[Isolation and quantification of a 17-epi-dammarane triterpenoid rhuslactone from roots of Rhus chinensis and its preventive effects on coronary heart disease and thrombosis in zebrafish].

Based on mass spectrometry(MS)-guided separation strategy, compound 1 was obtained from the roots of Rhus chinensis. By comprehensive analysis of high resolution-electrospray ionization-mass spectrometry(HR-ESI-MS), nuclear magnetic resonance(NMR) data, and quantum chemical calculation of NMR(qcc-NMR) parameters, compound 1 was elucidated as rhuslactone, a 17-epi-dammarane triterpenoid with a rare 17α-side chain. An HPLC-ELSD method for its quantification in R. chinensis was established and adopted for the quantification of rhuslactone in different batches of R. chinensis. Rhuslactone displayed a good linear relationship within the range of 0.021 3-1.07 µmol·mL~(-1 )(r=0.997 6), and the average recovery was 99.34% [relative standard deviation(RSD) 2.9%). Moreover, the results of the evaluation test of the preventive effects of rhusalctone on coronary heart disease(CHD) and thrombosis showed that rhuslactone(0.11 nmol·mL~(-1)) significantly alleviated heart enlargement and venous congestion and increased cardiac output(CO), blood flow velocity(BFV), and heart rate, thereby reducing thrombus formation in zebrafish with CHD. The effects of rhuslactone on CO and BFV were superior to that of digoxin(1.02 nmol·mL~(-1)), and its effect on improving heart rate was comparable to that of digoxin. This study provides experimental references for the isolation, identification, quality control, and application of rhuslactone from R. chinensis against CHD. It is worth mentioning that this study has discussed some omissions in the determination of the stereochemistry of C-17 in dammarane triterpenoids in the present coursebook Chemistry of Chinese Medicine and some research papers, that is, the compound may be 17-epi-dammarane triterpenoid. This paper has also proposed steps for the establishment of C-17 stereochemistry.

Stent placement to prevent strictures after esophageal endoscopic submucosal dissection: a systematic review and meta-analysis.

Endoscopic submucosal dissection (ESD) is an important method for the treatment of early esophageal cancer. However, post-procedure stenosis is one of the most common long-term complications. This meta-analysis aimed to investigate whether stent placement is effective in the stenosis prevention, and which type of stent would be more effective. A systematic and electronic search of clinical trials and observational studies conducted before March 2020 on the efficacy of stent placement in preventing esophageal stricture after ESD was performed. Search terms included "ESD," "esophageal stenosis," "esophageal stricture," and "stents." We conducted a bias risk assessment of the eligible reports and a meta-analysis of the data using Revman 5.3 software. We included two randomized controlled trials (RCTs) and a prospective cohort study involving 163 patients with esophageal mucosal defects encompassing at least three-quarters of the esophagus circumference after ESD. The meta-analysis results showed that post-ESD stenosis rates (RR, 0.37; 95% CI, 0.22-0.64; P = 0.0003) and the number of endoscopic balloon dilations (EBDs) (MD, -1.74; 95% CI, -2.46 to -1.01; P < 0.00001) were reduced in the pooled analysis of three studies, indicating that stent placement was effective for stenosis prevention, especially a polyglycolic acid (PGA) sheet combined with stent placement can prevent stenosis (RR, 0.41; 95% CI, 0.23-0.74; P = 0.003) and reduce the number of EBDs (MD, -1.65; 95% CI, -2.40 to -0.90; P < 0.0001) significantly. Stent placement can reduce the rate of esophageal stenosis after ESD, especially when stents are covered with PGA sheets. However, more high-quality, low-bias RCTs with a sufficient sample size are needed to demonstrate its effectiveness.

Direct sensing and signal transduction during bacterial chemotaxis toward aromatic compounds in Comamonas testosteroni.

