Effect of pH and buffer on butyric acid production and microbial community characteristics in bioconversion of rice straw with undefined mixed culture

This study was conducted to identify the optimum pH range and the appropriate buffer for butyric acid production from rice straw by fermentation using an undefined mixed culture. A series of experiments conducted at pH levels of 5.0 ~ 7.0 showed that neutral pH improved rice straw conversion and consequently carboxylic acid production. The highest butyric acid production (up to 6.7 g/L) was achieved at pH of 6.0 ~ 6.5, while it was only 1.7 g/L without pH control or at pH 5.0. Another series of experiments conducted at pH 6.0 ~ 6.5 buffered with CaCO₃, NaHCO₃, NH₄HCO₃ and their combinations indicated that different buffers had different effects onthe product spectrum, and that CaCO₃ combined with NaHCO₃ was an effective buffer for butyric acid production. The highest total volatile fatty acids (about 12.6 g/L) production and one of the two highest butyric acid concentrations (about 7.6 g/L) were obtained by buffering with CaCO₃ combined with NaHCO₃. PCR-DGGE analysis revealed that different pH and buffers also influenced the microbial population distribution. Bacteria were suppressed at low pH, while the bacterial community structures at higher pH varied slightly. Overall, this study presents an alternative method for butyric acid production from lignocellulosic biomass without supplementary cellulolytic enzyme.     

Checkpoint Activation of an Unconventional DNA Replication Program in Tetrahymena

The intra-S phase checkpoint kinase of metazoa and yeast, ATR/MEC1, protects chromosomes from DNA damage and replication stress by phosphorylating subunits of the replicative helicase, MCM2-7. Here we describe an unprecedented ATR-dependent pathway in Tetrahymena thermophila in which the essential pre-replicative complex proteins, Orc1p, Orc2p and Mcm6p are degraded in hydroxyurea-treated S phase cells. Chromosomes undergo global changes during HU-arrest, including phosphorylation of histone H2A.X, deacetylation of histone H3, and an apparent diminution in DNA content that can be blocked by the deacetylase inhibitor sodium butyrate. Most remarkably, the cell cycle rapidly resumes upon hydroxyurea removal, and the entire genome is replicated prior to replenishment of ORC and MCMs. While stalled replication forks are elongated under these conditions, DNA fiber imaging revealed that most replicating molecules are produced by new initiation events. Furthermore, the sole origin in the ribosomal DNA minichromosome is inactive and replication appears to initiate near the rRNA promoter. The collective data raise the possibility that replication initiation occurs by an ORC-independent mechanism during the recovery from HU-induced replication stress.     

Improving Intra-Fractional Target Position Accuracy Using a 3D Surface Surrogate for Left Breast Irradiation Using the Respiratory-Gated Deep-Inspiration Breath-Hold Technique

Purpose

To evaluate the use of 3D optical surface imaging as a surrogate for respiratory gated deep-inspiration breath-hold (DIBH) for left breast irradiation.

Material and Methods

Patients with left-sided breast cancer treated with lumpectomy or mastectomy were selected as candidates for DIBH treatment for their external beam radiation therapy. Treatment plans were created on both free breathing (FB) and DIBH computed tomography (CT) simulation scans to determine dosimetric benefits from DIBH. The Real-time Position Management (RPM) system was used to acquire patient''s breathing trace during DIBH CT acquisition and treatment delivery. The reference 3D surface models from FB and DIBH CT scans were generated and transferred to the “AlignRT” system for patient positioning and real-time treatment monitoring. MV Cine images were acquired during treatment for each beam as quality assurance for intra-fractional position verification. The chest wall excursions measured on these images were used to define the actual target position during treatment, and to investigate the accuracy and reproducibility of RPM and AlignRT.

Results

Reduction in heart dose can be achieved using DIBH for left breast/chest wall radiation. RPM was shown to have inferior correlation with the actual target position, as determined by the MV Cine imaging. Therefore, RPM alone may not be an adequate surrogate in defining the breath-hold level. Alternatively, the AlignRT surface imaging demonstrated a superior correlation with the actual target positioning during DIBH. Both the vertical and magnitude real-time deltas (RTDs) reported by AlignRT can be used as the gating parameter, with a recommended threshold of ±3 mm and 5 mm, respectively.

Conclusion

The RPM system alone may not be sufficient for the required level of accuracy in left-sided breast/CW DIBH treatments. The 3D surface imaging can be used to ensure patient setup and monitor inter- and intra- fractional motions. Furthermore, the target position accuracy during DIBH treatment can be improved by AlignRT as a superior surrogate, in addition to the RPM system.     

Dominance of CTX-M-Type Extended-Spectrum β-Lactamase (ESBL)-Producing Escherichia coli Isolated from Patients with Community-Onset and Hospital-Onset Infection in China

Objective

To investigate CTX-M genotypes among extended-spectrum β-lactamase-producing Escherichia coli (ESBL-EC) isolated from patients with community-onset and hospital-onset infections in China, their clonality and the distribution of CTX-M variants in different specimens of community-onset and hospital-onset infections.

