Structure and dynamics of the gut bacterial microbiota of the bark beetle, Dendroctonus rhizophagus (Curculionidae: Scolytinae) across their life stages

Bark beetles play an important role as agents of natural renovation and regeneration in coniferous forests. Several studies have documented the metabolic capacity of bacteria associated with the gut, body surface, and oral secretions of these insects; however, little is known about how the bacterial community structure changes during the life cycle of the beetles. This study represents the first comprehensive analysis of the bacterial community of the gut of the bark beetle D. rhizophagus during the insect’s life cycle using 454 pyrosequencing. A total of 4 bacterial phyla, 7 classes, 15 families and 23 genera were identified. The α-diversity was low, as demonstrated in previous studies. The dominant bacterial taxa belonged to the Enterobacteriaceae and Pseudomonadaceae families. This low α-diversity can be attributed to the presence of defensive chemical compounds in conifers or due to different morpho-physiological factors in the gut of these insects acting as strong selective factors. Members of the genera Rahnella, Serratia, Pseudomonas and Propionibacterium were found at all life stages, and the first three genera, particularly Rahnella, were predominant suggesting the presence of a core microbiome in the gut. Significant differences in β-diversity were observed, mainly due to bacterial taxa present at low frequencies and only in certain life stages. The predictive functional profiling indicated metabolic pathways related to metabolism of amino acids and carbohydrates, and membrane transport as the most significant in the community. These differences in the community structure might be due to several selective factors, such as gut compartmentalization, physicochemical conditions, and microbial interactions.

Identification of extensive drug resistant Pseudomonas aeruginosa strains: New clone ST1725 and high-risk clone ST233

Several microorganisms produce nosocomial infections (NIs), among which Pseudomonas aeruginosa stands out as an opportunist pathogen with the capacity to develop multiresistance to first-choice antibiotics. From 2007 to 2013, forty-six NIs produced by P. aeruginosa were detected at a pediatric tertiary care hospital in Mexico with a significant mortality rate (17.39%). All isolates (n = 58/46 patients) were characterized by evaluating their response to several antibiotics as panresistant (PDR), extensively resistant (XDR), multiresistant (MDR) or sensitive (S). In addition, all isolates were typified through multilocus sequencing of seven genes: acsA, aroE, guaA, mutL, nuoD, ppsA and trpE. Furthermore, to establish the genetic relationships among these isolates, we carried out a phylogenetic inference analysis using maximum likelihood to construct a phylogenetic network. To assess evolutionary parameters, recombination was evaluated using the PHI test, and the ratio of nonsynonymous to synonymous substitutions was determined. Two of the strains were PDR (ST1725); 42 were XDR; four were MDR; and ten were S. Twenty-one new sequence types were detected. Thirty-three strains exhibited novel sequence type ST1725. The ratio of nonsynonym to synonym substitutions was 1:1 considering all genes. Phylogenetic analysis showed that the genetic relationship of the PDR, XDR and MDR strains was mainly clonal; however, the PHI test and the phylogenetic network suggest that recombination events occurred to produce a non-clonal population. This study aimed not only to determine the genetic diversity of clinical P. aeruginosa but also to provide a warning regarding the identification and spreading of clone ST1725, its ability to cause outbreaks with high mortality rates, and to remain in the hospital environment for over seven years. These characteristics highlight the need to identify clonal outbreaks, especially where high resistance to most antibiotics is observed, and control measures are needed. This study also represents the first report of the PDR ST1725.

Illustrated Key to Species of Genus Dendroctonus (Coleoptera: Curculionidae) Occurring in Mexico and Central America

We provide an illustrated key of species of Dendroctonus Erichson from Mexico and Central America based on characters of the male genitalia and external morphology. The key incorporates newly identified diagnostic characters for this genus that enhance discrimination of particularly difficult sibling species.

