Self-sensing in Bacillus subtilis quorum-sensing systems

Abstract

Bacterial cell-cell signaling, or quorum sensing, is characterized by the secretion and group-wide detection of small diffusible signal molecules called autoinducers. This mechanism allows cells to coordinate their behavior in a density-dependent manner. A quorum-sensing cell may directly respond to the autoinducers it produces in a cell-autonomous and quorum-independent manner, but the strength of such self-sensing effect and its impact on bacterial physiology are unclear. Here, we explored the existence and impact of self-sensing in the Bacillus subtilis ComQXP and Rap-Phr quorum-sensing systems. By comparing the quorum-sensing response of autoinducer-secreting and non-secreting cells in co-culture, we found that secreting cells consistently showed a stronger response than non-secreting cells. Combining genetic and quantitative analyses, we demonstrated this effect to be a direct result of self-sensing and ruled out an indirect regulatory effect of the autoinducer production genes on response sensitivity. In addition, self-sensing in the ComQXP system affected persistence to antibiotic treatment. Together, these findings indicate the existence of self-sensing in the two most common designs of quorum-sensing systems of Gram-positive bacteria.

Environmental sensing in dynamic quorum responses

“…S14, Movie 17-19) . The higher-than-basal levels of AI produced by the induced subpopulation could be key to the maintenance of the high stable state of expression of QS genes 37,38 in the presence of active environmental suppression. Indeed, simultaneous induction and repression with exogenous AI and glucose, respectively, stably maintained an induced subpopulation (Fig.…”

Intracellular signaling through thecomRSsystem inStreptococcus mutansgenetic competence

“…They argued that ComS does not diffuse through or accumulate in the medium, although it may be able to signal between cells that are in physical contact. This proximity model for ComS resembles a “self-sensing” quorum system [31] in which the secreted signal is retained at elevated concentrations in the immediate surroundings of the cell, possibly associated with the cell surface, so that the cell responds somewhat more strongly to its own secreted signal than to that of the rest of the population.…”

“…Individual feedback can convert a graded (or unimodal) population response to a switched or bimodal response [38]. Depending on parameters such as the rate of signal production, noise levels or the cell density, the response of the cells may then span a range from strongly social or quorum behavior to purely autocrine or self-sensing [31] behavior in which cells respond independently and the population becomes heterogeneous [39]. Synthetic biology has exploited this phenomenon in several bacterial quorum sensing systems to amplify the cell’s sensitivity to an exogenous signal.…”

Ratiometric population sensing by a pump-probe signaling system in Bacillus subtilis

“…Theoretically, they could indeed function as sensitive devices for cell-density monitoring 12 , but whether RRNPP signaling networks actually implement a "quorum-sensing" type of regulation has been questioned 13,14 . They have also been hypothesized to function as timers for (multi-)cellular development [15][16][17] , to coordinate the development of cellular subpopulations 18,19 and, under certain conditions, signaling could be self-directed and act in cis rather than in trans 20 . It is indeed conceivable that the more complex pump-probe network architecture allows for different types of extracellular information processing.…”