Structural Diversity of Bacterial Volatiles
Bacterial volatile organic compounds (VOCs) represent a structurally very broad mixture of compounds, likely not less diverse than plant or animal volatiles. Within this diversity individual compounds might be commonly found in many, often unrelated strai
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Structural Diversity of Bacterial Volatiles Stefan Schulz, Christian Schlawis, Diana Koteska, Tim Harig, and Peter Biwer
Abstract Bacterial volatile organic compounds (VOCs) represent a structurally very broad mixture of compounds, likely not less diverse than plant or animal volatiles. Within this diversity individual compounds might be commonly found in many, often unrelated strains, while others are restricted to a certain group of strains. In addition, strain specific compounds occur. In the following chapter we will describe the reason for this diversity, the use of different biosynthetic pathways for the production of bacterial VOCs. The use of the primary metabolism machinery, the fatty acid and polyketide biosynthetic pathways, the sulfur metabolism, pyrazine and aromatic compound formation, and terpene biosynthesis will be described and the formation of important representative compounds will be discussed. Keywords Fatty acid derivatives · Amino acid derivatives · Terpenes · Sulfur compounds · Aromatic compounds · Lactones
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Introduction
Bacterial volatiles show high structural variability leading to an enormous number of compounds reported so far (Schulz and Dickschat 2007; Lemfack et al. 2018). Before taking a tour through the chemistry and biosynthesis of these diverse structures, the term volatile compound, which are mostly organic (VOC), has to be defined. A simple definition uses the headspace above a bacterial culture as defining space. Every compound that can be trapped from the gas phase (headspace) above the culture is therefore volatile. This can be easily checked by gas chromatography/ mass spectrometry (GC/MS), indicating a molecular weight limit around 300 Da. Usually only one or two functional groups are present, adding to a very often lipophilic character of the VOCs. The 300 Da limit is markedly reduced when the S. Schulz (*) · C. Schlawis · D. Koteska · T. Harig · P. Biwer Institute of Organic Chemistry, Technische Universität Braunschweig, Braunschweig, Germany e-mail: [email protected]; [email protected]; [email protected]; [email protected]; [email protected] © Springer Nature Singapore Pte Ltd. 2020 C.-M. Ryu et al. (eds.), Bacterial Volatile Compounds as Mediators of Airborne Interactions, https://doi.org/10.1007/978-981-15-7293-7_3
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compound is polar due to strong H-bonding, as found, e.g., in amines, diols, or cyclic dipeptides (Groenhagen et al. 2014). Surprisingly, lipophilic VOCs are also emitted into the water phase. Although water solubility is usually low, small amounts of the compounds are dissolved and diffuse through the water phase. This diffusion is believed to be fast (Boland 1995) because most VOCs have a low effective size. This effect originates from their low number of functional groups that hinders hydration due to missing H-bond acceptors or multiple polarized bonds. This is in contrast to other compounds such as antibiotics that usually show a fair number of functional groups, leading to a larger hydration sphere and therefore t
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