Abstract
Since its introduction from North America, Dendroctonus valens LeConte has become a destructive forest pest in China. Although gut aerobic bacteria have been investigated and some are implicated in beetle pheromone production, little is known about the abundance and significance of facultative anaerobic bacteria in beetle gut, especially with regards to effects of oxygen on their role in pheromone production. In this study, we isolated and identified gut bacteria of D. valens adults in an anaerobic environment, and further compared their ability to convert cis-verbenol into verbenone (a multi-functional pheromone of D. valens) under different O2 concentrations. Pantoea conspicua, Enterobacter xiangfangensis, Staphylococcus warneri were the most frequently isolated species among the total of 10 species identified from beetle gut in anaerobic conditions. Among all isolated species, nine were capable of cis-verbenol to verbenone conversion, and the conversion efficiency increased with increased oxygen concentration. This O2-mediated conversion of cis-verbenol to verbenone suggests that gut facultative anaerobes of D. valens might play an important role in the frass, where there is higher exposure to oxygen, hence the higher verbenone production. This claim is further supported by distinctly differential oxygen concentrations between gut and frass of D. valens females.
Highlights
Symbioses between insects and associated gut microbiota are the driver behind the success of the majority of the destructive pests of forests (Moran et al, 2005; Adams et al, 2011; Sun et al, 2013; Lu et al, 2016)
Host monoterpene α-pinene has been converted to cis- and transverbenol, and myrtenol by bacteria isolated from the bark beetle Ips paraconfusus Lanier (Renwick et al, 1976). α-Pinene is a precursor in the biosynthesis of verbenone, one of the common pheromones of bark beetles (Gitau et al, 2013)
The oxygen levels in the gut of herbivorous insects is considered a low oxygen environment (Johnson and Barbehenn, 2000), and little is known about oxygen levels in the gut lumen and frass of bark beetles
Summary
Symbioses between insects and associated gut microbiota are the driver behind the success of the majority of the destructive pests of forests (Moran et al, 2005; Adams et al, 2011; Sun et al, 2013; Lu et al, 2016). The concentration of verbenone production in D. valens mainly depends upon the rate of conversion of cis-verbenol and transverbenol to verbenone This conversion is an oxidation process, which was proven to be accelerated by gut-associated bacteria (Xu et al, 2015). In this study we have investigated the role of gut bacteria involved in verbenone production in D. valens under anaerobic and low oxygen conditions. The anaerobic bacteria from the guts of D. valens adults in the two life history stages (dispersing and colonizing) were isolated and comparisons of their conversion efficiency of cis-verbenol to verbenone were made under different O2 concentrations. Our findings could further shed light on the role of oxygen on facultative anaerobes in verbenone production and increase understanding of the chemical ecology of red turpentine beetle and bark beetles in general
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