泰国狐尾藻(小二仙草科)，中国水生植物一新记录种

报道了近期在我国海南岛发现的小二仙草科狐尾藻属新记录种：泰国狐尾藻[Myriophyllum siamense (Craib) Tardieu],并对该种进行了描述。该植物半水生,无羽状叶,雄花高度退化,在形态特征上同马达加斯加、澳洲和大洋洲的一些种类存在相关性,为狐尾藻属跨洲际散布提供了佐证。其发现也说明了海南岛至今还有不少植物采集的薄弱地区和盲区。     

Enhancement of pyruvate production by osmotic-tolerant mutant of Torulopsis glabrata

Pyruvate production by Torulopsis glabrata was used as a model to study the mechanism of product inhibition and the strategy for enhancing pyruvate production. It was found that the concentration of cell growth and pyruvate deceased with the increase of NaCl and sorbitol concentrations. To enhance the osmotic stress resistance of the strain, an NaCl-tolerant mutant RS23 was screened and selected through a pH-controlled continuous culture with 70 g/L NaCl as the selective criterion. Compared with the parent strain, mutant RS23 could grow well on the medium containing 70 g/L NaCl or 0.6 mol/L sorbitol. Pyruvate concentration by the mutant strain RS23 reached 94.3 g/L at 82 h (yield on glucose 0.635 g/g) in a 7-l fermentor with 150 g/L glucose as carbon source. Pyruvate concentration and yield of mutant RS23 were 41.1% and 11.1% higher than those of the parent strain, respectively. The strategy for enhancing pyruvate production by increasing osmotic stress resistance may provide an alternative approach to enhance organic acids production with yeast.     

pH Influences the Importance of Niche-Related and Neutral Processes in Lacustrine Bacterioplankton Assembly

pH is an important factor that shapes the structure of bacterial communities. However, we have very limited information about the patterns and processes by which overall bacterioplankton communities assemble across wide pH gradients in natural freshwater lakes. Here, we used pyrosequencing to analyze the bacterioplankton communities in 25 discrete freshwater lakes in Denmark with pH levels ranging from 3.8 to 8.8. We found that pH was the key factor impacting lacustrine bacterioplankton community assembly. More acidic lakes imposed stronger environmental filtering, which decreased the richness and evenness of bacterioplankton operational taxonomic units (OTUs) and largely shifted community composition. Although environmental filtering was determined to be the most important determinant of bacterioplankton community assembly, the importance of neutral assembly processes must also be considered, notably in acidic lakes, where the species (OTU) diversity was low. We observed that the strong effect of environmental filtering in more acidic lakes was weakened by the enhanced relative importance of neutral community assembly, and bacterioplankton communities tended to be less phylogenetically clustered in more acidic lakes. In summary, we propose that pH is a major environmental determinant in freshwater lakes, regulating the relative importance and interplay between niche-related and neutral processes and shaping the patterns of freshwater lake bacterioplankton biodiversity.     

背角无齿蚌对浮游藻类的滤食选择性与滤水率研究

以滇池及其附近水体中分布的背角无齿蚌为研究对象,分析其滤水速率及相关的影响因素,研究其食物组成和滤食浮游藻类的选择性,并初步估算其自然种群的滤水能力和控制浮游藻类的潜力.结果表明,背角无齿蚌的滤水率有一定的日变化,傍晚时较高;滤水率与水体中的悬浮物质含量密切相关,随着悬浮物质浓度增加而减少;滤水率与蚌的个体大小有关,体重增加,滤水率下降.对比水体中与蚌消化道内浮游藻类所占的百分比,发现其对浮游藻类的滤食没有显著的选择性.自然水体中背角无齿蚌的滤水能力很低.     

