No abstract

Background Biofilms with immobilized cells encased in extracellular polymeric substance are beneficial for industrial fermentation. Their formation is regulated by various factors, including nitric oxide (NO), which is recognized as a quorum-sensing and signal molecule. The mechanisms by which NO regulates bacterial biofilms have been studied extensively and deeply, but were rarely studied in fungi. In this study, we observed the effects of low concentrations of NO on biofilm formation in Saccharomyces cerevisiae. Transcriptional and proteomic analyses were applied to study the mechanism of this regulation. Results Adding low concentrations of NO donors (SNP and NOC-18) enhanced biofilm formation of S. cerevisiae in immobilized carriers and plastics. Transcriptional and proteomic analyses revealed that expression levels of genes regulated by the transcription factor Mac1p was upregulated in biofilm cells under NO treatment. MAC1 promoted yeast biofilm formation which was independent of flocculation gene FLO11 . Increased copper and iron contents, both of which were controlled by Mac1p in the NO-treated and MAC1 -overexpressing cells, were not responsible for the increased biofilm formation. CTR1 , one out of six genes regulated by MAC1 , plays an important role in biofilm formation. Moreover, MAC1 and CTR1 contributed to the cells’ resistance to ethanol by enhanced biofilm formation. Conclusions These findings suggest that a mechanism for NO-mediated biofilm formation, which involves the regulation of CTR1 expression levels by activating its transcription factor Mac1p, leads to enhanced biofilm formation. The role of CTR1 protein in yeast biofilm formation may be due to the hydrophobic residues in its N-terminal extracellular domain, and further research is needed. This work offers a possible explanation for yeast biofilm formation regulated by NO and provides approaches controlling biofilm formation in industrial immobilized fermentation by manipulating expression of genes involved in biofilm formation. Electronic supplementary material The online version of this article (10.1186/s13068-019-1359-1) contains supplementary material, which is available to authorized users.

The operating characteristic of two-phase rotating detonation fueled by kerosene in a hollow combustor with the isolation section is experimentally studied. When the air mass flow rate is 1.5 kg/s, the equivalence ratio is 0.98, and the total temperature of the mixture is 650 K, the stable rotating detonation wave (RDW) is obtained, which verifies the feasibility of the designed two-phase rotating detonation combustor (RDC). It is found that there is a high-frequency oblique shock induced by the upstream rotating detonation wave in the isolation section. A series of experimental tests have been carried out by changing the total temperature of incoming air , which is an important factor affecting the initiation. When the equivalent ratio of reactants is between 0.950–1.152, a stable single-wave detonation is formed. With the increase of equivalent ratio, the time of detonation wave establishment decreases, the intensity and frequency of detonation wave increases, and the temperature of engine tail flame rises. The equivalent chamber pressure Δpφ was defined, and the curve of the performance of the RDC with the equivalent ratio was obtained. The velocity of the RDW increases with the increase of equivalent ratio, and the chamber pressure has an optimal value, a higher or lower equivalent ratio will lead to the decrease of equivalent chamber pressure and the combustion chamber performance.

The power network's operation security contributes to the power grid's smooth operation. Aiming at the problem that each network node in the conventional power communication network attack penetration system is fragile, and the global network attack graph cannot be generated, which leads to the failure of the network attack penetration vulnerability test, this study introduces the knowledge map into it and designs a power communication network attack penetration test system. In hardware, the FPGA chips and RAM are designed. In terms of software, the software architecture of the test system is established to control the network attack penetration globally, and then the knowledge map is used to construct the communication network attack graph model and generate the network global attack graph, so as to realize the effective test of the electric power communication network attack penetration vulnerability. By using the method of system testing, it is verified that the number of vulnerabilities tested by the system is consistent with the actual situation, and it can be applied to real life.

No abstract