Strategies for improved rhamnolipid production byPseudomonas aeruginosaPA1

Alexandre Soares Dos Santos,Denise M.G Freire,Nei Pereira Jr

doi:10.7717/peerj.2078

Alexandre Soares Dos Santos, Denise M.G Freire + Show 1 more

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https://doi.org/10.7717/peerj.2078

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Abstract

Rhamnolipids are biosurfactants with potential for diversified industrial and environmental uses. The present study evaluated three strategies for increasing the production of rhamnolipid-type biosurfactants produced by Pseudomonas aeruginosa strain PA1. The influence of pH, the addition of P. aeruginosa spent culture medium and the use of a fed-batch process were examined. The culture medium adjusted to pH 7.0 was the most productive. Furthermore, the pH of the culture medium had a measurable effect on the ratio of synthesized mono- and dirhamnolipids. At pH values below 7.3, the proportion of monorhamnolipids decreased from 45 to 24%. The recycling of 20% of the spent culture medium in where P. aeruginosa was grown up to the later stationary phase was responsible for a 100% increase in rhamnolipid volumetric productivity in the new culture medium. Finally, the use of fed-batch operation under conditions of limited nitrogen resulted in a 3.8-fold increase in the amount of rhamnolipids produced (2.9 g L−1–10.9 g L−1). These results offer promising pathways for the optimization of processes for the production of rhamnolipids.

Highlights

The qualitative effect of pH on rhamnolipid synthesis was evaluated by thin layer chromatography
The more hydrophilic dirhamnolipids interact more strongly with the TLC stationary phase because of the presence of two rhamnose rings linked to lipid chain, whereas only one sugar ring exists in the monorhamnolipids species
Observe that the increase in the production of rhamnolipids was due to an increase in the capacity of the microorganisms to synthesize rhamnolipids. These results suggest that the amount of spent culture medium added at the beginning of cultivation probably contributed to the increase in the synthesis of rhamnosiltransferases because the natural unfolding of the quorum sensing system, which is responsible for the transcriptional regulation of rhamnolipid synthesis in presence of endogenous autoinducers

Summary

Introduction

They present low toxicity and high resistance to extreme conditions of pH, salinity and temperature (Kesting et al, 1996). These signaling molecules, paired with the LasR and RhlR regulators, initiate the expression of the enzymes involved in rhamnolipid synthesis (rhamnosyltransferases) (Ochsner et al, 1994; Ochsner, Hembach & Fiechter, 1995; Rahim et al, 2001; Reis et al, 2011)

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