Micro-organisms sense and chemotactically respond to aromatic compounds. Although the existence of chemoreceptors that bind to aromatic attractants and subsequently trigger chemotaxis have long been speculated, such a chemoreceptor has not been demonstrated. In this report, we demonstrated that the chemoreceptor MCP2901 from Comamonas testosteroni CNB-1 binds to aromatic compounds and initiates downstream chemotactic signaling in addition to its ability to trigger chemotaxis via citrate binding. The function of gene MCP2901 was investigated by genetic deletion from CNB-1 and genetic complementation of the methyl-accepting chemotaxis protein (MCP)-null mutant CNB-1Δ20. Results showed that the expression of MCP2901 in the MCP-null mutant restored chemotaxis toward nine tested aromatic compounds and nine carboxylic acids. Isothermal titration calorimetry (ITC) analyses demonstrated that the ligand-binding domain of MCP2901 (MCP2901LBD) bound to citrate, and weakly to gentisate and 4-hydroxybenzoate. Additionally, ITC assays indicated that MCP2901LBD bound strongly to 2,6-dihydroxybenzoate and 2-hydroxybenzoate, which are isomers of gentisate and 4-hydroxybenzoate respectively that are not metabolized by CNB-1. Agarose-in-plug and capillary assays showed that these two molecules serve as chemoattractants for CNB-1. Through constructing membrane-like MCP2901-inserted Nanodiscs and phosphorelay activity assays, we demonstrated that 2,6-dihydroxybenzoate and 2-hydroxybenzoate altered kinase activity of CheA. This is the first evidence of an MCP binding to an aromatic molecule and triggering signal transduction for bacterial chemotaxis.

Tumebacillus algifaecis sp. nov., isolated from decomposing algal scum.

Bacterial strain THMBR28(T) was isolated from decomposing algal scum that was collected during an algal bloom in Taihu lake, China. Cells of strain THMBR28(T) were Gram-staining-positive, facultatively anaerobic and rod-shaped. Growth was observed at 20-45 °C (optimum, 30 °C), at pH 5.0-9.5 (optimum, pH 6.5-7.5), and in the presence of 0-1.0% (w/v) NaCl (optimum, 0.5%). Strain THMBR28(T) contained MK-7 as the major menaquinone and iso-C15 : 0 as the major cellular fatty acid. The polar lipid profile contained phosphatidylglycerol, phosphatidylmonomethylethanolamine, phosphatidylethanolamine and six unidentified polar lipids. The diamino acid found in the cell-wall peptidoglycan was meso-diaminopimelic acid. The DNA G+C content was 57.6 mol% (Tm). Phylogenetic analysis of 16S rRNA gene sequences showed that strain THMBR28(T) belonged to the genus Tumebacillus, most closely related to Tumebacillus ginsengisoli DSM 18389(T) (95.0%) and Tumebacillus permanentifrigoris Eur1 9.5(T) (93.4%). Based on phylogenetic and phenotypic characterization, it is concluded that strain THMBR28(T) represents a novel species of the genus Tumebacillus, for which the name Tumebacillus algifaecis sp. nov. is proposed, with THMBR28(T) ( = CGMCC 1.10949(T) = NBRC 108765(T)) as the type strain.

Alicyclobacillus fodiniaquatilis sp. nov., isolated from acid mine water.

Two novel, Gram-stain-variable, moderately thermophilic, acidophilic, rod-shaped, endospore-forming bacteria, G45-16T and G45-17, were isolated from acid mine water of Zijin copper mine in Fujian Province, China. Phylogenetic analysis of 16S rRNA gene sequences showed that they were closely related to Alicyclobacillus acidoterrestris ATCC 49025T with sequence similarities of 96.8 %. Cells grew aerobically at 20-45 °C (optimum, 40 °C), at pH 2.5-5.5(optimum, pH 3.5) and in the presence of 0-4.0 % (w/v) NaCl. Strains contained MK-7 as the major menaquinone and the major cellular fatty acids were ω-cyclohexane C19 : 0 and ω-cyclohexane C17 : 0. The DNA G+C content was 51.3 and 49.8 mol% (Tm) for G45-16T and G45-17, respectively. On the basis of phenotypic, chemotaxonomic and phylogenetic comparisons with their relatives and DNA-DNA relatedness values, it is concluded that strains G45-16T and G45-17 represent a novel species within the genus Alicyclobacillus, for which the name Alicyclobacillus fodiniaquatilis sp. nov. is proposed; the type strain is G45-16T(=CGMCC 1.15049T=NBRC 111483T).

A novel chemoreceptor MCP2983 from Comamonas testosteroni specifically binds to cis-aconitate and triggers chemotaxis towards diverse organic compounds.

