Exploiting Substrate Promiscuity of Ectoine Hydroxylase for Regio- and Stereoselective Modification of Homoectoine

2-Homoectoine: An Additional Member of the Ectoine Family from Phyto- and Bacterioplankton Involved in Osmoadaptation

Ectoine is a central osmolyte in marine plankton due to its excellent cytoprotective traits and its multifunctional roles supporting the survival of microalgae and bacteria under unfavorable environmental conditions. The protective effect of ectoine toward several kinds of stresses stirred interest in biotechnology, pharmacy, and other fields including cosmetics. Also, its hydroxylated derivative, 5-hydroxyectoine, exhibits functions similar to ectoine. Here we introduce a molecular networking-based approach to expand the family of ectoine derivatives from phyto- and bacterioplankton. A ZIC-HILIC separation protocol coupled with HRMS/MS-based molecular networking allowed us to identify the new ectoine derivative 1,4,5,6-tetrahydro-2-ethyl-4-pyrimidinecarboxylic acid, or 2-homoectoine (1). 1 is found in many algae including dinoflagellates, chlorophytes, and haptophytes. In axenic strains, the content of 1 is substantially lower. In accordance, we found that marine bacteria are prolific producers of the compound as well. This suggests that the microalgae with their associated microbiome have to be considered as sources of the compound. Increasing concentrations of the compound under high salinity suggest a role as a protectant against osmotic stress.

Microbial conversion of carbon dioxide and hydrogen into the fine chemicals hydroxyectoine and ectoine

This study explores a novel conversion of CO₂ into the chemicals hydroxyectoine and ectoine, which are compounds with high retail values in the pharmaceutical industry. Firstly, 11 species of microbes able to use CO₂ and H₂ and that have the genes for ectoines synthesis (ectABCD) were identified through literature search and genomic mining. Laboratory tests were then conducted to ascertain the capacity of these microbes to produce ectoines from CO₂. Results showed that the most promising bacteria for CO₂ to ectoines bioconversion areHydrogenovibrio marinus, Rhodococcus opacus, and Hydrogenibacillus schlegelii.Upon salinity and H₂/CO₂/O₂ ratio optimization,H. marinus accumulated 85 mg of ectoine g biomass^-1. Interestingly, R.opacusand H. schlegelii mainly produced hydroxyectoine (53 and 62 mg g biomass^-1), which has a higher commercial value. Overall, these results constitute the first proof of a novel valorization platform of CO₂ and lay the foundation for a new economic niche aimed at CO₂ recircularization into pharmaceuticals.

Methanotrophs as a reservoir for bioactive secondary metabolites: Pitfalls, insights and promises

Methanotrophs are potent natural producers of several bioactive secondary metabolites (SMs) including isoprenoids, polymers, peptides, and vitamins. Cryptic biosynthetic gene clusters identified from these microbes via genome mining hinted at the vast and hidden SM biosynthetic potential of these microbes. Central carbon metabolism in methanotrophs offers rare pathway intermediate pools that could be further diversified using advanced synthetic biology tools to produce valuable SMs; for example, plant polyketides, rare carotenoids, and fatty acid-derived SMs. Recent advances in pathway reconstruction and production of isoprenoids, squalene, ectoine, polyhydroxyalkanoate copolymer, cadaverine, indigo, and shinorine serve as proof-of-concept. This review provides theoretical guidance for developing methanotrophs as microbial chassis for high-value SMs. We summarize the distinct secondary metabolic potentials of type I and type II methanotrophs, with specific attention to products relevant to biomedical applications. This review also includes native and non-native SMs from methanotrophs, their therapeutic potential, strategies to induce silent biosynthetic gene clusters, and challenges.

Bioactivity profiling of the extremolyte ectoine as a promising protectant and its heterologous production

Ectoine is a compatible solutes that is diffusely dispersed in bacteria and archaea. It plays a significant role as protectant against various external pressures, such as high temperature, high osmolarity, dryness and radiation, in cells. Ectoine can be utilized in cosmetics due to its properties of moisturizing and antiultraviolet. It can also be used in the pharmaceutical industry for treating various diseases. Therefore, strong protection of ectoine creates a high commercial value. Its current market value is approximately US$1000 kg-1. However, traditional ectoine production in high-salinity media causes high costs of equipment loss and wastewater treatment. There is a growing attention to reduce the salinity of the fermentation broth without sacrificing the production of ectoine. Thus, heterologous production of ectoine in nonhalophilic microorganisms may represent the new generation of the industrial production of ectoine. In this review, we summarized and discussed the biological activities of ectoine on cell and human health protection and its heterologous production.

A review on the immobilization of pepsin: A Lys-poor enzyme that is unstable at alkaline pH values

Pepsin is a protease used in many different applications, and in many instances, it is utilized in an immobilized form to prevent contamination of the reaction product. This enzyme has two peculiarities that make its immobilization complex. The first one is related to the poor presence of primary amino groups on its surface (just one Lys and the terminal amino group). The second one is its poor stability at alkaline pH values. Both features make the immobilization of this enzyme to be considered a complicated goal, as most of the immobilization protocols utilize primary amino groups for immobilization. This review presents some of the attempts to get immobilized pepsin biocatalyst and their applications. The high density of anionic groups (Asp and Glu) make the anion exchange of the enzyme simpler, but this makes many of the strategies utilized to immobilize the enzyme (e.g., amino-glutaraldehyde supports) more related to a mixed ion exchange/hydrophobic adsorption than to real covalent immobilization. Finally, we propose some possibilities that can permit not only the covalent immobilization of this enzyme, but also their stabilization via multipoint covalent attachment.

Taking Advantage of Promiscuity of Cold-Active Enzymes

Cold-active enzymes increase their catalytic efficiency at low-temperature, introducing structural flexibility at or near the active sites. Inevitably, this feat seems to be accompanied by lower thermal stability. These characteristics have made cold-active enzymes into attractive targets for the industrial applications, since they could reduce the energy cost in the reaction, attenuate side-reactions, and simply be inactivated. In addition, the increased structural flexibility could result in broad substrate specificity for various non-native substrates, which is called substrate promiscuity. In this perspective, we deal with a less addressed aspect of cold-active enzymes, substrate promiscuity, which has enormous potential for semi-synthesis or enzymatic modification of fine chemicals and drugs. Further structural and directed-evolutional studies on substrate promiscuity of cold-active enzymes will provide a new workhorse in white biotechnology.