The catabolic specialization of the marine bacterium Polaribacter sp. Q13 to red algal ß1,3/1,4-mixed-linkage xylan.

Catabolism of algal polysaccharides by marine bacteria is a significant process of marine carbon cycling. ß1,3/1,4-Mixed-linkage xylan (MLX) is a class of xylan in the ocean, widely present in the cell walls of red algae. However, the catabolic mechanism of MLX by marine bacteria remains elusive. Recently, we found that a marine Bacteroidetes strain, Polaribacter sp. Q13, is a specialist in degrading MLX, which secretes a novel MLX-specific xylanase. Here, the catabolic specialization of strain Q13 to MLX was studied by multiomics and biochemical analyses. Strain Q13 catabolizes MLX with a canonical starch utilization system (Sus), which is encoded by a single xylan utilization locus, XUL-Q13. In this system, the cell surface glycan-binding protein SGBP-B captures MLX specifically, contributing to the catabolic specificity. The xylanolytic enzyme system of strain Q13 is unique, and the enzymatic cascade dedicates the stepwise hydrolysis of the ß1,3- and ß1,4-linkages in MLX in the extracellular, periplasmic, and cytoplasmic spaces. Bioinformatics analysis and growth observation suggest that other marine Bacteroidetes strains harboring homologous MLX utilization loci also preferentially utilize MLX. These results reveal the catabolic specialization of MLX degradation by marine Bacteroidetes, leading to a better understanding of the degradation and recycling of MLX driven by marine bacteria.IMPORTANCERed algae contribute substantially to the primary production in marine ecosystems. The catabolism of red algal polysaccharides by marine bacteria is important for marine carbon cycling. Mixed-linkage ß1,3/1,4-xylan (MLX, distinct from hetero-ß1,4-xylans from terrestrial plants) is an abundant red algal polysaccharide, whose mechanism of catabolism by marine bacteria, however, remains largely unknown. This study reveals the catabolism of MLX by marine Bacteroidetes, promoting our understanding of the degradation and utilization of algal polysaccharides by marine bacteria. This study also sets a foundation for the biomass conversion of MLX.

A novel class of xylanases specifically degrade marine red algal ß1,3/1,4-mixed-linkage xylan.

Xylans are polysaccharides composed of xylose and include ß1,4-xylan, ß1,3-xylan, and ß1,3/1,4-mixed-linkage xylan (MLX). MLX is widely present in marine red algae and constitutes a significant organic carbon in the ocean. Xylanases are hydrolase enzymes that play an important role in xylan degradation. While a variety of ß1,4-xylanases and ß1,3-xylanases involved in the degradation of ß1,4-xylan and ß1,3-xylan have been reported, no specific enzyme has yet been identified that degrades MLX. Herein, we report the characterization of a new MLX-specific xylanase from the marine bacterium Polaribacter sp. Q13 which utilizes MLX for growth. The bacterium secretes xylanases to degrade MLX, among which is Xyn26A, an MLX-specific xylanase that shows low sequence similarities (<27%) to ß1,3-xylanases in the glycoside hydrolase family 26 (GH26). We show that Xyn26A attacks MLX precisely at ß1,4-linkages, following a ß1,3-linkage toward the reducing end. We confirm that Xyn26A and its homologs have the same specificity and mode of action on MLX, and thus represent a new xylanase group which we term as MLXases. We further solved the structure of a representative MLXase, AlXyn26A. Structural and biochemical analyses revealed that the specificity of MLXases depends critically on a precisely positioned ß1,3-linkage at the -2/-1 subsite. Compared to the GH26 ß1,3-xylanases, we found MLXases have evolved a tunnel-shaped cavity that is fine-tuned to specifically recognize and hydrolyze MLX. Overall, this study offers a foremost insight into MLXases, shedding light on the biochemical mechanism of bacterial degradation of MLX.

Gilvimarinus xylanilyticus sp. nov., a novel 1,3-xylanase-secreting bacterium isolated from a marine green alga.