Comamonas testosteroni CNB-1 behaves chemotactically toward a wide range of organic compounds, and 19 methyl-accepting chemotaxis proteins (MCPs) were annotated from the genome of strain CNB-2, a plasmid-curing derivative from strain CNB-1. The MCP-free mutant CNB-1Δ20 completely lost its chemotactic responses. In this study, we found that a chemoreceptor, namely MCP2983, restored chemotactic responses toward nine carboxylic acids and ten aromatic compounds to CNB-1Δ20. Isothermal titration calorimetry analysis indicated that the ligand-binding domain (LBD) of MCP2983 specifically binds to cis-aconitate but not other tested compounds. Deletion of the LBD of MCP2983 impaired chemotactic responses toward cis-aconitate as well as other tested compounds, indicating that the LBD of MCP2983 was essential for triggering chemotactic responses. Five amino acid residues (M(81), S(156), E(157), I(158), and L(159)) that are located at a putative ligand-binding pocket were identified to be involved in binding to cis-aconitate. So far, the MCP2983 represents the sole biochemically identified chemoreceptor that specifically binds to cis-aconitate and is able to trigger chemotaxis towards diverse organic compounds.

Clostridium algifaecis sp. nov., an anaerobic bacterial species from decomposing algal scum.

Two anaerobic bacterial strains, MB9-7(T) and MB9-9, were isolated from decomposing algal scum and were characterized using a polyphasic approach. Phylogenetic analysis of 16S rRNA gene sequences showed that strains MB9-7(T) and MB9-9 are closely related to each other (99.7% similarity) and they are also closely related to Clostridium tyrobutyricum (96.5%). The two strains were Gram-stain positive and rod-shaped. Growth occurred at 20-45 °C, at pH 4.0-8.0 and at NaCl concentrations of up to 2% (w/v). Acid was produced from glucose, xylose and mannose. Products of fermentation in PYG medium were mainly butyrate, acetate, carbon dioxide and hydrogen. The predominant cellular fatty acids were C(14:0) and C(16:0). The cellular polar lipids comprised phosphatidylglycerol, diphosphatidylglycerol, phosphatidylethanolamine, two glycolipids, one phospholipid, one aminophospholipid and two aminolipids. The DNA G+C contents of strain MB9-7(T) and MB9-9 were 27.9 and 28.7 mol%, respectively. These results support the assignment of the new isolates to the genus Clostridium and also distinguish them from other species of the genus Clostridium. Hence, it is proposed that strains MB9-7(T) and MB9-9 represent a novel species of the genus Clostridium, with the suggested name Clostridium algifaecis sp. nov. The type strain is MB9-7(T) ( =CGMCC 1.5188(T) =DSM 28783(T)).

Chryseobacterium taihuense sp. nov., isolated from a eutrophic lake, and emended descriptions of the genus Chryseobacterium, Chryseobacterium taiwanense, Chryseobacterium jejuense and Chryseobacterium indoltheticum.

Bacterial strain THMBM1(T) was isolated from decomposing algal scum that was collected during an algal bloom in Lake Taihu, Wuxi City, Jiangsu Province, China. Cells of strain THMBM1(T) were Gram-negative, facultatively anaerobic, non-motile rods. Colonies on tryptic soy agar were translucent and shiny with entire edges; yellow flexirubin-type pigments were produced. Growth was observed at 15-45 °C (optimum 30-37 °C), at pH 5.0-9.0 (optimum pH 8.0) and in the presence of 0-4.0 % (w/v) NaCl (optimum 0-1.0 %). Strain THMBM1(T) contained MK-6 as the sole respiratory quinone and sym-homospermidine as the predominant polyamine. The predominant cellular fatty acids were iso-C15 : 0 (53.2 %), iso-C17 : 0 3-OH (15.6 %) and iso-C17 : 1ω9c (11.9 %). The polar lipid profile consisted of phosphatidylethanolamine and five unidentified lipids. The DNA G+C content was 36.8 mol% (Tm). Strain THMBM1(T) was closely related to members of the genus Chryseobacterium, with 16S rRNA gene sequence similarities ranging from 92.9 to 97.2 %, the highest sequence similarities being with Chryseobacterium taiwanense BCRC 17412(T) (97.2 %) and C. gambrini 5-1St1a(T) (97.1 %). DNA-DNA relatedness between strain THMBM1(T) and C. taiwanense JCM 21767(T) and C. gambrini DSM 18014(T) was 34.1  and 23.0 %, respectively. Based on these results, it is concluded that strain THMBM1(T) represents a novel species, for which the name Chryseobacterium taihuense sp. nov. is proposed. The type strain is THMBM1(T) ( = CGMCC 1.10941(T)  = NBRC 108747(T)). Emended descriptions of the genus Chryseobacterium and C. taiwanense, C. jejuense and C. indoltheticum are also proposed.

