Antivirulence strategy comprises of interference with bacterial virulence and/or
cell-to-cell signaling pathways without killing bacteria or preventing their growth
(Rasko and Sperandio 2010 ; LaSarre and Federle 2013 ). One major focus of our
research work onCannabisplants was to study endophyte-mediated attenuation of
virulence factors released by pathogens and not their growth inhibition (Kusari et al.
2014b,d). Our work exemplifies the association ofC. sativaplants with endophytes
under various abiotic and biotic selection pressures leading to the development of
different functional traits; an important one being the“quorum quenching”ability of
endophytes to disrupt the quorum sensing signaling inChromobacterium vio-
laceum. Studies on quorum sensing, an important cell-to-cell communication sys-
tem enabling microbe-microbe interaction, colonization, bacterial pathogenesis and
invasion across populations, have been reported to exhibit immense biotechno-
logical implications in disease management and antibiotic resistance (Hartman et al.
2014 ; Cornforth et al. 2014 ; Safari et al. 2014 ). We used a combination of high
performance liquid chromatography high-resolution mass spectrometry
(HPLC-ESI-HRMSn) and matrix assisted laser desorption ionization imaging
high-resolution mass spectrometry (MALDI-imaging-HRMS) to quantify and
visualize the spatial distribution of cell-to-cell quorum sensing signals ofC. vio-
laceum. We further showed that potent endophytic bacteria harbored inC. sativa
plants can selectively and differentially quench the quorum sensing molecules ofC.
violaceum. N-acylated L-homoserine lactones (AHLs) are released as quorum
signals in Gram negative bacteria whereas oligopeptides in Gram positive ones.
These autoinducers further coordinate communication across pathogenic microbial
populations for invasion, colonization, pathogenesis, thwarting chemical defense
like antibiotics of other microorganisms (Teplitski et al. 2011 ). Therefore, using
combinations of HPLC-HRMS and MALDI MSI, we proved that potent endophytic
bacterial isolates selectively attenuate four different quorum signals, namely the
AHLs [N-hexanoyl-L-homoserine lactone (C6-HSL), N-octanoyl-L-homoserine
lactone (C8-HSL), N-decanoyl-L-homoserine lactone (C10-HSL), and N-
(3-oxodecanoyl)- L-homoserine lactone (3-oxo-C10-HSL)] used byC. violaceum.
This work was supported by further experiments to show significant reduction of
the virulence factor (violacein in this case) by the selected endophytes without
inhibiting growth ofC. violaceum. This work, therefore, affords fundamental
insights into the potential of endophytic bacteria as biocontrol agents against
bacterial pathogens as well as antivirulence agents that might be useful in
quorum-inhibiting therapies. Attenuation of these signals will lead to suppression of
pathogen virulence without introducing additional resistance-inducing selection
pressures (Cegelski et al. 2008 ). Quorum quenching is one of such antivirulence
strategies that are developed by selected endophytic bacteria. Such strategy could
be utilized in biotechnology to inhibit specific mechanisms that promote infection
and are essential to persistence in a pathogenic cascade (for example, binding,
invasion, subversion of host defenses and chemical signaling), and/or cause disease
symptoms (for example, the secretion of toxins), but without affecting the growth.
Further, this interesting concept can be translated in the future to quorum-inhibiting
antivirulence therapies without triggering resistance in bacteria. Antivirulence
20 Cannabis Endophytes and Their Application... 429