RESUMO
The bacteria Pseudomonas aeruginosa use the size and density of their colonies to regulate the production of a large variety of substances, including toxins. This phenomenon, called quorum sensing, apparently enables colonies to grow to sufficient size undetected by the immune system of the host organism. In this paper, we present a mathematical model of quorum sensing in P. aeruginosa that is based on the known biochemistry of regulation of the autoinducer that is crucial to this signalling mechanism. Using this model we show that quorum sensing works because of a biochemical switch between two stable steady solutions, one with low levels of autoinducer and one with high levels of autoinducer.
Assuntos
Proteínas de Bactérias , Regulação Bacteriana da Expressão Gênica , Leucocidinas/biossíntese , Modelos Biológicos , Infecções por Pseudomonas/microbiologia , Pseudomonas aeruginosa/patogenicidade , Comunicação Celular/genética , Fibrose Cística/microbiologia , Regulação Enzimológica da Expressão Gênica , Leucocidinas/genética , Metaloendopeptidases/biossíntese , Metaloendopeptidases/genética , Análise Numérica Assistida por Computador , Infecções por Pseudomonas/enzimologia , Infecções por Pseudomonas/genética , Pseudomonas aeruginosa/enzimologia , Pseudomonas aeruginosa/genéticaRESUMO
A phenomenological model has been developed to describe biomass distribution and substrate depletion in porous diatomaceous earth (DE) pellets colonized by Pseudomonas aeruginosa. The essential features of the model are diffusion, attachment and detachment to/from pore walls of the biomass, diffusion of substrate within the pellet, and external mass transfer of both substrate and biomass in the bulk fluid of a packed bed containing the pellets. A bench-scale reactor filled with DE pellets was inoculated with P. aeruginosa and operated in plug flow without recycle using a feed containing glucose as the limiting nutrient. Steady-state effluent glucose concentrations were measured at various residence times, and biomass distribution within the pellet was measured at the lowest residence time. In the model, microorganism/substrate kinetics and mass transfer characteristics were predicted from the literature. Only the attachment and detachment parameters were treated as unknowns, and were determined by fitting biomass distribution data within the pellets to the mathematical model. The rate-limiting step in substrate conversion was determined to be internal mass transfer resistance; external mass transfer resistance and microbial kinetic limitations were found to be nearly negligible. Only the outer 5% of the pellets contributed to substrate conversion.
