Adherence Inhibition of <Emphasis Type="Italic">Cronobacter sakazakii</Emphasis> to Intestinal Epithelial Cells by Prebiotic Oligosaccharides

Cronobacter sakazakii is an opportunistic pathogen that has been implicated in meningitis, NEC, and sepsis in neonates. Colonization and subsequent infection and invasion of C. sakazakii require that the organism adheres to host cell surfaces. Agents that inhibit or block attachment of the pathogen to epithelial cells could be useful in reducing infections. The goal of this research was to assess the ability of prebiotic galactooligosaccharides (GOS) and polydextrose (PDX) to inhibit adherence of C. sakazakii 4603 to a HEp-2 human cell line. Adherence experiments were performed in the presence or absence of prebiotics using HEp-2 cells grown to confluency on glass coverslips. Prebiotics and bacteria were added and incubated for 3 h. Coverslips were washed, and adherence was determined by cultural and microscopic methods. When measured microscopically or by cultural methods, significant reductions in adherence (56 and 71%, respectively) of C. sakazakii were observed in the presence of GOS (16 mg/ml). Adherence inhibition also occurred (48%) when a GOS–PDX blend (8 mg/ml each) was tested, although PDX by itself had less effect. Similar results were also observed for Caco-2 cells and also for another strain of C. sakazakii (29004). These results suggest that GOS and PDX, alone and in combination, may have an anti-adhesive effect on C. sakazakii and directly inhibit the adherence to gastrointestinal epithelial cells.     

The lactoferrin receptor may mediate the reduction of eosinophils in the duodenum of pigs consuming milk containing recombinant human lactoferrin

Lactoferrin is part of the immune system and multiple tissues including the gastrointestinal (GI) tract, liver, and lung contain receptors for lactoferrin. Lactoferrin has many functions, including antimicrobial, immunomodulatory, and iron binding. Additionally, lactoferrin inhibits the migration of eosinophils, which are constitutively present in the GI tract, and increase during inflammation. Lactoferrin suppresses eosinophil infiltration into the lungs and eosinophil migration in -vitro. Healthy pigs have a large population of eosinophils in their small intestine and like humans, pigs have small intestinal lactoferrin receptors (LFR); thus, pigs were chosen to investigate the effects of consumption of milk containing recombinant human lactoferrin (rhLF-milk) on small intestinal eosinophils and expression of eosinophilic cytokines. In addition, LFR localization was analyzed in duodenum and circulating eosinophils to determine if the LFR could play a role in lactoferrin’s ability to inhibit eosinophil migration. In the duodenum there were significantly fewer eosinophils/unit area in pigs fed rhLF-milk compared to pigs fed control milk (p = 0.025); this was not seen in the ileum (p = 0.669). In the duodenum, no differences were observed in expression of the LFR, or any eosinophil migratory cytokines, and the amount of LFR protein was not different (p = 0.386). Immunohistochemistry (IHC) showed that within the duodenum the LFR localized on the brush border of villi, crypts, and within the lamina propria. Circulating eosinophils also contained LFRs, which may be a mechanism allowing lactoferrin to directly inhibit eosinophil migration.     

Outer Membrane Proteins A (OmpA) and X (OmpX) Are Essential for Basolateral Invasion of Cronobacter sakazakii