Paenibacillus taihuensis sp. nov., isolated from an eutrophic lake.

Two Gram-stain-negative, facultatively anaerobic and endospore-forming rod-shaped bacterial strains, THMBG22(T) and R24, were isolated from decomposing algal scum. Phylogenetic analysis of 16S rRNA gene sequences showed that the two strains were closely related to each other (99.7 % similarity) and that they were also closely related to Paenibacillus sacheonensis DSM 23054(T) (97-97.1 %) and Paenibacillus phyllosphaerae DSM 17399(T) (96.1-96.4 %). This affiliation was also supported by rpoB-based phylogenetic analyses. Growth was observed at 20-40 °C (optimum, 30-37 °C) and at pH 5.0-9.0 (optimum, pH 6.0-7.0). The cells contained MK-7 as the sole respiratory quinone and anteiso-C15 : 0 as the major cellular fatty acid. Their cellular polar lipids were composed of phosphatidylglycerol, diphosphatidylglycerol, phosphatidylethanolamine and 12 unidentified polar lipids. The diamino acid of their cell-wall peptidoglycan was meso-diaminopimelic acid. The DNA-DNA hybridization value between THMBG22(T) and R24 was 84 %, and DNA-DNA relatedness to the most closely related species with a validly published name (P. sacheonensis) was 35-37 %. These results supported the assignment of the new isolates to the genus Paenibacillus and also distinguished them from the previously described species of the genus Paenibacillus. Hence, it is proposed that strains THMBG22(T) and R24 represent a novel species of the genus Paenibacillus, with the name Paenibacillus taihuensis sp. nov. The type strain is THMBG22(T) ( = CGMCC 1.10966(T) = NBRC 108766(T)).

Primary prostate Burkitt's lymphoma resected with holmium laser enucleation of the prostate: A rare case report.

BACKGROUND: Primary prostate Burkitt's lymphoma is a rare and aggressive condition with a poor prognosis. Its clinical presentation can be challenging to differentiate from benign prostatic hyperplasia. Given the rarity of primary prostate Burkitt's lymphoma, its diagnosis and treatment remain unclear. CASE SUMMARY: This report presents a case of a 57-year-old male with primary prostate Burkitt's lymphoma, initially misdiagnosed as prostatic hyperplasia. This case's operative process, intraoperative findings and postoperative management are discussed in detail. CONCLUSION: Primary prostate lymphoma is difficult to distinguish from other prostate diseases. Holmium laser enucleation of the prostate (HoLEP), a minimally invasive procedure, is crucial in diagnosing and treating this rare disease. Clinicians should remain vigilant and thoroughly combine physical examination, imaging and test results when encountering patients of younger age with small prostate size but a rapid progression of lower urinary tract symptoms. HoLEP is an essential diagnostic and therapeutic tool in managing primary prostate Burkitt's lymphoma.

Efficacy of endoscopic ultrasound in the evaluation of small gastrointestinal stromal tumors.

BACKGROUND: Gastrointestinal stromal tumors (GISTs) with a diameter of < 2 cm are called small GISTs. Currently, endoscopic ultrasound (EUS) is widely used as a regular follow-up method for GISTs, which can also provide a preliminary basis for judging the malignancy potential of lesions. However, there are no studies on the accuracy of EUS to assess the malignant potential of small GISTs. AIM: To evaluate the efficacy of EUS in the diagnosis and risk assessment of small GISTs. METHODS: We collected data from patients with small GISTs who were admitted to Shengjing Hospital of China Medical University between October 2014 and July 2019. The accurate diagnosis and risk classifications of patients were based on the pathological assessment according to the modified National Institute of Health criteria after endoscopic resection or laparoscopic surgery. Preoperative EUS features (marginal irregularity, cystic changes, homogeneity, ulceration, and strong echogenic foci) were retrospectively analyzed. The assessment results based on EUS features were compared with the pathological features. RESULTS: A total of 256 patients (69 men and 187 women) were enrolled. Pathological results included 232, 16, 7, and 1 very low-, low-, intermediate-, and high-risk cases, respectively. The most frequent tumor location was the gastric fundus (78.1%), and mitoses were calculated as > 5/50 high power field in 8 (3.1%) patients. Marginal irregularity, ulceration, strong echo foci, and heterogeneity were detected in 1 (0.4%), 2 (0.8%), 22 (8.6%), and 67 (65.1%) patients, respectively. However, cystic changes were not detected. Tumor size was positively correlated with the mitotic index (P < 0.001). Receiver operating curve analysis identified 1.48 cm as the best cut-off value to predict malignant potential (95% confidence interval: 0.824-0.956). EUS heterogeneity with tumor diameters > 1.48 cm was associated with higher risk classification (P < 0.05). CONCLUSION: Small GISTs (diameters > 1.48 cm) with positive EUS features should receive intensive surveillance or undergo endoscopic surgery. EUS and dissection are efficient diagnostic and therapeutic approaches for small GISTs.

