Abstract
Diketopiperazines can be generated by non-enzymatic cyclization of linear dipeptides at extreme temperature or pH, and the complex medium used to culture bacteria and fungi including phytone peptone and trypticase peptone, can also produce cyclic peptides by heat sterilization. As a result, it is not always clear if many diketopiperazines reported in the literature are artifacts formed by the different complex media used in microorganism growth. An ideal method for analysis of these compounds should identify whether they are either synthesized de novo from the products of primary metabolism and deliver true diketopiperazines. A simple defined medium (X. fastidiosa medium or XFM) containing a single carbon source and no preformed amino acids has emerged as a method with a particularly high potential for the grown of X. fastidiosa and to produce genuine natural products. In this work, we identified a range of diketopiperazines from X. fastidiosa 9a5c growth in XFM, using Ultra-Fast Liquid Chromatography coupled with mass spectrometry. Diketopiperazines are reported for the first time from X. fastidiosa, which is responsible for citrus variegated chlorosis. We also report here fatty acids from X. fastidiosa, which were not biologically active as diffusible signals, and the role of diketopiperazines in signal transduction still remains unknown.
Highlights
Xylella fastidiosa has been associated with diseases of economically important crops including citrus, grapevine, plum, almond, peach, and coffee [1]
As part of our continued investigation into C. sinensis, C. limonia and their grafts to determine the chemical basis involved in the interaction between plant-X. fastidiosa and how the rootstock interferes in the metabolism of scion, we recently reported a screening by high performance liquid chromatography-ultraviolet spectroscopy (HPLC-UV) to check whether compounds from secondary metabolites were associated with the citrus infection
Diketopiperazines can be generated by non-enzymatic cyclization of linear dipeptides at extremes of temperature or pH, and the complex medium used to culture X. fastidiosa 9a5c includes phytone peptone and trypticase peptone, which could produce cyclic peptides by heat sterilization [11]
Summary
Xylella fastidiosa has been associated with diseases of economically important crops including citrus, grapevine, plum, almond, peach, and coffee [1]. Molecules 2017, 22, 985; doi:10.3390/molecules22060985 www.mdpi.com/journal/molecules in Brazilian orchards have resulted in an extensive research program starting with the sequencing of the entire genome of X. fastidiosa [2] This Gram-negative bacterium is a fastidious organism that is able to colonize the xylem vessel of several host plants and the cibarium of sharpshooter leafhopper vectors [1]. Campestris genes, including genes associated with the synthesis and perception of a signal molecule that regulates the expression of pathogenicity factors such as plant cell wall degrading enzymes and extracellular polysaccharides [2] It seems that a minimum X. fastidiosa cellular density in the host xylem needs to be reached so that CVC symptoms are observed. This fact strongly suggests that pathogenicity factor synthesis is dependent on a quorum-sensing mechanism
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