The membrane-cytoplasmic linker defines activity of FtsH proteases in Pseudomonas aeruginosa clone C.

Pandemic Pseudomonas aeruginosa clone C strains encode two inner-membrane associated ATP-dependent FtsH proteases. PaftsH1 is located on the core genome and supports cell growth and intrinsic antibiotic resistance, whereas PaftsH2, a xenolog acquired through horizontal gene transfer from a distantly related species, is unable to functionally replace PaftsH1. We show that purified PaFtsH2 degrades fewer substrates than PaFtsH1. Replacing the 31-amino acid-extended linker region of PaFtsH2 spanning from the C-terminal end of the transmembrane helix-2 to the first seven highly divergent residues of the cytosolic AAA+ ATPase module with the corresponding region of PaFtsH1 improves hybrid-enzyme substrate processing in vitro and enables PaFtsH2 to substitute for PaFtsH1 in vivo. Electron microscopy indicates that the identity of this linker sequence influences FtsH flexibility. We find membrane-cytoplasmic (MC) linker regions of PaFtsH1 characteristically glycine-rich compared to those from FtsH2. Consequently, introducing three glycines into the membrane-proximal end of PaFtsH2's MC linker is sufficient to elevate its activity in vitro and in vivo. Our findings establish that the efficiency of substrate processing by the two PaFtsH isoforms depends on MC linker identity and suggest that greater linker flexibility and/or length allows FtsH to degrade a wider spectrum of substrates. As PaFtsH2 homologs occur across bacterial phyla, we hypothesize that FtsH2 is a latent enzyme but may recognize specific substrates or is activated in specific contexts or biological niches. The identity of such linkers might thus play a more determinative role in the functionality of and physiological impact by FtsH proteases than previously thought.

Evolution of cyclic di-GMP signalling on a short and long term time scale.

Diversifying radiation of domain families within specific lineages of life indicates the importance of their functionality for the organisms. The foundation for the diversifying radiation of the cyclic di-GMP signalling network that occurred within the bacterial kingdom is most likely based in the outmost adaptability, flexibility and plasticity of the system. Integrative sensing of multiple diverse extra- and intracellular signals is made possible by the N-terminal sensory domains of the modular cyclic di-GMP turnover proteins, mutations in the protein scaffolds and subsequent signal reception by diverse receptors, which eventually rewires opposite host-associated as well as environmental life styles including parallel regulated target outputs. Natural, laboratory and microcosm derived microbial variants often with an altered multicellular biofilm behaviour as reading output demonstrated single amino acid substitutions to substantially alter catalytic activity including substrate specificity. Truncations and domain swapping of cyclic di-GMP signalling genes and horizontal gene transfer suggest rewiring of the network. Presence of cyclic di-GMP signalling genes on horizontally transferable elements in particular observed in extreme acidophilic bacteria indicates that cyclic di-GMP signalling and biofilm components are under selective pressure in these types of environments. On a short and long term evolutionary scale, within a species and in families within bacterial orders, respectively, the cyclic di-GMP signalling network can also rapidly disappear. To investigate variability of the cyclic di-GMP signalling system on various levels will give clues about evolutionary forces and discover novel physiological and metabolic pathways affected by this intriguing second messenger signalling system.

Deciphering Molecular Mechanism Underlying Self-Flocculation of Zymomonas mobilis for Robust Production.