Cronobacter sakazakii is an opportunistic pathogen that actively invades host eukaryotic cells. To identify invasion factors responsible for the intestinal translocation of C. sakazakii, we constructed for the first time outer membrane protein X (OmpX) and A (OmpA) deletion mutants using the lambda Red recombination system. The ompX and ompA deletion mutants showed significantly reduced invasion of human enterocyte-like epithelial Caco-2 and human intestinal epithelial INT-407 cells, and significantly fewer mutant cells were recovered from the livers and spleens of rat pups. Furthermore, compared with intact target cells, the invasion and initial association potentials of the mutants increased at a rate similar to that of the wild type in tight-junction-disrupted target cells, suggesting that OmpX and OmpA are involved in basolateral invasion by C. sakazakii. This is the first report of C. sakazakii virulence determinants that are essential for basolateral invasion and that may be critical for the virulence of C. sakazakii.Enterobacter sakazakii is an emerging pathogen associated with several outbreaks of meningitis and local necrotizing enterocolitis in premature infants (2, 28, 37). There was considerable diversity among E. sakazakii isolates (13, 14), and the original taxonomic name of E. sakazakii was reclassified as Cronobacter spp., which included Cronobacter sakazakii (13, 14). Therefore, C. sakazakii will be used throughout this paper. Although the incidence of Cronobacter infection is rare, the mortality rate is as high as 33 to 80% (11, 27, 32, 39). Even when infants survive Cronobacter infection, they often experience serious sequelae, including brain abscesses, developmental delay, and impairment of sight and hearing (8). Premature infants, whose immune systems are not fully developed, may be at high risk for Cronobacter infection (26).Very little is known about the mechanisms of pathogenicity and the virulence determinants of the genus Cronobacter. Adhesion of Cronobacter spp. to eukaryotic cells showed two distinct patterns, i.e., a diffuse pattern and the formation of localized clusters, which was nonfimbrial (21). Pagotto et al. (29) reported that the genus Cronobacter produced enterotoxins and was lethal on intraperitoneal injection into suckling mice at levels as low as 10⁵ CFU per mouse. The genus Cronobacter interacts with and damages intestinal epithelial cells, which results in intestinal injury and villus disruption (12). In addition, the cell-bound zinc-containing metalloprotease encoded by zpx caused rounding of Chinese hamster ovary (CHO) cells (19), which may be important in dissemination of the pathogen into the systemic circulation. Furthermore, Townsend et al. (36) showed that Cronobacter can persist within rat macrophages.As an oral pathogen causing a systemic infection, C. sakazakii must translocate from the intestinal lumen into the blood circulation. The genus Cronobacter is capable of actively invading various epithelial and endothelial cells of human and animal origin (17, 25, 31). Kim and Loessner (17) reported that the active invasion of human intestinal Caco-2 cells by C. sakazakii requires de novo bacterial protein synthesis and the host cell cytoskeleton and that the invasion efficiency of C. sakazakii was enhanced in the absence of cellular tight junctions. With regard to the virulence determinants related to Cronobacter penetration of the host cells, Mohan Nair and Venkitanarayanan (25) and Singamsetty et al. (31) reported that outer membrane protein A (OmpA) of Cronobacter plays an important role in the invasion of human intestinal epithelial INT-407 cells and human brain microvascular endothelial cells (HBMECs); invasion was dependent on both microfilaments and microtubules in INT-407 cells but only on microtubule condensation in HBMECs. Obviously, bacterial translocation in the intestines is multifactorial, and more detailed studies are needed to gain a better understanding of C. sakazakii pathogenesis.Outer membrane protein X (OmpX) of C. sakazakii was identified in this study. Previously, OmpX in other bacteria was shown to be involved in the invasion of host cells (7, 18), neutralizing host defense mechanisms, and bacterial defense against the complement systems of the host (10, 38).In this study, we report for the first time a successful application of the lambda Red recombination system to construct in-frame OmpX and/or OmpA deletion mutants in C. sakazakii. We further report that both outer membrane proteins (OMPs) of C. sakazakii, OmpX and OmpA, play critical roles in its invasion through not only the apical side, but also the basolateral side, of the host cells. We also show that OmpX and OmpA are responsible for C. sakazakii translocation into the deeper organs (i.e., liver and spleen).     

Immune responses of mice to poly(L-Tyr-L-Glu-L-Ala-Gly) and its oligomers

C57BL/6 (H-2 ^b) mice, when immunized with the sequential polymer (T-G-A-Gly)_n and its low-molecular-weight oligomers, respond only to theα-helical oligomers with molecular weights of 9700 and above. Only the sameα-helical oligomers were able to inhibit the homologous antigen-antibody reaction. Random copolymers of GA, GT, and GAT¹⁰ did not inhibit. In vitro stimulation of peritoneal exudate lymphocyte (PETLES) cultures showed that the cellular response (T-cell) against (T-G-A-Gly)_n is antigen-specific. In vitro antigen-induced stimulation of whole spleen or lymph node lymphocytes indicated that (T-G-A-Gly)_n might also be a B-cell mitogen.     

