How Chlamydomonas keeps track of the light once it has reached the right phototactic orientation.

By using a real-time assay that allows measurement of the phototactic orientation of the unicellular alga Chlamydomonas with millisecond time resolution, it can be shown that single photons not only induce transient direction changes but that fluence rates as low as 1 photon cell(-1) s(-1) can already lead to a persistent orientation. Orientation is a binary variable, i.e., in a partially oriented population some organisms are fully oriented while the rest are still at random. Action spectra reveal that the response to a pulsed stimulus follows the Dartnall-nomogram for a rhodopsin while the response to a persistent stimulus falls off more rapidly toward the red end of the spectrum. Thus light of 540 nm, for which chlamy-rhodopsin is equally sensitive as for 440-nm light, induces no measurable persistent orientation while 440-nm light does. A model is presented which explains not only this behavior, but also how Chlamydomonas can track the light direction and switches between a positive and negative phototaxis. According to the model the ability to detect the direction of light, to make the right turn and to stay oriented, is a direct consequence of the helical path of the organism, the orientation of its eyespot relative to the helix-axis, and the special shielding properties of eyespot and cell body. The model places particular emphasis on the fact that prolonged swimming into the correct direction not only requires making a correct turn initially, but also avoiding further turns once the right direction has been reached.     

Body-size control: how an insect knows it has grown enough

Insulin signaling controls organ growth and final body size in insects. Recent results have begun to clarify how insulin signaling drives organ growth to match nutrient levels, but have not yet elucidated how insulin signaling controls final body size.     

2007年重庆市流脑流行季节前健康人群抗体水平和带菌率调查

为了解重庆市流脑流行季节前健康人群免疫水平和带菌状况,预测发病趋势,提出新的免疫策略,提供有效的预防措施。按照全国流脑监测方案并结合重庆市2006年流脑疫情情况,选择重庆市北碚区、长寿区和万盛区为2007年流脑监测点,采集0~、5~、10~、15~、25~、35~及45岁以上共7个年龄组人群的静脉血和咽拭子,分别进行抗体水平和带菌率检测。结果显示,重庆市健康人群A群流脑IgG抗体的阳性率为76.02%(485/638),C群流脑IgG抗体的阳性率为47.65%(304/638),健康人群脑膜炎奈瑟菌(简称Nm)带菌率为0.47%(3/638)。重庆市健康人群A群流脑IgG抗体阳性率维持在较高水平,而C群流脑IgG抗体的阳性率较低,提示该市大部分人群对A群流脑有免疫作用,但C群抗体水平较低,有引起局部流脑爆发的风险。     

The thermostability of glucoamylase immobilized in different ways has a certain limit.

Thermostability of glucoamylase from Aspergillus niger is increased both by immobilization and substrate binding. However, the total superimposed stabilization effect at a given condition is apparently restricted by a certain limit which hardly depends on the mode of immobilization of the enzyme, and is determined mostly by the enzyme-substrate complex formation.     

某部作训前后真菌性皮肤病调查

为进一步提高部队作训期间皮肤病健康保障的质量,针对性地开展常见真菌性皮肤病的预防、治疗和健康宣教工作,笔者于2009年7～10月对某部执行任务前后全体官兵真菌感染性皮肤病的发病情况进行了调查。     

Forest maturity has a stronger influence on the prevalence of spider monkeys than howler monkeys in an anthropogenically impacted rainforest landscape

Primates - The transformation and depletion of primary forest over the past few decades have placed almost half of the world’s primate species under the threat of extinction. Developing any...     

How to obtain clues from the otoliths of an adult fish about the aquatic environment it has been in as a larva

Analyses by mass spectrometry of carbon/oxygen isotope compositions of lapilli and sagittal otoliths in the catadromous New Zealand mullet Mugil cephalus permit us to draw the following conclusions:

• 1.1. Information on the type of aquatic environment a larval fish has experienced can be obtained from otoliths of the adult in two ways: drilled cores along the long axis of the sagitta can be analysed sequentially for carbon/oxygen isotope composition.
• 2.2. The oldest isotope ratios, representing the time when the first aragonite was laid down, are closest to the centre, while material nearer to the edges of the earstone reflects carbon/oxygen isotope values of the environment the fish had experienced at the time of capture.
• 3.3. The second approach involves the lapilli. These otoliths are universally smaller than the sagittae in adult fish, but at hatching the two are of equal size in many species of fish, including the mullet.
• 4.4. Consequently, the lapillus carbon/oxygen isotope ratio closely resembles that of the larval environment (in our case, the estuarine waters of New Zealand's North Island), whereas averaged carbon/oxygen isotope ratios of the sagittae more closely agree with those of river water.

     

Clostridium difficile has an original peptidoglycan structure with a high level of N-acetylglucosamine deacetylation and mainly 3-3 cross-links

The structure of the vegetative cell wall peptidoglycan of Clostridium difficile was determined by analysis of its constituent muropeptides with a combination of reverse-phase high pressure liquid chromatography separation of muropeptides, amino acid analysis, mass spectrometry and tandem mass spectrometry. The structures assigned to 36 muropeptides evidenced several original features in C. difficile vegetative cell peptidoglycan. First, it is characterized by a strikingly high level of N-acetylglucosamine deacetylation. In addition, the majority of dimers (around 75%) contains A(2)pm(3) → A(2)pm(3) (A(2)pm, 2,6-diaminopimelic acid) cross-links and only a minority of the more classical Ala(4) → A(2)pm(3) cross-links. Moreover, a significant amount of muropeptides contains a modified tetrapeptide stem ending in Gly instead of D-Ala(4). Two L,D-transpeptidases homologues encoding genes present in the genome of C. difficile 630 and named ldt(cd1) and ldt(cd2), were inactivated. The inactivation of either ldt(cd1) or ldt(cd2) significantly decreased the abundance of 3-3 cross-links, leading to a marked decrease of peptidoglycan reticulation and demonstrating that both ldt(cd1)-and ldt(cd2)-encoded proteins have a redundant L,D-transpeptidase activity. The contribution of 3-3 cross-links to peptidoglycan synthesis increased in the presence of ampicillin, indicating that this drug does not inhibit the L,D-transpeptidation pathway in C. difficile.