Expression, purification and characterization of an endoglucanase from Serratia proteamaculans CDBB-1961, isolated from the gut of Dendroctonus adjunctus (Coleoptera: Scolytinae)

Serratia proteamaculans CDBB-1961, a gut symbiont from the roundheaded pine beetle Dendroctonus adjunctus, displayed strong cellulolytic activity on agar-plates with carboxymethyl cellulose (CMC) as carbon source. Automatic genome annotation of S. proteamaculans made possible the identification of a single endoglucanase encoding gene, designated spr cel8A. The predicted protein, named Spr Cel8A shows high similarity (59–94 %) to endo-1,4-β-d-glucanases (EC 3.2.1.4) from the glycoside hydrolase family 8 (GH8). The gene spr cel8A has an ORF of 1113 bp, encoding a 371 amino acid residue protein (41.2 kDa) with a signal peptide of 23 amino acid residues. Expression of the gene spr cel8A in Escherichia coli yields a mature recombinant endoglucanase 39 kDa. Cel8A displayed optimal activity at pH 7.0 and 40 °C, with a specific activity of 0.85 U/mg. The enzyme was stable at pH from 4 to 8.5, retaining nearly 40–80 % of its original activity, and exhibited a half-life of 8 days at 40 °C. The K_m and V_max values for Spr Cel8A were 6.87 mg/ml and 3.5 μmol/min/mg of protein, respectively, using CMC as substrate. The final principle products of Spr Cel8A-mediated hydrolysis of CMC were cellobiose, cello oligosaccharides and a small amount of glucose, suggesting that Spr Cel8A is an endo-β-1,4-glucanase manifesting exo-activity. This is the first report regarding the functional biochemical and molecular characterization of an endoglucanase from S. proteamaculans, found in the gut-associated bacteria community of Dendroctonus bark beetles. These results contribute to improved understanding of the functional role played by this bacterium as a symbiont of bark beetles.

One-step zymogram method for the simultaneous detection of cellulase/xylanase activity and molecular weight estimation of the enzyme

Here, we describe a zymographic method for the simultaneous detection of enzymatic activity and molecular weight (MW) estimation, following a single electrophoresis step. This involved separating cellulase and xylanase activities from bacteria and fungi, obtained from different sources, such as commercial extracts, crude extract and purified proteins, under denaturing conditions, by 10% polyacrylamide gel electrophoresis, using polyacrylamide gels copolymerized with 1% (w/v) carboxymethylcellulose or beechwood xylan as substrates. Then, enzymes were refolded by treatment with 2.5% Triton X-100 in an appropriate buffer for each enzymatic activity, and visualized by Coomassie blue staining for MW estimation. Finally, Congo red staining revealed bio-active cellulase and xylanase bands after electrophoretic separation of the proteins in the preparations. This method may provide a useful additional tool for screening of particular cellulase and xylanase producers, identification and MW estimation of polypeptides that manifest these activities, and for monitoring and control of fungal and bacterial cellulase and xylanase production.

Diversification of the vacAs1m1 and vacAs2m2 Strains of Helicobacter pylori in Meriones unguiculatus

The bacterium Helicobacter pylori exhibits great genetic diversity, and the pathogenic roles of its virulence factors have been widely studied. However, the evolutionary dynamics of H. pylori strains during stomach colonization are not well-characterized. Here, we analyzed the microevolutionary dynamics of the toxigenic strain vacAs1m1, the non-toxigenic strain vacAs2m2, and a combination of both strains in an animal model over time. Meriones unguiculatus were inoculated with the following bacteria: group 1-toxigenic strain vacAs1m1/cagA+/cagE+/babA2+; ST181, group 2-non-toxigenic strain vacAs2m2/cagA+/cagE+/babA2+; ST2901, and group 3-both strains. The gerbils were euthanized at different time points (3, 6, 12, and 18 months). In group 1, genetic alterations were observed at 6 and 12 months. With the combination of both strains, group 3 also exhibited genetic alterations at 3 and 18 months; moreover, a chimera, vacA m1-m2, was detected. Additionally, four new sequence types (STs) were reported in the PubMLST database for H. pylori. Synonymous and non-synonymous mutations were analyzed and associated with alterations in amino acids. Microevolutionary analysis of the STs (PHYLOViZ) identified in each group revealed many mutational changes in the toxigenic (vacAs1m1) and non-toxigenic (vacAs2m2) strains. Phylogenetic assessments (eBURST) did not reveal clonal complexes. Our findings indicate that the toxigenic strain, vacAs1m1, and a combination of toxigenic and non-toxigenic strains acquired genetic material by recombination. The allelic combination, vacAs2m1, displayed the best adaptation in the animal model over time, and a chimera, m1-m2, was also identified, which confirmed previous reports.