Clostridium butyricum reduce lipogenesis through bacterial wall components and butyrate

Intervention strategies for obesity are global issues that require immediate attention. The objective of this study was to assess the possibility that Clostridium butyricum and its potential components could reduce lipogenesis. Co-culture experiments of Caco-2 cells and 1?×?10⁶, 1?×?10⁷, and 1?×?10⁸ CFU/ml of C. butyricum were set up to monitor the cytotoxicity of C. butyricum and the changes of angiopoietin-like protein 4 (ANGPTL4) mRNA expression. It was found that cell viability was not affected by C. butyricum, and ANGPTL4 mRNA expression in Caco-2 cells was highly induced by 1?×?10⁷ CFU/ml of C. butyricum. Co-culture experiment of Caco-2 cells and potential components of C. butyricum were set up to monitor any ensuing alteration in ANGPTL4. It was observed that bacterial wall components and potentially secreted factors from C. butyricum could induce ANGPTL4 mRNA expression and protein secretion. To determine whether butyrate could affect the ANGPTL4 production in Caco-2 cells, the role of monocarboxylate transporter 1 (MCT1) in mediating potentially secreted factors from C. butyricum-induced ANGPTL4 production in Caco-2 cells and the effect of 0.1 mM of butyrate on ANGPTL4 production in Caco-2 cells were investigated. It is confirmed that butyrate was the factor secreted by C. butyricum to stimulate ANGPTL4 production. Besides, the soluble factors secreted by live C. butyricum-Caco-2 cells interaction, bacterial wall components-Caco-2 cells interaction, and the main metabolites butyrate-Caco-2 cells interaction reduced lipogenic gene expression in HepG2 cells. In conclusion, 1?×?10⁷ CFU/ml of C. butyricum could reduce lipogenesis through the bacterial wall components and the metabolites such as butyrate.     

Bacterial Overexpression of Recombinant Heteroscorpine-1 (rHS-1), a Toxin from Heterometrus laoticus Scorpion Venom: Trends for Antibacterial Application and Antivenom Production

Heteroscorpine-1 (HS-1) was identified as a member of the scorpine family. HS-1 shows insecticidal activities, exhibiting a low median lethal dose (LD₅₀) in mealworm (Tenebrio molitor L.) and inhibitory activities against Bacillus subtilis, Klebsiella pneumoniae, and Pseudomonas aeruginosa. In this study, a recombinant HS-1 (rHS-1) was produced by overexpression in E. coli. A large yield of product was obtained. The structure of purified rHS-1 was confirmed through mass spectrometry. Both anti-crude venom and anti-rHS-1 antibodies specifically recognized rHS-1, suggesting its structural similarity. Reactivated rHS-1 caused roughening and blebbing of bacterial cell surfaces. It showed higher activity than that of pre-refolded protein. Antisera raised against a partially purified and mis- or unfolded peptide can inhibit relevant bioactivity.     

Membrane-active mechanism of LFchimera against Burkholderia pseudomallei and Burkholderia thailandensis

LFchimera, a construct combining two antimicrobial domains of bovine lactoferrin, lactoferrampin265–284 and lactoferricin17–30, possesses strong bactericidal activity. As yet, no experimental evidence was presented to evaluate the mechanisms of LFchimera against Burkholderia isolates. In this study we analyzed the killing activity of LFchimera on the category B pathogen Burkholderia pseudomallei in comparison to the lesser virulent Burkholderia thailandensis often used as a model for the highly virulent B. pseudomallei. Killing kinetics showed that B. thailandensis E264 was more susceptible for LFchimera than B. pseudomallei 1026b. Interestingly the bactericidal activity of LFchimera appeared highly pH dependent; B. thailandensis killing was completely abolished at and below pH 6.4. FITC-labeled LFchimera caused a rapid accumulation within 15 min in the cytoplasm of both bacterial species. Moreover, freeze-fracture electron microscopy demonstrated extreme effects on the membrane morphology of both bacterial species within 1 h of incubation, accompanied by altered membrane permeability monitored as leakage of nucleotides. These data indicate that the mechanism of action of LFchimera is similar for both species and encompasses disruption of the plasma membrane and subsequently leakage of intracellular nucleotides leading to cell dead.     

