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[Objective] This study examined the ecological and hydrological variability and regime shift during the Medieval Climate Anomaly (MCA) and Little Ice Age (LIA) in the middle reaches of the Yangtze River. This region is climatically governed by the Asian monsoon, with increased precipitation in summer and decreased in winter. Our study helps deepen our understanding of the history of the regional ecological and hydrological changes and their connections to the monsoon climate. [Methods] Based on two high-resolution stalagmite (YX262 and YX275) δ13C records from Yongxing cave, Hubei province in the middle reaches of the Yangtze River, we reconstructed the history of the local paleoclimate and environment from 1 044-1 954 A.D. by creating a composite of the two records using the iscam program. [Results] The δ13C records show two completely different states during the MCA and LIA, with the lower δ13C values characterizing the MCA period, and the higher δ13 C values the LIA. During the transition from MCA to LIA, δ13C shows an abrupt change. This phenomenon indicates a regime shift from a strong to weak state for the vegetation respiration activity and precipitation variation. This variation is consistent with many stalagmite δ13C records in southwest China and the middle reaches of the Yangtze River. Here, our stalagmite δ13C record shows that the shift of the vegetation cover was rapid from the MCA to LIA. A Rampfit analysis shows that the stalagmite δ13C shift occurred between 1 434-1 460 A.D., lasting 26 years, which is more rapid and significantly longer than the stalagmite δ18O shift. This variation is attributed to both climate deterioration and human activity influences, leading to a reduction of vegetation cover during this period. On the one hand, the rapid transformation of the stalagmite δ13C record in Yongxing cave may be related to the great migration event in the early Ming Dynasty. A large number of migrants swarmed into Hubei province, inevitably leading to large-scale deforestation and land reclamation and changing the ecological environment of the surface soil vegetation. Those behaviors cause positive stalagmite δ13C. On the other hand, the Yongxing δ13C record is correlated with changes in the total solar radiation, intertropical convergence zone (ITCZ), temperature in eastern China, and El Nino-Southern Oscillation (ENSO) on the MCA and LIA event scales. During the MCA period, the total solar irradiance was larger, and the ITCZ was farther north, with a high frequency of El Nino states. However, during the LIA period, the total solar irradiance was relatively small, and the position of ITCZ was more southerly, in the low frequency period of El Nino states. This correlation indicates that the changes of hydrological circulation and vegetation cover in the middle reaches of the Yangtze River had a dynamic relationship with the regional and global climate change during the past millennium, and the impacts of human activities on surface vegetation may be related to the background of regional or global climate change. [Conclusions] By studying the δ13 C record of stalagmites in Yongxing cave in the past millennium, the eco-hydrological characteristics of MCA and LIA were found to be significantly different, which may be related to global climate change and human activities. The study not only clearly establishes the time boundary between MCA and LIA in the middle reaches of the Yangtze River, but also deepens our understanding of the characteristics and causes of eco-hydrological environment changes in the region during the two periods. [ABSTRACT FROM AUTHOR]

Pseudomonas aeruginosa is a major cause of nosocomial infections, particularly in immunocompromised patients or in individuals with cystic fibrosis. The notable ability of P. aeruginosa to inhabit a broad range of environments, including humans, is in part due to its large and diverse genomic repertoire. The genomes of most strains contain a significant number of large and small genomic islands, including those carrying virulence determinants (pathogenicity islands). The pathogenicity island PAPI-1 of strain PAl4 is a cluster of 115 genes, and some have been shown to be responsible for virulence phenotypes in a number of infection models. We have previously demonstrated that PAPI-1 can be transferred to other P. aeruginosa strains following excision from the chromosome of the donor. Here we show that PAPI-1 is transferred into recipient P. aeruginosa by a conjugative mechanism, via a type IV pilus, encoded in PAPI-l by a 10-gene cluster which is closely related to the genes in the enterobacterial plasmid R64. We also demonstrate that the precursor of the major pilus subunit, PilS2, is processed by the chromosomally encoded prepillin peptidase PilD but not its paralog FppA. Our results suggest that the pathogenicity island PAPI-1 may have evolved by acquisition of a conjugation system but that because of its dependence on an essential chromosomal determinant, its transfer is restricted to P. aeruginosa or other species capable of providing a functional prepilin peptidase. doi: 10.1128/JB.00041-10