Effect of cadmium on phenolic compounds, antioxidant enzyme activity and oxidative stress in blueberry (Vaccinium corymbosum L.) plantlets grown in vitro

Cadmium (Cd(2+)) can affect plant growth due to its mobility and toxicity. We evaluated the effects of Cd(2+) on the production of phenolic compounds and antioxidant response of Vaccinium corymbosum L. Plantlets were exposed to Cd(2+) at 50 and 100µM for 7, 14 and 21 days. Accumulation of malondialdehyde (MDA), hydrogen peroxide (H2O2) and the antioxidant enzyme SOD was determined. The profile of phenolic compounds was evaluated using LC-MS. The antioxidant activity was measured using 1,1-diphenyl-2-picrylhydrazyl (DPPH) and the ferric reducing antioxidant power test (FRAP). Cd(2+) increased the content of MDA, with the highest increase at 14 days. The presence of Cd(2+) resulted in changes in phenolic compounds. The main phenolic compound found in blueberry plantlets was chlorogenic acid, whose abundance increased with the addition of Cd(2+) to the medium. The changes in the composition of phenolic compounds showed a positive correlation with the antioxidant activity measured using FRAP. Our results suggest that blueberry plantlets produced phenolic compounds with reducing capacity as a selective mechanism triggered by the highest activity of Cd(2+).

Degradation capacities of bacteria and yeasts isolated from the gut of Dendroctonus rhizophagus (Curculionidae: Scolytinae)

Bark beetles (Curculionidae: Scolytinae) feed on the xylem and phloem of their host, which are composed of structural carbohydrates and organic compounds that are not easily degraded by the insects. Some of these compounds might be hydrolyzed by digestive enzymes produced by microbes present in the gut of these insects. In this study, we evaluated the enzymatic capacity of bacteria (Acinetobacter lwoffii, Arthrobacter sp., Pseudomonas putida, Pseudomonas azotoformans, and Rahnella sp.) and yeasts (Candida piceae, Candida oregonensis, Cyberlindnera americana, Zygoascus sp., and Rhodotorula mucilaginosa) isolated from the Dendroctonus rhizophagus gut to hydrolyze cellulose, xylan, pectin, starch, lipids, and esters. All isolates, with the exception of C. piceae, showed lipolytic activity. Furthermore, P. putida, P. azotoformans, C. americana, C. piceae, and R. mucilaginosa presented amylolytic activity. Esterase activity was shown by A. lwoffii, P. azotoformans, and Rahnella sp. Cellulolytic and xylanolytic activities were present only in Arthrobacter sp. and P. azotoformans. The pectinolytic activity was not recorded in any isolate. This is the first study to provide evidence on the capacity of microbes associated with the D. rhizophagus gut to hydrolyze specific substrates, which might cover part of the nutritional requirements for the development, fitness, and survival of these insects.

Phenotypic and Genetic Variations in Obligate Parthenogenetic Populations of Eriosoma lanigerum Hausmann (Hemiptera: Aphididae)

The study of phenotypic and genetic variation of obligate parthenogenetic organisms contributes to an understanding of evolution in the absence of genetic variation produced by sexual reproduction. Eriosoma lanigerum Hausmann undergoes obligate parthenogenesis in Mexico City, Mexico, due to the unavailability of the host plants required for sexual reproduction. We analysed the phenotypic and genetic variation of E. lanigerum in relation to the dry and wet season and plant phenology. Aphids were collected on two occasions per season on a secondary host plant, Pyracantha koidzumii, at five different sites in the southern area of Mexico City, Mexico. Thirteen morphological characteristics were measured from 147 to 276 individuals per site and per season. A multivariate analysis of variance was performed to test the effect of the season, site and their interaction on morphological traits. Morphological variation was summarised using a principal component analysis. Genetic variation was described using six enzymatic loci, four of which were polymorphic. Our study showed that the site and season has a significant effect on morphological trait variation. The largest aphids were recorded during cold temperatures with low relative humidity and when the plant was at the end of the fruiting period. The mean genetic diversity was low (mean H e =  .161), and populations were genetically structured by season and site. Morphological and genetic variations appear to be associated with environmental factors that directly affect aphid development and/or indirectly by host plant phenology.

