Abstract
Sufficient supply of oxygen is a major bottleneck in industrial biotechnological synthesis. One example is the heterologous production of rhamnolipids using Pseudomonas putida KT2440. Typically, the synthesis is accompanied by strong foam formation in the reactor vessel hampering the process. It is caused by the extensive bubbling needed to sustain the high respirative oxygen demand in the presence of the produced surfactants. One way to reduce the oxygen requirement is to enable the cells to use the anode of a bioelectrochemical system (BES) as an alternative sink for their metabolically derived electrons. We here used a P. putida KT2440 strain that interacts with the anode using mediated extracellular electron transfer via intrinsically produced phenazines, to perform heterologous rhamnolipid production under oxygen limitation. The strain P. putida RL-PCA successfully produced 30.4 ± 4.7 mg/L mono-rhamnolipids together with 11.2 ± 0.8 mg/L of phenazine-1-carboxylic acid (PCA) in 500-mL benchtop BES reactors and 30.5 ± 0.5 mg/L rhamnolipids accompanied by 25.7 ± 8.0 mg/L PCA in electrode containing standard 1-L bioreactors. Hence, this study marks a first proof of concept to produce glycolipid surfactants in oxygen-limited BES with an industrially relevant strain.
Highlights
Rhamnolipids (RL) are among the best explored microbial glycolipid surfactants
Our work started with a phenazine-1-carboxylic acid (PCA) producing strain of P. putida KT2440 carrying the plasmid pBNT.14phz2 for the expression of the genes phzA2-G2 from P. aeruginosa PA14, as this strain showed superior phenazine production and bioelectrochemical activity in our previous work [19]
These plasmids were separately transformed into the PCA producing P. putida KT2440 strain
Summary
Rhamnolipids (RL) are among the best explored microbial glycolipid surfactants. Rhamnolipids possess eco-friendly characteristics such as biodegradability, a low eco-toxicity, and they can be produced from renewable resources [4]. The expansion of their production to industrial scale is desirable. The biotechnological production with the native microbial producers, especially with Pseudomonas aeruginosa, is not desirable. P. aeruginosa is a facultative pathogen and its rhamnolipid production is controlled by a complex quorum sensing network [5,6,7]. Research in the past years has focused on heterologous production with the non-pathogenic P. putida KT2440 [8,9,10]
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