Search

Bee pollen is a favorable microhabitat for many microorganisms and its dissemination via commercialization must be of important consideration. Here the data presented describe the characterization ...

The potential presence of spore-forming bacteria related to the Bacillus cereus group in Mexican chili powder elaborated from Capsicum annuum L. is of commercial and clinical interest, because chili powder is an essential spice in the Mexican diet and in diets around the globe. To facilitate detection and isolation of members of this group of spore-forming bacteria from Mexican chili powder samples, we identified colonies that grew on agar medium selective for Bacillus cereus sensu lato, supplemented with polymyxin B (10 µg/mL) and ampicillin (10 to 100 µg/mL). The presumptive B. cereus (s.l.) isolates were tested using a tRNACys-PCR-based approach and the results identified species related phylogenetically to B. cereus, B. thuringiensis, and B. toyonensis. Their toxigenic potential was assessed by serological tests to detect enterotoxins (Nhe and Hbl) and by PCR targeting the hemolysin BL (hbl) component C (hblC) and non-hemolytic enterotoxin component A (nheA). The antibiotic profiles of the isolates showed a high resistance to β-lactams (100% of the isolates), trimethoprim-sulfamethoxazole (100%), tetracycline (90%), erythromycin (77%), clindamycin (74%), and chloramphenicol (42%). Our results indicate the presence of B. cereus s.l. with toxigenic characteristics in Mexican chili powder. Because of the potential for these organisms to cause disease through their production of various toxins, and resistance to antibiotics, we recommend that a microbiological risk assessment must be considered in the Mexican regulatory requirements.

Candidatus Liberibacter solanacearum (CaLso) is associated with diseases in tomato crops and transmitted by the tomato psyllid Bactericera cockerelli. A polymeric water-dispersible nanobactericide (PNB) was evaluated against CaLso as a different alternative. PNB is a well-defined polycationic diblock copolymer designed to permeate into the vascular system of plants. Its assessment under greenhouse conditions was carried out with tomato plants previously infected with CaLso. Using a concentration as low as 1.0 mg L−1, a small but significant reduction in the bacterial load was observed by real-time qPCR. Thus, to achieve an ecologically friendly dosage and set an optimum treatment protocol, we performed experiments to determine the effective concentration of PNB to reduce ~65% of the initial bacterial load. In a first bioassay, a 40- or 70-fold increase was used to reach that objective. At this concentration level, other bioassays were explored to determine the effect as a function of time. Surprisingly, a real reduction in the symptoms was observed after three weeks, and there was a significant decrease in the bacterial load level (~98%) compared to the untreated control plants. During this period, flowering and formation of tomato fruits were observed in plants treated with PNB.

In Bacillus subtilis, the tRNA(Cys) lacks an encoded CCA 3′ end. To gain insight into the role of CCAase and RNases in tRNA(Cys) processing, several mutant strains were generated. Northern blot and RT-PCR results suggest that enzymes other than CCAase can participate in CCA addition at the 3′ end of the immature tRNA(Cys). ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s42770-019-00075-5) contains supplementary material, which is available to authorized users.

The bean (Phaseolus vulgaris) pathogen Pseudomonas syringae pv. phaseolicola NPS3121 synthe-sizes phaseolotoxin in a thermoregulated way, with optimum production at 18 °C. Gene PSPPH_4550 was previously shown to be thermoregulated and required for phaseolotoxin bio-synthesis. Here, we established that PSPPH_4550 is part of a cluster of 16 genes, the Pbo cluster, included in a genomic island with a limited distribution in P. syringae and unrelated to the posses-sion of the phaseolotoxin biosynthesis cluster. We identified typical non-ribosomal peptide syn-thetase, and polyketide synthetase domains in several of the pbo deduced products. RT-PCR and the analysis of polar mutants showed that the Pbo cluster is organized in four transcriptional units, including one monocistronic and three polycistronic. Operons pboA and pboO are both es-sential for phaseolotoxin biosynthesis, while pboK and pboJ only influence the amount of toxin produced. The three polycistronic units were transcribed at high levels at 18 °C but not at 28 °C, whereas gene pboJ was constitutively expressed. Together, our data suggest that the Pbo cluster synthesizes secondary metabolite(s), which could participate in the regulation of phaseolotoxin biosynthesis. The authors thank the Consejo Nacional de Ciencia y Tecnología (CONACyT) for the scholarship granted to Lizeth Guardado-Valdivia. The work reported was funded by research grant CB-2015-01-255155 from the CONACyT, to S. Aguilera, and by the Spanish Plan Nacional I+D+I grant AGL2017-82492-C2-2-R, from the Ministerio de Economía y Competitividad (MINECO), co-financed by the Fondo Europeo de Desarrollo Regional (FEDER), to J. Murillo.

