Microbial production of volatile organic compounds in soil microcosms

A study was conducted to evaluate the use of volatile organic microbial metabolites, particularly geosmin and 2-methylisoborneol, as indicators of activity of specific groups of microorganisms (actinomycetes, bacteria, or fungi) in soil. Substrates and selective antibiotics were added to soil microcosms to establish different soil microbial communities; volatile organic compounds (VOCs) in the headspace atmosphere of the microcosms were collected by purge-and-trap methods and analyzed by gas chromatography-mass spectrometry. Treatments differed in total amount of VOCs produced, numbers and kinds of VOCs detected, and in temporal patterns of VOC production. The greatest total amount of VOCs and largest number of different VOCs were produced in the treatment with greatest actinomycetal and bacterial activity, followed by the treatment dominated by fungal activity. Geosmin was occasionally detected in small amounts but only in microcosms with substantial activity of all three groups of microorganisms (actinomycetes, bacteria, and fungi). 2-Methylisoborneol was regularly detected in significant amounts but only in the treatment dominated by actinomycetes and bacteria. Terpenes were the VOCs produced in greatest quantity in the treatment with the most fungal activity. Results indicate that VOCs from soil may provide information as to the nature of the soil microbial community; however, relating the structure of the microbial community to soil VOC emissions is complicated because VOCs present in natural soils may be derived from a variety of sources and their production is strongly influenced by environmental conditions.