Jesús Muñoz-Rojas

Doctor en Ciencias
Head of Department
Meritorious Autonomous Univers... · Laboratorio de Ecología Molecular Microbiana CICM

Publications

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    ABSTRACT: In an attempt to quantify the number of bacteria present in a high number of samples, routine procedures are usually very time-consuming. During this period of time, bacterial population could be modified. In this work, an alternative for a mas-sive, quick and economic method was evaluated in order to count viable bacteria, consisting in the sealing or stamping of serial dilutions performed in samples from different origins. The time required to prepare 22 samples for plate stamping is only 15 minutes. The quantification was based in performing serial dilutions (10-fold) of the original liquid samples contai-ned in a multiwell plate using a multichannel micropipette. Afterwards, using a replicator, the same volume of each sample (approximately 1,65 μl) was recovered from each well, and then it was inoculated and sealed in a solid growth media of interest. Plates were incubated as needed, colonies were counted in the quantifiable dilution and Colony Forming Units per milliliter (CFU/ml) was calculated for each sample. We called this method “Massive Stamping Drop Plate” (MSDP) and it has been successfully applied to count bacteria from different lab samples, including liquid cultures, clinical samples (exudates and secretions) and bacteria recovered from the rhizosphere of corn plants. However, MSDP could also be applied to mas-sively count bacteria from any other source.
    Revista Colombiana de Biotecnología. 12/2012; XIV(2):147-156.
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    ABSTRACT: The rhizospheric soil interacts with substances of low molecular weight such as carboxylic acids, among other substances, whose sorption dynamics of mineral particle surface is unknown. Adsorption of water and volatile carboxylic acids from plants and bacteria (methane, ethane, propane and butane) was determined by the chromatographic method in an agricultural soil in San Juan Atenco, Puebla, Mexico. The soil under study was characterized by their physical, chemical, biological and surface properties. Porosity was determined by the method of N2 adsorption at its boiling point (76 K). Specific surface area values were determined using the method of Brunauer-Emmett-Teller (BET); pore volume was obtained using the Gursvitch rule and pore size distribution was studied by the Barrett-Joyner-Halenda (BJH) approach. The adsorption of the adsorbates was determined in the temperature range 423-523 K using gas chromatography with thermal conductivity detector and using helium as carrier gas. The Freundlich and Langmuir equations were applied to all cases. The results showed that the adsorption of water and volatile carboxylic acids, derived from biological metabolism in soil, is a function of the differential structure of molecules that impact the degree of interaction with the porous soil system.
    Terra Latinoamericana. 08/2012; 30(1):261-270.
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    ABSTRACT: Pineapple is the second most important tropical fruit in international trade and Mexico ranks ninth in world production. Pink disease is asymptomatic in the field and is characterized by the production of dark discoloration (amber-reddish brown) and its initial effects are not recognized until the fruits are cored and canned. Hence pink disease is considered a major problem in the pineapple canning industry.Four hundred and eighty isolates of pineapple were tested for antagonistic activity vs. Tatumella, causal agent of pink disease, and strain UAPS07070 was selected for further assays.Population dynamics were explored in co-inoculation in vitro and in planta with strain UAPS07070 and T. ptyseos UAPS07007. The population of UAPS07007, the producer strain of the disease severely declined in comparison with the controls.This work contributes to the knowledge of the ecology of pink disease in pineapple, as well as to the comprehension of the interactions between microorganisms colonizing the habitat of the plant.Highlights► We determined the antagonism of B. gladioli on a pink disease causative agent. ► We detected inhibition of T. ptyseos by B. gladioli in in vitro experiments. ► We detected inhibition of T. ptyseos by B. gladioli in in planta experiments. ► We detected pigmentation decline by cultivating T. ptyseos with B. gladioli.