The molecular control of meiotic double-strand break (DSB) formation and its significance in human infertility.

Meiosis is an essential step in gametogenesis which is the key process in sexually reproducing organisms as meiotic aberrations may result in infertility. In meiosis, programmed DNA double-strand break (DSB) formation is one of the fundamental processes that are essential for maintaining homolog interactions and correcting segregation of chromosomes. Although the number and distribution of meiotic DSBs are tightly regulated, still abnormalities in DSB formation are known to cause meiotic arrest and infertility. This review is a detailed account of molecular bases of meiotic DSB formation, its evolutionary conservation, and variations in different species. We further reviewed the mutations of DSB formation genes in association with human infertility and also proposed the future directions and strategies about the study of meiotic DSB formation.

Endoscopic full-thickness resection using an over-the-scope device: A prospective study.

BACKGROUND: Endoscopic submucosal dissection to treat mucosal and submucosal lesions sometimes results in low rates of microscopically margin-negative (R0) resection. Endoscopic full-thickness resection (EFTR) has a high R0 resection rate and allows for the definitive diagnosis and treatment of selected mucosal and submucosal lesions that are not suitable for conventional resection techniques. AIM: To evaluate the efficacy and safety of EFTR using an over-the-scope clip (OTSC). METHODS: This prospective, single-center, non-randomized clinical trial was conducted at the endoscopy center of Shengjing Hospital of China Medical University. The study included patients aged 18-70 years who had gastric or colorectal submucosal tumors (SMTs) (≤ 20 mm in diameter) originating from the muscularis propria based on endoscopic ultrasound (EUS) and patients who had early-stage gastric or colorectal cancer (≤ 20 mm in diameter) based on EUS and computed tomography. All lesions were treated by EFTR combined with an OTSC for wound closure between November 2014 and October 2016. We analyzed patient demographics, lesion features, histopathological diagnoses, R0 resection (negative margins) status, adverse events, and follow-up results. RESULTS: A total of 68 patients (17 men and 51 women) with an average age of 52.0 ± 10.5 years (32-71 years) were enrolled in this study, which included 66 gastric or colorectal SMTs and 2 early-stage colorectal cancers. The mean tumor diameter was 12.6 ± 4.3 mm. The EFTR procedure was successful in all cases. The mean EFTR procedure time was 39.6 ± 38.0 min. The mean OTSC defect closure time was 5.0 ± 3.8 min, and the success rate of closure for defects was 100%. Histologically complete resection (R0) was achieved in 67 (98.5%) patients. Procedure-related adverse events were observed in 11 (16.2%) patients. The average post-procedure length of follow-up was 48.2 ± 15.7 mo. There was no recurrence during follow-up. CONCLUSION: EFTR combined with an OTSC is an effective and safe technique for the removal of select subepithelial and epithelial lesions that are not amenable to conventional endoscopic resection techniques.

Comprehensive review of diagnostic modalities for early chronic pancreatitis.

Chronic pancreatitis (CP) is a progressive condition caused by several factors and characterised by pancreatic fibrosis and dysfunction. However, CP is difficult to diagnose at an early stage. Various advanced methods including endoscopic ultrasound based elastography and confocal laser endomicroscopy have been used to diagnose early CP, although no unified diagnostic standards have been established. In the past, the diagnosis was mainly based on imaging, and no comprehensive evaluations were performed. This review describes and compares the advantages and limitations of the traditional and latest diagnostic modalities and suggests guidelines for the standardisation of the methods used to diagnose early CP.

