ALBERT

Description: As a leading pathogen, Edwardsiella piscicida can cause hemorrhagic septicemia in fish and gastro-intestinal infections in humans. The two-component regulatory system EsrA-EsrB plays essential roles in pathogenesis through the type III and type VI secretion systems, and hemolysin production in E. piscicida . It is unclear whether other virulence- or stress response-associated genes are regulated by EsrA-EsrB. In this study, the proteomes of wild-type E. piscicida EIB202 and esrB mutant strains were compared to reveal EsrB regulon components after growth in Luria–Bertani broth (LB). Overall, the expression levels of nine genes exhibited significant changes, and five of them required the presence of EsrB, while others exhibited higher levels in the esrB mutant. The diverse functions of these proteins were identified, including amino acid metabolism, oxidative stress defense and energy production. Interestingly, superoxidase dismutase and thiol peroxidase were the most significantly down-regulated by EsrB. Furthermore, other reported reactive oxygen species (ROS) resistance-related genes were also down-regulated by EsrB as revealed by quantitative real-time. Compared with the wild-type and the complement strain esrB + , esrB displayed a significantly enhanced ROS resistance. These results demonstrated that EsrB plays important roles in the ROS resistance pathway in E. piscicida grown in LB conditions.

Description: The sepsis caused by Vibrio vulnificus is characterized by an average incubation period of 26 h and a high mortality rate exceeding 50%. The fast growth and dissemination of V. vulnificus in vivo lead to poor clinical outcomes in patients. Therefore, elucidation of the proliferation mechanisms of this organism in vivo may lead to the development of an effective therapeutic strategy. In this study, we focused on the low oxygen concentration in the intestinal milieu because of its drastic difference from that in air. Fumarate and nitrate reduction regulatory protein (FNR) is known to be a global transcriptional regulator for adaptation to anaerobic conditions in various bacteria. We generated a strain of V. vulnificus in which the fnr gene was replaced with an erythromycin resistance gene ( fnr :: erm mutant). When the fnr :: erm mutant was tested in a growth competition assay against the wild-type (WT) in vivo , the competitive index of fnr :: erm mutant to WT in the intestinal loop and liver was 0.378 ± 0.192 (mean ± SD) and 0.243 ± 0.123, respectively. These data suggested that FNR is important for the proliferation of V. vulnificus in the intestine to achieve a critical mass to be able to invade the systemic circulation.

Description: Helicobacter pylori is an important cause of gastric pathologies and persistent infection can lead to stomach cancer. Virulent H. pylori strains encode a type IV secretion system responsible for translocation of the oncogenic CagA protein into cells of the gastric mucosa. Gene HP0522 encodes the essential component Cag (Cag3), and we show by gel filtration and cross-linking that purified Cag forms high molecular mass complexes. In contrast, its interaction partner CagT is mostly monomeric, but co-fractionates after gel filtration. Analysis by transmission electron microscopy revealed that purified Cag complexes can self-assemble ring-like structures. Cag-overexpressing Escherichia coli exhibits membrane-associated circular profiles in regions of the cell envelope with intense immunogold labelling with a Cag-specific antiserum. Our results suggest that Cag has the capacity to form macromolecular structures contributing to the assembly of the type IV secretion system.

Description: Helicobacter pylori commonly infects the epithelial layer of the human stomach and in some individuals causes peptic ulcers, gastric adenocarcinoma or gastric lymphoma. Helicobacter pylori is a genetically diverse species, and the most important bacterial virulence factor that increases the risk of developing disease, versus asymptomatic colonization, is the cytotoxin associated gene pathogenicity island ( cag PAI). Socially housed rhesus macaques are often naturally infected with H. pylori similar to that which colonizes humans, but little is known about the cag PAI. Here we show that H. pylori strains isolated from naturally infected rhesus macaques have a cag PAI very similar to that found in human clinical isolates, and like human isolates, it encodes a functional type IV secretion system. These results provide further support for the relevance of rhesus macaques as a valid experimental model for H. pylori infection in humans.

Description: Sporisorium scitamineum is the fungus that causes sugarcane smut disease. Despite of the importance of sugarcane for Brazilian agribusiness and the persistence of the pathogen in most cropping areas, genetic variation studies are still missing for Brazilian isolates. In this study, sets of isolates were analyzed using two molecular markers (AFLP and telRFLP) and ITS sequencing. Twenty-two whips were collected from symptomatic plants in cultivated sugarcane fields of Brazil. A total of 41 haploid strains of compatible mating types were selected from individual teliospores and used for molecular genetic analyses. telRFLP and ITS analyses were expanded to six Argentine isolates, where the sugarcane smut was first recorded in America. Genetic relationship among strains suggests the human-mediated dispersal of S. scitamineum within the Brazilian territory and between the two neighboring countries. Two genetically distinct groups were defined by the combined analysis of AFLP and telRFLP. The opposite mating-type strains derived from single teliospores were clustered together into these main groups, but had not always identical haplotypes. telRFLP markers analyzed over two generations of selfing and controlled outcrossing confirmed the potential for emergence of new variants and occurrence of recombination, which are relevant events for evolution of virulence and environmental adaptation.

Description: Burkholderia pseudomallei causes melioidosis, a potentially fatal infectious disease in tropical and subtropical countries worldwide. The intracellular behaviour of this pathogen in host cells has been reported to impact the severity of melioidosis, including the development of septicaemia, a consequence of pneumonia melioidosis. We previously identified a predicted cation transporter protein, BPSS1228, that participates in the transitional stage of this intracellular pathogen. For further analysis, in this study B. pseudomallei bpss1228 mutant and complemented strains were constructed and bacterial infectivity on human lung epithelial cells, A549, investigated in vitro . Burkholderia pseudomallei bpss1228 mutant showed impaired bacterial adhesion and invasion into A549 cells compared with wild-type strain, while the deficient phenotypes were restored to wild-type levels by the complemented strain. Additionally, the inactivation of bpss1228 in the mutant strain affected flagella-based swimming on a semi-solid surface and resistance to acid stresses simulating intracellular environments. These observations of BPSS1228 relating to B. pseudomallei infection strategies shed a new light on its association with intracellular B. pseudomallei during the interaction with host cells.

