Expression of genes involved in rhamnolipid synthesis in Pseudomonas aeruginosa PAO1 in a bioreactor cultivation

Abstract

There is a growing demand for economic bioprocesses based on sustainable resources rather than petrochemical-derived substances. Particular attention has been paid to rhamnolipids--surface-active glycolipids--that are naturally produced by Pseudomonas aeruginosa. Rhamnolipids have gained increased attention over the past years due to their versatile chemical and biological properties as well as numerous biotechnological applications. However, rhamnolipid synthesis is tightly governed by a complex growth-dependent regulatory network. Quantitative comprehension of the molecular and metabolic mechanisms during bioprocesses is key to manipulating and improving rhamnolipid production capacities in P. aeruginosa. In this study, P. aeruginosa PAO1 was grown under nitrogen limitation with sunflower oil as carbon and nitrate as nitrogen source in a batch fermentation process. Gene expression was monitored using quantitative PCR over the entire time course. Until late deceleration phase, an increase in relative gene expression of the las, rhl, and pqs quorum-sensing regulons was observed. Thereafter, expression of the rhamnolipid synthesis genes, rhlA and rhlC, as well as the las regulon was downregulated. RhlR was shown to remain upregulated at the late phase of the fermentation process.

Mechanism of azithromycin inhibition of HSL synthesis in Pseudomonas aeruginosa

“…In the early growth phase (2–4 h) of the PAO1 strain, there were no HSLs detected; 3-oxo-C12-HSL was first detected at 6 h. 3-Oxo-C12-HSL was first secreted in the exponential growth phase and was maintained until the early stationary phase. These results are in agreement with a previous report on PAO1, in which 3-oxo-C12-HSL at a concentration of 0.8 μmol/L was detected at 70.5 h 39 . Moreover, in this study, our detection limit was 0.05 ng/mL (0.17 nmol/L), more senstive than previous reports of 0.2 μmol/L 40 .…”

The Oxidative Stress Agent Hypochlorite Stimulates c-di-GMP Synthesis and Biofilm Formation in Pseudomonas aeruginosa

“…RNA isolation, cDNA synthesis and subsequent qRT-PCR experiments were carried out as described previously ( Strempel et al, 2013 ). Obtained Ct values were normalized to expression of housekeeping genes rpoD and fabD as described elsewhere ( Schmidberger et al, 2013 ).…”

Production of microbial biosurfactants: Status quo of rhamnolipid and surfactin towards large‐scale production

“…Schmidberger et al investigated the time‐course of the expression of genes in a batch process with nitrogen limitation . Henkel et al developed a kinetic model for cell‐density dependent quorum sensing dynamics .…”

“…So far, many facets of an efficient process for rhamnolipid production in P. aeruginosa strains, many of them being wild-type, have been investigated, including research on the complex quorum sensing regulatory network, gene expression monitoring, modeling of rhamnolipid production, optimization of medium composition and process control, as well as techniques for downstream processing. Schmidberger et al investigated the time-course of the expression of genes in a batch process with nitrogen limitation [28]. Henkel et al developed a kinetic model for cell-density dependent quorum sensing dynamics [29].…”