Aerobic endospore-forming bacteria isolated from Antarctic soils as producers of bioactive compounds of industrial interest

Spore-forming bacteria are known to produce various enzymes and bioproducts valuable to different industries and to bear the harsh conditions found in the Antarctic environment. However, aerobic or facultative spore-forming bacterial communities found in maritime Antarctic soils yet remain poorly studied. In this study, 80 spore-forming and cold-adapted bacterial strains were isolated from nine different soil samples of King George Island, in maritime Antarctica, and further clustered into amplified ribosomal DNA restriction analysis groups within each soil. Representative strains were then identified as belonging to Bacillus, Rummeliibacillus, Paenibacillus and Sporosarcina by 16S rRNA gene sequencing. The ability to produce extracellular enzymes, antimicrobial substances and biosurfactants was determined in all isolates. The enzymatic activities most frequently found among the isolates were as follows: esterase (45 %), caseinase (30 %), amylase (16.2 %) and gelatinase (15 %). Biosurfactant production was detected in 25 % of the isolates. The growth inhibition of methicillin-resistant Staphylococcus aureus was observed in 13.7 % of the strains tested, but only two strains inhibited the growth of Candida albicans. The isolated spore-forming bacterial species were also compared with the characteristics of the different Antarctic soils sampled based on their physicochemical properties, showing that pH, C and P were the main factors correlated with the distribution of this group of bacteria in the Antarctic soils studied. These Antarctic endospore-forming bacterial strains may have a potential for industrial processes occurring at low temperatures.     

Environmental Heterogeneity and Microbial Inheritance Influence Sponge-Associated Bacterial Composition of Spongia lamella

Sponges are important components of marine benthic communities. High microbial abundance sponges host a large diversity of associated microbial assemblages. However, the dynamics of such assemblages are still poorly known. In this study, we investigated whether bacterial assemblages present in Spongia lamella remained constant or changed as a function of the environment and life cycle. Sponges were collected in multiple locations and at different times of the year in the western Mediterranean Sea and in nearby Atlantic Ocean to cover heterogeneous environmental variability. Co-occurring adult sponges and offsprings were compared at two of the sites. To explore the composition and abundance of the main bacteria present in the sponge mesohyl, embryos, and larvae, we applied both 16S rRNA gene-denaturing gradient gel electrophoresis (DGGE) and sequencing of excised DGGE bands and quantitative polymerase chain reactions (qPCR). On average, the overall core bacterial assemblage showed over 60 % similarity. The associated bacterial assemblage fingerprints varied both within and between sponge populations, and the abundance of specific bacterial taxa assessed by qPCR significantly differed among sponge populations and between adult sponge and offsprings (higher proportions of Actinobacteria in the latter). Sequences showed between 92 and 100 % identity to sequences previously reported in GenBank, and all were affiliated with uncultured invertebrate bacterial symbionts (mainly sponges). Sequences were mainly related to Chloroflexi and Acidobacteria and a few to Actinobacteria and Bacteroidetes. Additional populations may have been present under detection limits. Overall, these results support that both ecological and biological sponge features may shape the composition of endobiont bacterial communities in S. lamella.     

Pyrosequencing-based analysis of fecal microbial communities in three purebred pig lines

This study examined the fecal bacterial diversity of 15-weekold pigs from three purebred lines: Duroc, Landrace, and Yorkshire. Taxon-dependent and -independent analyses were performed to evaluate differences in the fecal bacterial communities and to identify bacterial genera that can be used to discriminate breeds, following high-throughput pyrosequencing of 16S rRNA genes. Among the breeds evaluated, Landrace had the most diverse bacterial community composition. Prevotella, Blautia, Oscillibacter, and Clostridium were detected in all samples regardless of breed. On the other hand, Catenibacterium, Blautia, Dialister, and Sphaerochaeta were differentially detected among breeds, as demonstrated by the canonical loading plot. The discriminant analysis of principal components plot also showed clear separation of the three purebred pig lines, with a certain degree of similarity between Landrace and Yorkshire pigs and a distinct separation between Duroc pigs and the other two breeds. Other factors not related to breed, such as season or time of sampling and pen effects, may contribute to shaping the gut microbiota of pigs.     

