A novel Rap-Phr system in Bacillus velezensis NAU-B3 regulates surfactin production and sporulation via interaction with ComA.

Several quorum sensing systems occurring in Bacillus subtilis, e.g. Rap-Phr systems, were reported to interact with major regulatory proteins, such as ComA, DegU, and Spo0A, in order to regulate competence, sporulation, and synthesis of secondary metabolites. In this study, we characterized a novel Rap-Phr system, RapA4-PhrA4, in Bacillus velezensis NAU-B3. We found that the rapA4 and phrA4 genes were co-transcribed in NAU-B3. When rapA4 was expressed in the heterologous host Bacillus subtilis OKB105, surfactin production and sporulation were severely inhibited. However, when the phrA4 was co-expressed, the RapA4 activity was inhibited. The transcription of the surfactin synthetase srfA gene and sporulation-related genes were also regulated by the RapA4-PhrA4 system. In vitro results obtained from electrophoretic mobility shift assay (EMSA) proved that RapA4 inhibits ComA binding to the promoter of the srfA operon, and the PhrA4 pentapeptide acts as anti-activator of RapA4. We also found that the F24 residue plays a key role in RapA4 function. This study indicated that the novel RapA4-PhrA4 system regulates the surfactin synthesis and sporulation via interaction with ComA, thereby supporting the bacterium to compete and to survive in a hostile environment. KEY POINTS: •Bacillus velezensis NAU-B3 has a novel Rap-Phr quorum sensing system, which does not occur in model strains Bacillus subtilis 168 and B. velezensis FZB42. •RapA4-PhrA4 regulates surfactin production and sporulation. •RapA4-PhrA4 interacts with the ComA protein from ComP/ComA two-component system.

A Prospective Randomized Multicenter Controlled Trial on Salvianolate for Treatment of Unstable Angina Pectoris in A Chinese Elderly Population.

OBJECTIVE: To evaluate the efficacy and safety of salvianolate in elderly patients with unstable angina pectoris (UAP). METHODS: A prospective double-blind randomized placebo-controlled multicenter trial in elderly patients with UAP from 13 third-grade class-A hospitals in China was performed. A total of 318 patients were randomly allocated in a 1:1 ratio to an experimental group (160 patients) and a control group (158 patients). The experimental group was treated with salvianolate for 14 days on the basis of conventional medicine, and the control group was given a placebo for 14 days with the same criteria. Follow-up was lasted 28 days in both groups. The primary endpoint was biweekly frequency of angina pectoris attacks. The secondary endpoints included biweekly dosage of nitroglycerin, the Seattle Angina Questionnaire, angina pectoris severity and duration, myocardial injury markers, high-sensitivity C-reactive protein (hs-CRP) and N-terminal pro-B-type natriuretic peptide (NT-proBNP), as well as major adverse cardiovascular events (MACEs). Safety was assessed according to adverse events and serious adverse events. RESULTS: Baseline characteristics were similar between treatment groups. Compared with those in the control group, the frequency of biweekly angina attacks (2.92 vs . 4.08, P=0.025), the biweekly dosage of nitroglycerin, as well as the severity and duration of angina attacks (P<0.01) were reduced by salvianolate. The Seattle Angina Questionnaire score was also significantly improved in the experimental group than in the control group (P<0.05). No significant differences were observed between the two groups with respect to the incidence of MACEs. Salvianolate was well tolerated. CONCLUSIONS: Salvianolate appear to have efficacy and well tolerated for elderly patients with UAP. [ClinicalTrials.gov identifier: NCT03037047].

A plasmid-born Rap-Phr system regulates surfactin production, sporulation and genetic competence in the heterologous host, Bacillus subtilis OKB105.

