Polylactic acid (PLA) is a biodegradable, biocompatible, and non-toxic alternative to petroleum-based plastics. Since PLA is stiff and brittle, it has been modified by copolymer synthesis or blending with other polymers including the polyesters polyhydroxyalkanoates (PHAs). PHAs can be synthesized by microbial fermentation or chemical polymerization using monomer precursors provided by diverse metabolic pathways. Recently, a complete biological process for the production of PLA and PLA copolymers from renewable resources has been developed by direct fermentation of recombinant bacteria. In this issue, Si Jae Park and Sang Yup Lee (KAIST, Korea) review recent advances in the production of lactate-containing homo- and co-polyesters by metabolically engineered bacteria. The authors discuss remaining challenges to efficiently produce PLA and its copolymers and strategies to overcome these challenges through metabolic engineering combined with enzyme engineering.
Succinate has been recognized as an important platform chemical that can be produced from biomass. The molecule is valuable in specialized applications and can be converted to a variety of other industrial chemicals and polymers. Applications range from use in the food industry to synthesis of surfactants, which is, for example, a component of the Corexit dispersant used in the recent Gulf oil-spill cleanup operations. The metabolism of Escherichia coli has previously been engineered to produce succinic acid from a variety of feedstocks. Important features of a succinate production system are the optimal balance of reducing byproducts while maximizing the amount of carbon channeled into the product. In this issue, George Bennett (Houston, TX, USA) and colleagues review bio-based succinate production from sugar feedstocks using engineered E. coli and strategies to improve its economical production.
Industrial production of β-lactam antibiotics such as penicillin G is based on successive classical strain improvement cycles of the filamentous fungus Penicillium chrysogenum. Genomic and transcriptional analysis of strain lineages has led to the identification of several important alterations in high-yielding strains. Through advanced metabolic engineering and synthetic biology approaches the penicillin biosynthesis pathway can be redirected towards the production of cephalosporins and penicillins that are normally produced through semi-synthetic means. This technology now enables more sustainable methods for the fermentative production of unnatural antibiotics and related compounds. In this issue, Arnold Driessen et al. from Groningen, the Netherlands, summarize our current knowledge on the results of classical strain improvement processes, and review avenues to improve β-lactam biosynthesis as well as other antibiotics and peptide products.