    Applied Soil Ecology 01/2012; · 2.11 Impact Factor
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    ABSTRACT: Bacteria have been found in all niches explored on Earth, their ubiquity derives from their enormous metabolic diversity and their capacity to adapt to changes in the environment. Some bacterial strains are able to thrive in the presence of high concentrations of toxic organic chemicals, such as aromatic compounds, aliphatic alcohols and solvents. The extrusion of these toxic compounds from the cell to the external medium represents the most relevant aspect in the solvent tolerance of bacteria, however, solvent tolerance is a multifactorial process that involves a wide range of genetic and physiological changes to overcome solvent damage. These additional elements include reduced membrane permeabilization, implementation of a stress response programme, and in some cases degradation of the toxic compound. We discuss the recent advances in our understanding of the mechanisms involved in solvent tolerance.
    Current opinion in biotechnology 12/2011; 23(3):415-21. · 7.82 Impact Factor
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    ABSTRACT: Forty soil samples were collected from four rural communities in the Municipality of Huauchinango (Puebla, Mexico), a region with endemic dermatomycoses. Classical and molecular approaches allowed the identification of 30 different species, including several agents of superficial, subcutaneous and opportunistic mycoses. The most prevalent pathogenic agents identified by micro-morphological characteristics were: Trichophyton mentagrophytes (12.5%), T. rubrum (7.5%), and Aspergillus flavus (7.5%). A lower number of isolates was obtained in soils having acidic pH (5.19). Fungal diversity of Ascomycetes was also found in the studied area by sequence analysis of the ITS1-5.8S-ITS2 rDNA region. Our results showed a high prevalence of pathogenic and potential agents of mycoses, as well as the importance of molecular tools to identify microbial populations in soil.
    Micología Aplicada Internacional. 01/2011;
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    ABSTRACT: A maize rhizosphere isolate was phenotypically and genotypically characterized and identified as Enterobacter spp. bacterium. Germinated seeds were inoculated, the plantlets were sown in vermiculite and in soil and grown under laboratory and field conditions, respectively. The adherence, colonization and plant growth promotion capability of Enterobacter sp. UAPS03001 was evaluated in "Rojo-Criollo" maize under laboratory conditions. Twenty days after inoculation, the treated plantlets showed larger biomass than non-inoculated ones. In field grown plants, the kernel biomass was also greater in inoculated than in non-inoculated plants. The inoculation of maize sprouts with plant growth- promoting bacteria before their sowing in the field would be an alternative practice for achieving successful yield in temporal agriculture.
    Revista Argentina de microbiología 01/2011; 43(4):287-93. · 0.54 Impact Factor
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    ABSTRACT: Bacteria sustain life on earth, and even thought we only known around 1% of its diversity, several of them could result beneficial when used in different domains, including agriculture, biomedicine, bioremediation, and others. Nowadays, strong effort has been put into elucidating both new bacterial species and the function encoded in their genes; through mutagenesis and sequencing methods. Given the importance of working with bacteria from different sources, it is necessary to count on reliable methods to preserve bacteria successfully, allowing the researcher to use the precise same strain over his research. At the present work, we discuss several methodologies to preserve bacteria properly, while ensuring that they maintain a high viability as well as their phenotypic and genotypic characteristics. The improvement of these preserving techniques will ensure the conservation of the great biotechnological potential that bacteria contain in their genomes. Key words: Bacteria, preservation, freeze, freeze drying.
    BioTecnología. 05/2010; 14(2):11-29.
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    ABSTRACT: Pink disease is a major problem in the pineapple canning industry. Affected fruit acquire a brownish pigment after pasteurization and can contaminate non-affected fruit before they are released to the consumer. In the last few years, Pantoea citrea has been described as the causative agent of pink disease. In this study, over 300 bacterial isolates from pineapple plants, growing in Mexican commercial fields, and from soil close to plant roots were recovered. Over 250 isolates showed a very high similarity in their phenotypic and genotypic traits with Tatumella ptyseos, a close relative of Pantoea. These isolates exhibited typical pathogenicity reactions in pineapple juice tests, pineapple slices and fruit. On this basis, molecular identification procedures for the Tatumella isolates associated with pink disease were implemented. In affected fruit populations around 106 CFU/g of fresh tissue were recovered. This is first time that T. ptyseos is demonstrated as a causal agent of pink disease.