Inhibition of gene expression and growth of multidrug-resistant Acinetobacter baumannii by antisense peptide nucleic acids

Acinetobacter baumannii causes common and severe community- and hospital-acquired infections. The increasing emergence of multidrug-resistant (MDR) and pan-drug resistant A. baumannii has limited the therapeutic options, highlighting the need for new therapeutic strategies. The goal of this study was to investigate whether antisense peptide nucleic acids (PNAs) could mediate gene-specific inhibition effects in MDR A. baumannii. We described a screening strategy based on computational prediction and dot hybridization for identifying potential inhibitory PNAs, and evaluated the in vitro growth inhibition potency of two PNAs conjugated to the (KFF)₃K peptide (pPNA1 and pPNA2), both of which targeted the growth essential gene gyrA of A. baumannii. Both pPNAs showed strong inhibition effects on bacterial growth and gyrA mRNA expression in a dose-dependent manner. The lowest inhibitory and bactericidal concentration were 5 and 10 μM, respectively. Combination of the two pPNAs showed superimposed effect other than synergistic effect. Control PNAs without (KFF)₃K peptide conjugation or with mismatched antisense sequence had no inhibition effects on bacterial growth or mRNA expression. Our study suggests that anti-gyrA pPNAs can efficiently inhibit gene expression and bacterial growth, and has the potential as a new therapeutic option for MDR A. baumannii.     

Reproductive relationships between annual species ofCalendula (Compositae)

Breeding experiments were carried out inCalendula species. In the annuals, which are selfers, rarely some outcrossing was observed only in the most peripheral flowers. In experimental crosses fruit was produced in all combinations. Fertile F₁ and F₂ hybrids could be grown from crosses between parents with similar chromosome numbers:C. palaestina ×C. pachysperma and crosses of different morphological forms ofC. arvensis. In crosses of species with different chromosome numbers at least partly fertile F₁ hybrids were obtained fromC. tripterocarpa ×C. stellata andC. tripterocarpa ×C. arvensis and crosses of the latter withC. palaestina. Fertile F₂ plants were grown from the combination ofC. arvensis ×C. tripterocarpa. Considering this information and previously obtained data, a scheme is proposed for explaining speciation in the genusCalendula.     

Comparative analysis of bacterial community-metagenomics in coastal Gulf of Mexico sediment microcosms following exposure to Macondo oil (MC252)

The indigenous bacterial communities in sediment microcosms from Dauphin Island (DI), Petit Bois Island (PB) and Perdido Pass (PP) of the coastal Gulf of Mexico were compared following treatment with Macondo oil (MC252) using pyrosequencing and culture-based approaches. After quality-based trimming, 28,991 partial 16S rRNA sequence reads were analyzed by rarefaction, confirming that analyses of bacterial communities were saturated with respect to species diversity. Changes in the relative abundances of Proteobacteria, Bacteroidetes and Firmicutes played an important role in structuring bacterial communities in oil-treated sediments. Proteobacteria were dominant in oil-treated samples, whereas Firmicutes and Bacteroidetes were either the second or the third most abundant taxa. Tenericutes, members of which are known for oil biodegradation, were detected shortly after treatment, and continued to increase in DI and PP sediments. Multivariate statistical analyses (ADONIS) revealed significant dissimilarity of bacterial communities between oil-treated and untreated samples and among locations. In addition, a similarity percentage analysis showed the contribution of each species to the contrast between untreated and oil-treated samples. PCR amplification using DNA from pure cultures of Exiguobacterium,  Pseudoalteromonas,  Halomonas and Dyadobacter, isolated from oil-treated microcosm sediments, produced amplicons similar to polycyclic aromatic hydrocarbon-degrading genes. In the context of the 2010 Macondo blowout, the results from our study demonstrated that the indigenous bacterial communities in coastal Gulf of Mexico sediment microcosms responded to the MC252 oil with altered community structure and species composition. The rapid proliferation of hydrocarbonoclastic bacteria suggests their involvement in the degradation of the spilt oil in the Gulf of Mexico ecosystem.     