Abstract Background Ecological, biochemical and genetic resemblance as well as clear differences of virulence between L. monocytogenes and L. innocua make this bacterial clade attractive as a model to examine evolution of pathogenicity. This study was attempted to examine the population structure of L. innocua and the microevolution in the L. innocua-L. monocytogenes clade via profiling of 37 internalin genes and multilocus sequence typing based on the sequences of 9 unlinked genes gyrB, sigB, dapE, hisJ, ribC, purM, gap, tuf and betL. Results L. innocua was genetically monophyletic compared to L. monocytogenes, and comprised four subgroups. Subgroups A and B correlated with internalin types 1 and 3 (except the strain 0063 belonging to subgroup C) and internalin types 2 and 4 respectively. The majority of L. innocua strains belonged to these two subgroups. Subgroup A harbored a whole set of L. monocytogenes-L. innocua common and L. innocua-specific internalin genes, and displayed higher recombination rates than those of subgroup B, including the relative frequency of occurrence of recombination versus mutation (ρ/θ) and the relative effect of recombination versus point mutation (r/m). Subgroup A also exhibited a significantly smaller exterior/interior branch length ratio than expected under the coalescent model, suggesting a recent expansion of its population size. The phylogram based on the analysis with correction for recombination revealed that the time to the most recent common ancestor (TMRCA) of L. innocua subgroups A and B were similar. Additionally, subgroup D, which correlated with internalin type 5, branched off from the other three subgroups. All L. innocua strains lacked seventeen virulence genes found in L. monocytogenes (except for the subgroup D strain L43 harboring inlJ and two subgroup B strains bearing bsh) and were nonpathogenic to mice. Conclusions L. innocua represents a young species descending from L. monocytogenes and comprises four subgroups: two major subgroups A and B, and one atypical subgroup D serving as a link between L. monocytogenes and L. innocua in the evolutionary chain. Although subgroups A and B appeared at approximately the same time, subgroup A seems to have experienced a recent expansion of the population size with higher recombination frequency and effect than those of subgroup B, and might represent the possible evolutionary direction towards adaptation to enviroments. The evolutionary history in the L. monocytogenes-L. innocua clade represents a rare example of evolution towards reduced virulence of pathogens.

The article presents a study which discusses prevalence and antimicrobial susceptibility of Aeromonads species from diseased Chinese soft-shelled turtles (Trionyx sinens). Topics include presence of Aeromonads in aquatic environment, involvement of Aeromonads in fish diseases, such as septicaemia and furunculosis, and Chinese soft-shelled turtle being the important aquaculture species. The study concludes that prevalence of Aeromonads depends on water and sanitation facilities.

Listeria monocytogenes is an important foodborne pathogen encompassing four phylogenetic lineages. Lineages III and IV are rare, but have been reported to show considerable biodiversity, providing important clues for the evolutionary history in Listeria. In this study, analysis of the ascB-dapE locus reveals genetic diversity in lineages III and IV, and is consistent with the classification of sublineages. Four of the six genetic patterns (two of sublineage IIIC and two of lineage IV) are specific to these two lineages. The ascB-dapE locus suggests a hot spot for genome diversification, and serves as an attractive molecular marker for better understanding of the biodiversity and population structure of lineages III and IV strains. [ABSTRACT FROM AUTHOR]

Abstract: In this study, we examined Listeria monocytogenes isolates from Chinese food sources in an attempt to gain further insights on the molecular characteristics and virulence potential of this important foodborne pathogen. Of the 88 L. monocytogenes food isolates recovered, 42 (47.7%) were of serovars 1/2a or 3a; 23 (26.1%) of serovars 1/2b or 3b; 15 (17.0%) of 1/2c or 3c; 6 (6.8%) of serovars 4b, 4d or 4e; and 2 (2.2%) of serovars 4a or 4c. In contrast to inlAB locus conserved in all serovars, internalin cluster between ascB and dapE varies with different serovars, with inlC2DE, inlGC2DE and inlGHE predominantly in serovars 1/2b or 4b, serovar 1/2a and serovar 1/2c. While inlF existed in all the inlGHE- and inlGC2DE-containing isolates but 17.4% of those having inlC2DE, lmo2026 existed in all the inlGHE-containing isolates but 20.0% of those bearing inlGC2DE, suggesting that inlF might have co-evolved with inlGC2DE and inlGHE while lmo2026 with inlGHE only. With the exception of serovar 4a isolate, most serovar isolates demonstrated remarkable ability to form plaques on L929 cells and produced significant mouse mortality irrespective of the internalin gene organization and whether an intact actA gene is present or not. These results indicate that majority of these food isolates may have the potential to cause human diseases if ingested via contaminated foods. Given that serovar 4b accounts for nearly half of human clinical listeriosis cases documented, the relative low proportion of serovar 4b food isolates suggests that this serovar is probably more tolerant of the adverse conditions in the host''s stomach and/or more efficient in entering host cells than serovars 1/2a, 1/2b and 1/2c. [Copyright &y& Elsevier]