El cempasúchil (Tagetes erecta) es una planta asterácea comúnmente utilizada como flor ornamental y ceremonial durante la temporada de otoño en México. Las plantas de cempasúchil cultivadas en el campo presentaron síntomas de la enfermedad de la mancha foliar bacteriana. Se aisló una cepa bacteriana que potencialmente causa la enfermedad de las manchas. El objetivo principal de esta investigación fue clasificar esta bacteria y evaluar su patogenicidad en cempasúchil y otras especies vegetales. El perfil bioquímico identificó esta cepa como Pseudomonas syringae LF2012. El análisis filogenético del gen ARNr 16S reveló una estrecha relación con genomoespecies de Pseudomonas. El perfil de macrorestricción I-CeuI del cromosoma confirmó su alto grado de similitud con distintos patovares de P. syringae. P. syringae LF2012 causa la enfermedad de las manchas cuando se inocula por aspersión en hojas de cempasúchil. Los ensayos de infección de plantas de otras familias (Asteraceae, Brassicaceae, Amaranthaceae, Poaceae y Solanaceae) sugirieron que la enfermedad podría limitarse al cempasúchil. Además, esta cepa provoca respuestas de tipo hipersensible en hojas de Nicotiana tabacum.

Background: In spore-forming bacteria, the molecular mechanisms of accumulation of transfer RNA (tRNA) during sporulation must be a priority as tRNAs play an essential role in protein synthesis during spore germination and outgrowth. However, tRNA processing has not been extensively studied in these conditions, and knowledge of these mechanisms is important to understand long-term stress survival. Methods:To gain further insight into tRNA processing during spore germination and outgrowth, the expression of the single copy tRNA Cys gene was analyzed in the presence and absence of 1.2 M NaCl in Bacillus subtilis using RNA-Seq data obtained from the Gene Expression Omnibus (GEO) database. The CLC Genomics work bench 12.0.2 (CLC Bio, Aarhus, Denmark, https://www.qiagenbioinformatics.com/) was used to analyze reads from the tRNA Cys gene. Results:The results show that spores store different populations of tRNA Cys-related molecules. One such population, representing 60% of total tRNA Cys, was composed of tRNA Cys fragments. Half of these fragments (3´-tRF) possessed CC, CCA or incorrect additions at the 3´end. tRNA Cys with correct CCA addition at the 3´end represented 23% of total tRNA Cys, while with CC addition represented 9% of the total and with incorrect addition represented 7%. While an accumulation of tRNA Cys precursors was induced by upregulation of the rrnD operon under the control of σ A -dependent promoters under both conditions investigated, salt stress produced only a modest effect on tRNA Cys expression and the accumulation of tRNA Cys related species. Conclusions:The results demonstrate that tRNA Cys molecules resident in spores undergo dynamic processing to produce functional molecules that may play an essential role during protein synthesis.