According to the change of environment, soil-dwelling Bacillus species differentiate into distinct subpopulations, such as spores and competent cells. Rap-Phr systems have been found to be involved in this differentiation circuit by interacting with major regulatory proteins, such as Spo0A, ComA, and DegU. In this study, we report that the plasmid-born RapQ-PhrQ system found in Bacillus amyloliquefaciens B3 affects three regulatory pathways in the heterologous host Bacillus subtilis. Expression of rapQ in B. subtilis OKB105 strongly suppressed its sporulation efficiency, transformation efficiency, and surfactin production. Co-expression of phrQ or addition of synthesized PhrQ pentapeptide in vitro could compensate for the suppressive effects caused by rapQ. We also found that expression of rapQ decreased the transcriptional level of the sporulation-related gene spoIIE and surfactin synthesis-related gene srfA; meanwhile, the transcriptional levels of these genes could be rescued by co-expression of phrQ and in vitro addition of PhrQ pentapeptide. Electrophoretic mobility shift (EMSA) result also showed that RapQ could bind to ComA without interacting with ComA binding to DNA, and PhrQ pentapeptide antagonized RapQ activity in vitro. These results indicate that this new plasmid-born RapQ-PhrQ system controls sporulation, competent cell formation, and surfactin production in B. subtilis OKB105.

Plant growth promotion by spermidine-producing Bacillus subtilis OKB105.

The interaction between plants and plant-growth-promoting rhizobacteria (PGPR) is a complex, reciprocal process. On the one hand, plant compounds such as carbohydrates and amino acids serve as energy sources for PGPR. On the other hand, PGPR promote plant growth by synthesizing plant hormones and increasing mineral availability in the soil. Here, we evaluated the growth-promoting activity of Bacillus subtilis OKB105 and identified genes associated with this activity. The genes yecA (encoding a putative amino acid/polyamine permease) and speB (encoding agmatinase) are involved in the secretion or synthesis of polyamine in B. subtilis OKB105. Disruption of either gene abolished the growth-promoting activity of the bacterium, which was restored when polyamine synthesis was complemented. Moreover, high-performance liquid chromatography analysis of culture filtrates of OKB105 and its derivatives demonstrated that spermidine, a common polyamine, is the pivotal plant-growth-promoting compound. In addition, real-time polymerase chain reaction analysis revealed that treatment with B. subtilis OKB105 induced expansin gene (Nt-EXPA1 and Nt-EXPA2) expression and inhibited the expression of the ethylene biosynthesis gene ACO1. Furthermore, enzyme-linked immunosorbent assay analysis showed that the ethylene content in plant root cells decreased in response to spermidine produced by OKB105. Therefore, during plant interactions, OKB105 may produce and secrete spermidine, which induces expansin production and lowers ethylene levels.

[Screening and identification of low temperature-adapted antagonistic Bacillus isolated from Kekexili region of West China and the analysis of the isolates lipopeptide compounds].

The research and exploitation of special microbial resources in extreme environment is of scientific significance and has broad applied prospect. In this paper, eight Bacillus strains isolated from the vegetation rhizospheres in Kekexili extreme region of Qinghai Province and presented good growth status at low temperature 4 and 10 degrees C were identified. Through physiological and biochemical analysis, rep-PCR fingerprinting, and 16S rDNA and gyrB partial sequence analyses, the eight strains were identified as Bacillus mojavensis (3 isolates), Bacillus amyloliquefaciens (1 isolate), and Bacillus simplex (4 isolates). The agar plate antagonistic test showed that four of the isolates presented distinct antagonistic activity to Sclerotinia sclerotiorum and Xanthomonas oryzae pv. oryzae. The MALDI-TOF-MS analysis showed that the strain KKD1 (B. mojavensis) produced fengycin and surfactin, whereas the strain KKD2 (B. amyloliquefaciens) produced iturin A, surfactin and fengycin, suggesting that the bio-control efficacy of the Bacillus strains could be related to the synthesis and excretion of the antifungal lipopeptide compounds. This study provided the bacterial resources for the research and exploitation of low temperature-adapted Bacillus bio-fertilizers and bio-pesticides.

Cloning, expression and characterization of a new aspartate aminotransferase from Bacillus subtilis B3.

