Biosynthesis and biological function of phosphonates in Fusarium spp.
by Maria de los Ángeles Vinas Meneses
Date of Examination:2018-02-06
Date of issue:2018-04-09
Advisor:Prof. Dr. Petr Karlovsky
Referee:PD Dr. Franz Hadacek
Referee:Prof. Dr. Axel Zeeck
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EnglishPhosphonates are natural or synthetic compounds with a direct carbon-phosphorus bond. Their similarity to the abundant phosphate esters and carboxylic acids and the stability of the C-P bond makes them suitable for diverse applications in medicine and agriculture. Bioactive natural phosphonates are produce by many species of bacteria, most of them belonging to the Streptomyces genera. The interest in these compounds is increasing year by year since recent evidence suggest that their abundance in the biosphere is much higher than expected. In fungi only one phosphonate has been described so far named fosfonochlorin; a low molecular weight phosphonic acid with antibiotic activity produced by some species of Fusarium and one species of Talaromyces. The main objectives of the present study were to corroborate that Fusarium is able to produce phosphonates, to determine their biological function and to identify other phosphonates in the fungus. Based on our Fusarium genome-based survey we have found homologous genes codifying the main enzymes involved in phosphonates biosynthesis [phosphoenolpyruvate phosphomutase (pepm) and phosphonopyruvate decarboxylase (ppd)] in several Fusarium species. This is an important finding since the first steps of phosphonates biosynthetic pathways are conserved among different organisms and pepm sequence can be used to predict phosphonates producers. Moreover, these genes together with others inside the putative cluster in F. oxysporum were up-regulated when the fungus was cultivated with bacteria, suggesting a function related with fungal-bacteria interaction. However, using phosphonates disrupted F. oxysporum strains and the wild type we could not observed any differential effect on bacteria growth. On the other hand, when the same F. oxysporum wt and disrupted strains were used against mycoparasitic fungi and mealworms some effect was observed on their growth and feeding behavior, however more research is needed in order to corroborate the results. Finally, some possible phosphonates, including the already known fosfonochlorin was identified in F. oxysporum and F. avenaceum cultures, reinforcing our hypothesis that Fusarium can biosynthesize phosphonates. This is the first study related with fungal phosphonates in which a gene-based approach was followed in order to predict fungal species with the capacity to biosynthesize phosphonates. Based on our findings, one could anticipate that the discovery of new phosphonates of fungal origin is going to increase in the coming years. Although, the biological function of these compounds for Fusarium is still unclear, we generated phosphonates-disrupted strains that can be used, not only to clarify their biological function but also to identify novel F. oxysporum phosphonates through HR-MS and 31P NMR.
Keywords: Phosphonates; Fusarium; C-P compounds