Endospore-forming bacteria related to the Bacillus cereus group produce toxins that cause illnesses in organisms from invertebrates to mammals, including foodborne illnesses in humans. As commercial bee pollen can be contaminated with these bacteria, a comprehensive microbiological risk assessment of commercial bee pollen must be incorporated into the relevant regulatory requirements, including those that apply in Mexico. To facilitate detection of members of this group of bacteria, we have developed a PCR strategy that is based on the amplification of the single-copy tRNACys gene and specific genes associated with tRNACys to detect Bacillus cereus sensu lato (B. cereus s.l.). This tRNACys-PCR-based approach was used to examine commercial bee pollen for endospore-forming bacteria. Our analysis revealed that 3% of the endospore-forming colonies isolated from a commercial source of bee pollen were related to B. cereus s.l., and this result was corroborated by phylogenetic analysis, bacterial identification via MALDI-TOF MS, and detection of enterotoxin genes encoding the HBL and NHE complexes. The results show that the isolated colonies are closely related phylogenetically to B. cereus, B. thuringiensis, and B. bombysepticus. Our results indicate that the tRNACys-PCR, combined with other molecular tools, will be a useful approach for identifying B. cereus s.l. and will assist in controlling the spread of potential pathogens.

Traditional mining activities are usually correlated with high levels of soil pollution, which is a major environmental concern. Extensive mining activities have taken place in the San Joaquin region in the State of Queretaro, Mexico resulting in high levels of mercury soil pollution (up to 1532 ± 300 mg/kg). We isolated mercury-resistant fungal strains from the San Joaquin region soils and identified them through morphologic characteristics and ITS rDNA region sequence analysis. We determined that fungi isolated belong to the genus Trichoderma. All the isolates selected showed the ability to catalyze the volatilization of Hg. For air sampling, an active sampling device was constructed and using acid KMnO4 as an absorbent, the concentration of mercury in solution was determined through the cold vapor atomic absorption method. The results show mercury volatilization from the fungal species assay, with a maximum of 213.04 ± 32.6 μg/m3 while mycelium accumulation ranged from less than 17.5 ± 2.9 to 20.0 ± 3.4 μg/g. The fungal isolates were also evaluated for their ability to reduce mercury uptake in Arabidopsis thaliana. These observations suggest the utility of Trichoderma for the mobilization of mercury in those contaminated soils.

American foulbrood (AFB) caused by Paenibacillus larvae is the most destructive honeybee bacterial disease and its dissemination via commercial bee pollen is an important mechanism for the spread of this bacterium. Because Mexico imports bee pollen from several countries, we developed a tRNA(Cys)-PCR strategy and complemented that strategy with MALDI-TOF MS and amplicon-16S rRNA gene analysis to evaluate the presence of P. larvae in pollen samples. P. larvae was not detected when the tRNA(Cys)-PCR approach was applied to spore-forming bacterial colonies obtained from three different locations and this result was validated by bacterial identification via MALDI-TOF MS. The genera identified in the latter analysis were Bacillus (fourteen species) and Paenibacillus (six) species. However, amplicon-16S rRNA gene analysis for taxonomic composition revealed a low presence of Paenibacillaceae with 0.3 to 16.2% of relative abundance in the commercial pollen samples analyzed. Within this family, P. larvae accounted for 0.01% of the bacterial species present in one sample. Our results indicate that the tRNA(Cys)-PCR, combined with other molecular tools, will be a useful approach for identifying P. larvae in pollen samples and will assist in controlling the spread of the pathogen.

Bee pollen is a highly nutritive natural foodstuff. Because of its use as a comestible, the association of bacteria with bee pollen is commercially and biologically important. We report here the bacterial diversity of seven bee pollen samples (five from Europe, one from Chile, and one from Mexico) based on 16S rRNA gene amplicon metagenome sequencing.

A novel strain of Pectobacterium, isolated from infected sunflower plants (Helianthus annuus L.) in Mexico was characterized. Inoculated sunflower plants developed both tissue chlorosis and soft-rot on leaves. The broad host range shown by this pathogen, which included members of the Agavaceae, Asteraceae, Brassicaceae and Solanaceae, was characteristic of the genus Pectobacterium. The metabolic profile and molecular data, in addition to the secretion of plant-cell-wall-degrading enzymes, confirmed its identification as a member of the Pectobacterium genus. A phylogenetic tree constructed on the basis of its 16S rDNA sequence revealed a high identity (98 %) with P. cacticidum. Amplification and restriction-fragment-length-polymorphism analysis of internal transcribed sequences further confirmed its classification as P. cacticidum. Similar to strains of P. atrosepticum, P. carotovorum and Dickeya spp., the new P. cacticidum strain FHLGJ22 has a coronafacic ligase gene and produces coronatine, a virulence factor usually associated with phytopathogenic strains of Pseudomonas syringae. Our results suggest that this strain may utilize a dual infection process involving cell maceration and plant toxins, which is synchronized via an unknown mechanism, might confer an adaptive advantage to colonize different plant hosts.