In the present study, we report the identification of a new gene from the Bacillus subtilis B3 strain (aatB3), which comprises 1308 bp encoding a 436 amino acid protein with a monomer molecular weight of 49.1 kDa. Phylogenetic analyses suggested that this enzyme is a member of the Ib subgroup of aspartate aminotransferases (AATs; EC 2.6.1.1), although it also has conserved active residues and thermostability characteristic of Ia-type AATs. The Asp232, Lys270 and Arg403 residues of AATB3 play a key role in transamination. The enzyme showed maximal activity at pH 8.0 and 45 °C, had relatively high activity over an alkaline pH range (pH 7.0-9.0) and was stable up to 50 °C. AATB3 catalyzed the transamination of five amino acids, with L-aspartate being the optimal substrate. The K(m) values were determined to be 6.7 mM for L-aspartate, 0.3 mM for α-ketoglutarate, 8.0 mM for L-glutamate and 0.6 mM for oxaloacetate. A 32-residue N-terminal amino acid sequence of this enzyme has 53% identity with that of Bacillus circulans AAT, although it is absent in all other AATs from different organisms. Further studies on AATB3 may confirm that it is potentially beneficial in basic research as well as various industrial applications.

Functional analysis and application of the cryptic plasmid pBSG3 harboring the RapQ-PhrQ system in Bacillus amyloliquefaciens B3.

This work sequenced and characterized a cryptic plasmid called pBSG3 from wild-type Bacillus amyloliquefaciens B3--a powerful agent for suppression of plant pathogenic organisms. It is an 8439 bp circular molecule, with G+C content of 40.3%. We provide evidence that pBSG3 replicates via the rolling-circle (RC) mechanism and, sequence comparisons place it in the pC194 family of rolling-circle-replicons. The plasmid contains seven putative open reading frames (ORFs), including genes repB3, mobB3, rapQ, phrQ, pgsR, and two unknown ORFs (orf1c and orf2). Our observations reveal that the RapQ-PhrQ (response regulator aspartate phosphatase-phosphatase regulator) system is involved in sporulation and RapQ can delay the onset of sporulation. Two Escherichia coli and Bacillus potential shuttle vectors, pTRD (containing the minimal replicon) and pTRDS (containing the minimal replicon and the single-strand origin) were developed from pBSG3 and tested the stability. Moreover, HpaG(xooc) protein, which can induce disease and insect resistance in plants, was tried to express with the stable vector pTRDS in Bacillus subtilis. In summary, the pBSG3 plasmid containing various genes is not only a candidate tool for vector development in Bacillus genus research but also a potential vehicle for the exchange of genetic elements among Bacillus populations that contributes to the survival of bacilli in natural environments.

Assessment of inheritance pattern and agronomic performance of transgenic rapeseed having harpin Xooc-encoding hrf2 gene.

hrf2 gene is a member of the harpin-encoding gene family of rice-pathogenic bacterium Xanthomonas oryzae pv. oryzicola. In our previous studies, we observed that harpin(Xooc) could elicit hypersensitive cell death in non-host plants, induce disease and insect resistance in plants, and enhance plant growth. In this study, the rapeseed cultivar, Yangyou 4, was genetically engineered via Agrobacterium-mediated transformation to express the hrf2 gene. Polymerase chain reaction (PCR) and southern blot analyses of T(1) generation of transgenic rapeseed revealed stable integration and expression of the inserted gene hrf2. In addition, the resistance to Sclerotinia sclerotiorum was greatly enhanced. A comparison between agronomic characters of transgenic and control lines displayed significant differences in terms of plant height, stem width, number of pods per plant, number of seeds per pod, 1,000-seed weight, and seed yield per plant. Among lines with resistance to S. sclerotiorum, T(1)1 had improved agronomic traits compared with controls with a 22.7% seed yield increase. These results suggest that the introduction of the hrf2 gene into rapeseed can be an effective strategy for enhancing resistance to S. sclerotiorum.