Abstract
Polyhydroxyalkanoates (PHAs) have attracted much attention as a good substitute for petroleum-based plastics, especially mcl-PHA due to their superior physical and mechanical properties with broader applications. Artificial microbial consortia can solve the problems of low metabolic capacity of single engineered strains and low conversion efficiency of natural consortia while expanding the scope of substrate utilization. Therefore, the use of artificial microbial consortia is considered a promising method for the production of mcl-PHA. In this work, we designed and constructed a microbial consortium composed of engineered Escherichia coli MG1655 and Pseudomonas putida KT2440 based on the “nutrition supply–detoxification” concept, which improved mcl-PHA production from glucose-xylose mixtures. An engineered E. coli that preferentially uses xylose was engineered with an enhanced ability to secrete acetic acid and free fatty acids (FFAs), producing 6.44 g/L acetic acid and 2.51 g/L FFAs with 20 g/L xylose as substrate. The mcl-PHA producing strain of P. putida in the microbial consortium has been engineered to enhance its ability to convert acetic acid and FFAs into mcl-PHA, producing 0.75 g/L mcl-PHA with mixed substrates consisting of glucose, acetic acid, and octanoate, while also reducing the growth inhibition of E. coli by acetic acid. The further developed artificial microbial consortium finally produced 1.32 g/L of mcl-PHA from 20 g/L of a glucose–xylose mixture (1:1) after substrate competition control and process optimization. The substrate utilization and product synthesis functions were successfully divided into the two strains in the constructed artificial microbial consortium, and a mutually beneficial symbiosis of “nutrition supply–detoxification” with a relatively high mcl-PHA titer was achieved, enabling the efficient accumulation of mcl-PHA. The consortium developed in this study is a potential platform for mcl-PHA production from lignocellulosic biomass.
Highlights
Due to environmental problems such as energy waste and “white pollution” caused by petroleum-based plastics, the search for biodegradable alternatives to petroleum-based plastics has received increasing attention (Muneer et al, 2020)
We introduced an engineered E. coli in which the four genes ptsG, manZ, atpFH, and envR were knocked out, while further strengthened its functions, and co-cultured it with engineered P. putida to form a microbial consortium to produce medium-chain-length polyhydroxyalkanoate (mcl-PHA) from glucose and xylose
The optimized microbial consortium based on the “nutrition supply–detoxification” concept is expected to enable the industrial production of mclPHA from glucose-xylose mixtures
Summary
Due to environmental problems such as energy waste and “white pollution” caused by petroleum-based plastics, the search for biodegradable alternatives to petroleum-based plastics has received increasing attention (Muneer et al, 2020). Polyhydroxyalkanoates (PHAs) are among the most wellstudied biodegradable materials Their polymer properties are similar to petroleum-based plastics, including low crystallinity, high tensile strength, high elongation at break, and low glass transition temperature (Chen and Patel, 2012), while offering good biodegradability and biocompatibility, which makes them an excellent substitute for petroleum-based plastics (Raza et al, 2018). In terms of the physical properties, most sclPHA has high crystallinity, brittleness, and hardness (Koning, 1995), except for individual monomers such as 4HB and 3HV, and et al (Cavalheiro et al, 2013); while mcl-PHA is a thermoplastic, with low crystallinity, Tm values between 40 to 60°C, Tg values between −50 and −25°C, low tensile strength and high elongation at break (Kessler and Witholt, 1998)
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