Characterization of a new carotenoid biosynthesis route in planctopirus limnophila

Abstract

Terpenoids encompass a large variety of important isoprenoid lipids including polycyclic triterpenes and carotenoids that are key components to maintain cell membrane homeostasis and to adapt to the environment. Polycyclic triterpenes are biosynthesized from squalene, which is then cyclized into hopanoids, or sterols. Carotenoids, however, are linear terpenes produced by independent pathways to the one of polycyclic triterpenes. Polycyclic triterpenes and carotenoids have been traditionally associated to different functions, although their functional similarities in modulating membrane properties are becoming more evident. Nonetheless further functions of both kind of molecules in specific bacterial groups such the membrane intricate Planctomycetes, remains virtually unexplored. In the present research we characterize the biosynthesis route for carotenoids in Planctopirus limnophila, demonstrating the production of C30 carotenoids from the precursor squalene, through the HpnCDE pathway. This pathway showcases the first description in nature of a connection between hopanoids and carotenoids biosynthesis, involving the simultaneous action of the enzymes presqualene diphosphate synthase (HpnD), hydroxysqualene synthase (HpnC) and hydroxysqualene dehydroxylase (HpnE) enzymes for the common precursor, squalene, synthesis. Wild type extracts contained the orange 4,4’-Diapolycopene, the deep-red 4,4-Diapolycopene dial, the pink 4,4’-Diapolycopen-4,4’-dioic C30 carotenoids with mono- and di- glycosyl esters moieties. In addition, we performed functional assays to associate the possible functions of carotenoids, hopanoids and squalene to different membrane-related stresses. Our results suggest that carotenoids, hopanoids and squalene at a lower degree, can alleviate the cell against osmotic, oxidative and desiccation stresses. These results hint at the fact that those carotenoids and hopanoids share some functions, providing an insight look at the physiology of Planctomycetes.

Date of Award	15 Jul 2021
Original language	English
Awarding Institution	Universidade Católica Portuguesa
Supervisor	Damien Paul Devos (Supervisor) & Elena Rivas-Marín (Co-Supervisor)