Bee pollen is a valuable natural product and by its nutritional composition is important for the development of insects of agricultural interest. In this work, we determined whether gamma irradiation can minimize the risk of microbial contamination of commercial bee pollen used for the mass rearing of bumblebees. Bee pollen samples were treated with target doses of 0, 2, 5, 7 and 9 kGy of gamma radiation emitted by a 60Co source and then analyzed for microbial content. Neither fungi nor coliform bacteria were detected in samples irradiated at 5 kGy or higher. Yeasts and aerobic bacteria were not detected in the samples irradiated at 7 kGy or higher (

Pseudomonas syringae pv. phaseolicola produces phaseolotoxin in a temperature dependent manner, being optimally synthesized between 18ºC and 20ºC, while no detectable amounts are present above 28ºC. The Pht cluster, involved in the biosynthesis of phaseolotoxin, contains 23 genes that are organized in five transcriptional units. The function of most of the genes from the Pht cluster is still unknown and little information about the regulatory circuitry leading to expression of these genes has been reported. The purpose of the present study was to investigate the participation of pht genes in the regulation of the operons coded into the Pht cluster. We conducted Northern blot, uidA fusions and reverse transcription- PCR assays of pht genes in several mutants unable to produce phaseolotoxin. This allowed us to determine that, in P. syringae pv. phaseolicola NPS3121, genes phtABC are essential to prevent their own expression at 28ºC, a temperature at which no detectable amounts of the toxin are present. We obtained evidence that the phtABC genes also participate in the regulation of the phtD, phtM and phtL operons. According to our results, we propose that PhtABC and other Pht product activities could be involved in the synthesis of the sulfodiaminophosphinyl moiety of phaseolotoxin, which indirectly could be involved in the transcriptional regulation of the phtA operon. This work was funded by grants from the Consejo Nacional de Ciencia y Tecnología (CONACyT), research grant CB-2015-01-255155 to SA, and from the Spanish Plan Nacional I + D + i grant AGL2014-53242-C2-2-R, from the Ministerio de Economía y Competitividad, co-financed by the Fondo Europeo de Desarrollo Regional (FEDER) to JM.

Oxidative stress occurs when cells are exposed to elevated levels of reactive oxygen species that can damage biological molecules. One bacterial response to oxidative stress involves disulfide bond formation either between protein thiols or between protein thiols and low-molecular-weight (LMW) thiols. Bacillithiol was recently identified as a major low-molecular-weight thiol in Bacillus subtilis and related Firmicutes. Four genes (bshA, bshB1, bshB2, and bshC) are involved in bacillithiol biosynthesis. The bshA and bshB1 genes are part of a seven-gene operon (ypjD), which includes the essential gene cca, encoding CCA-tRNA nucleotidyltransferase. The inclusion of cca in the operon containing bacillithiol biosynthetic genes suggests that the integrity of the 3′ terminus of tRNAs may also be important in oxidative stress. The addition of the 3′ terminal CCA sequence by CCA-tRNA nucleotidyltransferase to give rise to a mature tRNA and functional molecules ready for aminoacylation plays an essential role during translation and expression of the genetic code. Any defects in these processes, such as the accumulation of shorter and defective tRNAs under oxidative stress, might exert a deleterious effect on cells. This review summarizes the physiological link between tRNACys regulation and oxidative stress in Bacillus.

