RESUMO
Mass spectrometry was applied to the identification of the destruxins (dtxs), cyclic peptides that are commonly produced by the fungal insect-pathogen, Metarhizium anisopliae. The aim of the study was to optimise a methodology in order to firstly determine whether these compounds were present in other species and to determine the effect of differing growth conditions upon the dtx content detected. Matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-ToF-MS) was initially used to analyse the dtxs, but limitations were indicated. Nano-scale high-performance liquid chromatography/electrospray ionisation mass spectrometry (HPLC/ESI-MS) and automated 'data-dependent' tandem mass spectrometric (MS/MS) analysis were also applied, utilising characteristic neutral losses during fragmentation to confirm the presence of the dtxs. This latter approach distinguished the dtx E and B isoforms by retention time and diagnostic neutral losses during fragmentation allowing extraction of the destruxin data from a complex dataset. This process revealed the presence of a number of dtxs in the fungal species Lecanicillium longisporum, a species previously not known to produce dtxs, and dtx production in this species was shown to be significantly higher in aerated cultures compared with still cultures.