Comparison of orthologous cytochrome P450 genes relative expression patterns in the bark beetles Dendroctonus rhizophagus and Dendroctonus valens (Curculionidae: Scolytinae) during host colonization

Bark beetles of the genus Dendroctonus are important components of coniferous forests. During host colonization, they must overcome the chemical defences of their host trees, which are metabolized by cytochrome P450 (CYP or P450) enzymes to compounds that are readily excreted. In this study, we report the relative expression (quantitative real-time PCR) of four orthologous cytochrome P450 genes (CYP6BW5, CYP6DG1, CYP6DJ2 and CYP9Z20) in Dendroctonus rhizophagus and Dendroctonus valens forced to attack host trees at 8 and 24 h following forced attack and in four stages during natural colonization [solitary females boring the bark (T1); both male and female members of couples before oviposition (T2); both male and female members of couples during oviposition (T3), and solitary females inside the gallery containing eggs (T4)]. For both species gene expression was different compared with that observed in insects exposed to single monoterpenes in the laboratory, and the expression patterns were significantly different amongst species, sex, gut region and exposure time or natural colonization stage. The induction of genes (CYP6BW5v1, CYP6DJ2v1 and CYP9Z20v1 from D. rhizophagus, as well as CYP6DG1v3 from D. valens) correlated with colonization stage as well as with the increase in oxygenated monoterpenes in the gut of both species throughout the colonization of the host. Our results point to different functions of these orthologous genes in both species.

Genetic variation in the Cytb gene of human cerebral Taenia solium cysticerci recovered from clinically and radiologically heterogeneous patients with neurocysticercosis

Neurocysticercosis (NC) is a clinically and radiologically heterogeneous parasitic disease caused by the establishment of larval Taenia solium in the human central nervous system. Host and/or parasite variations may be related to this observed heterogeneity. Genetic differences between pig and human-derived T. solium cysticerci have been reported previously. In this study, 28 cysticerci were surgically removed from 12 human NC patients, the mitochondrial gene that encodes cytochrome b was amplified from the cysticerci and genetic variations that may be related to NC heterogeneity were characterised. Nine different haplotypes (Ht), which were clustered in four haplogroups (Hg), were identified. Hg 3 and 4 exhibited a tendency to associate with age and gender, respectively. However, no significant associations were found between NC heterogeneity and the different T. solium cysticerci Ht or Hg. Parasite variants obtained from patients with similar NC clinical or radiological features were genetically closer than those found in groups of patients with a different NC profile when using the Mantel test. Overall, this study establishes the presence of genetic differences in the Cytb gene of T. solium isolated from human cysticerci and suggests that parasite variation could contribute to NC heterogeneity.

Molecular markers in the epidemiology and diagnosis of coccidioidomycosis

The prevalence of coccidioidomycosis in endemic areas has been observed to increase daily. To understand the causes of the spread of the disease and design strategies for fungal detection in clinical and environmental samples, scientists have resorted to molecular tools that allow fungal detection in a natural environment, reliable identification in clinical cases and the study of biological characteristics, such as reproductive and genetic structure, demographic history and diversification. We conducted a review of the most important molecular markers in the epidemiology of Coccidioides spp. and the diagnosis of coccidioidomycosis. A literature search was performed for scientific publications concerning the application of molecular tools for the epidemiology and diagnosis of coccidioidomycosis. The use of molecular markers in the epidemiological study and diagnosis of coccidioidomycosis has allowed for the typing of Coccidioides spp. isolates, improved understanding of their mode of reproduction, genetic variation and speciation and resulted in the development specific, rapid and sensitive strategies for detecting the fungus in environmental and clinical samples. Molecular markers have revealed genetic variability in Coccidioides spp. This finding influences changes in the epidemiology of coccidioidomycosis, such as the emergence of more virulent or antifungal resistant genotypes. Furthermore, the molecular markers currently used to identify Coccidioides immitis and Coccidioides posadasii are specific and sensitive. However, they must be validated to determine their application in diagnosis. This manuscript is part of the series of works presented at the "V International Workshop: Molecular genetic approaches to the study of human pathogenic fungi" (Oaxaca, Mexico, 2012).