Oxidative stress occurs when cells are exposed to elevated levels of reactive oxygen species that can damage biological molecules. One bacterial response to oxidative stress involves disulfide bond formation either between protein thiols or between protein thiols and low-molecular-weight (LMW) thiols. Bacillithiol was recently identified as a major low-molecular-weight thiol in Bacillus subtilis and related Firmicutes. Four genes (bshA, bshB1, bshB2, and bshC) are involved in bacillithiol biosynthesis. The bshA and bshB1 genes are part of a seven-gene operon (ypjD), which includes the essential gene cca, encoding CCA-tRNA nucleotidyltransferase. The inclusion of cca in the operon containing bacillithiol biosynthetic genes suggests that the integrity of the 3′ terminus of tRNAs may also be important in oxidative stress. The addition of the 3′ terminal CCA sequence by CCA-tRNA nucleotidyltransferase to give rise to a mature tRNA and functional molecules ready for aminoacylation plays an essential role during translation and expression of the genetic code. Any defects in these processes, such as the accumulation of shorter and defective tRNAs under oxidative stress, might exert a deleterious effect on cells. This review summarizes the physiological link between tRNACys regulation and oxidative stress in Bacillus.

Pseudomonas syringae pv. phaseolicola is the causal agent of halo blight disease of beans (Phaseolus vulgaris L.), which is characterized by watersoaked lesions surrounded by a chlorotic halo resulting from the action of a non-host specific toxin known as phaseolotoxin. This toxin inhibits the enzyme ornithine carbamoyltransferase involved in the arginine biosynthesis pathway. It was previously reported that genes within the Pht cluster were involved in the regulation and synthesis of phaseolotoxin. The GacS/GacA two-component signal transduction system controls important pathogenicity and virulence mechanisms in several Gram-negative bacteria. Tox(-) phenotype gacA(-) and gacS(-) mutants were obtained and gacA(-) transcriptome analysis revealed that this response activator controls expression of genes within the Pht cluster as well as another gene located in a different region in the bacterial chromosome and that has been unambiguously shown to be directly involved in phaseolotoxin biosynthesis. Results presented in this work suggest that phaseolotoxin biosynthesis involve elements within and outside the Pht Cluster, and that the GacS/GacA two-component system exerts control over them.

Pseudomonas syringae pv. phaseolicola synthesizes a non-host-specific toxin, phaseolotoxin, and also synthesizes a phaseolotoxin-resistant ornithine carbamoyltransferase (ROCT) to protect itself from its own toxin. ROCT is encoded by argK , which is expressed coordinately with phaseolotoxin synthesis at 18°C. To investigate the regulatory mechanisms of this system, null mutants were constructed for argK , argF (encoding the phaseolotoxin-sensitive OCTase [SOCT]), and amtA (encoding an amidinotransferase involved in phaseolotoxin synthesis). The argF mutant did not exhibit arginine auxotrophy when grown in M9 medium at 28°C, because under this condition SOCT was replaced by ROCT. This loss of thermoregulation of argK was apparently caused by accumulation of carbamoylphosphate, one of the substrates of SOCT. Carbamoylphosphate, which has a structure similar to that of the inorganic moiety of phaseolotoxin, was used in induction assays with wild-type P. syringae pv. phaseolicola and was shown to be able to induce argK expression in M9 medium at 28°C. These results indicate that argK expression is independent of temperature and is regulated directly by a compound resembling the inorganic moiety of phaseolotoxin.

Trichomonas vaginalisis the causal agent of trichomoniasis, which is associated with preterm child delivery, low birth weight, and an increased risk of infection by human papilloma virus and human immunodeficiency virus following exposure. Several reports have established increasing numbers of trichomoniasis cases resistant to metronidazole, the agent used for treatment, and it is therefore important to identify new therapeutic alternatives. Previously, our group reported the effect of tritrpticin, a synthetic peptide derived from porcine prophenin, onT. vaginalis; however, the hemolytic activity of this small peptide complicates its possible use as a therapeutic agent. In this study, we report that the propeptide and the processed peptide of prophenin 2 (cleaved with hydroxylamine) affected the integrity and growth ofT. vaginalisand that pro-prophenin 2 displays some resistance to proteolysis byT. vaginalisproteinases at 1 h. Its effect onT. vaginalisas well as its low hemolytic activity and short-time stability to parasite proteinases makes prophenin 2 an interesting candidate for synergistic or alternative treatment againstT. vaginalis.