Endoscopic fenestration in the diagnosis and treatment of delayed anastomotic submucosal abscess: A case report and review of literature.

BACKGROUND: Abscess formation is one of the complications after radical resection of rectal cancer; cases with delayed postoperative anastomotic abscess are rare. Here, we report a rare case of postoperative anastomotic abscess with a submucosal neoplasm appearing after rectal surgery. Ultimately, the patient was diagnosed and treated by endoscopic fenestration. In addition, we review the literature on the appearance of an abscess as a complication after rectal cancer surgery. CASE SUMMARY: A 57-year-old man with a history of rectal malignancy resection complained of a smooth protuberance near the anastomotic stoma. Endoscopic ultrasonography revealed a hypoechoic structure originating from the muscularis propria, and a submucosal tumor was suspected. The patient was subsequently referred to our hospital and underwent pelvic contrast-enhanced computed tomography, which revealed no thickening or strengthening of the anastomotic wall. In order to clarify the origin of the lesion and obtain the pathology, endoscopic fenestration was performed. After endoscopic procedure, a definitive diagnosis of delayed anastomotic submucosal abscess was established. The patient achieved good recovery and prognosis after the complete clearance of abscess. CONCLUSION: Endoscopic fenestration may be safe and effective for the diagnosis/treatment of delayed intestinal smooth protuberance after rectal cancer surgery.

Endoscopic ultrasound-measured muscular thickness of the lower esophageal sphincter and long-term prognosis after peroral endoscopic myotomy for achalasia.

BACKGROUND: People with achalasia typically have a thick lower esophageal muscularis propria (LEMP), and peroral endoscopic myotomy (POEM) has been effective in treating most patients. LEMP thickness may be associated with the outcomes and prognosis after POEM. However, more evidence is needed regarding the relationship between LEMP thickness and patient prognosis after POEM. AIM: To assess the association between LEMP thickness, measured using endoscopic ultrasound (EUS), and long-term prognosis, especially relapse, after POEM for achalasia. METHODS: All medical records, including EUS data, of patients who underwent POEM to treat achalasia at Shengjing Hospital of China Medical University from January 2012 to September 2018 were retrospectively reviewed. LEMP thickness was measured by EUS, and a thickness of ≥ 3 mm was defined as thickened. The severity of patient symptoms was evaluated using the Eckardt score. Relapse was defined as a 3-point rise in the Eckardt score after a period of clinical remission. The relationship between patient characteristics, muscle thickness, and recurrence was analyzed. RESULTS: Eighty-two patients (32 males and 50 females, aged 17-78 years) and 85 POEM procedures were included. In total, 76.8% (63/82 patients) of patients had a thickened muscularis propria. Older age and longer disease course were associated with muscularis propria thickening (P < 0.05). The mean postoperative follow-up time was 35.4 ± 17.2 mo (range, 8-87.5 mo) in 60 patients. Five patients with Eckardt scores > 3 refused further management after their symptoms were relieved. The relapse rate was 12.73% (7/55 cases). Five patients, four of whom had muscularis propria thickening, had disease recurrence within 12 mo after the procedure. Achalasia relapsed in one patient who had a thickened muscularis propria after 24 mo and in another patient who did not have a thickened muscularis propria after 30 mo. Patients with recurrence were typically younger and had a shorter disease course (P < 0.05). The relapse rate in patients with a non-thickened muscularis propria tended to be higher (18.2%, 2/11 patients) than that in patients with a thickened muscularis propria (11.4%, 5/44 patients), although no significant difference was found. Age (hazard ratio = 0.92; 95% confidence interval: 0.865-0.979; P < 0.05) and being male (hazard ratio = 7.173; 95% confidence interval: 1.277-40.286; P < 0.05) were identified as risk factors for symptomatic recurrence by multivariable analysis using the Cox model. CONCLUSION: Patients with a thickened muscularis are typically older and have a longer disease course. Younger age and the male sex are associated with increased recurrence. Patients with a thin muscularis propria may be prone to relapse, although further validation is needed.

Enhanced Microbial Interactions and Deterministic Successions During Anoxic Decomposition of Microcystis Biomass in Lake Sediment.

