VN-NDP: A Neighbor Discovery Protocol Based on Virtual Nodes in Mobile WSNs

As an indispensable part of Internet of Things (IoT), wireless sensor networks (WSNs) are more and more widely used with the rapid development of IoT. The neighbor discovery protocols are the premise of communication between nodes and networking in energy-limited self-organizing wireless networks, and play an important role in WSNs. Because the node energy is limited, neighbor discovery must operate in an energy-efficient manner, that is, under the condition of a given energy budget, the neighbor discovery performance should be as good as possible, such that the discovery latency would be as small as possible and the discovered neighbor percentage as large as possible. The indirect neighbor discovery mainly uses the information of the neighbors that have been found by a pairwise discovery method to more efficiently make a re-planning of the discovery wake-up schedules of the original pairwise neighbor discovery, thereby improving the discovery energy efficiency. The current indirect neighbor discovery methods are mainly divided into two categories: one involves removing the inefficient active slots in the original discovery wake-up schedules, and the other involves adding some efficient active slots. However, the two categories of methods have their own limitations. The former does not consider that this removal operation destroys the integrity of the original discovery wake-up schedules and hence the possibility of discovering new neighbors is reduced, which adversely affects the discovered neighbor percentage. For the latter category, there are still inefficient active slots that were not removed in the re-planned wake-up schedules. The motivation of this paper is to combine the advantages of these two types of indirect neighbor discovery methods, that is, to combine the addition of efficient active slots and the removal of inefficient active slots. To achieve this goal, this paper proposes, for the first time, the concept of virtual nodes in neighbor discovery to maximize the integrity of the original wake-up schedules and achieve the goals of adding efficient active slots and removing inefficient active slots. Specifically, a virtual node is a collaborative group that is formed by nodes within a small range. The nodes in a collaborative group share responsibility for the activating task of one member node, and the combination of these nodes’ wake-up schedules forms the full wake-up schedule of a node that only uses a pairwise method. In addition, this paper proposes a set of efficient group management mechanisms, and the key steps affecting energy efficiency are analyzed theoretically to obtain the energy-optimal parameters. The extended simulation experiments in multiple scenarios show that, compared with other methods, our neighbor discovery protocol based on virtual nodes (VN-NDP) has a significant improvement in average discovery delay and discovered neighbor percentage performance at a given energy budget. Compared with the typical indirect neighbor discovery algorithm EQS, a neighbor discovery with extended quorum system, our proposed VN-NDP method reduces the average discovery delay by up to 10 . 03 % and increases the discovered neighbor percentage by up to 18 . 35 % .

Prospects of using Avocado oil for attenuating quorum sensing regulated virulence, bio-filming formation and its antibacterial and antioxidant activities

Background: Quorum sensing inhibition (QSI) is considered as an attractive strategy for the development of anti-pathogenic agents, mainly for drug resistant bacteria. Methods: The anti-quorum sensing activity was investigated by biosensor bioassay using Chromobacterium violaceum CVO26 and Pseudomonas aeruginosa PAO1. Quorum sensing is a key regulator of virulence factors of Pseudomonas aeruginosa such as bio-film formation, motility, productions of proteases, hemolysin, and Pyocyanin production. Additionally, the GC/MS technique was employed to detect the essential components of avocado oil. Results: Avocado oil inhibits quorum system-mediated virulence factor production such as violacein in C. Violaceum CVO26 and elastase, Pyocyanin production in Pseudomonas aeruginosa PAO1. Additionally, the use of sub-minimum inhibitory concentrations (sub-MICs) of avocado oil significantly inhibits the quorum system-mediated biofilm formation, exopolysaccride production (EPS) and swarming motility. Furthermore, this study concerned the potent activity of avocado oil antibacterial and antioxidant agent. Moreover, a total of 23 components was identified in avocado oil by GC/MS. Conclusion: Avocado oil could be exploited as a natural source of anti-pathogenic, where the pathogenicity is mediated through quorum sensing, antibacterial as well as antioxidant agents.

Intracellular Signaling by thecomRSSystem inStreptococcus mutansGenetic Competence

ABSTRACTEntry into genetic competence in streptococci is controlled by ComX, an alternative sigma factor for genes that enable the import of exogenous DNA. InStreptococcus mutans, the immediate activator ofcomXis the ComRS quorum system. ComS is the precursor of XIP, a seven-residue peptide that is imported into the cell and interacts with the cytosolic receptor ComR to form a transcriptional activator for bothcomXandcomS. Although intercellular quorum signaling by ComRS has been demonstrated, observations of bimodal expression ofcomXsuggest thatcomRSmay also function as an intracellular feedback loop, activatingcomXwithout export or detection of extracellular XIP. Here we used microfluidic and single-cell methods to test whether ComRS induction ofcomXrequires extracellular XIP or ComS. We found that individualcomS-overexpressing cells activate their owncomX, independently of the rate at which their growth medium is replaced. However, in the absence of lysis they do not activatecomS-deficient mutants growing in coculture. We also found that induction ofcomRandcomSgenes introduced intoEscherichia colicells leads to activation of acomXreporter. Therefore, ComRS control ofcomXdoes not require either the import or extracellular accumulation of ComS or XIP or specific processing of ComS to XIP. We also found that endogenously and exogenously produced ComS and XIP have inequivalent effects oncomXactivation. These data are fully consistent with identification of intracellular positive feedback incomStranscription as the origin of bimodalcomXexpression inS. mutans.IMPORTANCEThe ComRS system can function as a quorum sensing trigger for genetic competence inS. mutans. The signal peptide XIP, which is derived from the precursor ComS, enters the cell and interacts with the Rgg-type cytosolic receptor ComR to activatecomX, which encodes the alternative sigma factor for the late competence genes. Previous studies have demonstrated intercellular signaling via ComRS, although release of the ComS or XIP peptide to the extracellular medium appears to require lysis of the producing cells. Here we tested the complementary hypothesis that ComRS can drivecomXthrough a purely intracellular mechanism that does not depend on extracellular accumulation or import of ComS or XIP. By combining single-cell, coculture, and microfluidic approaches, we demonstrated that endogenously produced ComS can enable ComRS to activatecomXwithout requiring processing, export, or import. These data provide insight into intracellular mechanisms that generate noise and heterogeneity inS. mutanscompetence.