Femtosecond primary charge separation in Synechocystis sp. PCC 6803 photosystem I

AbstractThe ultrafast (<100fs) conversion of delocalized exciton into charge-separated state between the primary donor P700 (bleaching at 705nm) and the primary acceptor A0 (bleaching at 690nm) in photosystem I (PS I) complexes from Synechocystis sp. PCC 6803 was observed. The data were obtained by application of pump–probe technique with 20-fs low-energy pump pulses centered at 720nm. The earliest absorbance changes (close to zero delay) with a bleaching at 690nm are similar to the product of the absorption spectrum of PS I complex and the laser pulse spectrum, which represents the efficiency spectrum of the light absorption by PS I upon femtosecond excitation centered at 720nm. During the first ∼60fs the energy transfer from the chlorophyll (Chl) species bleaching at 690nm to the Chl bleaching at 705nm occurs, resulting in almost equal bleaching of the two forms with the formation of delocalized exciton between 690-nm and 705-nm Chls. Within the next ∼40fs the formation of a new broad band centered at ∼660nm (attributed to the appearance of Chl anion radical) is observed. This band decays with time constant simultaneously with an electron transfer to A1 (phylloquinone). The subtraction of kinetic difference absorption spectra of the closed (state P700+A0A1) PS I reaction center (RC) from that of the open (state P700A0A1) RC reveals the pure spectrum of the P700+A0− ion–radical pair. The experimental data were analyzed using a simple kinetic scheme: An* →k1 [(PA0)*A1→<100fs P+A0−A1] →k2P+A0A1−, and a global fitting procedure based on the singular value decomposition analysis. The calculated kinetics of transitions between intermediate states and their spectra were similar to the kinetics recorded at 694 and 705nm and the experimental spectra obtained by subtraction of the spectra of closed RCs from the spectra of open RCs. As a result, we found that the main events in RCs of PS I under our experimental conditions include very fast (<100fs) charge separation with the formation of the P700+A0−A1 state in approximately one half of the RCs, the ∼5-ps energy transfer from antenna Chl* to P700A0A1 in the remaining RCs, and ∼25-ps formation of the secondary radical pair P700+A0A1−

Molecular typing of ST239-MRSA-III from diverse geographic locations and the evolution of the SCCmec III element during its intercontinental spread

ST239-MRSA-III is probably the oldest truly pandemic MRSA strain, circulating in many countries since the 1970s. It is still frequently isolated in some parts of the world although it has been replaced by other MRSA strains in, e.g., most of Europe. Previous genotyping work (Harris et al., 2010; Castillo-Ramírez et al., 2012) suggested a split in geographically defined clades. In the present study, a collection of 184 ST239-MRSA-III isolates, mainly from countries not covered by the previous studies were characterized using two DNA microarrays (i) targeting an extensive range of typing markers, virulence and resistance genes and (ii) a SCCmec subtyping array. Thirty additional isolates underwent whole-genome sequencing (WGS) and, together with published WGS data for 215 ST239-MRSA-III isolates, were analyzed using in-silico analysis for comparison with the microarray data and with special regard to variation within SCCmec elements. This permitted the assignment of isolates and sequences to 39 different SCCmec III subtypes, and to three major and several minor clades. One clade, characterized by the integration of a transposon into nsaB and by the loss of fnbB and splE was detected among isolates from Turkey, Romania and other Eastern European countries, Russia, Pakistan, and (mainly Northern) China. Another clade, harboring sasX/sesI is widespread in South-East Asia including China/Hong Kong, and surprisingly also in Trinidad & Tobago. A third, related, but sasX/sesI-negative clade occurs not only in Latin America but also in Russia and in the Middle East from where it apparently originated and from where it also was transferred to Ireland. Minor clades exist or existed in Western Europe and Greece, in Portugal, in Australia and New Zealand as well as in the Middle East. Isolates from countries where this strain is not epidemic (such as Germany) frequently are associated with foreign travel and/or hospitalization abroad. The wide dissemination of this strain and the fact that it was able to cause a hospital-borne pandemic that lasted nearly 50 years emphasizes the need for stringent infection prevention and control and admission screening

Role of hydrogen bond alternation and charge transfer states in photoactivation of the Orange Carotenoid Protein

Here, we propose a possible photoactivation mechanism of a 35-kDa blue light-triggered photoreceptor, the Orange Carotenoid Protein (OCP), suggesting that the reaction involves the transient formation of a protonated ketocarotenoid (oxocarbenium cation) state. Taking advantage of engineering an OCP variant carrying the Y201W mutation, which shows superior spectroscopic and structural properties, it is shown that the presence of Trp201 augments the impact of one critical H-bond between the ketocarotenoid and the protein. This confers an unprecedented homogeneity of the dark-adapted OCP state and substantially increases the yield of the excited photoproduct S*, which is important for the productive photocycle to proceed. A 1.37 Å crystal structure of OCP Y201W combined with femtosecond time-resolved absorption spectroscopy, kinetic analysis, and deconvolution of the spectral intermediates, as well as extensive quantum chemical calculations incorporating the effect of the local electric field, highlighted the role of charge-transfer states during OCP photoconversion

Role of hydrogen bond alternation and charge transfer states in photoactivation of the Orange Carotenoid Protein

