ABSTRACT
At present, headspace analyses of around 490 microbial species resulted in the identication of around 1200 volatiles (for review, see Effmert et al. 2012; Lemfack et al. 2014; Schulz and Dickschat 2007), which are divided into 48 chemical classes dominated by alcohols, alkenes, ketones, and terpenoids (Wenke et al. 2012b). Due to the incredible microbial diversity (10,000 species are known, more than 1 million are expected on Earth) it is foreseen that the actual number of known microbial volatiles represents just the “tip of the iceberg.” Furthermore, microorganisms have not been systematically investigated regarding their capabilities of volatile emissions but the present available results indicate that microbes are a good source for novel and unusual volatiles (Lemfack et al. 2014; Von Reuss et al. 2010). The biological and ecological functions of mVOCs are diverse, for example: (i) they play a role in the food chain of the microbial loop since they are assimilated and incorporated into organic matter (bioconversion); (ii) they inuence physiological processes in various target organisms (e.g., laccase activity, nitrication, and nitrogen mineralization); (iii) they function as electron acceptors or donors to support metabolic reactions; (iv) they play a role in quorum sensing/quenching; (v) they act as defense compounds against fungi, nematodes/animals, and bacteria; (vi) they act as communication signals; or (vii) their functions remain to be elusive (summarized in Effmert et al. 2012; Kai et al. 2009; Wenke et al. 2010 and 2012). Nevertheless, the detailed reactions and adaptations at the physiological, transcriptional, protein and metabolic levels of the target organisms were only recently investigated (Bailly and Weisskopf 2012; Wenke et al. 2012a).
