Kinetic modeling of the time course of N-butyryl-homoserine lactone concentration during batch cultivations of Pseudomonas aeruginosa PAO1

Abstract

Quorum sensing affects the regulation of more than 300 genes in Pseudomonas aeruginosa, influencing growth, biofilm formation, and the biosynthesis of several products. The quorum sensing regulation mechanisms are mostly described in a qualitative character. Particularly, in this study, the kinetics of N-butyryl-homoserine lactone (C4-HSL) and rhamnolipid formation in P. aeruginosa PAO1 were of interest. In this system, the expression of the rhamnolipid biosynthesis genes rhlAB is directly coupled to the C4-HSL concentration via the rhl system. Batch cultivations in a bioreactor with sunflower oil have been used for these investigations. 3-oxo-dodecanoyl-homoserine lactone (3o-C12-HSL) displayed a lipophilic character and accumulated in the hydrophobic phase. Degradation of C4-HSL has been found to occur in the aqueous supernatant of the culture by yet unknown extracellular mechanisms, and production was found to be proportional to biomass concentration rather than by autoinduction mechanisms. Rhamnolipid production rates, as determined experimentally, were shown to correlate linearly with the concentration of autoinducer C4-HSL. These findings were used to derive a simple model, wherein a putative, extracellular protein with C4-HSL degrading activity was assumed (putative C4-HSL acylase). The model is based on data for catalytic efficiency of HSL-acylases extracted from literature (k cat/K m), experimentally determined basal C4-HSL production rates (q C4 - HSL (basal)), and two fitted parameters which describe the formation of the putative acylase and is therefore comparatively simple.

Investment in secreted enzymes during nutrient-limited growth is utility dependent

“…Under such conditions, secreted protease production would be scaled back due to catabolite repression (36). An abrupt decline in nutrient import could lead to scaling back of investment in secreted proteases as a result of autoinducer degradation, which can occur by spontaneous hydrolysis or by autoinducer-degrading enzymes produced by P. aeruginosa or other organisms in the environment (37)(38)(39)(40)(41). Moreover, it has been demonstrated in an autocrine signaling model that the combination of signal degradation and positive feedback can result in a bimodal activation response (42), implying the coexistence of secreting and nonsecreting cells.…”

Novel insights into biosynthesis and uptake of rhamnolipids and their precursors

“…In P. aeruginosa , the two rhl -operons are transcriptionally regulated by the q uorum sensing (QS) regulatory network (Ochsner et al 1994b; Ochsner and Reiser 1995; Pearson et al 1997) and probably by other signaling systems (Wilhelm et al 2007; Rosenau et al 2010; Henkel et al 2013). The QS autoinducer molecules butanoyl-homoserine-lactone (C 4 -HSL) and 3-oxo-dodecanoyl-homoserine-lactone (3-oxo-C 12 -HSL) are synthesized by RhlI and LasI, respectively.…”

Integrated foam fractionation for heterologous rhamnolipid production with recombinant Pseudomonas putida in a bioreactor

“…Production of rhamnolipids is mainly described in the opportunistic pathogen Pseudomonas aeruginosa using shake flask, batch, fed-batch or continuous systems (Mulligan et al 1989 ; Wei et al 2005 ; Müller et al 2010 , 2012 ). Heterologeous production of rhamnolipids in Pseudomonas putida counteracts obstacles of strain pathogenicity and the native quorum sensing regulation in P. aeruginosa (Ochsner et al 1995 ; Cha et al 2008 ; Wittgens et al 2011 ; Henkel et al 2013 , 2014 ). First heterologous rhamnolipid production was described by Ochsner et al ( 1995 ) using P. putida , Escherichia coli and Pseudomonas fluorescens as recombinant production hosts.…”