Characterization of Two Polyketide Synthase Genes Involved in Zearalenone Biosynthesis in Gibberella zeae

Zearalenone, a mycotoxin produced by several Fusarium spp., is most commonly found as a contaminant in stored grain and has chronic estrogenic effects on mammals. Zearalenone is a polyketide derived from the sequential condensation of multiple acetate units by a polyketide synthase (PKS), but the genetics of its biosynthesis are not understood. We cloned two genes, designated ZEA1 and ZEA2, which encode polyketide synthases that participate in the biosynthesis of zearalenone by Gibberella zeae (anamorph Fusarium graminearum). Disruption of either gene resulted in the loss of zearalenone production under inducing conditions. ZEA1 and ZEA2 are transcribed divergently from a common promoter region. Quantitative PCR analysis of both PKS genes and six flanking genes supports the view that the two polyketide synthases make up the core biosynthetic unit for zearalenone biosynthesis. An appreciation of the genetics of zearalenone biosynthesis is needed to understand how zearalenone is synthesized under field conditions that result in the contamination of grain.     

Characterization of two polyketide synthase genes involved in zearalenone biosynthesis in Gibberella zeae

Zearalenone, a mycotoxin produced by several Fusarium spp., is most commonly found as a contaminant in stored grain and has chronic estrogenic effects on mammals. Zearalenone is a polyketide derived from the sequential condensation of multiple acetate units by a polyketide synthase (PKS), but the genetics of its biosynthesis are not understood. We cloned two genes, designated ZEA1 and ZEA2, which encode polyketide synthases that participate in the biosynthesis of zearalenone by Gibberella zeae (anamorph Fusarium graminearum). Disruption of either gene resulted in the loss of zearalenone production under inducing conditions. ZEA1 and ZEA2 are transcribed divergently from a common promoter region. Quantitative PCR analysis of both PKS genes and six flanking genes supports the view that the two polyketide synthases make up the core biosynthetic unit for zearalenone biosynthesis. An appreciation of the genetics of zearalenone biosynthesis is needed to understand how zearalenone is synthesized under field conditions that result in the contamination of grain.     

Variation in 8-ketotrichothecenes and zearalenone production by Fusarium graminearum isolates from corn and barley in Korea

A total of 214 Fusarium graminearum isolates were obtained from corn and barley which were collected from Kangwon province and the southern part of Korea, respectively, and were tested for 8-ketotrichothecenes and zearalenone (ZEA) production on rice grains. The incidences of trichothecene production by 105 isolates of F. graminearum from corn were 59.0% for deoxynivalenol (DON), 37.1% for 15-acetyldeoxynivalenol(15-ADON), 13.3% for 3-acetyldeoxynivalenol (3-ADON), 7.6% for 3,15-diacetyldeoxynivalenol (3,15-DADON), 20.0% for nivalenol (NIV), 6.7% for 4-acetylnivalenol (4-ANIV), and 1.0% for 4,15-diacetylnivalenol (4,15-DANIV). DON chemotypes frequently produced 15-ADON as the major isomer rather than 3-ADON and 9 of the 61 DON chemotypes produced low levels of NIV. On the other hand, the incidences of trichothecene production of 109 isolates by F. graminearum from barley were 24.8% for DON, 72.5% for NIV, 62.4% for 4-ANIV, and 10.1% for 4,15-DANIV. Of these isolates, 78 were NIV chemotypes and only one isolate produced DON and 3-ADON as major toxins. In addition, 26 of the 78 NIV chemotypes produced low levels of DON. ZEA was frequently produced by the trichothecene-producing isolates and the incidences of ZEA were 51.4% and 31.2% for the isolates from corn and barley, respectively. There was a great regional difference in trichothecene production by F. graminearum isolates between corn- and barley-producing areas in Korea.     

Metabolic engineering of Escherichia coli for the production of cadaverine: A five carbon diamine

A five carbon linear chain diamine, cadaverine (1,5‐diaminopentane), is an important platform chemical having many applications in chemical industry. Bio‐based production of cadaverine from renewable feedstock is a promising and sustainable alternative to the petroleum‐based chemical synthesis. Here, we report development of a metabolically engineered strain of Escherichia coli that overproduces cadaverine in glucose mineral salts medium. First, cadaverine degradation and utilization pathways were inactivated. Next, L ‐lysine decarboxylase, which converts L ‐lysine directly to cadaverine, was amplified by plasmid‐based overexpression of the cadA gene under the strong tac promoter. Furthermore, the L ‐lysine biosynthetic pool was increased by the overexpression of the dapA gene encoding dihydrodipicolinate synthase through the replacement of the native promoter with the strong trc promoter in the genome. The final engineered strain was able to produce 9.61 g L⁻¹ of cadaverine with a productivity of 0.32 g L⁻¹ h⁻¹ by fed‐batch cultivation. The strategy reported here should be useful for the bio‐based production of cadaverine from renewable resources. Biotechnol. Bioeng. 2011; 108:93–103. © 2010 Wiley Periodicals, Inc.