Secondary metabolisms

As mentioned in Section 12.5, each strain harbors quite a number of different secondary metabolite pathways. Although most of these are currently of unknown function, each strain usually produces several compound families which is why myxobacteria are considered as multiproducers of bioactive compounds. 

One impressive example is S. cdlulosum So cel2 (see Table 12.2). From this species, five compound famihes have so far been identified the highly effective disorazoles as tubulin destabilizers currently under preclinical development 

Species Natural products Biological activity mode of action  

Taken together, it is clear that myxobacteria continue to be a most promising source for novel bioactive secondary metabolites with potential use in therapy. In the following sections, two myxobacterial genera most prominent for their secondary metabolism are described together with some of their intriguing natural products. 

---

Several analyses of known marine natural products according to the phylum of the source organism have revealed the richest sources of marine secondary metabolism (Figure It is clear from the data that marine algae and... 

The major dasses of antibiotics are secondary metabolic products of micro-organisms. Many were discovered by empirically screening culture filtrates or cell extracts for antimicrobial activity. A range of techniques (examples are methods using, impregnated discs, porous cylinders, cut wells, see Figure 6.2) have been used to carry out such screening. 

Hara Y (1996) In DiCosmo F, Misawa M (eds) Plant cell culture secondary metabolism -towards industrial application. CRC, Boca Raton, p 187... 

In the interdisciplinary field of biophysics and biotechnology, the bioeffects of electric field have received considerable interest for both fundamental studies on these interaction mechanisms and potential application. However, the effects of pulsed electric field (PEF) on secondary metabolism in plant cell cultures and fermentation processes have been unknown. Therefore, it would be very interesting to find out whether PEF could be used as a new tool for stimulating secondary metabolism in plant cell cultures for potential application to the value-added plant-specific secondary metabolite production. Furthermore, if the PEF permeabilization and elicitation are discovered in a cell culture system, the combination of... 

On the basis of morphological and secondary metabolic differences, Masuda et al. (1997c) concluded that an alga previously known as Laurencia obtusa (Hudson) Lamouroux var. snackeyi (Weber-van Bosse) Yamada (earlier name was L paniculata... 

In a few cases, information obtained from macromolecular methods is included where such data might have a bearing on interpretation of how a given secondary metabolic profile could have come about. Specifically, it is possible to speculate on... 

Understanding mechanisms controlling metabolon localization in plastids of different membrane architectures Little is known about metabolon structure, assembly, and membrane targeting. The carotenoid biosynthetic pathway exists on plastid membranes. However, plastids have different membrane architectures and therefore tissue- and plastid-specific differences in membrane targeting of the biosynthetic metabolon can be expected. Localization in chloroplasts that harbor both thylakoid and envelope membranes differs from the envelope membranes in endosperm amy-loplasts. In fact, localization on both thylakoid and envelope membranes implies that the carotenoid pathway is really not a single pathway, but a duplicated pathway that may very well have membrane-specific roles with regard to functions in primary and secondary metabolism. 

Morgan, J.A. and Shanks, J.V., Quantification of metabolic flux in plant secondary metabolism by a biogenetic organizational approach, Metabol. Eng. 4, 257, 2002. 

Girod, R-A. and Zryd, J.-R, Secondary metabolism in cultured red beet Beta vulgaris L.) cells Differential regulation of betaxanthin and betacyanin biosynthesis. Plant Cell Tiss. Org. Cult., 25, 1, 1991. 

Lange B, Kremer S, Sterner O, Anke H (1995) Indnction of secondary metabolism by environmental pollutants metabolism of pyrene and formation of 6,8-dihydroxy-3-methylisocoumarin by Crinipellis stipitaria JK 364. ZNaturforsch 50c 806-812. 

N. Chishaki and T. Horiguchi, Re.sponses of secondary metabolism in plants to nutrient deficiency. Soil Sci. Plant Nutr. 43 981 (1997). 

Chemical manipulation of phenolic allelochemical production in plants has two potential values 1) for study of the role of phenolic allelochemicals in plant interactions with other organisms and 2) to alter such interactions for agricultural purposes. The first of these uses has already been accomplished on a limited scale (21, 22, 50, 51, 84, 86), however, there is no published evidence of the latter. This does not mean that herbicide and growth regulator-influences on plant secondary metabolism do not affect agricultural ecosystems by changing allelochemic compositions of plants. It is likely that this is the case, but it... 

Application of Isotopic Methods to Secondary Metabolic Pathways T.J. Simpson... 

Conventionally, central and special metabolic pathways are distinguished. Central pathways are common to the decomposition and synthesis of major macromolecules. Actually, they are much alike in all representatives of the living world. Special cycles are characteristic of the synthesis and decomposition of individual monomers, macromolecules, cofactors, etc. Special cycles are extremely diversified, especially in the plant kingdom. For this reason, the plant metabolism is conventionally classified into primary and secondary metabolisms. The primary metabolism includes the classical processes of synthesis and deeradation of major macromolecules (proteins, carbohydrates, lipids, nucleic acids, etc.), while the secondary metabolism ensuing from the primary one includes the conversions of special biomolecules (for example, alkaloids, terpenes, etc.) that perform regulatory or other functions, or simply are metabolic end byproducts. 

The activity of PK and NRPSs is often precluded and/or followed by actions upon the natural products by modifying enzymes. There exists a first level of diversity in which the monomers for respective synthases must be created. For instance, in the case of many NRPs, noncanonical amino acids must be biosynthesized by a series of enzymes found within the biosynthetic gene cluster in order for the peptides to be available for elongation by the NRPS. A second level of molecular diversity comes into play via post-synthase modification. Examples of these activities include macrocyclization, heterocyclization, aromatization, methylation, oxidation, reduction, halogenation, and glycosylation. Finally, a third level of diversity can occur in which molecules from disparate secondary metabolic pathways may interact, such as the modification of a natural product by an isoprenoid oligomer. Here, we will cover only a small subsection of... 

The production of ligninolytic enzymes takes place during the secondary metabolism of several WRF. The lignin degrading system is induced when starvation of C or N occurs moreover, agitation and temperature can significantly affect the levels of these enzymes factors affecting LMEs are reviewed by Gao et al. [1]. 

Koricheva J, Larsson S, Haukioja E and Keinanen M (1998), Regulation of woody plant secondary metabolism by resource availability hypothesis testing by means of metaanalysis , Oikos, 83, 212-226. 

Lydon J and Duke S D (1989), Pesticides effects on secondary metabolism of higher plants , Pest Sci, 25, 361-374. 

---