## 3 Discussion  
In this work we investigated the biosynthetic potential of the _P. polymyxia_ strains DSM 32871 and M1. Both strains produce among some other bioactive compounds three lipopeptide complexes, the fusaricidins, the polymyxins and the tridecaptins. Our efforts were focused on the mass spectrometric analysis of the fusaricidins and polymyxins formed by the DSM 32871 strain, which were compared with those produced by the well characterized M1 strain [10; 11; 44]. Both lipopeptide families are of high commercial interest because of their potential importance for applications both in agroobiotechnology and medicine. The fusaricidins being the main products of DSM 32871 and M1 are known to exert potent antifungal activities. They show an unusual complexity because of manifold variations both in their peptide moiety as well as in their fatty acid part. For the reference strain M1 more than 80 variants have been reported so far [11]. Interestingly, by MALDI-TOF mass spectrometric analysis of the fusaricidin complex of strain DSM 32871 three novel series of yet unknown fusaricidins were detected specifically when cultivated in the Landy/LOP medium. Prominent mass peaks of high intensity were found for fusaricidin variants modified at the free hydroxyl group of their allo-Thr component in position 4 by esterification with an alanine residue. Small amounts of such species have previously been found also for strain M1 specifically for fusaricidin C and D [10]. Another set of novel fusaricidins was detected, which are modified by an additional OH-group in their fatty acid part, which still remains to be precisely located. Fusaricidins have been utilized for biocontrol of numerous fungal plant diseases [26; 27; 29; 30; 31]. The aim of future studies will be the purification and provision in semi/preparative scale of selected fusaricidins by high resolution separation techniques for biocontrol applications in plant biotechnology. Another prominent lipopeptide family produced by _P. polymyxia_ DSM 32871 and M1 are the polymyxins which are cyclic decapeptides. They are well suited to inactivate Gram-negative pathogens, such as _Klebsiella, Enterobacteriaceae, A. baumannii_ and _P. aeruginosa_[44; 45; 46]. DSM 32871 produces polymyxins E (colistins), while M1 forms polymyxins P. Polymyxins were discovered in 1947 [76] and used for at least two decades as efficient antibiotics. Due to nephrotoxic and neurotoxic side effects they were taken from the market; however, recently polymyxins were retrieved again as last-resort antibiotics to counteract multiresistant super bugs [32; 37; 45; 46]. High financial investment is made in several countries to optimize their structure, activities and pharmacokinetic properties with the aim to create novel efficient agents to contribute to the pertinent problem to overcome antibiotic multiresistance, which is one of the most urgent issues to protect mankind against otherwise invincible dangerous pathogens. By MALDI-TOF mass spectrometric analysis of the polymyxin E and P complexes produced by DSM 32871 and M1 we detected modified minor polymyxin species (see Table 2), which would be worth testing therapeutically. For example, for both polymyxin species we found variants which showed the polymyxin E or P sequence, but in addition contain a residue of 146 Da which could not yet be identified. We hypothesize that they may be glycosylated. The aim of our forthcoming studies will be to isolate and upgrade these variants in pure form by high resolution separation methodology for enabling structure elucidation and clinical testing. Another important aspect of polymyxins is their application as biocontrol agents in agroobiotechnology to inactivate deleterious phytopathogens in order to prevent and cure plant diseases caused by Gram-negative plant pathogenic bacteria. For example, polymyxins P produced by the M1 strain were recently applied successfully against _Erwinia_ strains [44]. In the third part of our work, we investigated the manifold volatile organic compounds (VOCs) produced by _P.