Volatile organic compounds from Bacillus, Serratia and Pseudomonas promote growth and alter the transcriptional landscape of Solanum tuberosum in a passively-ventilated growth system

The interaction of an array of volatile organic compounds (VOCs) termed bacterial volatile compounds (BVCs) with plants is now a major area of study under the umbrella of plant-microbe interactions. Many growth systems have been developed to mediate the investigation of these interactions in vitro. However, each of these systems have their benefits and drawbacks with respect to one another and can greatly influence the end-point interpretation of the BVC effect on plant physiology. To address the need for novel growth systems in BVC-Plant interactions our study investigated the use of a passively-ventilated growth system, made possible via Microbox® growth chambers, to determine the effect of BVCs emitted by six bacterial isolates from the genera Bacillus, Serratia and Pseudomonas. Solid-phase microextraction/GC-MS was utilized to determine the BVC profile of each bacterial isolate when cultured in three different growth media each with varying carbon content. 70 BVCs were identified in total with alcohols and alkanes being the most abundant. When cultured in tryptic soy broth, all six isolates were capable of producing 2,5-dimethylpyrazine, however BVC emission associated with this media were deemed to have negative effects on plant growth. The two remaining media types, namely Methyl Red-Voges Proskeur and Murashige and Skoog, were selected for bacterial growth in co-cultivation experiments with Solanum tuberosum cv. 'Golden Wonder'. The BVC emissions of Bacillus and Serratia isolates cultured on MR-VP induced alterations in the transcriptional landscape of potato across all treatments with 956 significantly differentially expressed genes. Our results indicate that this novel approach to determining BVC-mediated growth effects on plants is a viable alternative and induced differential growth-promotion based on bacterial isolate and the respective media type on which they were cultured. Surprisingly, genes associated with plant defence were often observed to be downregulated in our system whereas genes associated with photosynthesis and plant cell division were upregulated. Overall design: Exposure of potato to bacterial volatile organic compounds. Study included 4 treatments to plants; absolute controls, controls grown in proximity to axenic MR-VP media, plants exposed to FZB24 Bacillus VOC's, plants exposed to LAC2 Serratia VOC's. Each treatment consisted of three replicates. Each replicate comprised RNA from 4 individual plants. Plants were exposed to treatments for 4 weeks. Experiments took place in microbox growth chambers, with 18/6 hour day/night exposure to light.