RESUMO
The carotenoids, a subfamily of the isoprenoids, are among the most widespread, ancient, diverse, and rich class of all natural products and biomolecules. Microorganisms, as well as microalgae and bacteria synthesize isoprenoids from isopentenyl diphosphate (IPP) and its isomer dimethylallyl diphosphate (DMAPP). For long time, mevalonic acid was assumed to be the only natural precursor for IPP and DMAPP in the cytosolic acetate/mevalonate pathway for the biosynthesis of sterols, sesquiterpenes, triterpenoids, and carotenoids. At present, it is accepted that the relatively new route, the methylerythritol 4-phosphate (MEP), or 1-deoxy-D: -xylulose-5-phosphate (DOXP) is the main pathway for the biosynthesis of plastidic isoprenoids, such as carotenoids, phytol (a side chain of chlorophylls), plastoquinone-9, isoprene, mono-, and diterpenes. Cytosolic isoprenoids (sterols) biosynthesized by MEP have been reported in eubacteria and algae (Chlorella, Chlamydomonas, Scenedesmus, and Dunaliella). This review summarizes current knowledge of the biosynthetic pathways leading to the formation of different isoprenoids and carotenoids in bacteria and microalgae. Particular attention was given to the last early steps of the biosynthesis of the key C(5)-precursor and the final steps of the biosynthesis of carotenoids including selected examples in microalgae and bacteria as well as the recent advances in genomics and metabolic engineering.
Assuntos
Bactérias/metabolismo , Carotenoides/biossíntese , Microalgas/metabolismoRESUMO
Dunaliella salina has become the most important microorganism for the production of ß-carotene around the world. Natural carotenoids are a source of active metabolites utilized in different areas of food nutrition and pharmaceuticals, both in humans and also in animals. Identification of Dunaliella species from natural environments or certified culture collections is not precise and it is time consuming. However, accurate identification is extremely important because a slight difference in Dunaliella species generates great differences in carotenoids production. Here, we describe an intron-sizing method to make a rapid and precise identification for each of the most important carotenogenic species, showing that each hyperproducer species has an exclusive 18S rDNA fingerprint profile.
Assuntos
Clorófitas/genética , Impressões Digitais de DNA , Íntrons , Primers do DNA , Reação em Cadeia da PolimeraseRESUMO
In Dunaliella salina, we studied the early steps in the isoprenoid pathway for the biosynthesis of carotenoids and beta-carotene and the effects of metabolic inhibitors. When D. salina was grown under carotenogenic and non-carotenogenic conditions, mevinolin did not inhibit growth or the accumulation of carotenoids, beta-carotene or chlorophyll. In contrast, fosmidomycin progressively inhibited cell growth and the biosynthesis of carotenoids, beta-carotene and chlorophyll. In this work, we reported for the first time that in D. salina, beta-carotene biosynthesis does not proceed via the classical acetate/mevalonate pathway but via the novel glyceraldehyde 3-phosphate/pyruvate pathway. This favours the yield of C(5) isoprenoid units for synthesis of isopentenyl diphosphate, the precursor in the biosynthesis of C(20) compounds, including geranylgeranyl diphosphate. Consequently, this pathway promotes carotenogenesis and the biosynthesis of C(40) beta-carotene in D. salina.
Assuntos
Clorófitas/metabolismo , beta Caroteno/biossíntese , Fosfomicina/análogos & derivados , Gliceraldeído 3-Fosfato/metabolismo , Lovastatina , Redes e Vias Metabólicas , Ácido Pirúvico/metabolismoRESUMO
D. salina is one of the recognized natural sources to produce beta-carotene, and an useful model for studying the role of inhibitors and enhancers of carotenogenesis. However there is little information in D. salina regarding whether the isoprenoid substrate can be influenced by stress factors (carotenogenic) or selective inhibitors which in turn may further contribute to elucidate the early steps of carotenogenesis and biosynthesis of beta-carotene. In this study, Dunaliella salina (BC02) isolated from La Salina BC Mexico, was subjected to the method of isoprenoids-beta-carotene interference in order to promote the interruption or accumulation of the programmed biosynthesis of carotenoids. When Carotenogenic and non-carotenogenic cells of D. salina BC02 were grown under photoautotrophic growth conditions in the presence of 200 microM fosmidomycin, carotenogenesis and the synthesis of beta-carotene were interrupted after two days in cultured D. salina cells. This result is an indirect consequence of the inhibition of the synthesis of isoprenoids and activity of the recombinant DXR enzyme thereby preventing the conversion of 1-deoxy-D-xylulose 5-phosphate (DXP) to 2-C-methyl-D-erythritol (MEP) and consequently interrupts the early steps of carotenogenesis in D. salina. The effect at the level of proteins and RNA was not evident. Mevinolin treated D. salina cells exhibited carotenogenesis and beta-carotene levels very similar to those of control cell cultures indicating that mevinolin not pursued any indirect action in the biosynthesis of isoprenoids and had no effect at the level of the HMG-CoA reductase, the key enzyme of the Ac/MVA pathway.