Osmoregulated periplasmic glucans are needed for competitive growth and biofilm formation by Salmonella enterica serovar Typhimurium in leafy-green vegetable wash waters and colonization in mice

Osmoregulated periplasmic glucans (OPGs) are major periplasmic constituents of Gram-negative bacteria. The role of OPGs has been postulated in symbiotic as well as pathogenic host–microorganism interactions. Here, we report the role of OPGs from Salmonella enterica serovar Typhimurium during growth and biofilm formation in leafy-green vegetable wash water. The opgGH mutant strain, which was defective in OPG biosynthesis, initiated the growth at a slower rate in wash waters obtained from spinach, lettuce and green collard and severely impaired biofilm formation. The lack of OPG synthesis did not influence biofilm formation by the opgGH mutant in low-nutrient low-osmolarity laboratory media. In coculture experiments initiated with equal proportions of cells, the opgGH mutant was outnumbered by the wild-type strain under the planktonic as well as the biofilm growth conditions. The opgGH mutant strain poorly colonized mouse organs when introduced orally along with the wild-type strain. This is the first report demonstrating the role of OPGs of Salmonella in competitive colonization of biofilms, planktonic cultures and mouse organs.     

不同生长环境下水稻穗伸出度的QTL分析

以十和田/昆明小白谷225个F14家系为作图群体,在云南省弥勒县(正常生长环境)、嵩明县(自然低温胁迫环境)、丽江市(自然低温胁迫环境)等3个试点不同年份共5种不同生长环境下进行了水稻主穗和分蘖穗穗伸出度的异地鉴定,并利用SSR标记对水稻穗伸出度进行了QTL分析。检测结果表明,在5种不同的生长环境下共检测到12个与水稻穗伸出度相关的QTL,分别分布于第1(2个QTLs)、2、4、6(3个QTLs)、7(3个QTLs)、9(2个QTLs)号染色体,对表型的贡献率为3.72%~22.17%。其中与主穗穗伸出度相关的QTL共11个,与分蘖穗穗伸出度相关的QTL共7个,其中6个在主穗和分蘖穗上均检测到。在与主穗穗伸出度相关的11个QTL中,q PE-7-1在4种环境下均被检测到,解释的表型变异为9.49%~22.17%;q PE-1-1、q PE-1-2、q PE-6-1和q PE-9-2 4个QTL在2种环境下均被检测到。在与分蘖穗穗伸出度相关的7个QTL中,q PE-1-2、q PE-7-1和q PE-6-1 3个QTL在2种环境中均被检测到,解释的表型变异率分别为4.35%~12.64%、13.22%~20.89%和11.49%~15.73%。     

GENETIC VARIATION AND THE EVOLUTION OF EPIGENETIC REGULATION

Epigenetic variation has been observed in a range of organisms, leading to questions of the adaptive significance of this variation. In this study, we present a model to explore the ecological and genetic conditions that select for epigenetic regulation. We find that the rate of temporal environmental change is a key factor controlling the features of this evolution. When the environment fluctuates rapidly between states with different phenotypic optima, epigenetic regulation may evolve but we expect to observe low transgenerational inheritance of epigenetic states, whereas when this fluctuation occurs over longer time scales, regulation may evolve to generate epigenetic states that are inherited faithfully for many generations. In all cases, the underlying genetic variation at the epigenetically regulated locus is a crucial factor determining the range of conditions that allow for evolution of epigenetic mechanisms.     

Nucleic acid and protein factors involved in Escherichia coli polynucleotide phosphorylase function on RNA

It has been reported that polynucleotide phosphorylase (PNPase) binds to RNA via KH and S1 domains, and at least two main complexes (I and II) have been observed in RNA-binding assays. Here we describe PNPase binding to RNA, the factors involved in this activity and the nature of the interactions observed in vitro. Our results show that RNA length and composition affect PNPase binding, and that PNPase interacts primarily with the 3′ end of RNA, forming the complex I-RNA, which contains trimeric units of PNPase. When the 5′ end of RNA is blocked by a hybridizing oligonucleotide, the formation of complex II-RNA is inhibited. In addition, PNPase was found to form high molecular weight (>440 kDa) aggregates in vitro in the absence of RNA, which may correspond to the hexameric form of the enzyme. We confirmed that PNPase in vitro RNA binding, degradation and polyadenylation activities depend on the integrity of KH and S1 domains. These results can explain the defective in vivo autoregulation of PNPase71, a KH point substitution mutant. As previously reported, optimal growth of a cold-sensitive strain at 18 °C requires a fully active PNPase, however, we show that overexpression of a novel PNPaseΔS1 partially compensated the growth impairment of this strain, while PNPase71 showed a minor compensation effect. Finally, we propose a mechanism of PNPase interactions and discuss their implications in PNPase function.     

