The quest for new antibiotics, especially those with activity against Gram-negative bacteria, is urgent; however, very few new antibiotics have been marketed in the last 40 years, with this limited number falling into only four new structural classes. Several nucleoside natural product antibiotics target bacterial translocase MraY, involved in the lipid-linked cycle of peptidoglycan biosynthesis, and fungal chitin synthase. Biosynthetic studies on the nikkomycin, caprazamycin and pacidamycin/mureidomycin families are also reviewed.

Nonribosomal peptides are amongst the most widespread and structurally diverse secondary metabolites in nature with many possessing bioactivity that can be exploited for therapeutic applications. Due to the major challenges associated with total- and semi-synthesis, bioengineering approaches have been developed to increase yields and generate modified peptides with improved physicochemical properties or altered bioactivity. Here we review the major advances that have been made over the last decade in engineering the biosynthesis of nonribosomal peptides. Structural diversity has been introduced by the modification of enzymes required for the supply of precursors or by heterologous expression of tailoring enzymes. The modularity of nonribosomal peptide synthetase (NRPS) assembly lines further supports module or domain swapping methodologies to achieve changes in the amino acid sequence of nonribosomal peptides. We also review the new synthetic biology technologies promising to speed up the process, enabling the creation and optimisation of many more assembly lines for heterologous expression, offering new opportunities for engineering the biosynthesis of novel nonribosomal peptides.

A convenient and high yielding procedure for the Suzuki-Miyaura cross-coupling of unprotected bromo- and chlorotryptophans in water provides fluorescent aryltryptophans.

Biofilm, friend not foe: Single species biofilms can be engineered to form robust biocatalysts with greater catalytic activity and significantly improved catalytic longevity than purified and immobilised enzymes. We report the engineering, structural analysis and biocatalytic capability of a biofilm that can mediate the conversion of serine and haloindoles to halotryptophans (see scheme).

The amide functional group is ubiquitous in nature and one of the most important motifs in pharmaceuticals, agrochemicals and other valuable products. Whilst coupling amides and carboxylic acids is a trivial synthetic transformation, it often requires protective group manipulation, along with stoichiometric quantities of expensive and deleterious coupling reagents. Nature has evolved a range of enzymes to construct amide bonds the vast majority of which utilize adenosine triphosphate (ATP) to activate the carboxylic acid substrate for amine coupling. Despite the fact that these enzymes operate under mild conditions, as well as possessing chemoselectivity and regioselectivity that obviates the need for protecting groups, their synthetic potential has been largely unexplored. In this review we discuss recent research into the discovery, characterisation and development of amide bond forming enzymes, with an emphasis on stand-alone ligase enzymes that can generate amides directly from simple carboxylic acid and amine substrates.

β‐Methyltryptophans (β‐mTrp) are precursors in the biosynthesis of bioactive natural products and are used in the synthesis of peptidomimetic‐based therapeutics. Currently β‐mTrp is produced by inefficient multistep synthetic methods. Here we demonstrate how an engineered variant of tryptophan synthase from Salmonella (StTrpS) can catalyse the efficient condensation of l‐threonine and various indoles to generate β‐mTrp and derivatives in a single step. Although l‐serine is the natural substrate for TrpS, targeted mutagenesis of the StTrpS active site provided a variant (βL166V) that can better accommodate l‐Thr as a substrate. The condensation of l‐Thr and indole proceeds with retention of configuration at both α‐ and β‐positions to give (2S,3S)‐β‐mTrp. The integration of StTrpS (βL166V) with l‐amino acid oxidase, halogenase enzymes and palladium chemocatalysts provides access to further d‐configured and regioselectively halogenated or arylated β‐mTrp derivatives.

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The robust nature of biofilms makes them medicinally difficult to treat, however this same property renders them an attractive method for protecting and immobilising enzymes for biotransformation. Although biofilms consisting of a consortium of different microbial species have been routinely used in water purification for many decades, there are few reported examples of single species biofilms being harnessed for industrial applications. The potential of using tailored single species biofilms in order to catalyse a biotransformation of choice is attractive; we reflect upon recent advances in the use and generation of such platforms, from both biological and process engineering viewpoints.