Here, we propose a possible photoactivation mechanism of a 35-kDa blue light-triggered photoreceptor, the Orange Carotenoid Protein (OCP), suggesting that the reaction involves the transient formation of a protonated ketocarotenoid (oxocarbenium cation) state. Taking advantage of engineering an OCP variant carrying the Y201W mutation, which shows superior spectroscopic and structural properties, it is shown that the presence of Trp201 augments the impact of one critical H-bond between the ketocarotenoid and the protein. This confers an unprecedented homogeneity of the dark-adapted OCP state and substantially increases the yield of the excited photoproduct S*, which is important for the productive photocycle to proceed. A 1.37 Å crystal structure of OCP Y201W combined with femtosecond time-resolved absorption spectroscopy, kinetic analysis, and deconvolution of the spectral intermediates, as well as extensive quantum chemical calculations incorporating the effect of the local electric field, highlighted the role of charge-transfer states during OCP photoconversion

Children’s migration and chronic illness among older parents ‘left behind’ in China

The relationship between adult children’s migration and the health of their older parents ‘left behind’ is an emerging research area and existing studies reflect mixed findings. This study aims to investigate the association between having migrant (adult) children and older parents’ chronic illness in China, using chronic stomach or other digestive diseases as a proxy. Secondary analysis of the national baseline survey of the 2011 China Health and Retirement Longitudinal Study (CHARLS) was conducted. Analyses were conducted in a total of sample of 6495 individuals aged 60 years and above from 28 out of 31 provinces in China, who had at least one child at the baseline survey. Binary logistic regression was used. The prevalence of any of the diagnosed conditions of chronic stomach or other digestive diseases was higher among older people with a migrant son than among those without (27 percent vs 21 percent, p < 0.001). More specifically, the odds ratio of reporting a disease was higher among older adults with at least one adult son living in another county or province than among those with all their sons living closer (OR = 1.29, 95% CI = 1.10–1.51). The results from this large sample of older adults support the hypothesis that migration of sons significantly increases the risk of chronic stomach and other digestive diseases among ‘left behind’ elderly parents in contemporary China

The structure of IS<i>256</i> and its extrachromosomal circular DNA in OC8.

<p>In A, the structure of IS<i>256</i> (OC8) is based on the OC8 genome sequence (GenBank accession number AP017377); the structure was very similar to previously described IS<i>256</i> structures [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0164168#pone.0164168.ref027" target="_blank">27</a>,<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0164168#pone.0164168.ref048" target="_blank">48</a>,<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0164168#pone.0164168.ref049" target="_blank">49</a>]. PCR primers to detect an IS<i>256</i> circular DNA were designed based on the OC8 genome sequence. In B, the PCR primer set (R-R1 and L-R2, shown in A) exactly detected IS<i>256</i> circular DNA for OC8 (PCR product size, approximately 200 bp), while there were no amplified bands for strain USA300-0114, which lacked IS<i>256</i>. In C (and B), the 194-bp nucleotide sequence of the estimated PCR product, perfectly matched the IR_L side and IR_R side regions of IS<i>256</i> (OC8), and contained a 6-bp stretch, marked in red; 26-bp imperfect IR sequences and 6-bp stretch sequences were underlined in C. However, the 6-bp stretch data showed a “mixed” result, with TTTTTT as the highest base content (followed by AAAAAA). Since the 6-bp stretch originates from a flanking <i>att</i> sequence [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0164168#pone.0164168.ref048" target="_blank">48</a>] and OC8 carries 19 IS<i>256</i> copies with distinct <i>att</i> sequences, the “mixed” 6-bp stretch reflects the presence of heterogeneous circular DNA (in terms of stretch sequences) in OC8. This observation is consistent with the AT-rich <i>att</i> sequences of 19 IS<i>256</i> copies on the genome.</p

Relevant characteristics of MRSA strains^a.

<p>Relevant characteristics of MRSA strains<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0164168#t001fn001" target="_blank">^a</a>.</p

Sequence comparison between OC8 and USA300 FPR3757 genomes and visualization of a large genomic inversion.

<p>Genomic sequence comparisons were performed using WebACT for the visualization of genomic inversions. The genome sequence of USA300 FPR3757 was from GenBank Accession number CP000255. The OC8 inverted region relative to USA300 FPR3757 is highlighted in blue.</p

PCR targeting the OC8-type megabase inversion (MbIN).

<p>In A and B, PCR primers targeting the junction sites of OC8 MbIN (A-C and B-D) and those targeting the corresponding region of USA300 FPR3757 (A-B and C-D) were designed based on the OC8 or USA300 FPR3757 complete genome sequence, respectively. The structures of the MbIN junction regions of OC8 and the corresponding regions of USA300 FPR3757 are from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0164168#pone.0164168.g005" target="_blank">Fig 5</a>. In C to E, PCR products with an asterisk were sequenced, and the sequences determined were consistent with the OC8 or USA300 FPR3757 genome sequence. ST8_Kras is ST8/SCC<i>mec</i>IVc MRSA from Krasnoyarsk, Siberian Russia. The geographical location of MRSA isolated in European Russia: Mow, Moscow; St. P, St. Petersburg; Yar, Yaroslavl. Regarding Far Eastern Russia, MRSA was isolated in Vladivostok.</p