"Cold spots" in protein cold adaptation: Insights from normalized atomic displacement parameters (B'-factors)

Many analyses published in the last decade suggest that enzymes isolated from cold-adapted organisms are characterized by a higher flexibility of their molecular structure. Recently, it has been argued that all cold-adapted enzymes with catalytic efficiency greater than that of their mesophilic counterparts display local flexibility or rigidity that are likely to cooperate, each acting on specific areas of the enzyme structure. Here we report an analysis of the normalized thermal B-factor distributions in psychrophilic proteins compared with those of their mesophilic and thermophilic counterparts with the aim to detect statistically significant local variations of relative backbone flexibility possibly linked to cold adaptation. We utilized a strategy based mainly on intra-family comparison of local distribution of normalized B-factors. After careful statistical treatment of data, the picture emerging from our results suggests that the distribution of the flexibility in psychrophilic enzymes is locally more heterogeneous than in their respective mesophilic homologues.     

Fruit and seed heteromorphism in the cold desert annual ephemeral Diptychocarpus strictus (Brassicaceae) and possible adaptive significance

Background and Aims

Diptychocarpus strictus is an annual ephemeral in the cold desert of northwest China that produces heteromorphic fruits and seeds. The primary aims of this study were to characterize the morphology and anatomy of fruits and seeds of this species and compare the role of fruit and seed hetermorphism in dispersal and germination.

Methods

Shape, size, mass and dispersal of siliques and seeds and the thickness of the mucilage layer on seeds were measured, and the anatomy of siliques and seeds, the role of seed mucilage in water absorption/dehydration, germination and adherence of seeds to soil particles, the role of pericarp of lower siliques in seed dormancy and seed after-ripening and germination phenology were studied using standard procedures.

Key Results

Plants produce dehiscent upper siliques with a thin pericarp containing seeds with large wings and a thick mucilage layer and indehiscent lower siliques with a thick pericarp containing nearly wingless seeds with a thin mucilage layer. The dispersal ability of seeds from the upper siliques was much greater than that of intact lower siliques. Mucilage increased the amount of water absorbed by seeds and decreased the rate of dehydration. Seeds with a thick mucilage layer adhered to soil particles much better than those with a thin mucilage layer or those from which mucilage had been removed. Fresh seeds were physiologically dormant and after-ripened during summer. Non-dormant seeds germinated to high percentages in light and in darkness. Germination of seeds from upper siliques is delayed until spring primarily by drought in summer and autumn, whereas the thick, indehiscent pericarp prevents germination for >1 year of seeds retained in lower siliques.

Conclusions

The life cycle of D. strictus is morphologically and physiologically adapted to the cold desert environment in time and space via a combination of characters associated with fruit and seed heteromorphism.     

不同低温胁迫下粳稻耐冷种质的孕穗期耐冷性比较

为粳稻孕穗期耐冷标准品种的建立和耐冷遗传育种研究提供优异基因资源,利用人工低温气候室,采用15℃、17℃、19℃3种胁迫温度,4d和6d两种胁迫时间,3×2交互式设计的方法,对来自黑龙江、吉林、辽宁和云南的12份粳稻种质进行了孕穗期耐冷性强度的研究。结果表明,随着低温胁迫的增强,各水稻品种的平均空壳率都随之增加;在15℃/6d胁迫下,供试品种平均空壳率的方差和变异系数达到最大,该胁迫强度可被选用于孕穗期强耐冷种质的筛选。依据15℃/6d胁迫下供试品种平均空壳率的方差分析及多重比较结果,空育131和龙稻3号具有极强的孕穗期耐冷性。不同地区可根据参试品种在本试验中的耐冷表现,并结合当地水稻种植区的光温条件选择相应的耐冷标准品种。     

Fluvial response to late Quaternary climate change in NE Queensland, Australia

Samples of alluvial and colluvial deposits from the coastal plain and coastal valleys north and south of Cairns (17°S) have been dated using optically stimulated luminescence (OSL) protocols, with additional thermoluminescence (TL) and Radiocarbon assays. Coarse fanglomerates from elevated coastal terraces date back to 81 ka, but most are clustered in oxygen isotope stage three (OIS3, 64-28 ka), indicating high-energy conditions during this period. Extensive fans and terraces of finer calibre sediments are widely represented grading from coarse gravels and cobbles in proximal zones fine sand and silt in distal areas. Dates show that vertical accumulation of 10-15 m of sediment occurred between ∼ 28 and 14 ka (OIS2), after which the fans were dissected and Holocene deposits become fragmentary. A number of deposits indicating hillslope instability were successfully dated and these fall mainly into OIS3 and post 12 ka. These results are interpreted as catchment responses to Late Pleistocene climate and vegetation changes, documented elsewhere from local pollen and ocean drilling sites. Correlation with these records and with evidence for regional climate change from the Austral-Asian region is good and indicates that these changes were sufficient to transform fluvial activity and slope processes.