Methods

ESBL-EC isolates were collected from general hospitals from 2011 to 2012 in China. Broth microdilution method antimicrobial susceptibility testing of 16 antibiotics was performed. Clinical data from community-onset and hospital-onset infections due to ESBL-EC were analyzed. ESBL-encoding genes were amplified by PCR and sequenced, and multilocus sequence typing (MLST) was performed for a random selection of predominant CTX-M type strains identified.

Results

A total of 1,168 ESBL-EC isolates were obtained from various clinical specimens, 41.7% of which were responsible for causing community-onset infections. The presence of urinary calculi was higher in community-onset infections, whereas malignancy, cardiovascular and cerebrovascular diseases, dementia, chronic renal disease, diabetes mellitus and surgical treatment were found to have higher proportions in hospital-onset infections. There was no significant difference in trauma between community-onset and hospital-onset infections. 96.2% of the isolates were detected to harbor bla _CTX-M genes. bla _CTX-M-1 group and bla _CTX-M-9 group were detected at 40.7% and 48.7% respectively, and both positive group accounted for 10.6%. bla _CTX-M-55 (24.8%) and bla _CTX-M-15 (18.2%) were the major genotypes in bla _CTX-M-1 group while bla _CTX-M-14 (46.8%) was predominant in bla _CTX-M-9 group. A comparison of bla _CTX-M distribution in different specimens between ESBL-EC causing community-onset and hospital-onset infection showed no significant difference. A total of 229 isolates were tested for MLST. ST131 (14%) was the predominant type. ST648, ST405 and ST1193 were also detected.

Conclusions

Community-onset ESBL-EC has emerged as a common pathogen in China. CTX-M-14 is the most commonly encountered, CTX-M-55 and CTX-M-15 have spread rapidly. ST131 is the predominant clonal group, and the great diversity of CTX-M-producing isolates of E. coli has emerged in China.     

基于光合系统参数建立马铃薯耐荫性综合评价体系

为构建便捷的马铃薯(Solanum tuberosum)耐荫性综合评价体系并发掘耐荫种质, 以35个马铃薯品种(系)为实验材料, 测定块茎膨大期遮荫下植株叶片叶绿素含量、光合能力和叶绿素荧光等光合参数及收获后块茎单株产量和淀粉含量等指标。根据耐荫系数, 利用主成分分析法、隶属函数法、聚类分析法和逐步回归分析法进行综合评价。通过主成分分析将马铃薯耐荫性相关的13个单项光合指标转换为6个综合指标, 代表了全部信息的87.51%。以此计算各种质的隶属函数值, 并以主成分的贡献率进行加权, 最终获得所用材料耐荫性的综合评价值(D值)。根据D值聚类分析结果将35个马铃薯分为4类, 其中Eshu10和Lishu6分别为耐荫性最强和最弱的品种。通过逐步回归分析建立了马铃薯耐荫性评价数学模型: D=0.060+0.106G_s+0.214qP+0.143NPQ。同时, 用该评价体系鉴定为耐荫性强的品种(系)在遮荫后其产量和/或淀粉含量等指标减幅均低于耐荫性弱的种质, 表明该评价体系可用于快速评价和预测马铃薯种质的耐荫性。     

5-脱氧杂氮胞苷抑制小鼠附植前的胚胎发育

DNA甲基化在哺乳动物发育过程中有关键作用．在小鼠附植前胚胎发育过程中,DNA甲基化一直处于动态变化过程中．通过将体外受精胚在5-AZA-CdR中持续培养,研究5-AZA-CdR对小鼠附植前胚胎发育的影响,为附植前胚胎发育机理的研究及5-AZA-CdR的毒副作用研究提供试验基础．从原核期加入不同浓度的5-AZA-CdR时,胚胎不能发育到桑椹胚(0.2 和1.0 μmol/L)和4-细胞胚(5.0 μmol/L);从2-细胞期加入时,胚胎阻滞于未致密化的8-细胞(0.2 和1.0 μmol/L)和3/4-细胞期(5.0 μmol/L);而当从4-细胞加入时,虽然胚胎能够发育到早期桑椹胚,但发育比例同对照相比显著降低(P < 0.05)．进一步检测凋亡、基因组DNA甲基化和整体转录活性,结果显示,高浓度的5-AZA-CdR导致8-细胞和早期桑椹胚发生早期凋亡,而低浓度的5-AZA-CdR引起8-细胞和早期桑椹胚基因组DNA甲基化的降低和转录活性的降低,并且这种降低呈浓度依赖性．所以加入低浓度的5-AZA-CdR时,胚胎的DNA甲基化降低,引起转录活性的降低,进而导致胚胎发育的停滞．     

中国石灰岩专性凤仙花叶表皮特征及其分类学意义

通过光学显微镜和扫描电镜技术对中国产的8种凤仙花科植物叶表皮微形态特征进行了实验研究,其中6种产于石灰岩地区,另外2种作为对照.结果表明,中国石灰岩地区的6种凤仙花的叶表皮微形态上、下表皮差异明显,上表皮细胞为不规则形和多边形,一般不具气孔器;下表皮细胞均为不规则形,均具气孔器,气孔器多为不等型.上、下表皮细胞形状、垂...