A Non-Enzymatic Pathway with Superoxide in Intracellular Terpenoid Synthesis

Isolation and structural determination of natural products bearing tetrahydrogenated isoprenoid side-chains at their ω-termini

Hydrogenated isoprenoids are found in a range of biologically important natural products, such as isoprenoid quinones, chlorophyll, vitamin E, and dolichol. In this study, a new method was developed for determining the chirality of the tetrahydrogenated isoprenoid (THI) structures of two natural products, namely heptaprenylcycli-14E,18E-diene and (22R,5E,9E,13E,17E)-6,10,14,18,22,26-hexamethylheptacosa-5,9,13,17-tetraen-2-one, for which the chiral carbon centres have never been elucidated. Our research group previously isolated the former sesquarterpene from Mycobacterium chlorophenolicum, while the latter was isolated as a new polyprenyl acetone from Conexibacter woesei in the current study. To determine their chiralities, these two THI-containing terpenoids were subjected to ozonolysis to produce (R)-6,10-dimethyl-2-undecanones. The optically active (S)-6,10-dimethyl-2-undecanone was prepared as an authentic chiral sample by the reduction of (S,E)-6,10-dimethylundeca-3,9-dien-2-one. Chiral high-performance liquid chromatographic analysis of the ozonolysis products and of authentic (S)- and racemic 6,10-dimethyl-2-undecanone samples unambiguously assigned the THI chiral carbon centres of both compounds as R. This new method could be a useful tool for determining the chiralities of other THIs. It is also expected to contribute to our understanding of the biosynthetic mechanisms and biological roles of THIs.

Bacterial terpenome

Covering: up to mid-2020 Terpenoids, also called isoprenoids, are the largest and most structurally diverse family of natural products. Found in all domains of life, there are over 80 000 known compounds. The majority of characterized terpenoids, which include some of the most well known, pharmaceutically relevant, and commercially valuable natural products, are produced by plants and fungi. Comparatively, terpenoids of bacterial origin are rare. This is counter-intuitive to the fact that recent microbial genomics revealed that almost all bacteria have the biosynthetic potential to create the C5 building blocks necessary for terpenoid biosynthesis. In this review, we catalogue terpenoids produced by bacteria. We collected 1062 natural products, consisting of both primary and secondary metabolites, and classified them into two major families and 55 distinct subfamilies. To highlight the structural and chemical space of bacterial terpenoids, we discuss their structures, biosynthesis, and biological activities. Although the bacterial terpenome is relatively small, it presents a fascinating dichotomy for future research. Similarities between bacterial and non-bacterial terpenoids and their biosynthetic pathways provides alternative model systems for detailed characterization while the abundance of novel skeletons, biosynthetic pathways, and bioactivies presents new opportunities for drug discovery, genome mining, and enzymology.

Identification of volatiles from six marine Celeribacter strains

The volatiles emitted from six marine Rhodobacteraceae species of the genus Celeribacter were investigated by GC-MS. Besides several known compounds including dimethyl trisulfide and S-methyl methanethiosulfonate, the sulfur-containing compounds ethyl (E)-3-(methylsulfanyl)acrylate and 2-(methyldisulfanyl)benzothiazole were identified and their structures were verified by synthesis. Feeding experiments with [methyl-2H3]methionine, [methyl-13C]methionine and [34S]-3-(dimethylsulfonio)propanoate (DMSP) resulted in the high incorporation into dimethyl trisulfide and S-methyl methanethiosulfonate, and revealed the origin of the methylsulfanyl group of 2-(methyldisulfanyl)benzothiazole from methionine or DMSP, while the biosynthetic origin of the benzothiazol-2-ylsulfanyl portion could not be traced. The heterocyclic moiety of this compound is likely of anthropogenic origin, because 2-mercaptobenzothiazole is used in the sulfur vulcanization of rubber. Also in none of the feeding experiments incorporation into ethyl (E)-3-(methylsulfanyl)acrylate could be observed, questioning its bacterial origin. Our results demonstrate that the Celeribacter strains are capable of methionine and DMSP degradation to widespread sulfur volatiles, but the analysis of trace compounds in natural samples must be taken with care.

Volatiles from the Psychrotolerant Bacterium Chryseobacterium polytrichastri

The flavobacterium Chryseobacterium polytrichastri was investigated for its volatile profile by use of a closed-loop stripping apparatus (CLSA) and subsequent GC-MS analysis. The analyses revealed a rich headspace extract with 71 identified compounds. Compound identification was based on a comparison to library mass spectra for known compounds and on a synthesis of authentic standards for unknowns. Important classes were phenylethyl amides and a series of corresponding imines and pyrroles.

Harnessing biocompatible chemistry for developing improved and novel microbial cell factories

White biotechnology relies on the sophisticated chemical machinery inside living cells for producing a broad range of useful compounds in a sustainable and environmentally friendly way. However, despite the impressive repertoire of compounds that can be generated using white biotechnology, this approach cannot currently fully replace traditional chemical production, often relying on petroleum as a raw material. One challenge is the limited number of chemical transformations taking place in living organisms. Biocompatible chemistry, that is non‐enzymatic chemical reactions taking place under mild conditions compatible with living organisms, could provide a solution. Biocompatible chemistry is not a novel invention, and has since long been used by living organisms. Examples include Fenton chemistry, used by microorganisms for degrading plant materials, and manganese or ketoacids dependent chemistry used for detoxifying reactive oxygen species. However, harnessing biocompatible chemistry for expanding the chemical repertoire of living cells is a relatively novel approach within white biotechnology, and it could potentially be used for producing valuable compounds which living organisms otherwise are not able to generate. In this mini review, we discuss such applications of biocompatible chemistry, and clarify the potential that lies in using biocompatible chemistry in conjunction with metabolically engineered cell factories for cheap substrate utilization, improved cell physiology, efficient pathway construction and novel chemicals production.