Microbial production of fuels and chemicals serves as a sustainable alternative to the current processes relying on fossil resources or limited natural resources. Lignocellulose has been considered a promising renewable feedstock for microbial production. However, efficient utilization of lignocellulose is hindered, as lignin, a primary component of lignocellulose, is produced in large quantities as a side stream from lignocellulosic biorefineries. Valorizing lignin into more valuable products is critical in improving the economic viability of lignocellulosic biorefineries and minimizing waste streams.
Due to the intrinsic heterogeneity of lignin, its depolymerization typically yields a mixture of different aromatic compounds, posing a challenge to the downstream purification and upgrading processes.
“Biological lignin valorization offers a solution to this challenge by funneling the aromatic mixture into single products, taking advantage of the natural aromatic-catabolizing ability of some microorganisms. However, the toxicity of lignin-derived aromatics to microorganisms hinders their use as substrates for bioproduction,” Jin Luo says.
A novel approach discovers genetic mutations that add to substrate-tolerance
In his study, Jin Luo evaluated a bacterium called Acinetobacter baylyi ADP1 for its ability to use lignin-derived aromatics. The need for using lignin-derived aromatics as the substrate necessitates the development of a highly substrate-tolerant host microorganism.
“To this end, an evolutionary strategy was employed, successfully improving the tolerance of the bacterium to lignin-derived aromatics. The bacterium was further metabolically modified to demonstrate the upgrading of lignin-derived aromatics to produce a non-native product, 1-undecene,” Luo explains.
Subsequently, to reveal the genetic basis behind the improved tolerance, Luo analyzed the genome of the aromatic-tolerant bacterium. He developed a novel approach to discover the genetic mutations conferring the enhanced tolerance, which takes advantage of the genetic tractability of the bacterium.
“The identified beneficial mutations can provide insights into rational engineering for improving aromatic tolerance in other host bacteria,” Jin Luo says.
A feasible bioprocess also requires efficient production of the target products. This can be achieved by properly modulating the metabolic pathway of the bacterium. In terms of intracellular products, such as wax esters, the high-value lipids naturally produced by A. baylyi ADP1, cell morphology can impact product accumulation.
“For example, a large-sized cell can allow a high product content. With the help of different genetic tools, it is possible to manipulate cell morphology by controlling the expression of specific genes,” he adds.
The doctoral dissertation of M.Sc. Jin Luo in the field of biotechnology titled Engineering Acinetobacter baylyi ADP1: New tools and strategies for enhanced production of chemicals using non-conventional substrates will be publicly examined in the Faculty of Engineering and Natural Sciences at Tampere University at 12 o’clock on Friday, 28 October 2022. The venue is the Small Auditorium 1 (FA032 ) of the Festia building, Korkeakoulunkatu 8. The Opponent will be Assistant Professor Pauli Kallio from the University of Turku. The Custos will be Associate Professor Ville Santala from Tampere University.
The doctoral dissertation is available online.
Photo: Elena Efimova