基于Perl脚本在NCBI网站自动或批量获取物种信息

根据物种学名、分类号、任意一段核酸或蛋白质的序列,判定其属于什么物种及其详细分类的信息如何,是生物信息分析的最为基础且重要的环节,但该过程的分析及结果的获取均为手动,费时费力且容易出错。本研究旨在解决如何在NCBI网站上自动或批量获取物种信息。通过解析NCBI在线BLAST结果及其网页源程序特点,利用Perl语言编写自动化脚本,以达到批量获取查询或比对结果的物种分类信息。本研究编写的Perl语言脚本可解决序列在NCBI在线比对后自动或批量获取物种的分类信息问题,适用于细菌、真菌、动物、植物等物种学名、分类号、核酸或蛋白质的任意序列,可以为同行生物数据分析提供参考。     

Bile acid-independent protection against Clostridioides difficile infection

Clostridioides difficile infections occur upon ecological / metabolic disruptions to the normal colonic microbiota, commonly due to broad-spectrum antibiotic use. Metabolism of bile acids through a 7α-dehydroxylation pathway found in select members of the healthy microbiota is regarded to be the protective mechanism by which C. difficile is excluded. These 7α-dehydroxylated secondary bile acids are highly toxic to C. difficile vegetative growth, and antibiotic treatment abolishes the bacteria that perform this metabolism. However, the data that supports the hypothesis that secondary bile acids protect against C. difficile infection is supported only by in vitro data and correlative studies. Here we show that bacteria that 7α-dehydroxylate primary bile acids protect against C. difficile infection in a bile acid-independent manner. We monoassociated germ-free, wildtype or Cyp8b1^-/- (cholic acid-deficient) mutant mice and infected them with C. difficile spores. We show that 7α-dehydroxylation (i.e., secondary bile acid generation) is dispensable for protection against C. difficile infection and provide evidence that Stickland metabolism by these organisms consumes nutrients essential for C. difficile growth. Our findings indicate secondary bile acid production by the microbiome is a useful biomarker for a C. difficile-resistant environment but the microbiome protects against C. difficile infection in bile acid-independent mechanisms.     

气候变化和不同强度造林对大兴安岭主要树种林分信息和地上生物量的长期影响

气候变化及相应火干扰在不同尺度上影响着我国大兴安岭地区森林动态,且在未来的影响可能继续加剧。为了提高森林生态功能和应对气候变暖,国家在分类经营基础上全面实施抚育采伐和补植造林,效果较好,但抚育采伐对森林主要树种的长期影响知之甚少,其在未来气候下的可持续性也有待进一步评估,同时,探讨造林措施对未来森林的影响也显得尤为重要。本文运用森林景观模型LANDIS PRO,模拟气候变化及火干扰、采伐和造林对大兴安岭地区主要树种的长期影响。结果表明:1)模型初始化、短期和长期模拟结果均得到了有效验证,模拟结果与森林调查数据之间无显著性差异(P0.05),基于火烧迹地数据的林火干扰验证亦能够反映当前火干扰的效果,模型模拟结果的可信度较高;2)与当前气候相比,气候变暖及火干扰明显改变了树种组成、年龄结构和地上生物量,B1气候下研究区森林基本上以针叶树种为主要树种,A2气候下优势树种向阔叶树转变;3)与无采伐预案相比,当前气候下,抚育采伐使落叶松的林分密度和地上生物量分别降低了(165±94.9)株/hm~2和(8.5±5.1) Mg/hm~2,增加了樟子松、白桦和云杉等树木株数和地上生物量(3.3—753.4株/hm~2和0.2—4.0 Mg/hm~2),而对山杨的影响较小;B1和A2气候下抚育采伐显著改变林分密度,降低景观尺度地上生物量,进而表现为不可持续;4)B1气候下,推荐实施中低强度造林预案(10%和20%强度),在A2气候下,各强度造林均可在模拟后期增加树种地上生物量。     

Cache algorithms based on adaptive invalidation reports for mobile environments

Caching of frequently accessed data items can reduce the bandwidth requirement in a mobile wireless computing environment. Periodical broadcast of invalidation reports is an efficient cache invalidation strategy. However, this strategy is severely affected by the disconnection and mobility of the clients. In this paper, we present three adaptive cache invalidation report methods, in which the server broadcasts different invalidation reports according to the update and query rates/patterns and client disconnection time while spending little uplink cost. Simulation results show that the adaptive invalidation methods are efficient in improving mobile caching and reducing the uplink and downlink costs without degrading the system throughput. This revised version was published online in July 2006 with corrections to the Cover Date.