ABSTRACT
Autoinducer 2 (or AI-2) is one of the molecules used by bacteria to trigger the Quorum Sensing (QS) response, which activates expression of genes involved in a series of alternative mechanisms, when cells reach high population densities (including bioluminescence, motility, biofilm formation, stress resistance, and production of public goods, or pathogenicity factors, among others). Contrary to most autoinducers, AI-2 can induce QS responses in both Gram-negative and Gram-positive bacteria, and has been suggested to constitute a trans-specific system of bacterial communication, capable of affecting even bacteria that cannot produce this autoinducer. In this work, we demonstrate that the ethanologenic Gram-negative bacterium Zymomonas mobilis (a non-AI-2 producer) responds to exogenous AI-2 by modulating expression of genes involved in mechanisms typically associated with QS in other bacteria, such as motility, DNA repair, and nitrogen fixation. Interestingly, the metabolism of AI-2-induced Z. mobilis cells seems to favor ethanol production over biomass accumulation, probably as an adaptation to the high-energy demand of N2 fixation. This opens the possibility of employing AI-2 during the industrial production of second-generation ethanol, as a way to boost N2 fixation by these bacteria, which could reduce costs associated with the use of nitrogen-based fertilizers, without compromising ethanol production in industrial plants.
Subject(s)
Ethanol/metabolism , Homoserine/analogs & derivatives , Lactones/pharmacology , Nitrogen Fixation/drug effects , Quorum Sensing/drug effects , Zymomonas/metabolism , Homoserine/pharmacologyABSTRACT
Bacteria control the expression of specific genes by Quorum Sensing (QS). This works using small signaling molecules called Autoinducers (AIs), for example, the Autoinducer-2 (AI-2). In this work, we present a mathematical model that represents the AI-2 dynamics on Escherichia coli, which is linked to the cell growth and the lsr operon expression. The model is adjusted using experimental data. Our results suggest that the extracellular AI-2 activity level depends on the cell growth rate, and this activity depends on the cell exponential growth phase. The model was adapted to simulate the interference of QS mechanisms in a co-culture of two E. coli strains: a wild type strain and a knock out strain that detects AI-2 but does not produce it. Co-culture simulations unveiled two conditions to avoid the QS on the wild strain: when the knock out takes control of the growth medium and overcomes the wild strain, or when is pre-cultured to its mid-exponential phase and then added to the wild strain culture. Model simulations unveiled new insights about the interference of bacterial communication and offer new tools for QS control.
ABSTRACT
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.
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.(AU)
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.(AU)
Subject(s)
Quorum Sensing , Enterococcus faecium/chemistry , Enterococcus faecalis/chemistry , Bacillus cereus/chemistry , Dairy Products/microbiology , Polymerase Chain ReactionABSTRACT
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.