AFLP analysis reveals high genetic diversity but low population structure in Coccidioides posadasii isolates from Mexico and Argentina

Background

Coccidioides immitis and C. posadasii cause coccidioidomycosis, a disease that is endemic to North and South America, but for Central America, the incidence of coccidioidomycosis has not been clearly established. Several studies suggest genetic variability in these fungi; however, little definitive information has been discovered about the variability of Coccidioides fungi in Mexico (MX) and Argentina (AR). Thus, the goals for this work were to study 32 Coccidioides spp. isolates from MX and AR, identify the species of these Coccidioides spp. isolates, analyse their phenotypic variability, examine their genetic variability and investigate the Coccidioides reproductive system and its level of genetic differentiation.

Methods

Coccidioides spp. isolates from MX and AR were taxonomically identified by phylogenetic inference analysis using partial sequences of the Ag2/PRA gene and their phenotypic characteristics analysed. The genetic variability, reproductive system and level of differentiation were estimated using AFLP markers. The level of genetic variability was assessed measuring the percentage of polymorphic loci, number of effective allele, expected heterocygosity and Index of Association (I_A). The degree of genetic differentiation was determined by AMOVA. Genetic similarities among isolates were estimated using Jaccard index. The UPGMA was used to contsruct the corresponding dendrogram. Finally, a network of haplotypes was built to evaluate the genealogical relationships among AFLP haplotypes.

Results

All isolates of Coccidioides spp. from MX and AR were identified as C. posadasii. No phenotypic variability was observed among the C. posadasii isolates from MX and AR. Analyses of genetic diversity and population structure were conducted using AFLP markers. Different estimators of genetic variability indicated that the C. posadasii isolates from MX and AR had high genetic variability. Furthermore, AMOVA, dendrogram and haplotype network showed a small genetic differentiation among the C. posadasii populations analysed from MX and AR. Additionally, the I_A calculated for the isolates suggested that the species has a recombinant reproductive system.

Conclusions

No phenotypic variability was observed among the C. posadasii isolates from MX and AR. The high genetic variability observed in the isolates from MX and AR and the small genetic differentiation observed among the C. posadasii isolates analysed, suggest that this species could be distributed as a single genetic population in Latin America.

Nitrogen-fixing and uricolytic bacteria associated with the gut of Dendroctonus rhizophagus and Dendroctonus valens (Curculionidae: Scolytinae)

The bark beetles of the genus Dendroctonus feed on phloem that is a nitrogen-limited source. Nitrogen fixation and nitrogen recycling may compensate or alleviate such a limitation, and beetle-associated bacteria capable of such processes were identified. Raoultella terrigena, a diazotrophic bacteria present in the gut of Dendroctonus rhizophagus and D. valens, exhibited high acetylene reduction activity in vitro with different carbon sources, and its nifH and nifD genes were sequenced. Bacteria able to recycle uric acid were Pseudomonas fluorescens DVL3A that used it as carbon and nitrogen source, Serratia proteomaculans 2A CDF and Rahnella aquatilis 6-DR that used uric acid as sole nitrogen source. Also, this is the first report about the uric acid content in whole eggs, larvae, and adults (male and female) samples of the red turpentine beetle (Dendroctonus valens). Our results suggest that the gut bacteria of these bark beetles could contribute to insect N balance.