1,3-xylan, an important organic carbon in the ocean, is peculiar to marine algae. 1,3-xylanase-secreting bacteria and their extracellular 1,3-xylanases play pivotal roles in the degradation and biomass conversion of 1,3-xylan. However, only a few 1,3-xylanase-secreting bacteria and 1,3-xylanases have been reported. Here, we identified a novel marine bacterium capable of secreting 1,3-xylanases, designated as strain HB14T. Phylogenetic analysis revealed that strain HB14T clustered tightly with known species of the genus Gilvimarinus, showing the highest 16S rRNA gene sequence similarity (97.7%) with the type strain of Gilvimarinus chinensis. Based on phylogenetic, genomic, chemotaxonomic and phenotypic studies, strain HB14T was classified as a representative of a novel species in the genus Gilvimarinus, for which the name Gilvimarinus xylanilyticus sp. nov. was proposed. The type strain is HB14T (=CCTCC AB 2022109T = KCTC 92379T). Four 1,3-xylanases secreted by strain HB14T were identified based on genome and secretome analyses, and the two (Xyn65 and Xyn80) with relatively higher abundance in secretome were successfully expressed in Escherichia coli and biochemically characterized. They showed the highest activity at pH 6.0-7.0 and 40°C and released mainly 1,3-xylobiose and 1,3-xylotriose from 1,3-xylan. These data suggest that strain HB14T acts as a player in marine 1,3-xylan degradation and recycling and that its extracellular 1,3-xylanases may have a good potential in 1,3-xylooligosaccharides preparation.

[Effect of unicompartmental knee arthroplasty in patients over 75 years old with knee osteoarthritis].

OBJECTIVE: To investigate the clinical effect of unicompartmental knee arthroplasty in patients with knee osteoarthritis over 75 years old. METHODS: From April 2010 to May 2015, 42 patients with knee medial compartment osteoarthritis were treated with Oxford third-generation unicompartmental knee arthroplasty. According to the single and bilateral replacement, the patients were divided into bilateral simultaneous replacement group and unilateral replacement group:11 patients in the simultaneous replacement group, 3 males and 8 females, aged (79.18±3.06) years;There were 31 cases in the unilateral replacement group, 13 males and 18 females, aged (78.16±3.48) years. The survival status of patients with knee prosthesis, the changes of hematocrit before and after operation, and the total amount of blood loss during and after operation were observed and compared;The HSS (Hospital for Special Surgery knee rating) scores of patients before and after operation were compared. RESULTS: There was significant difference in perioperative complications between two groups(P<0.05). All 42 patients were followed up for(5.7±2.3) years. One patient with a history of previous hypertension developed cerebral thrombosis in the 4th month after operation, one patient developed pad dislocation in the 4th month after operation, and two patients died of other medical diseases(1 myocardial infarction and 1 lung cancer) 3 years after operation. The total amount of postoperative blood loss in bilateral simultaneous replacement group was higher than that in unilateral replacement group(P<0.05);Four patients with bilateral simultaneous replacement received 2U blood transfusion after operation. The HSS score and total score of the two groups at 9 months after operation were higher than those before operation(P<0.05). CONCLUSION: Unicompartmental knee arthroplasty is a feasible surgical treatment for osteoarthritis patients over 75 years old with medial single compartment degeneration. For elderly patients over 75 years old with bilateral knee lesions, bilateral simultaneous unicompartmental knee arthroplasty is more traumatic than unilateral unicompartmental knee arthroplasty, which will increase the incidence of perioperative complications, affect the rapid postoperative recovery and increase the blood loss. Although the long-term effect is equivalent to that of unilateral unicompartmental knee arthroplasty, staged operation is still recommended to ensure the safety of operation.

Diversity of Marine 1,3-Xylan-Utilizing Bacteria and Characters of Their Extracellular 1,3-Xylanases.