Microcystis biomass remineralization after blooming represents a hotspot of nutrient recycling in eutrophic lakes. Because Microcystis blooms are massively deposited on lake sediments, resulting in anoxic conditions, it is important to understand the response and role of benthic microbial communities during the anoxic decomposition of Microcystis in freshwater lakes. In the present study, we employed a microcosm method, combined with high-throughput sequencing, functional prediction, and network analysis, to investigate microbial succession during the short-term (30 days) anaerobic decomposition of Microcystis in a eutrophic sediment. Continuous accumulation of CH4 and CO2 and increasing relative abundance of methanogens were observed during the incubation. The microbial community composition (MCC) significantly changed after addition of Microcystis biomass, with a shift in the community from a stochastic to a functional, deterministic succession. Families, including Clostridiaceae, Rhodocyclaceae, Rikenellaceae, Peptostreptococcaceae, Syntrophomonadaceae, Lachnospiraceae, and Methanosarcinaceae, were predominantly enriched and formed diverse substitution patterns, suggesting a synergistic action of these family members in the decomposition of Microcystis biomass. Importantly, intense species-to-species interactions and weak resistance to disturbance were observed in the microbial community after Microcystis biomass addition. Collectively, these results suggest that the addition of Microcystis induce phylogenetic clustering and structure instability in the sediment microbial community and the synergistic interactions among saprotrophic bacteria play a key role in Microcystis biomass remineralization.

Dipeptidyl aminopeptidase IV from Stenotrophomonas maltophilia exhibits activity against a substrate containing a 4-hydroxyproline residue.

The crystal structure of dipeptidyl aminopeptidase IV from Stenotrophomonas maltophilia was determined at 2.8-A resolution by the multiple isomorphous replacement method, using platinum and selenomethionine derivatives. The crystals belong to space group P4(3)2(1)2, with unit cell parameters a = b = 105.9 A and c = 161.9 A. Dipeptidyl aminopeptidase IV is a homodimer, and the subunit structure is composed of two domains, namely, N-terminal beta-propeller and C-terminal catalytic domains. At the active site, a hydrophobic pocket to accommodate a proline residue of the substrate is conserved as well as those of mammalian enzymes. Stenotrophomonas dipeptidyl aminopeptidase IV exhibited activity toward a substrate containing a 4-hydroxyproline residue at the second position from the N terminus. In the Stenotrophomonas enzyme, one of the residues composing the hydrophobic pocket at the active site is changed to Asn611 from the corresponding residue of Tyr631 in the porcine enzyme, which showed very low activity against the substrate containing 4-hydroxyproline. The N611Y mutant enzyme was generated by site-directed mutagenesis. The activity of this mutant enzyme toward a substrate containing 4-hydroxyproline decreased to 30.6% of that of the wild-type enzyme. Accordingly, it was considered that Asn611 would be one of the major factors involved in the recognition of substrates containing 4-hydroxyproline.

Substitution of Glu122 by glutamine revealed the function of the second water molecule as a proton donor in the binuclear metal enzyme creatininase.

Creatininase is a binuclear zinc enzyme and catalyzes the reversible conversion of creatinine to creatine. It exhibits an open-closed conformational change upon substrate binding, and the differences in the conformations of Tyr121, Trp154, and the loop region containing Trp174 were evident in the enzyme-creatine complex when compared to those in the ligand-free enzyme. We have determined the crystal structure of the enzyme complexed with a 1-methylguanidine. All subunits in the complex existed as the closed form, and the binding mode of creatinine was estimated. Site-directed mutagenesis revealed that the hydrophobic residues that show conformational change upon substrate binding are important for the enzyme activity. We propose a catalytic mechanism of creatininase in which two water molecules have significant roles. The first molecule is a hydroxide ion (Wat1) that is bound as a bridge between the two metal ions and attacks the carbonyl carbon of the substrate. The second molecule is a water molecule (Wat2) that is bound to the carboxyl group of Glu122 and functions as a proton donor in catalysis. The activity of the E122Q mutant was very low and it was only partially restored by the addition of ZnCl(2) or MnCl(2). In the E122Q mutant, k(cat) is drastically decreased, indicating that Glu122 is important for catalysis. X-ray crystallographic study and the atomic absorption spectrometry analysis of the E122Q mutant-substrate complex revealed that the drastic decrease of the activity of the E122Q was caused by not only the loss of one Zn ion at the Metal1 site but also a critical function of Glu122, which most likely exists for a proton transfer step through Wat2.