Development of a Basic Biosensor System for Wood Degradation using Volatile Organic Compounds

Abstract

Wood inspection and durability testing of wood against microorganisms, as fungi, play an important role in forestry and wood-related material industries. An efficient testing method is required in order to facilitate inspections and to provide the accurate and precise assessment process. Monitoring volatile organic compounds (VOCs) released from wood substrates and from fungal metabolisms are marker compounds of the wood condition, i.e., indicating the type and stage of fungal infection. Insect antennae, which are recognised for their high sensitivity and selectivity in odour perception, are an alternative method for wood testing. On the basis of intact insect antenna biosensor it is possible to monitor wood released VOCs with high selectivity. This technique can be a complement to the traditional wood testing methods, providing a high throughput and non-destructive method. This work was begun with the investigation of VOCs released from four different types of samples with gas chromatography-mass spectrometry. Firstly, VOCs from beech wood (Fagus sylvatica) infected with three wood rotting fungi; Trametes versicolor, Poria placenta, and Gloeophyllum trabeum were analysed. These fungi are commonly used in the durability testing of wood against microorganisms. The VOCs released from the fungal-infected beech showed species specific volatile patterns. The volatiles were grouped to five- and to eight- carbon (C5-C8) containing compounds and terpenoids. 1-Octen-3-ol, 3-octanone, and 3-octanol (C8-compounds) were commonly present in all samples, while terpenoids were species specific. α- and β-Barbatene were characteristic of T. versicolor-infected beech, protuillud-6-ene was characteristic of G. trabeum-infected beech, and daucene was characteristic of P. placenta-infected beech. Secondly, VOCs released from the minimally insect-colonised fruiting body (<10%) and fully insect-colonised fruiting body (~100%) of Trametes gibbosa were identified. The minimally insect-colonised fruiting body released 1-octen-3-ol, the typical fungal odour, at almost 20 times higher than in fully insect-colonised fruiting body. Thirdly, VOCs released during the fruiting body development of the ink-cap Coprinopsis cinerea, from the stage of mycelium to fruiting body autolysis, were studied. VOCs patterns of C. cinerea were specifically altered by the developmental stages. 1-Octen-3-ol and 3-octanone were largely released during primodia formation and were gradually reduced in amount in later developmental stages. The terpenoids β-himachalene and cuparene drastically increased when the C. cinerea stipe elongated and became mature. Finally, the volatiles released during fruiting bodies autolysis of C. cinerea and other two ink-cap decomposing fungi (Coprinus comatus, Coprinopsis atramentaria), were investigated. In all three cases, N-containing and S-containing compounds were additionally released during the autolytic stage. The fungivorous beetle Cis boleti (Coloptera: Ciidae) and the fungal associated fly Suillia mikii (Diptera: Heleomizydae) were chosen for examining their olfactory perception since their life cycles are strongly related to fungi. For instance, C. boleti preferentially colonises fungi from the genus Trametes and S. mikii purposely land on the ink-cap fungi at a specific developmental stage. Gas chromatography-mass spectrometry with parallel electroantennographic detection was employed to demonstrate that both insect species are able to perceive the typical fungal odour 1-octen-3-ol with high selectivity and sensitivity. In addition, behavioural tests of C. boleti showed that this insect is able to discriminate the enantiomers of 1-octen-3-ol, where the female beetles were significantly more attracted to the (S)-(+) enantiomer at lower doses than male beetles. The fly S. mikii reproducibly responded to the VOCs 1-undecene, 2-butanone, and dimethyl trisulfide, released from the autolysis fruiting bodies of the ink-cap fungi. The C. boleti antenna perceived the typical fungal odour, 1-octen-3-ol, with high selectivity and sensitivity of down to 5 ng ml-1 in air. The antenna life time lasted up to one day. Consequently, as a proof of principle C. boleti antenna was used as a biocomponent in a biosensor system for testing beech wood samples infected by T. versicolor. The biosensor system using the superposition method in combination with a recalibration system was adopted. In this configuration C. boleti antenna yielded reproducible responses to the fungal marker volatile compound released from fungal-infected beech wood. Altogether these results lead to a promising possibility to set up a biosensor based on intact antenna as a highly sensitive and selective testing method for wood durability against decay fungi.