Diversity and expression of P450 genes from Dendroctonus valens LeConte (Curculionidae: Scolytinae) in response to different kairomones

Bark beetles (Curculionidae: Scolytinae) are major cause of woody plants death in the world. They colonize the stem and other parts of trees recognizing host-produced specific compounds (kairomones) and insect pheromones. Bark beetle's antennae and alimentary canal participate in the host selection identifying chemical compounds produced by trees and insects, and also in the metabolism and detoxification of these compounds. The red turpentine beetle (RTB), Dendroctonus valens LeConte, is an unaggressive species that colonize > 40 pine species (Pinaceae) in North and Central America. Several studies suggest that bark beetle cytochrome P450 enzymes are involved in monoterpene oxidation. In this study we identified by means of PCR, cloning, sequencing, and bioinformatic analysis, eleven full-length genes: five CYP4, four CYP6, and two CYP9 in the antennae and gut region of RTB, after stimulation with vapors of monoterpenes: (±)-α-pinene, (R)-(+)-α-pinene, (S)-(-)-β-pinene, (S)-(-)-α-pinene and (+)-3-carene; pine trees volatiles used by RTB as kairomones. The recovered cDNA of these genes vary from 1.5 kb to 1.8 kb and the open frame encodes from 496 to 562 amino acid proteins. The bioinformatic analysis suggests that the majority of P450 proteins encoded by these genes are membrane anchored in the endoplasmic reticulum. RT-qPCR assays showed differential expression of all CYP genes between male and female. The gene expression was dependent of monoterpenes and exposure time, with some of them sex, antennae and gut region specific. Significant differences among monoterpenes, gut region, antennae and exposure time were found. Our results suggest that some of these genes may be involved in the detoxification process of these compounds during tree colonization.

Atriplex atacamensis and Atriplex halimus resist As contamination in Pre-Andean soils (northern Chile)

The Pre-Andean area of Chile exhibits saline soils of volcanic origin naturally contaminated with arsenic (As), and we hypothesise that revegetation with resistant species may be a valid alternative for soil management in this area. Thus, the xerophytic and halophytic shrubs Atriplex halimus and Atriplex atacamensis were cultivated in containers for 90 days in Pre-Andean soil, As-soil, (111±19 mg As kg(-1), pH8.4±0.1) or control soil (12.7±1.1 mg As kg(-1), pH7.8±0.1) to evaluate As accumulation and resistance using stress bioindicators (chlorophylls, malondialdehyde (MDA) and total thiols). Sequential extraction of As-soil indicated that 52.3% of As was found in the most available fraction. The As distribution was significantly different between the species: A. halimus translocated the As to leaves, whilst A. atacamensis retained the As in roots. At 30 and 90 days, A. halimus showed similar As concentrations in the leaves (approximately 5.5 mg As kg(-1)), and As increased in stems and roots (up to 4.73 and 16.3 mg As kg(-1), respectively). In A. atacamensis, As concentration was lower (2.6 in leaves; 3.2 in stems and 6.9 in roots in mg As kg(-1)). Both species exhibited a high concentration of B in leaves (362-389 mg kg(-1)). If the plants are used for animal feed, it should be considered that A. halimus accumulates higher concentration of As and B in the leaves than A. atacamensis. Neither plant growth nor stress bioindicators were negatively affected by the high levels of available As, with the exception of MDA in the leaves of A. halimus. The results indicate that these plants resist contamination by arsenic, accumulating mainly the metalloid in the roots and can be recommended to generate plant cover in As-contaminated soils in the Pre-Andean region, under saline conditions controlled, preventing the dispersion of this metalloid via wind and leaching.

[Genotyping of clinical isolates of Aspergillus flavus and its relationship with environmental isolates of an oncohematological center]

BACKGROUND

During 4 months, and while conducting an environmental sampling of air, 2 cases of aspergillosis by Aspergillus flavus (A. flavus) were diagnosed at an oncohematological center in Buenos Aires, Argentina.

AIMS

The aim of this study was to know the variability and the genetic relationship between the clinical and environmental isolates, obtained in the oncohematological center.

METHODS

Two genotyping techniques of different discriminatory power (RAPD and AFLP) were used. A genetic similarity matrix was calculated using Jaccard method and was the basis for the construction of a dendrogram by UPGMA. The level of genetic variability was assessed by measuring the percentage of polymorphic loci, number of effective allele, expected heterocygozity and association index test (I(A)).

RESULTS

The dendrogram reveals that the A. flavus isolates recovered from the patients were not genetically related to those gotten from the rooms occupied by the patients. The environmental isolates had higher values of genetic diversity than the clinical isolates. The I(A) estimated for all the isolates suggest that recombination events occurred.

