谷氨酸棒杆菌代谢工程高效生产L-缬氨酸北大核心CSCD

L-缬氨酸作为一种支链氨基酸,广泛应用于医药和饲料等领域。本研究借助多种代谢工程策略相结合的方法,构建了生产L-缬氨酸的微生物细胞工厂,实现了L-缬氨酸的高效生产。首先,通过增强糖酵解途径、减弱副产物代谢途径相结合的方式,强化了L-缬氨酸合成前体丙酮酸的供给;其次,针对L-缬氨酸合成路径关键酶—乙酰羟酸合酶进行定点突变,提高了菌株的抗反馈抑制能力,并利用启动子工程策略,优化了路径关键酶的基因表达水平;最后,利用辅因子工程策略,改变了乙酰羟酸还原异构酶和支链氨基酸转氨酶的辅因子偏好性,由偏好NADPH转变为偏好NADH,从而提高了L-缬氨酸的合成能力。在5L发酵罐中,最优谷氨酸棒杆菌工程菌株Corynebacterium glutamicum K020的L-缬氨酸产量、得率和生产强度分别达到了110g/L、0.51g/g和2.29 g/(L·h)。     

水分梯度下胡杨荒漠河岸林种内竞争及空间格局变化特征

为查明塔里木河下游不同水分梯度下胡杨种内竞争以及空间分布格局的变化规律,在塔里木河下游阿拉干断面选取3条样带,每条样带内依照水分梯度布设3个样方,采用Hegyi单木竞争模型与点格局等分析方法,探究了水分梯度下胡杨林种内竞争及空间格局变化特征。结果表明：1)塔里木河下游胡杨的最适竞争范围为10m; 2)胡杨竞争指数与胸径服从幂函数关系(P<0.001),胡杨竞争指数随对象木胸径的增加而逐渐减小,当对象木胸径达到20cm以上时,其竞争指数逐渐稳定,且维持在较低水平;3)随水分梯度的降低,胡杨林分竞争指数呈下降趋势;4)在塔里木河下游,胡杨空间格局主要为聚集分布,随空间尺度的增加,胡杨逐渐趋向于随机分布;5)随水分梯度的降低,胡杨空间格局由聚集分布逐渐转变为随机分布。水分是决定极端干旱区荒漠植被空间分布与结构的主要因子;在胡杨林分管理中,应充分考虑胡杨的种内竞争、空间格局及其与水分梯度之间关系,为塔里木河下游胡杨林的保护与更新提供科学依据。     

Nonparametric and semiparametric estimation with sequentially truncated survival data

In observational cohort studies with complex sampling schemes, truncation arises when the time to event of interest is observed only when it falls below or exceeds another random time, that is, the truncation time. In more complex settings, observation may require a particular ordering of event times; we refer to this as sequential truncation. Estimators of the event time distribution have been developed for simple left-truncated or right-truncated data. However, these estimators may be inconsistent under sequential truncation. We propose nonparametric and semiparametric maximum likelihood estimators for the distribution of the event time of interest in the presence of sequential truncation, under two truncation models. We show the equivalence of an inverse probability weighted estimator and a product limit estimator under one of these models. We study the large sample properties of the proposed estimators and derive their asymptotic variance estimators. We evaluate the proposed methods through simulation studies and apply the methods to an Alzheimer's disease study. We have developed an R package, seqTrun , for implementation of our method.     

Subcellular Distribution and Chemical Forms of Cadmium in the Medicine Food Homology Plant <i>Platycodon grandiflorum</i> (Jacq.) A.DC.

Although Platycodon grandiflorum (Jacq.) A.DC. is a renowned medicine food homology plant, reports of excessive cadmium (Cd) levels are common, which affects its safety for clinical use and food consumption. To enable its Cd levels to be regulated or reduced, it is necessary to first elucidate the mechanism of Cd uptake and accumulation in the plant, in addition to its detoxification mechanisms. This present study used inductively couple plasma-mass-spectrometry to analyze the subcellular distribution and chemical forms of Cd in different tissues of P. grandiflorum. The experimental results showed that Cd was mainly accumulated in the roots [predominantly in the cell wall (50.96%–61.42%)], and it was found primarily in hypomobile and hypotoxic forms. The proportion of Cd in the soluble fraction increased after Cd exposure, and the proportion of insoluble phosphate Cd and oxalate Cd increased in roots and leaves, with a higher increase in oxalate Cd. Therefore, it is likely that root retention mechanisms, cell wall deposition, vacuole sequestration, and the formation of low mobility and low toxicity forms are tolerance strategies for Cd detoxification used by P. grandiflorum. The results of this study provide a theoretical grounding for the study of Cd accumulation and detoxification mechanisms in P. grandiflorum, and they can be used as a reference for developing Cd limits and standards for other medicine food homology plants.     

