## 1 Introduction
Dab (1) is part of a linear tripeptide segment Dab(1)-Thr(2)- Dab(3)-. Dab (4) is involved in formation of a heptapeptide ring by condensation of its free amino group with the carboxyl group of the C-terminal Thr (10). The heptapeptide ring harbors a variable motif at positions R(6) and R(7). These residues appearing in D-configuration are specific for the polymynxin type and can therefore be used for the classification of these antibiotics. The therapeutically most important species are polymxin B [17] and polymynxin E (colistin) [33; 34; 35]. Polymyrins E are produced by _P. polymyna_ DSM 32871. Here, positions 6 and 7 are occupied by two leucine residues, while for polymynxin B Leu (6) is replaced by Phe. The corresponding motif of polymynxin P produced by strain M1 is D-Phe-D-Thr [36; 37]. Polymynin B and E species showing numerous variations both in their fatty acid side chain as well as by amino acid substitutions in their peptide portion were extensively characterized by liquid chromatography electrospray ionization ion trap tandem mass spectrometry [38; 39; 40]. Biosynthesis of fusaricidins and polymyxins is accomplished nonribosomally at multifunctional protein templates. Fusaricidin formation is encoded by the _fus_ gene cluster. Fusaricidin synthetase FusA, the gene product of the central _fusA_ gene, consists of six modules for activation and condensation of all six amino acid components forming the complete peptide chain of fusaricidin [10]. Gene clusters _pmx_ responsible for the biosynthesis of polymyxins A, B, E and P were identified and sequenced from the genomes of their producer organisms [41; 42; 43; 44]. In each case _pmx_ comprises genes for three peptide synthetases and two putative ABC transporters. Polymyxin synthetase is a complex of three multienzymes PmxA, B and E. PmxE is a five module multienzyme, activating and condensing the first five amino acid components of polymyxins forming the pentapeptide intermediate L-Dab-L-Thr-  
PmxA contains four modules specific for the next four amino acid substrates extending the growing peptide chain until the nonapeptide. Finally, polymyxin synthesis is terminated by PmxB containing the module specific for the C-terminal L-Thr residue together with a thioester domain. The structural complexity of lipopeptides, such as fusaricidins and polymyxins, is not obvious from the gene level, but depends on the relatively high substrate variability at the reaction centers of the involved NRPS producer multienzymes. Polymyxins are in focus as last resort antibiotics against multiresistant Gram-negative pathogens, such as the majority of _Enterobacteriaceae_, _K. pneumoniae_, _A. baumannii_ or _P. aeruginosa_[45; 46]. The therapeutic application of polymyxins certainly is the most important public interest, but beyond this there are also promising aspects for their usage as biocontrol agents in plant biotechnology. Recently, polymyxin P was demonstrated to suppress phytopathogenic _Erwinia_ spp., the causative pathogen of fire blight and soft rot diseases [44]. Another class of attractive microbial secondary metabolites exhibiting manifold important activities are volatile organic compounds (VOCs), which display high chemical diversity [47; 48; 49]. They gain increasing attention particularly concerning plant growth promotion [50; 51; 52], biocontrol against bacterial and fungal pathogens [51; 52] and induction of systemic resistance against phytopathogens [53; 54; 55]. In our work we performed comprehensive studies on the variety of the fusaricidin and polymyxin lipopeptide complexes produced by _P. polymyxa_ DSM 32871 and M1 by MALDI-TOF mass spectrometry. These antifungal and antibacterial agents are of high relevance for inactivation of both human and plant pathogens. In addition, the diversity of volatile organic compounds (VOCs) released by these strains was studied with a specific headspace GC-MS analysis method under different growth conditions.