terreus towards lovastatin biosynthesis.

In filamentous fungi, biosynthesis of secondary metabolites is subject to complex regulations. This study focused on the influence of N and C sources on the regulation of lovastatin biosynthesis in A. terreus. Under all cultivation conditions, in complex and defined media, A. terreus produced neither monacolin J nor monacolin L nor mevastatin.

Polyketides in Aspergillus terreus : biosynthesis …

27/11/2000 · Lovastatin is a secondary metabolite produced by Aspergillus terreus

Hypolipidemic agent lovastatin produced by Aspergillus terreus ..

During growth on complex medium (glucose, peptonized milk, and yeast extract), glucose was rapidly metabolized under high oxygen consumption and biomass was formed (Fig. ). Ethanol was also formed, probably as result of a glycolytic overflow. Lactose and ethanol were consumed only after glucose exhaustion. The onset of lovastatin biosynthesis after glucose consumption can be attributed either to relief from carbon catabolite repression or to carbon source limitation. Carbon catabolite repression in Aspergillus is mediated by the negative-acting creA gene product (, ). The binding of protein CreAp to specific promoter sites of structural or regulatory genes involved in the utilization of alternative carbon sources, prevents their expression in the presence of glucose or another repressing carbon source (e.g., for alc genes see reference and for endoglucanase encoded by egl1 see reference ). The utilization of ethanol in A. nidulans is repressed by double lock control by CreAp of activator alcR and structural gene alcA, encoding alcohol dehydrogenase I (). The lovastatin biosynthetic gene cluster consists of 18 putative open reading frames (ORFs) (), among which 2 were annotated to encode regulatory proteins, lovE and ORF 13. Analysis of the lovastatin biosynthetic gene cluster revealed that closely spaced SYGGRG consensus sequences, the motif of functional CreAp binding sites in vivo (), are present in the 5′-proximal region of ORF 13 [SYGGRG(N)15SYGGRG] and in the putative promoter of the divergently transcribed ORF 8 and lovE [SYGGRG(N)7CYCCRW]. The presence of putative functional CreAp binding sites in two putative regulatory genes suggests that repression of lovastatin biosynthesis by glucose could be mediated by CreAp. Other carbon catabolite repression mechanisms might also be involved. Glucose represses penicillin synthesis in P. chrysogenum () by repressing pcbAB, pcbC, and penD, whereas in A. nidulans only pcbC is strongly repressed by glucose. In both species glucose repression of penicillin biosynthesis is not exclusively mediated by creA () but is mediated by another putative DNA-binding protein ().

Chisti, “Production of lovastatin by Aspergillus terreus: ..

Since growth requirements of A. terreus are limited, a chemically defined medium could be developed. The buffer capacity of this medium allowed us to keep the pH between 6.2 and 7.0. In the defined medium, all nitrogen sources tested (Table ) were consumed, which was confirmed by biomass formation. However, lovastatin biosynthesis proved dependent on the nitrogen source, as no lovastatin was detected during cultivation in presence of ammonium, nitrate, or urea (Table ). Only glutamate and histidine, and to a lesser extent glycine, supported lovastatin biosynthesis. Study of NAD- and NADP-glutamate dehydrogenase showed that glutamate and histidine play a key role in generation of idiophase conditions by the formation of α-ketoglutarate, which stimulates aflatoxin formation by inhibition of the tricarboxylic acid cycle (). The influence of nitrogen sources on secondary metabolism has been illustrated for fumonisin B1 biosynthesis in Gibberella fujikuroi (), for sterigmatocystin () and aflatoxin (, ) biosynthesis in Aspergillus nidulans and Aspergillus parasiticus, and for penicillin synthesis in Penicillium chrysogenum ().

terreus Biosynthesis of Lovastatin ..

Batch experiments on lactose as the unique carbon source showed that lactose was consumed by A. terreus (Fig. ) but consumption stopped when the residual concentration was 25 g liter−1. Lovastatin biosynthesis was low during ethanol and glycerol consumption in shake flasks (Table ). As nonrepressing carbon sources, lactose, ethanol, and glycerol cannot activate CreAp. Interestingly, lovastatin biosynthesis started only when lactose consumption had stopped. This suggests that lovastatin synthesis was elicited at the cessation of substrate consumption or growth limitation, i.e., under starvation conditions. The role of starvation in secondary metabolism was illustrated in Trichoderma atroviride, in which chitinase gene ech42 is only expressed after glucose or glycerol starvation (). An implication of starvation as an eliciting factor has been demonstrated for the induction of sterigmatocystin in A. nidulans (, ). The transcriptional regulator aflR is regulated by flbA, fluG, and aflR, showing that both asexual sporulation and sterigmatocystin require inactivation of proliferative growth through inhibition of fadA-dependent signaling (). In A. nidulans, brlA plays a central role in the switch from vegetative growth to sporulation, and glucose starvation induces high expression levels of brlA ().

terreus towards lovastatin biosynthesis.

In filamentous fungi many secondary metabolites with complex chemical structure are synthesized via the polyketide pathway (, , ). Lovastatin, monacolin J, monacolin L, and mevastatin can be produced by Monascus ruber (), Penicillium brevicompactum, and Aspergillus terreus (, ). Lovastatin is an inhibitor of the enzyme hydroxymethylglutaryl coenzyme A (HMG-CoA) reductase (mevalonate:NADP+ oxidoreductase [EC ]) that catalyzes the reduction of HMG-CoA to mevalonate during synthesis of cholesterol (, , ). The biosynthetic pathway of lovastatin in A. terreus has been investigated by nuclear magnetic resonance and mass spectroscopy (, , ). These studies concluded that lovastatin is composed of two distinct polyketide chains joined through an ester linkage. Proof that these two polyketides are assembled by two discrete polyketide synthases came from the cloning and partial characterization of the lovastatin biosynthetic gene cluster from A. terreus (, ).

Aspergillus terreus - Wikipedia

Lovastatin is a secondary metabolite produced by Aspergillus terreus. A chemically defined medium was developed in order to investigate the influence of carbon and nitrogen sources on lovastatin biosynthesis. Among several organic and inorganic defined nitrogen sources metabolized by A. terreus, glutamate and histidine gave the highest lovastatin biosynthesis level. For cultures on glucose and glutamate, lovastatin synthesis initiated when glucose consumption levelled off. When A. terreus was grown on lactose, lovastatin production initiated in the presence of residual lactose. Experimental results showed that carbon source starvation is required in addition to relief of glucose repression, while glutamate did not repress biosynthesis. A threefold-higher specific productivity was found with the defined medium on glucose and glutamate, compared to growth on complex medium with glucose, peptonized milk, and yeast extract.