A Meaningful Attempt: Applying Dielectric Barrier Discharge Plasma to Induce Polarization of Macrophages

Macrophage polarization plays an important role in many macrophage-related diseases. This study was designed to preliminarily explore the effects of dielectric barrier discharge (DBD) plasma on the polarization direction and cell activity of macrophages with different phenotypes (ie, M0, M1, and M2). The M1 macrophage marker inducible nitric oxide synthase (iNOS) and M2 macrophage marker cluster of differentiation 206 (CD206) were detected by western blot (WB). The effects of DBD plasma on macrophage viability were analyzed by using a cell counting kit-8 detection kit. M0, M1, and M2 macrophages exhibited a decrease in iNOS expression and an increase in CD206 expression after the DBD plasma intervention. Additionally, the decrease in macrophage viability remained non-significant after initiating the intervention. DBD plasma can promote the transformation of M0 and M1 macrophages to M2 macrophages, and can further enhance the expression of the M2 macrophage phenotype marker CD206. Our study not only demonstrates the potential therapeutic value of DBD plasma for macrophage-related diseases, but it also provides a new direction for research to improve the treatment of macrophage-related diseases. © 2023 Bioelectromagnetics Society.     

乙醛脱氢酶基因ALDH2对雄性小鼠生育能力的影响

本研究使用乙醛脱氢酶2(ALDH2)基因全敲除的雄性C57BL/6(B6)小鼠（Musmusculus domesticus）,通过分析不同周龄小鼠的睾丸脏器系数、睾丸组织细胞形态、精子运动参数、配种后母鼠产仔数及子代雄雌比等生育指标,探讨ALDH2基因敲除对雄性小鼠生育能力的影响。结果表明,与野生型（WT）小鼠相比,5、7、10周龄ALDH2基因敲除型（KO）雄性小鼠睾丸脏器系数显著降低（P <0.05）;睾丸组织细胞间质变大,精子活率显著降低（P <0.05）;产仔数和雄雌比显著降低（P <0.05）。本研究为揭示乙醛脱氢酶ALDH2基因在雄性小鼠生殖中的作用提供了一定的基础。     

信号分子在生物脱氮中的作用及检测方法

生物脱氮是由微生物主导的地球氮循环中的重要环节之一,主要包括硝化、反硝化和厌氧氨氧化(anaerobic ammonium oxidation,anammox)等过程。在微生物联合作用下,污水中的有机氮及氨氮经一系列作用转化为氮气,这种经济高效、环境友好的处理工艺在世界范围内得到广泛应用。群体感应(quorum sensing,QS)以信号分子为媒介通过改变菌群密度和周围环境变化来调节微生物的各种行为。大量的研究已证实调控QS信号分子在生物脱氮中具有应用潜力。本文介绍了各种信号分子类型,从基因组学、实际应用等方面综述了各类信号分子以及检测方法,同时针对酰基高丝氨酸内酯(acyl homoserine lactones,AHLs)类信号分子在生物脱氮中的作用进行详细介绍。然而不足之处在于信号分子研究只是停留在实验室阶段,仅仅研究了单一信号分子对生物脱氮的影响。未来可将信号分子应用于实际污水,研究多种信号分子共同作用以及多种微生物之间的QS现象。     

库木塔格沙漠土壤细菌多样性及具有群体感应抑制活性放线菌筛选

【背景】群体感应抑制剂(quorum sensing inhibitor,QSI)作为抗生素潜在替代品,可有效降低致病菌传染性和毒性。沙漠土壤蕴藏着丰富的放线菌资源,是挖掘群体感应抑制剂的重要来源。【目的】解析库木塔格沙漠土壤细菌群落多样性,筛选并挖掘群体感应抑制活性放线菌资源。【方法】采用Illumina Nova Seq高通量测序技术揭示库木塔格沙漠土壤细菌群落组成,利用可培养方法进行土壤放线菌分离和鉴定;选用紫色杆菌CV026模型筛选群体感应抑制活性放线菌,并对其功能特性进行初步评价。【结果】Illumina Nova Seq高通量测序结果显示,样品土壤细菌涉及23门96目150属,优势菌门为变形菌门(Proteobacteria,61%)、放线菌门(Actinobacteria,28%),其中分枝杆菌属(Mycobacterium)为放线菌门最优势菌属(87.3%),其次为红球菌属(Rhodococcus,6.8%)和丙酸杆菌属(Cutibacterium,0.9%)。可培养方法共分离到108株放线菌,归属9科10属,其中优势菌属为链霉菌属(Streptomyces),占65....     

圈养大熊猫肠道乳酸菌分离及益生特性

【背景】大熊猫数量稀少、繁殖困难,在其生长过程中极易感染消化系统疾病甚至死亡。【目的】分析圈养大熊猫肠道可培养乳酸菌的群落结构与功能,筛选具有益生特性的乳酸菌菌株,为大熊猫消化系统疾病的预防和肠道微生物研究提供理论参考及菌种资源。【方法】采用3种培养基分离大熊猫粪便中的乳酸菌,通过革兰氏染色镜检和过氧化氢试验对分离的菌株进行初步鉴定,基于BOXA1R-PCR图谱遗传多样性选取代表菌株进行16S rRNA基因测序分析并进行主成分分析(principal component analysis, PCA),同时分析乳酸菌菌株安全性和益生特性。【结果】通过初步鉴定共分离获得58株乳酸菌,根据BOXA1R-PCR结果挑选20株菌进行测序,结果显示20株菌分属于明串珠菌属(Leuconostoc)、肠球菌属(Enterococcus)、魏斯氏菌属(Weissella)和链球菌属(Streptococcus)这4个属,主成分分析结果表明不同年龄段的大熊猫肠道乳酸菌群落结构存在差异。20株乳酸菌均不溶血,17株乳酸菌对11种抗生素均敏感;11株菌耐pH值2.0酸性条件,14株菌对0.3%的胆盐具有良好...