Echinocandin B

Echinocandin B (ECB), an echinocandin type of lipopeptide antibiotic produced by Aspergillus nidulans, is a precursor for the synthesis of novel anti-fungal drug - anidulafungin. In this work, a separation strategy involving one-step macroporous resin adsorption chromatography was established for ECB purification from Aspergillus nidulans CCTCC M 2010275 fermentation broth. Among nine macroporous resin adsorbents tested, the non-polar resin HP-20 had the best adsorption and desorption performance. The static equilibrium adsorption data fitted well with the Langmuir equation, and the adsorption kinetic followed the pseudo-second order model. The separation parameters of ECB from broth were optimised by dynamic adsorption/desorption experiments with the column packed with HP-20 resin. Under optimal conditions, the purity increased by 3.8-fold from 23.2% in broth to 88.5% in eluent with 87.1% recovery yield by a one-step treatment. Our study provided a one-step and effective method for large-scale production of ECB, and offered references for separating other echinocandins from broth.

A combination of microbial strain improvement and statistical optimization is investigated to maximize echinocandin B (ECB) production from Aspergillus nidulans ZJB-0817. A classical sequential mutagenesis was studied first by using physical (ultraviolet irradiation at 254 nm) and chemical mutagens (lithium chloride and sodium nitrite). Mutant strain ULN-59 exhibited 2.1-fold increase in ECB production to 1583.1 ± 40.9 mg/L when compared with the parent strain (750.8 ± 32.0 mg/L). This is the first report where mutagenesis is applied in Aspergillus to improve ECB production. Further, fractional factorial design and central composite design were adopted to optimize the culture medium for increasing ECB production by the mutant ULN-59. Results indicated that four culture media including peptone, K2HPO4, mannitol and L-ornithine had significant effects on ECB production. The optimized medium provided another 1.4-fold increase in final ECB concentration to 2285.

Echinocandin B belongs to lipopeptide antifungal antibiotic bearing five types of direct precursor amino acids including proline, ornithine, tyrosine, threonine, and leucine. The objective of this study is to screen over-producing mutant in order to improve echinocandin B production; a stable mutant Aspergillus nidulans ZJB12073, which can use fructose as optimal carbon source instead of expensive mannitol, was selected from thousand isolates after several cycles of UV and microwave irradiation in turn. The results showed that mutant strain ZJB12073 exhibited 1.9-fold improvement in echinocandin B production to 1656.3 ± 40.3 mg/L when compared with the parent strain. Furthermore, the effects of precursor amino acids and some chemicals on echinocandin B biosynthesis in A. nidulans were investigated, respectively. Tyrosine, leucine, and biotin were selected as key factors to optimize the medium employing uniform design method. The results showed that the optimized fermentation medium provided another 63.

Anidulafungin, which noncompetitively inhibits β-(1,3)-D-glucan synthase in fungal cell wall biosynthesis, is the newest antifungal drug to be developed. Echinocandin B deacylase from Actinoplanes utahensis NRRL 12052 catalyzes the cleavage of the linoleoyl group of echinocandin B, a key step in the process of manufacturing anidulafungin. Unfortunately, the natural yield of echinocandin B nucleus is low. In our study, the echinocandin B deacylase gene was systematically overexpressed by genetic engineering in its original producer, A. utahensis, and in the heterologous hosts Streptomyces lividans TK24 and Streptomyces albus. The introduction of additional copies of the gene, under the control of PermE* or its native promoter, into hosts showed significant increases in its transcription level and in the efficiency of the bioconversion of echinocandin B to its nucleus. The conditions for the cultivation and bioconversion of A. utahensis have been optimized further to improve production.