Background Marine bacteria form complex relationships with eukaryotic hosts, from obligate symbioses to pathogenic interactions. These interactions can be tightly regulated by bioactive molecules, creating a complex system of chemical interactions through which these species chemically communicate thereby directly altering the host’s physiology and community composition. Quorum sensing (QS) signals were first described in a marine bacterium four decades ago, and since then, we have come to discover that QS mediates processes within the marine carbon cycle, affects the health of coral reef ecosystems, and shapes microbial diversity and bacteria-eukaryotic host relationships. Yet, only recently have alkylquinolone signals been recognized for their role in cell-to-cell communication and the orchestration of virulence in biomedically relevant pathogens. The alkylquinolone, 2-heptyl-4-quinolone (HHQ), was recently found to arrest cell growth without inducing cell mortality in selected phytoplankton species at nanomolar concentrations, suggesting QS molecules like HHQ can influence algal physiology, playing pivotal roles in structuring larger ecological frameworks. Results To understand how natural communities of phytoplankton and bacteria respond to HHQ, field-based incubation experiments with ecologically relevant concentrations of HHQ were conducted over the course of a stimulated phytoplankton bloom. Bulk flow cytometry measurements indicated that, in general, exposure to HHQ caused nanoplankton and prokaryotic cell abundances to decrease. Amplicon sequencing revealed HHQ exposure altered the composition of particle-associated and free-living microbiota, favoring the relative expansion of both gamma- and alpha-proteobacteria, and a concurrent decrease in Bacteroidetes. Specifically, Pseudoalteromonas spp., known to produce HHQ, increased in relative abundance following HHQ exposure. A search of representative bacterial genomes from genera that increased in relative abundance when exposed to HHQ revealed that they all have the genetic potential to bind HHQ. Conclusions This work demonstrates HHQ has the capacity to influence microbial community organization, suggesting alkylquinolones have functions beyond bacterial communication and are pivotal in driving microbial community structure and phytoplankton growth. Knowledge of how bacterial signals alter marine communities will serve to deepen our understanding of the impact these chemical interactions have on a global scale. Electronic supplementary material The online version of this article (10.1186/s40168-019-0711-9) contains supplementary material, which is available to authorized users.

A metal ion plasma thruster (MIPT) structure using a trumpet-shaped insulated anode with double micropores (TsIADM), which consists of a frustum-cone-shaped cathode, insulating sleeve, trumpet-shaped anode and anodic insulating layer with double micropores, is proposed. The differences in discharge characteristics and propulsion performance of the TsIADM-MIPT and two other structures, a trumpet-shaped semi-insulated anode MIPT and a conventional trumpet-shaped exposed anode (TsEA) MIPT, are compared and analyzed. Furthermore, the influence that the position of the double micropores has on the MIPT performance is discussed. The results show that the thrust and thrust-to-power ratio are all largest when the double micropores are set at the top end of the inner insulating layer of the trumpet-shaped anode (TsIADM(T)-MIPT). When compared with the TsEA-MIPT, the TsIADM(T)-MIPT demonstrates thrust and thrust-to-power ratios that are improved by 11.6 and 9.5 times respectively. The discharge parameters show that the number of charged particles flowing into the anode in a single shot decreases obviously when adopting the TsIADM(T). The discharge phenomena indicate that compared with the TsEA-MIPT, the luminescence intensity and ejection performance of the plasma plume using the TsIADM(T)-MIPT increases significantly.When the capacitor energy of the system is 5 J, Langmuir probe data show that the plasma density and plasma propagation speed are increased by 16.5 and 4.6 times respectively. These results are believed to be fundamental to the physical mechanisms behind the increased thrust and thruster-to-power ratio of the TsIADM(T)-MIPT.

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To improve the performance of a metal ion plasma jet in vacuum discharge, an anode-insulated cone-cylinder electrode with insulating sleeve is proposed in this paper. Discharge characteristics and generation characteristics of plasma of the electrode are investigated, effects of diameter of insulating sleeve, variety of cathode material and length of the insulating sleeve on characteristics of metal ion plasma jet are discussed. Results indicate that a directional and steady plasma jet is formed by using the novel electrode with insulating sleeve under high vacuum conditions. Moreover, the properties of metal ion plasma jet are improved by using the aluminum cathode and thin and long insulating sleeve. The study provides strong support for research of vacuum metal ion plasma thruster and ion implantation technology.

Five trans-A2B-type cobalt corroles with different substituents at the 5,15 meso-phenyl positions exhibit an excellent third-order nonlinear optical performance.