Bacterial Diversity in the Rhizosphere of Cucumbers Grown in Soils Covering a Wide Range of Cucumber Cropping Histories and Environmental Conditions

Rhizosphere microorganisms in soils are important for plant growth. However, the importance of rhizosphere microorganisms is still underestimated since many microorganisms associated with plant roots cannot be cultured and since the microbial diversity in the rhizosphere can be influenced by several factors, such as the cropping history, biogeography, and agricultural practice. Here, we characterized the rhizosphere bacterial diversity of cucumber plants grown in soils covering a wide range of cucumber cropping histories and environmental conditions by using pyrosequencing of bacterial 16S rRNA genes. We also tested the effects of compost addition and/or bacterial inoculation on the bacterial diversity in the rhizosphere. We identified an average of approximately 8,883 reads per sample, corresponding to around 4,993 molecular operational taxonomic units per sample. The Proteobacteria was the most abundant phylum in almost all soils. The abundances of the phyla Bacteroidetes, Actinobacteria, Firmicutes, Acidobacteria, and Verrucomicrobia varied among the samples, and together with Proteobacteria, these phyla were the six most abundant phyla in almost all analyzed samples. Analyzing all the sample libraries together, the predominant genera found were Flavobacterium, Ohtaekwangia, Opitutus, Gp6, Steroidobacter, and Acidovorax. Overall, compost and microbial amendments increased shoot biomass when compared to untreated soils. However, compost addition decreased the bacterial α-diversity in most soils (but for three soils compost increased diversity), and no statistical effect of microbial amendment on the bacterial α-diversity was found. Moreover, soil amendments did not significantly influence the bacterial β-diversity. Soil organic content appeared more important than compost and microbial amendments in shaping the structure of bacterial communities in the rhizosphere of cucumber.     

Genetic variation in the activity of the histidine catabolic enzymes between inbred strains of mice: A structural locus for a cytosol histidine aminotransferase isozyme (Hat-1)

Variation in activity of the main histidine catabolic enzymes (histidase, urocanase, and aminotransferase) has been surveyed using inbred strains of mice (C57BL, DBA, Peru, SM, and SWR). Some variation was found in the activity of all enzymes, but only in the case of cytosolic histidine aminotransferase was it greater than twofold (SM 3.3-fold greater than C57BL). The divergent strains for the activity of this enzyme were crossed and the F ₁ 's were backcrossed; the segregation analysis indicated a single locus with additively acting alleles (designated Hat-1: a allele SM, b allele C57BL). Cytosolic histidine aminotransferase differed in heat stability between SM and C57BL, indicating that Hat-1 is a structural locus. The conflict in the biochemical literature (Morris et al., 1973; Noguchi et al., 1976a, b) over the number and subcellular distribution of the histidine aminotransferase isozymes is partly resolved by the acquisition of a variant at the Hat-1 locus. Hat-1 affects the cytosolic form but not the mitochondrial form of the enzyme. Purification and analysis of the isozymes of histidine aminotransferase from livers of C57BL and SM mice will further clarify the situation.     