    Journal of Phytopathology 01/2010; 158(2):93 - 99. · 1.00 Impact Factor
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    Elementos : Ciencia y cultura. 01/2010;
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    Elementos : Ciencia y Cultura. 01/2010;
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    ABSTRACT: Bacterial isolates from maize plants showing a leaf spot disease were identified through molecular and phenotypic traits, showing that the isolates belong to Pantoea ananatis. Maize plants inoculated with those isolates showed a pathogenic reaction. This is the first report of a disease of Mexican maize caused by P. ananatis. Additional keywordsEnterobacteriaceae–Zea mays–phytopathogen
    Australasian Plant Disease Notes 01/2009; 4(1):96-99.
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    ABSTRACT: We used a two-step enrichment approach to isolate root-colonizing hexachlorocyclohexane (HCH)-degrading microorganisms. The first step consists of the use of classical liquid enrichment to isolate γ-HCH degraders. The γ-HCH-degrading microbes were attached in mass to corn seeds sown in soil with γ-HCH, and after plant development we rescued bacteria growing on root tips. Bacteria were then subjected to a second enrichment round in which growth on liquid medium with γ-HCH and inoculation of corn seeds were repeated. We then isolated bacteria on M9 minimal medium with γ-HCH from root tips. We were able to isolate four Sphingomonas strains, all of which degraded α-, β-, γ- and δ-HCH. Two of the strains were particularly good colonizers of corn roots, reaching high cell density in vegetated soil and partly removing γ-HCH. In contrast, these bacteria performed poorly in unplanted soils. This study supports the hypothesis that the removal of persistent toxic chemicals can be accelerated by combinations of plants and bacteria, a process generally known as rhizoremediation.
    Microbial Biotechnology 01/2008; 1(1):87-93. · 3.21 Impact Factor
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    ABSTRACT: Biological membranes have evolved different mechanisms to modify their composition in response to chemical stimuli in a process called 'homeoviscous adaptation'. Among these mechanisms, modifications in the ratio of saturated/unsaturated fatty acids and in cis/trans fatty acid isomers, cyclopropanation and changes in the phospholipids head group composition have been observed. To further understand the role of phospholipid head groups in solvent stress adaptation, we knocked out the cls (cardiolipin synthase) gene in Pseudomonas putida DOT-T1E. As expected, cls mutant membranes contained less cardiolipin than those of the wild-type strain. Although no significant growth rate defect was observed in the cls mutant compared with the wild-type strain, mutant cells were significantly smaller than the wild-type cells. The cls mutant was more sensitive to toluene shocks and to several antibiotics than the parental strain, suggesting either that the RND efflux pumps involved in the extrusion of these drugs were not working efficiently or that membrane permeability was altered in the mutant. Membranes of the cls mutant strain seemed to be more rigid than those of the parental strain, as observed by measurements of fluorescence polarization using the DPH probe, which intercalates into the membranes. Ethidium bromide is pumped out in Pseudomonas putida by at least one RND efflux pump involved in antibiotic and solvent resistance, and the higher rate of accumulation of ethidium bromide inside mutant cells indicated that functioning of the efflux pumps was compromised as a consequence of the alteration in phospholipid head group composition.
    Environmental Microbiology 06/2007; 9(5):1135-45. · 6.24 Impact Factor
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    ABSTRACT: Pseudomonas putida encodes 20 extracytoplasmic sigma factors (ECFs). In this study, we show that one of these ECFs, known as ECF-Pp12 (PP3006), plays a role in tolerance of toluene and other organic solvents. Based on this finding, we have called the gene that encodes this new ECF rpoT. The rpoT gene forms an operon with the preceding gene and with the gene located downstream. The translated gene product of the open reading frame PP3005 is an inner membrane protein, whereas the PP3007 protein is periplasmic. A nonpolar DeltarpoT mutant was generated by homologous recombination, and survival of the mutant was tested under various stress conditions. The mutant strain was hypersensitive to toluene and other solvents but just as tolerant as the wild type of stress imposed by heat, antibiotics, NaCl, paraquat, sodium dodecyl sulfate, H(2)O(2), and benzoate. In the DeltarpoT mutant background, expression of around 50 transcriptional units was affected: 31 cistrons were upregulated, and 23 cistrons were downregulated. This indicates that about 1% of all P. putida genes are under the direct or indirect influence of RpoT. The rpoT gene controls the expression of a number of membrane proteins, including components of the respiratory chains, porins, transporters, and multidrug efflux pumps. Hypersensitivity of the P. putida RpoT-deficient mutant to organic solvents can be attributed to the fact that in the DeltarpoT strain, expression of the toluene efflux pump ttgGHI genes is severalfold lower than in the parental strain.