CONCLUSIONS

Patients 1 and 2 were not infected with isolates from the nosocomial environment. Clinical and environmental isolates of A. flavus showed high genetic variability among them.

Asymmetric patterns in the cranial skeleton of zebrafish (Danio rerio) exposed to sodium pentachlorophenate at different embryonic developmental stages

Bilaterally symmetric organisms display mirror copies of their structures on both sides of the body, and the development of both sides is regulated by the same set of genes. Environmental variations can directly affect phenotype, and exposure to chemical contaminants at certain stages may modify embryonic development. The pesticide sodium pentachlorophenate (NaPCP) was used at the no-observable-effect concentration (NOEC) to determine the degree of susceptibility of zebrafish (Danio rerio) embryos in different developmentally susceptible windows (zygote, blastula, gastrula, segmentation, pharyngula and larva). Shape variation in the zebrafish viscerocranium and fluctuating asymmetry (FA), which increases in direct proportion to environmental stress, induced by exposure to NaPCP were measured with geometric morphometrics. Procrustes ANOVA was performed to estimate the shape variation around a symmetric consensus that accounted for the following factors: shape variation in individuals (I), variation by sides (S), the Individuals×Sides interaction (I×S), and the stages of exposure to the toxicant (Stages). Factors I, S and IxS accounted for most of the morphological variation (p<0.0001). Extensive deformities throughout the viscerocranium occurred during the window of exposure from gastrula to larva. Embryonic mortality occurred and was dependent on the stage of exposure. The NOEC concentration of NaPCP affected embryonic development in D. rerio and also induced lethal effects in embryos. FA was determined in both unexposed and NaPCP-exposed embryos and was greater in the control than in some exposure windows; besides, no correlation was found between FA and developmental stages, so our results do not support FA as a bioindicator of chemical stress but confirm its value in the study of morphological effects of toxicants.

Helicobacter pylori: detection of iceA1 and iceA2 genes in the same strain in Mexican isolates

BACKGROUND AND AIMS

Helicobacter pylori iceA1 and iceA2 gene amplification is usually performed to identify mixed populations as both genes are apparently reportedly exclusive. However, some strains isolated from Mexico show both iceA genes. The aim of this study was to establish the frequency of these genes in Mexican isolates and genomic diversity of the H. pylori strains.

METHODS

One hundred thirty six biopsies were obtained from 68 patients (39 children and 29 adults). The presence of H. pylori was confirmed in 3/18 children and 6/19 adults by culture. There were 93 clinical strains isolated from nine patients. Additionally, we studied 37 strains from a strain collection isolated from 10 patients. The strains were genotyped and dual iceA genes were identified by polymerase chain reaction (PCR) and amplicons were sequenced. In addition, an enterobacterial repetitive intergenic consensus PCR (ERIC-PCR) assay was performed as fingerprinting method.

RESULTS

The genotypification of the H. pylori isolates indicated that all strains were vacA+; 86% babA2+, 86% cagA+, 82% vacA s1m1+, 19% iceA1+, 9% iceA2+, and 72% of them carried both iceA1 and iceA2 genes. The ERIC-PCR profiling revealed that the strains clustered in eight genetic groups depending on the presence of iceA1, iceA2 or both. A basic local multiple alignment analysis of the nucleotide sequences revealed that the iceA1 and iceA2 genes exhibited no relevant similarity.

CONCLUSION

The results here showed the presence of triple-positive strains (babA, cagA, vacA) of H. pylori and strains carrying simultaneously both iceA1 and iceA2 genes.