The Adhesion AND Growth of Both the Human Primary Gingival Epithelial Cells and Streptococcus Mutans on Micro-Arc Oxidized Titanium

With good osseointegration properties, micro-arc oxidation has now gradually become the key point in basic research and clinical trials, but interface between the implant surface treated by micro-arc oxidation and gingival soft tissues has been seldom reported. The influences of micro-arc oxidation surface treatment on the biological behavior of primary human gingival epithelial cells (hGEC) and common pathogen Streptococcus mutans have been studied. MTT method was taken to test the adhesion and growth of hGEC on different treated surfaces. No significant changes were found between with or without MAO- treated surface. However, higher growth rate was observed in MAO group at first and third days, although it showed no significant difference at fifth and seventh day. Secretions of EGF of the cells grown on both surfaces were also no big changes (P > 0.05). RT-PCR showed adhesion gene of hGEC, E-cad on the first day of micro-arc oxidation surface treatment, expression level is higher than that of polishing group (P < 0.05), but no significant difference of the expression levels of Itgβ1, PCNA, and EGF. Finally, easier adhesion and high growth rate of Streptococcus mutans were found at MAO-treated surface (P < 0.05). In conclusion, our data suggested MAO-treated Ti surface may favor epithelial cell adhesion, but it also increase the risk of bacterial infection.     

Bacterial Distribution Along a 50 °C Temperature Gradient Reveals a Parceled Out Hot Spring Environment

Understanding the distribution of bacteria is a major goal of microbial ecology which remains to be fully deciphered. In this study, a model 50 °C temperature gradient at a Northern Thailand hot spring was analyzed to determine how the bacterial communities were structured in the environment. Communities were examined through 16S rRNA gene amplification, denaturing gradient gel electrophoresis, and sequencing. The two major phyla, Cyanobacteria and Chloroflexi, showed characteristic distributions along the temperature gradient. Different clades were allocated at specific portions of the gradient. Comparisons of the bacterial communities along the temperature gradient showed sharp decreases of similarity at increasing temperature difference. Peaks of maximum richness were observed at 50 and 70 °C. This study contributes to explain how environmental conditions and microbial interactions can influence the distribution of specific bacterial clades and phyla shaping the structure of microbial communities in nature.     

Magainin 2 Induces Bacterial Cell Death Showing Apoptotic Properties

Magainin 2 is pore-forming antimicrobial peptide on lipid matrix of bacterial membrane, secreted from the skin of the African clawed frog Xenopus laevis. The aim of this study was to investigate a new concept for antibacterial mechanisms called bacterial apoptosis-like cell death. We examined the morphological changes induced by magainin 2 in Escherichia coli, regarding apoptosis. Specifically, phosphatidylserine externalization from the inner to outer membrane surface was detected by Annexin V staining, and DNA fragmentation and chromatin condensation was detected by TUNEL and DAPI assay. We also found much mechanistic evidence to support the hypothesis that magainin 2 induces bacterial apoptosis-like death—including disturbance of membrane detected by DiBAC₄(3), caspase activation observed by FITC-VAD-FMK staining, and analyzing the role of RecA in bacterial apoptosis-like death through the RecA expression assay by Western blot—in E. Coli when treated with magainin 2. On the basis of these results, magainin 2 exerts antibacterial activity with a new mechanism which is bacterial apoptosis-like death. Searching antimicrobial agents with novel mechanisms of action can be an effective strategy to coping with the emergence of new resistance mechanisms. Magainin 2 deserves further research as a potential antimicrobial therapeutic agent.     

Cloning,expression and characterization of a novel aldehyde dehydrogenase gene from Flammeovirga pacifica

A novel putative aldehyde dehydrogenase (ALDH) gene aldh1413 from Flammeovirga pacifica isolated from deep sea sediment was cloned, expressed, and characterized. The molecular weight of the ALDH1413 (479 amino acids) was estimated by SDS-PAGE to be 53 kDa. The optimum temperature and pH for ALDH1413 were 35°C and 9.0, respectively. In the presence of either NAD⁺ or NADP⁺, the enzyme could oxidize a number of aliphatic aldehydes, particularly C3-and C5-aliphatic aldehydes and aromatic aldehydes such as benzaldehyde, which indicates that the enzyme belongs to broad-specific (ALDH) superfamily. Steady-state kinetic study revealed that ALDH1413 had a K _M value of 0.545 mM and a k _cat value of 7.48 s^?1 when propionaldehyde was used as the substrate. The Na⁺ could enhance ALDH1413 activity, which indicated it might be adapt to its habitat, marine environment.