Description: Formation of a transient sub-population of bacteria, referred to as persisters, is one of the most important and least understood mechanisms that bacteria employ to evade elimination. Persister cells appear to be slow-growing bacteria that are broadly protected from a wide range of antibiotics. Using both theoretical and experimental methods, we show that alternating the application and withdrawal of antibiotics can be an effective treatment—as long as the timing of the protocol is estimated with precision. More specifically, we demonstrate that timing the alternating treatment based on theoretical predictions is confirmed using experimental observations. These results support a large class of theoretical studies that show that, even without complete understanding of the biological mechanisms, these models can provide insight into properties of the system.

Description: The phytopathogen Pseudomonas syringae pv. tabaci 11528 ( P. syringae 11528), causing wild-fire disease in soybean and tobacco plants, processes PsyI-PsyR quorum-sensing (QS) system, in which PsyI is the N -(3-oxo-hexanoyl)-homoserine lactone (3OC6-HSL) synthase. In comparison to P. syringae 11528 AHL-deficient mutant, 845 3OC6-HSL-dependent genes were identified using RNA sequencing (RNA-seq) in the AHL-deficient mutant grown with exogenous 3OC6-HSL in the transition from the exponential to the stationary phase, and many of them were associated with virulence, which were negatively regulated. The gene ontology and KEGG pathway enrichment analysis of those genes presented that the most pronounced regulation was involved in bacterial motility. Moreover, similar expression profiles of genes during growth phases were observed in both the wild type and the AHL-deficient mutant with exogenous 3OC6-HSL compared with the AHL-deficient mutant. These findings imply that 3OC6-HSL has a critical contribution to the QS-dependent regulation on gene expression, and 3OC6-HSL-dependent regulation may play a significant role in plant infection.

Description: This is the second of three papers investigating properties of titanohematite-bearing quartzo-feldspathic rocks that create a significant remanent magnetic anomaly in the Modum District, South Norway. The first paper provided initial magnetic results, mineralogical characterization and evidence for the presence of lamellar magnetism. In this paper, knowledge of lamellar magnetic properties is explored through experiments where ilmenite lamellae were magnetized below 57 K, and interact magnetically along interfaces with the titanohematite host. Samples with known NRM directions were placed in specific orientations in an MPMS then cooled in zero field to 5 K, where hysteresis loops were measured in fields up to 5 Tesla. This assured that results were ultimately related to the natural lamellar magnetism produced during cooling ~1 billion years ago. In a second set of experiments the same oriented samples, were subjected to a +5 Tesla (T) field then field cooled to 5 K before hysteresis experiments. The first experiments consistently produced asymmetric shifted hysteresis loops with two loop separations, one in a positive field and one in a negative field. Without exception, when the NRM was oriented toward the negative field end of the MPMS, the bimodal loop showed a dominant loop separation in a positive field. By contrast, when the NRM was oriented toward the positive field end of the MPMS, the bimodal loop showed a dominant loop separation in a negative field. Both observations are consistent with antiferromagnetic coupling between the hard magnetization of ilmenite and the more easily shifted lamellar magnetism of the hematite. The bimodal nature of the loops indicates that the NRMs are vector sums of natural lamellar moments, which are oriented both positively and negatively, and that these opposite moments control the orientations of ilmenite magnetizations when cooling through 57 K. Here, extreme exchange biases up to 1.68 T were measured. The second set of experiments produced asymmetric shifted hysteresis loops with one opening always in the negative field. These observations indicate that the +5 T field applied at room temperature rotated the hematite lamellar magnetism in a positive direction, so that upon cooling all the ilmenite lamellae acquired negative magnetic moments, thus causing unimodal negatively shifted loops. Here, the largest exchange bias among the unimodal loops was only 0.7 T. These results will be used in paper III to build a better understanding of lamellar magnetism at the atomic layer scale.

Description: The temperature dependence of magnetic susceptibility ( –T curves) and magnetization ( M–T curves) has been used as a routine rock magnetic tool to characterize the magnetic mineralogy and magnetic granulometry of Chinese loess/palaeosols. However, palaeoclimatic interpretation of these thermomagnetic analyses remains controversial. In the present study, total organic carbon (TOC), thermomagnetic and low-temperature magnetic experiments on Mid-Late Pleistocene loess/palaeosols in Central Asia and the Chinese Loess Plateau (CLP) have been conducted. We found that the M ( T ) cooling curves at room temperature were mostly lower than the corresponding heating curves, whereas for the ( T ) analyses the cooling curves at room temperature were always much higher than the heating curves. Low-temperature magnetic measurements demonstrated that a large amount of superparamagnetic ferrimagnetic particles were produced during the thermal treatment and resulted in the aforementioned differences. This finding further indicated that the use of the M–T curves to estimate the relative content of maghemite in the loess/palaeosols from the CLP was problematic. In addition, a positive correlation exists between the TOC and the frequency-dependent susceptibility ( FD ) in the CLP, suggesting that stronger pedogenesis would result in the simultaneous increase in the content of both maghemite and organic matter. Consequently, the parameters 1 (representing the relative content of pedogenic maghemite), 2 ([ ph – ] + 1 ) and ph (related to the organic matter concentration), which can be calculated from the –T analyses, can potentially be used as new indicators of pedogenesis and palaeoclimate in Central Asia and the CLP.