Zymomonas mobilis metabolizes sugar anaerobically through the Entner-Doudoroff pathway with less ATP generated for lower biomass accumulation to direct more sugar for product formation with improved yield, making it a suitable host to be engineered as microbial cell factories for producing bulk commodities with major costs from feedstock consumption. Self-flocculation of the bacterial cells presents many advantages, such as enhanced tolerance to environmental stresses, a prerequisite for achieving high product titers by using concentrated substrates. ZM401, a self-flocculating mutant developed from ZM4, the unicellular model strain of Z. mobilis, was employed in this work to explore the molecular mechanism underlying this self-flocculating phenotype. Comparative studies between ZM401 and ZM4 indicate that a frameshift caused by a single nucleotide deletion in the poly-T tract of ZMO1082 fused the putative gene with the open reading frame of ZMO1083, encoding the catalytic subunit BcsA of the bacterial cellulose synthase to catalyze cellulose biosynthesis. Furthermore, the single nucleotide polymorphism mutation in the open reading frame of ZMO1055, encoding a bifunctional GGDEF-EAL protein with apparent diguanylate cyclase/phosphodiesterase activities, resulted in the Ala526Val substitution, which consequently compromised in vivo specific phosphodiesterase activity for the degradation of cyclic diguanylic acid, leading to intracellular accumulation of the signaling molecule to activate cellulose biosynthesis. These discoveries are significant for engineering other unicellular strains from Z. mobilis with the self-flocculating phenotype for robust production. IMPORTANCE Stress tolerance is a prerequisite for microbial cell factories to be robust in production, particularly for biorefinery of lignocellulosic biomass to produce biofuels, bioenergy, and bio-based chemicals for sustainable socioeconomic development, since various inhibitors are released during the pretreatment to destroy the recalcitrant lignin-carbohydrate complex for sugar production through enzymatic hydrolysis of the cellulose component, and their detoxification is too costly for producing bulk commodities. Although tolerance to individual stress has been intensively studied, the progress seems less significant since microbial cells are inevitably suffering from multiple stresses simultaneously under production conditions. When self-flocculating, microbial cells are more tolerant to multiple stresses through the general stress response due to enhanced quorum sensing associated with the morphological change for physiological and metabolic advantages. Therefore, elucidation of the molecular mechanism underlying such a self-flocculating phenotype is significant for engineering microbial cells with the unique multicellular morphology through rational design to boost their production performance.

Regulation of biofilm formation in Zymomonas mobilis to enhance stress tolerance by heterologous expression of pfs and luxS.

Zymomonas mobilis is a potential alternative of Saccharomyces cerevisiae to produce cellulosic ethanol with strengths in cofactor balance, but its lower tolerance to inhibitors in the lignocellulosic hydrolysate restricts the application. Although biofilm can improve bacteria stress tolerance, regulating biofilm formation in Z. mobilis is still a challenge. In this work, we constructed a pathway by heterologous expressing pfs and luxS from Escherichia coli in Z. mobilis to produce AI-2 (autoinducer 2), a universal quorum-sensing signal molecule, to control cell morphology for enhancing stress tolerance. Unexpectedly, the results suggested that neither endogenous AI-2 nor exogenous AI-2 promoted biofilm formation, while heterologous expression of pfs can significantly raise biofilm. Therefore, we proposed that the main factor in assisting biofilm formation was the product accumulated due to heterologous expression of pfs, like methylated DNA. Consequently, ZM4::pfs produced more biofilm, which presented an enhanced tolerance to acetic acid. All these findings provide a novel strategy to improve the stress tolerance of Z. mobilis by enhancing biofilm formation for efficient production of lignocellulosic ethanol and other value-added chemical products.

Potential of Zymomonas mobilis as an electricity producer in ethanol production.

BACKGROUND: Microbial fuel cell (MFC) convokes microorganism to convert biomass into electricity. However, most well-known electrogenic strains cannot directly use glucose to produce valuable products. Zymomonas mobilis, a promising bacterium for ethanol production, owns special Entner-Doudoroff pathway with less ATP and biomass produced and the low-energy coupling respiration, making Z. mobilis a potential exoelectrogen. RESULTS: A glucose-consuming MFC is constructed by inoculating Z. mobilis. The electricity with power density 2.0 mW/m2 is derived from the difference of oxidation-reduction potential (ORP) between anode and cathode chambers. Besides, two-type electricity generation is observed as glucose-independent process and glucose-dependent process. For the sake of enhancing MFC efficiency, extracellular and intracellular strategies are implemented. Biofilm removal and addition of c-type cytochrome benefit electricity performance and Tween 80 accelerates the electricity generation. Perturbation of cellular redox balance compromises the electricity output, indicating that redox homeostasis is the principal requirement to reach ideal voltage. CONCLUSION: This study identifies potential feature of electricity activity for Z. mobilis and provides multiple strategies to enhance the electricity output. Therefore, additional electricity generation will benefit the techno-economic viability of the commercial bulk production for biochemicals or biofuels in an efficient and environmentally sustainable manner.

[Efficacy and mechanism of electroacupuncture on insulin resistant polycystic ovary syndrome].

