Co-cultivation of the endophyte Chaetomium sp. with an autoclaved Gram-negative bacterium Pseudomonas aeruginosa on rice medium afforded six new compounds, including cheatoisochorismin (1), shikimeran B (2) and four new butenolide derivatives (3–6) [1]. Among the isolated compounds, chaetoisochorismin (1) features a rare 3-carbomethoxy-phenylpyruvate core structure, which is proposed to be biosynthetically derived from isochorismic acid [2,3]. The structures of the new compounds were elucidated by HRESIMS, 1D and 2D NMR analysis. The absolute configurations of 1 and 2 were established by ECD calculations as well as by the modified Mosher’s method. In addition, co-cultivation of Chaetomium sp. with P. aeruginosa resulted in an up to 33-fold increase of the accumulation of constitutively present fungal secondary metabolites compared to the axenic fungal control. Notably, the employed experimental protocol included autoclavation of P. aeruginosa after four-day preincubation, which offers a safer experimental alternative in comparison with mixed fermentation employing living human pathogenic bacterial cultures. Thus, the results of this work support the potential of mixed co-cultivation experiments with P. aeruginosa and serve as a further example of the successful application of co-culture as an important tool to trigger biosynthesis of new compounds and accumulation of constitutively present metabolites.
References:
[1] Ancheeva E, Küppers L, Akone S, Ebrahim W, Liu Z, Mandi A, Kurtan T, Lin W, Orfali R, Rehberg N, Kalscheuer R, Daletos G, Proksch P. Eur J Org Chem 2017; [Accepted manuscript]
[2] Zamir L O, Nikolakakis A, Bonner C A, Jensen R A. Bioorg Med Chem Lett 1993; 3: 1441–1446.
[3] DeClue M S, Baldridge K K, Kast P, Hilvert D. J Am Chem Soc 2006; 128: 2043–2051.
