters. According to our results, the model is adequate to describe the AI-2 dynamics in V. harveyi.

Resumen Una de las bacterias más utilizadas en los trabajos experimentales de detección de quorum (QS) es la Vibrio harveyi, que se utiliza como bacteria reportera para detectar la actividad de Autoinductores-2 (AI-2) de otras bacterias. Sin embargo, la descripción de su mecanismo de QS por medio del modelado matemático es un enfoque aún no explotado. En el caso de los sistemas biológicos, es necesario considerar la alta variabilidad de los datos experimentales, por lo que deben realizarse análisis de identificabilidad y fiabilidad paramétrica antes de que un modelo pueda ser usado. El siguiente trabajo describe una metodología para el ajuste de parámetros y el análisis de la identificabilidad paramétrica en un modelo que describe la dinámica de la AI-2 en las bacterias V. harveyi. Los análisis de identificabilidad mostraron que todos los parámetros son identificables, pero los análisis de dependencia paramétrica mostraron dos parámetros linealmente dependientes. De acuerdo con los resultados, el modelo es adecuado para describir la dinámica AI-2 en V. harveyi.

Quorum Sensing Regulation of Biofilm Formation by Periodontal Pathogens

Quorum sensing (QS) is a cell density-dependent communication mechanism between bacteria through small signaling molecules. When the number of QS signaling molecules reaches a threshold, they are transported back into the cells or recognized by membrane-bound receptors, triggering gene expression which affects various phenotypes including bioluminescence, virulence, adhesion, and biofilm formation. These phenotypes are beneficial for bacterial survival in harsh environments. This review summarizes the application of QS inhibitors for control of biofilm formation and virulence expression of periodontal pathogens.

Quorum sensing in Enterococcus faecium, Enterococcus faecalis and Bacillus cereus strains isolated from ricotta processing / Quorum sensing em cepas de Enterococcus faecium, Enterococcus faecalis e Bacillus cereus isoladas do processamento de ricota

ABSTRACT: The quorum sensing phenomenon is a process of intra- and inter-species microbial communication involving the production and detection of extracellular signaling molecules. The autoinducer AI-2 has been proposed to serve as a 'universal signal' for interspecies communication. This study aimed to evaluate the capability of Enterococcus faecium, Enterococcus faecalis, and Bacillus cereus strains isolated from ricotta processing to produce quorum sensing signalling molecules (AI-2). The strains were evaluated for the presence of the luxS gene using the polymerase chain reaction. AI-2 quorum sensing signalling molecules were measured in relative light units (RLUs) using a luminometer. A total of 74% of E. faecium, 91% of E. faecalis, and 95% of B. cereus isolates were positive for luxS gene. In addition, the induced bioluminescence in Vibrio harveyi BB170 was observed in all strains, indicating the presence of the AI-2 autoinducer.

RESUMO: O fenômeno quorum sensing corresponde a um processo de comunicação intra e interespécies microbianas e é mediado por sinais químicos extracelulares, denominados moléculas sinalizadoras ou auto indutoras (AI). A molécula AI2 está envolvida na comunicação interespécies, denominada sistema "universal" de comunicação. Este estudo teve como objetivo avaliar a capacidade de Enterococcus faecium, Enterococcus faecalis e Bacillus cereus isolados do processamento de ricota em produzir moléculas sinalizadoras de Quorum sensing (AI-2). Os isolados foram avaliados quanto à presença do gene luxS utilizando a reação em cadeia da polimerase (PCR). As moléculas sinalizadoras (AI-2) foram medidas em unidades relativas de luz (RLU) através de um luminômetro. Um total de 74% dos isolados de E. faecium, 91% de E. faecalis e 95% de B. cereus foram positivos para o gene luxS. Além disso, todos os isolados apresentaram capacidade de induzir o fenômeno de bioluminescência em Vibrio harveyi BB170, indicando a presença de auto indutores AI-2.

In vitro biosynthesis of autoinducer 2 of Streptococcus mutans UA1 59 and observation of the influence factors / 实用口腔医学杂志

Objective:To synthesize autoinducer-2 by the clone and prokaryotic expression of Streptococcus mutans(S.mutans)UAl59 luxS gene and to observe the influence factors.Methods:The expression vector pET21 a(+)-luxS of S.mutans UAl59 was transformed into Escheriehia coli BL2l(DE3).The S-ribosylhomocysteinase(Luxs)expression was induced by IPTG.The His tag fusion protein was isolated by Ni-chelating column and identified by Western blotting.Finally the protein was renatured by dialysis method.S-ribosylhomo-cysteine (SAH)was catalyzed by s-adenosylhomocysteine nucleosidas (Pfs)and LuxS,and then AI-2 was syntheszed.The AI-2 activi-ty was examined by luminescence of Vibrio harveyi BB1 70 when the concentration of LuxS protein or pH(4 -1 2)or the concentration of sodium fluoride was changed in reaction mixes of AI-2 synthesis.Results:Compared with the control group,with the increase of LuxS protein concentration,the relative activity of in vitro synthesized AI-2 increased gradually(P <0.001 ).When pH was between 6 -1 0, the relative activity of AI-2 were the highest,beyond the range of pH,the relative activity of AI-2 decreased(P <0.001 ).When a final concentration of sodium fluoride was more than 0.3%,the luminescence values decreased(P <0.05).Conclusion:LuxS fusion protein can promote the production of AI-2.Optimum pH for AI-2 biosynthesis in vitro must be between 6-1 0.Biosynthesis of AI-2 is inhibited by sodium fluoride with final concentration of more than 0.3%.