OBJECTIVE: To explore the therapeutic effect and partial mechanism of electroacupuncture (EA) for patients with insulin resistance (IR) polycystic ovary syndrome (PCOS). METHODS: Seventy patients with IR-PCOS were randomly divided into an EA group (36 cases, 5 cases dropped off) and a medication group (34 cases, 4 cases dropped off). The patients in the medication group were treated with oral administration of metformin hydrochloride, 500 mg each time, twice a day. The patients in the EA group were treated with EA (continuous wave, 2 Hz of frequency) at Zusanli (ST 36), Zhongwan (CV 12), Qihai (CV 6), Yishu (EX-B 3), Shenshu (BL 23), Pishu (BL 20), Ciliao (BL 32) for 30 min, three times a week. One menstrual cycle or 4 weeks were taken as a course of treatment, and 3 continuous courses were given. The follow-up was 3 months. The lipid metabolism indexes of triacylglycerol (TG), total cholesterol (TC), high-density lipoprotein (HDL) and low-density lipoprotein (LDL), homeostasis model assessment-insulin resistance index (HOMA-IR) and testosterone (T) in serum were compared before and after treatment, and the clinical effects of the two groups were evaluated during the follow-up. RESULTS: The total effective rate was 67.7% (21/31) in the EA group and 60.0% (18/30) in the medication group, with no significant difference between the two groups (P>0.05). After treatment, the levels of serum T, HOMA-IR, LDL, TG and TC were decreased significantly in the two groups (P<0.01, P<0.05), and HDL was increased significantly (P<0.01); the levels of TC in the EA group after treatment was lower than that in the medication group (P<0.05). CONCLUSION: EA may adjust some dyslipidemia in patients to correct IR and improve endocrine disorder of PCOS, which had superior/similar effects to metformin.

[Professor DONG Gui-rong's experience for the treatment of peripheral facial paralysis].

Professor DONG Gui-rong's theoretical principle and manipulation points for peripheral facial paralysis were introduced in details from the angels of syndrome differentiation, timing, acupoint prescription and needling methods. For the syndrome differentiation and timing, the professor emphasized to check the treatment timing and follow the symptoms, which should be treated by stages, besides, it was necessary to find and distinguish the reason and nature of diseases to have a combined treatment of tendons and muscles. For the acupoint prescription and needling methods, he has proposed that the acupoints selection should be compatible of distal and lacal, and made a best of Baihui (GV 20) to regulate the whole yang qi, also he has paid much attention to the needling methods and staging treatment. Under the consideration of late stage of peripheral facial paralysis, based on syndrome differentiation Back-shu points have been selected to regulate zang-fu function, should achieve much better therapeutic effect.

[Clinical study on acupuncture intervention time for treatment of peripheral facial paralysis].

OBJECTIVE: To observe effects of intervention time of local acupuncture at the affected side on the facial nerve injury and the therapeutic effect at acute stage of peripheral facial paralysis. METHODS: Two hundred and seventy-nine cases within 3 days of attack were randomly divided into 4 groups, group A (n=74), group B (n=70), group C (n=74) and control group (n=61). The 4 groups were treated with Prednisone on the third day after attack, and acupuncture was added in the group A, B and C, with Fengchi (GB 20), Yangbai (GB 14), Taiyang (EX-HN 5), Sibai (ST 2), Yingxiang (LI 20), etc. on the affected side and bilateral Hegu (LI 4) selected, and with superficial insertion method used for acupoints on the ear-face parts without manipulating the needles, and electroacupuncture was added from the fifth session of the treatment, and uniform reinforcing-reducing method was used for the distal acupoints selected. The needles were retained for 20 min and the treatment was given for 25 sessions, once other day. The therapeutic effects, the mean therapeutic courses for the cured patients and changes of electroneurography (ENoG) were compared among the groups. RESULTS: The clinical total effective rate was 98.6%, 95.7%, 94.6% and 72.1% in the group A, B, C and the control group, respectively, with a significant difference (P < 0.05), and the therapeutic course for the cured patients increased in the order of the group A, B, C and the control group; and there was no significant difference among the 4 groups in changes of ENoG at the third day and the fourteenth day (both P > 0.05). CONCLUSION: Acute stage is the best opportunity for acupuncture treatment of peripheral facial paralysis, and the earlier the intervention time, the better the therapeutic effect and the shorter the therapeutic course.