Gut-associated bacteria throughout the life cycle of the bark beetle Dendroctonus rhizophagus Thomas and Bright (Curculionidae: Scolytinae) and their cellulolytic activities

Dendroctonus rhizophagus Thomas and Bright (Curculionidae: Scolytinae) is an endemic economically important insect of the Sierra Madre Occidental in Mexico. This bark beetle has an atypical behavior within the genus because just one beetle couple colonizes and kills seedlings and young trees of 11 pine species. In this work, the bacteria associated with the Dendroctonus rhizophagus gut were analyzed by culture-dependent and culture-independent methods. Analysis of 16S rRNA sequences amplified directly from isolates of gut bacteria suggests that the bacterial community associated with Dendroctonus rhizophagus, like that of other Dendroctonus spp. and Ips pini, is limited in number. Nine bacterial genera of γ-Proteobacteria and Actinobacteria classes were detected in the gut of Dendroctonus rhizophagus. Stenotrophomonas and Rahnella genera were the most frequently found bacteria from Dendroctonus rhizophagus gut throughout their life cycle. Stenotrophomonas maltophilia, Ponticoccus gilvus, and Kocuria marina showed cellulolytic activity in vitro. Stenotrophomonas maltophilia, Rahnella aquatilis, Raoultella terrigena, Ponticoccus gilvus, and Kocuria marina associated with larvae or adults of Dendroctonus rhizophagus could be implicated in nitrogen fixation and cellulose breakdown, important roles associated to insect development and fitness, especially under the particularly difficult life conditions of this beetle.

Electrophysiological and behavioral responses of the bark beetle Dendroctonus rhizophagus to volatiles from host pines and conspecifics

The bark beetle Dendroctonus rhizophagus is endemic to northwestern Mexico where it kills immature pines < 3 m tall. We report the first investigation of the chemical ecology of this pest of forest regeneration. We used GC-EAD to assess olfactory sensitivity of this species to volatile compounds from: resin of a major host, Pinus arizonica; mid/hindguts of single, gallery-initiating females; and mate-paired males within galleries of attacked host trees in the field. Antennae of both sexes responded to monoterpenes α-pinene, β-pinene and 3-carene as well as to the beetle-derived oxygenated monoterpenes fenchyl alcohol, myrtenal, cis-verbenol, trans-verbenol, verbenone, and myrtenol. These monoterpenes were quantified from pre-emerged D. rhizophagus adults forced to attack host tissue in the laboratory, and from individuals dissected from naturally-attacked hosts at different stages of colonization. In both bioassays, myrtenol and trans-verbenol were the most abundant volatiles, and trans-verbenol was the only one produced in significantly greater quantities by females than males in a naturally-colonized host. Two field experiments were performed to evaluate behavioral responses of D. rhizophagus to antennally-active monoterpenes. Results show that 3-carene was significantly attractive either alone or in a ternary (1:1:1) combination with α-pinene and β-pinene, whereas neither α-pinene nor β-pinene alone were attractive. None of the beetle-associated oxygenated monoterpenes enhanced the attractiveness of the ternary mixture of monoterpenes, while verbenone either alone or combined with the other five oxygenated terpenes reduced D. rhizophagus attraction to the ternary mixture. The results suggest that attraction of D. rhizophagus to the host tree P. arizonica is mediated especially by 3-carene. There was no conclusive evidence for an aggregation or sex attractant pheromone.

Factors influencing the geographical distribution of Dendroctonus rhizophagus (Coleoptera: Curculionidae: Scolytinae) in the Sierra Madre Occidental, México

The bark beetle, Dendroctonus rhizophagus Thomas & Bright, is endemic to the Sierra Madre Occidental (SMOC) in México. This bark beetle is a major pest of the seedlings and young saplings of several pine species that are of prime importance to the nation's forest industry. Despite the significance of this bark beetle as a pest, its biology, ecology, and distribution are poorly known. Three predictive modeling approaches were used as a first approximation to identify bioclimatic variables related to the presence of D. rhizophagus in the SMOC and to obtain maps of its potential distribution within the SMOC, which is a morphotectonic province. Our results suggest that the bark beetle could have an almost continuous distribution throughout the major mountain ranges of the SMOC. This beetle has a relatively narrow ecological niche with respect to some temperature and precipitation variables and inhabits areas with climatic conditions that are unique from those usually prevalent in the SMOC. However, the bark beetle has a broad ecological niche with respect to the number of hosts that it attacks. At the macro-scale level, the D. rhizophagus distribution occurs within the wider distribution of its main hosts. The limit of the geographical distribution of this bark beetle coincides with the maximum temperature isotherms. Our results imply a preference for temperate habitats, which leads to the hypothesis that even minor changes in climate may have significant effects on its distribution and abundance.