Incluye material complementario The bacterium Pseudomonas syringae pv. phaseolicola produces phaseolotoxin in a temperature dependent manner, being optimally produced between 18 degrees C and 20 degrees C, while no detectable amounts are present above 28 degrees C. Phaseolotoxin is an effective inhibitor of ornithine carbamoyltransferase (OCTase) activity from plant, mammalian and bacterial sources and causes a phenotypic requirement for arginine. To protect the cell from its own toxin, P. syringae pv. phaseolicola synthesizes a phaseolotoxin-resistant OCTase (ROCT). The ROCT is the product of the argK gene and is synthesized only under conditions leading to phaseolotoxin synthesis. The argK gene is included in a chromosomal fragment named Pht cluster, which contains genes involved in the synthesis of phaseolotoxin. The aim of the present work was to investigate the possible involvement of other genes included in the Pht cluster in the regulation of gene argK. We conducted transcriptional analyses of argK in several mutants unable to produce phaseolotoxin, transcriptional fusions and electrophoretic mobility shift assays, which allowed us to determine that genes phtABC, located within the Pht cluster, participate in the transcriptional repression of gene argK at temperatures not permissive for phaseolotoxin biosynthesis. This repression is mediated by a protein present in both toxigenic and nontoxigenic strains of P. syringae and in E. coli, and requires the coordinated participation of phtA, phtB and phtC products in order to carry out an efficient argK repression. This work was funded by grants from CONACYT (Consejo Nacional de Ciencia y Tecnología; http://www.conacyt.mx), research grant SEP-2006-C01-49958/24089 to AAM and SA (Postdoctoral scholarship), and from the Spanish Plan Nacional I+D+I grant AGL2008-55311-CO2-01 (Ministerio de Ciencia e Innovación; http://micinn.es/), co financed by FEDER, to JM.

Pseudomonas syringae pv. phaseolicola is the causal agent of halo blight disease of beans ( Phaseolus vulgaris L.), which is characterized by water-soaked lesions surrounded by a chlorotic halo resulting from the action of a non-host-specific toxin known as phaseolotoxin. This phytotoxin inhibits the enzyme ornithine carbamoyltransferase involved in arginine biosynthesis. Different evidence suggested that genes involved in phaseolotoxin production were clustered. Two genes had been previously identified in our laboratory within this cluster: argK , which is involved in the immunity of the bacterium to its own toxin, and amtA , which is involved in the synthesis of homoarginine. We sequenced the region around argK and amtA in P. syringae pv. phaseolicola NPS3121 to determine the limits of the putative phaseolotoxin gene cluster and to determine the transcriptional pattern of the genes comprising it. We report that the phaseolotoxin cluster (Pht cluster) is composed of 23 genes and is flanked by insertion sequences and transposases. The mutation of 14 of the genes within the cluster lead to a Tox − phenotype for 11 of them, while three mutants exhibited low levels of toxin production. The analysis of fusions of selected DNA fragments to uidA , Northern probing, and reverse transcription-PCR indicate the presence of five transcriptional units, two monocistronic and three polycistronic; one is internal to a larger operon. The site for transcription initiation has been determined for each promoter, and the putative promoter regions were identified. Preliminary results also indicate that the gene product of phtL is involved in the regulation of the synthesis of phaseolotoxin.