1,3-xylan is present in the cell walls of some red and green algae and is an important organic carbon in the ocean. However, information on its bacterial degradation is quite limited. Here, after enrichment with 1,3-xylan, the diversity of bacteria recovered from marine algae collected in Hainan, China, was analyzed with both the 16S rRNA gene amplicon sequencing and the culture-dependent method. Bacteria recovered were affiliated with more than 19 families mainly in phyla Proteobacteria and Bacteroidetes, suggesting a high bacterial diversity. Moreover, 12 strains with high 1,3-xylanase-secreting ability from genera Vibrio, Neiella, Alteromonas, and Gilvimarinus were isolated from the enrichment culture. The extracellular 1,3-xylanases secreted by Vibrio sp. EA2, Neiella sp. GA3, Alteromonas sp. CA13-2, and Gilvimarinus sp. HA3-2, which were taken as representatives due to their efficient utilization of 1,3-xylan for growth, were further characterized. The extracellular 1,3-xylanases secreted by these strains showed the highest activity at pH 6.0-7.0 and 30-40°C in 0-0.5M NaCl, exhibiting thermo-unstable and alkali-resistant characters. Their degradation products on 1,3-xylan were mainly 1,3-xylobiose and 1,3-xylotriose. This study reveals the diversity of marine bacteria involved in the degradation and utilization of 1,3-xylan, helpful in our understanding of the recycling of 1,3-xylan driven by bacteria in the ocean and the discovery of novel 1,3-xylanases.

[Impact of smoking and smoking cessation on long-term outcome of patients after coronary artery bypass grafting].

OBJECTIVE: To determine the impact of smoking behaviors on long-term outcomes of coronary artery bypass grafting (CABG). METHODS: We conducted this survey in 2541 consecutive patients who underwent CABG in Fu Wai hospital from January 1, 2004 to December 30, 2005. The preoperative and postoperative smoking habits were obtained. The patients were divided into never smokers and ever smokers. The ever smokers were further divided into the current smokers who smoked before and after CABG and former smokers who stopped smoking before CABG, quitters who stopped smoking after CABG. Death, major adverse cardiovascular or cerebrovascular events and angina pectoris were observed. The relative risk of adverse events in different patients were analyzed by univariate and multivariate Cox analysis. RESULTS: The patients were followed up for 4.27 to 6.41 years (average 5.09 years). After CABG, the percentage of persistent smoking patients was 22.1%. After adjusting baseline characteristics, relative risk for tumor related death (RR: 2.38, 95%CI: 1.06 - 5.36), major adverse cardiovascular or cerebrovascular events (RR: 1.26, 95%CI: 1.01 - 1.57) and angina pectoris (RR: 1.29, 95%CI: 1.04 - 1.59) were significantly higher in ever smokers than in never smokers. Similarly, relative risk of death from all causes (RR: 2.60, 95%CI: 1.53 - 4.46), cardiac death (RR: 2.51, 95%CI: 1.32 - 4.78), tumor cause death (RR: 5.12, 95%CI: 2.08 - 12.59), major adverse cardiovascular or cerebrovascular events (RR: 1.83, 95%CI: 1.42 - 2.34) and angina pectoris (RR: 1.69, 95%CI: 1.33 - 2.16) were also significantly higher in current smokers than in never smokers. Outcome was similar between patients who stopped smoking and never smokers (all P > 0.05). CONCLUSIONS: Smoking prevalence is still high in patients after CABG in China. Persistent smoking is associated with higher rates of mortality and morbidity after CABG while smoking cessation is associated with reduction of morbidity and mortality in patients after CABG.

[Surgical treatment of aortico-left ventricular tunnel].

OBJECTIVE: To review 9 aortico-left ventricular tunnel (ALVT) patients in our hospital, describe the clinical features, diagnosis, treatments and follow-up. METHODS: We identified 9 patients from July 2002 to August 2008. Clinical and surgical details were reviewed. 7 patients were in NYHA class I and 2 in class III, 8 of 9 patients were diagnosed by echocardiography before operation. RESULTS: All patients underwent surgery under standard cardiopulmonary bypass. 2 with direct suture, 5 by patch closure of the aortic end and 1 by patch closure of both aortic end and left ventricular end of the AVLT. 1 underwent aortic valve replacement after incision of the ALVT. One patient died 2 month after operation because of endocarditis and acute heart failure. At follow-up (3 month to 6 years), 3 patients were in NYHA class I, 3 in Class II, 1 in class III and missed 1. No aortic regurgitation or trace in 2, little in 1, little to moderate in 2. The aortic mechanical valve is normal in 1 and paravalvular leakage in 1 patient. CONCLUSION: Aortico-left ventricular tunnel is a rare cardiac malformation with a good post-operative outcome. Surgery is an effective treatment. Long-term follow-up for post-operation is essential.