Microbial Valorization of Lignin to Bioplastic by Genome-Reduced Pseudomonas putida.

As the most abundant natural aromatic resource, lignin valorization will contribute to a feasible biobased economy. Recently, biological lignin valorization has been advocated since ligninolytic microbes possess proficient funneling pathways of lignin to valuable products. In the present study, the potential to convert an actual lignin stream into polyhydroxyalkanoates (PHAs) had been evaluated using ligninolytic genome-reduced Pseudomonas putida. The results showed that the genome-reduced P. putida can grow well on an actual lignin stream to successfully yield a high PHA content and titer. The designed fermentation strategy almost eliminated the substrate effects of lignin on PHA accumulation. Employing a fed-batch strategy produced the comparable PHA contents and titers of 0.35 g/g dried cells and 1.4 g/L, respectively. The molecular mechanism analysis unveiled that P. putida consumed more small and hydrophilic lignin molecules to stimulate cell growth and PHA accumulation. Overall, the genome-reduced P. putida exhibited a superior capacity of lignin bioconversion and promote PHA accumulation, providing a promising route for sustainable lignin valorization.

Bacterial conversion routes for lignin valorization.

As the largest renewable aromatic resource, lignin is a promising feedstock for production of value-added products. However, lignin valorization has not been implemented due to the recalcitrant and heterogeneity of lignin. Herein, this work provides a systematic overview of bacterial lignin valorization for producing value-added products from the viewpoint of a cascaded conversion route. The combinatorial depolymerization strategy facilitates the yield of a lignin-derived aromatic stream suitable for the bacterial conversion. Bacterial active transports are curial to improve the uptake of lignin-derived aromatics. Intracellular metabolic pathways of bacteria assimilate heterogenous lignin-derived aromatics through "biological funnel" into central aromatic intermediates. These intermediates can be effectively metabolized in bacteria through aromatic ring cleavage pathways to enable the biosynthesis of various value-added products. The techno-economic analysis highlights that bacterial conversion improves the feasibility of co-production of value-added products from lignin. Therefore, the bacterial cascaded conversion routes hold great promise for upgrading heterogeneous lignin into value-added products and thus contribute to the profitability of lignin valorization.

Microbial Adaptation to Enhance Stress Tolerance.

Microbial cell factories have been widely used in the production of various chemicals. Although synthetic biology is useful in improving the cell factories, adaptation is still widely applied to enhance its complex properties. Adaptation is an important strategy for enhancing stress tolerance in microbial cell factories. Adaptation involves gradual modifications of microorganisms in a stressful environment to enhance their tolerance. During adaptation, microorganisms use different mechanisms to enhance non-preferred substrate utilization and stress tolerance, thereby improving their ability to adapt for growth and survival. In this paper, the progress on the effects of adaptation on microbial substrate utilization capacity and environmental stress tolerance are reviewed, and the mechanisms involved in enhancing microbial adaptive capacity are discussed.