The bacterium Pseudomonas syringae pv. phaseolicola is the causal agent of the “halo blight” disease of beans (Phaseolus vulgaris L.). This bacterium shares wide evolutionary relatedness with Pseudomonas savastonoi, and it was proposed that its taxonomic status be changed to P. savastanoi pv. phaseolicola; however, this proposal has been rejected and the organism has been maintained within the P. syringae group66. The disease attacks both foliage and pods, and is a major problem in temperate areas of the world. Leaf symptoms appear several days after infection as small water-soaked spots on the lower surface. At 7-10 days after infection, the lesions appear as greasy water-soaked points of infections. Pods can also be infected and lesions appear as brown or red water-soaked spots.Seeds may also become infected and the disease may be transmitted through the infected seed. At temperatures between 18°C and 23°C and high humidity, a zone of yellow-green tissue may develop around the initial site of infection after 3–8 days, giving rise to what is known as the chlorotic halo. In cases of severe infection, the chlorosis may become systemic. In fact, halo blight is considered to be a low-temperature disease and epidemic potential is greatest at temperatures ranging between 18°C and 22°C.

Pseudomonas syringae pv. phaseolicola, the causal agent of halo blight in beans produces a non-host specific toxin capable of inhibiting the enzyme ornithine carbamoyltransferase (OCTase) of plant, bacterial and mammalian origin. When P. s. pv. phaseolicola grown under conditions leading to the synthesis of phaseolotoxin, synthesises a phaseolotoxin-resistant OCTase, the product of the argK gene. Under any other growth conditions, the synthesis of arginine is mediated by a phaseolotoxin-sensitive OCTase encoded by the argF gene. In P. aeruginosa genes involved in the catabolism of arginine, the synthesis of carbamoylphosphate and the expression of argF are regulated by arginine and the ArgR protein. We isolated and characterised the argR gene of P. s. pv phaseolicola, and constructed a null argR mutant. Northern blot analysis using this mutant showed that in this bacterium regulated expression of argF is dependent on the ArgR product, but argK expression and phaseolotoxin synthesis occur independent of this regulatory protein. Also, we have shown that exogenous arginine has an effect on the expression of argF but not on argK. These results strongly indicate a lack of metabolic coordination between the synthesis of phaseolotoxin and the system regulating arginine metabolism mediated by ArgR

Multidrug-resistant microorganisms are of great concern to public health. Genetic mobile elements, such as plasmids, are among the most relevant mechanisms by which bacteria achieve this resistance. We obtained an Escherichia coli strain CM6, isolated from cattle presenting severe diarrheic symptoms in the State of Querétaro, Mexico. It was found to contain a 70 kb plasmid (pMEX01) with a high similarity to the pHK01-like plasmids that were previously identified and described in Hong Kong. Analysis of the pMEX01 sequence revealed the presence of a blaCTX-M-14 gene, which is responsible for conferring resistance to multiple β-lactam antibiotics. Several genes putatively involved in the conjugative transfer were also identified on the plasmid. The strain CM6 is of high epidemiological concern because it not only displays resistance to multiple β-lactam antibiotics but also to other kinds of antibiotics.

Background Pseudomonas syringae pv. phaseolicola is a Gram-negative plant-pathogenic bacterium that causes "halo blight" disease of beans (Phaseolus vulgaris L.). This disease affects both foliage and pods, and is a major problem in temperate areas of the world. Although several bacterial genes have been determined as participants in pathogenesis, the overall process still remains poorly understood, mainly because the identity and function of many of the genes are largely unknown. In this work, a genomic library of P. syringae pv. phaseolicola NPS3121 was constructed and PCR amplification of individual fragments was carried out in order to print a DNA microarray. This microarray was used to identify genes that are differentially expressed when bean leaf extracts, pod extracts or apoplastic fluid were added to the growth medium. Results Transcription profiles show that 224 genes were differentially expressed, the majority under the effect of bean leaf extract and apoplastic fluid. Some of the induced genes were previously known to be involved in the first stages of the bacterial-plant interaction and virulence. These include genes encoding type III secretion system proteins and genes involved in cell-wall degradation, phaseolotoxin synthesis and aerobic metabolism. On the other hand, most repressed genes were found to be involved in the uptake and metabolism of iron. Conclusion This study furthers the understanding of the mechanisms involved, responses and the metabolic adaptation that occurs during the interaction of P. syringae pv. phaseolicola with a susceptible host plant.