    Journal of Bacteriology 02/2007; 189(1):207-19. · 3.19 Impact Factor
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    ABSTRACT: Chloramphenicol is a potent broad-spectrum antibiotic produced by diverse species of the Streptomyces genus. Because the chemical structure of this antibiotic is relatively simple, chloramphenicol ws one of the first antibiotics to be chemically synthesized and produced on a commercial scale. Even though chloramphenicol is a toxic molecule, it is used as a systemic antibiotic in excepcional cases. In addition, due to its reduced size and apolar characteristics, chloramphenicol represents an alternative for the tratment of infections located in sites with difficult accessibility, such as the brain. This revision offers a global view of the knowledge related to chloramphenicol including: its biosynthesis, the mechanisms of action and the strategies that microorganisms have developed to avoid the effects of this antibiotic.
    Revista Mexicana de Ciencias Farmaceuticas 01/2007; 38(1):58-69.
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    ABSTRACT: Pseudomonas putida KT2440, a saprophytic soil bacterium that colonizes the plant root, is a suitable microorganism for the removal of pollutants and a stable host for foreign genes used in biotransformation processes. Because of its potential use in agriculture and industry, we investigated the conditions for the optimal preservation of the strain and its derivatives for long-term storage. The highest survival rates were achieved with cells that had reached the stationary phase and which had been subjected to freeze-drying in the presence of disaccharides (trehalose, maltose, and lactose) as lyoprotectants. Using fluorescence polarization techniques, we show that cell membranes of KT2440 were more rigid in the stationary phase than in the exponential phase of growth. This is consistent with the fact that cells grown in the stationary phase exhibited a higher proportion of C17:cyclopropane as a fatty acid than cells in the exponential phase. Mutants for the cfaB gene, which encodes the main C17:cyclopropane synthase, and for the cfaA gene, which encodes a minor C17:cyclopropane synthase, were constructed. These mutants were more sensitive to freeze-drying than wild-type cells, particularly the mutant with a knockout in the cfaB gene that produced less than 2% of the amount of C17:cyclopropane produced by the parental strain.
    Applied and Environmental Microbiology 02/2006; 72(1):472-7. · 3.95 Impact Factor
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    ABSTRACT: In this study the antagonistic activity among 55 Gluconacetobacter diazotrophicus strains, belonging to 13 electrophoretic types (ETs), in culture media was analyzed. Antagonistic effects were seen only in strains belonging to two ETs named ET-1 and ET-3. Two out of 29 ET-1 strains, and 3 out of 7 ET-3 strains of G. diazotrophicus showed antagonistic effects against many other strains belonging to all the ETs of this species analyzed, and against closely related strains of Gluconacetobacter species, including Gluconacetobacter johannae, Gluconacetobacter azotocaptans and Gluconacetobacter liquefaciens but not against other phylogenetically distant bacterial species. Results showed that the substance responsible of such antagonistic activity is a low molecular mass molecule (approximately 3400 Da), stable from pH 3.5 to 8.5, and very stable at 4 degrees C for 10 months. This substance was sensitive to proteases, and the antagonistic activity was lost after 2 h at 95 degrees C. All of these features show that the substance is related to bacteriocin-like molecules. The antagonistic substance should be chromosomally encoded because ET-3 strains of G. diazotrophicus do not harbor any plasmids. The antagonistic ability of ET-3 strains of G. diazotrophicus could be an advantage for the natural colonization of the sugarcane environment, as was observed in experiments with micropropagated sterile sugarcane plantlets co-inoculated with a bacteriocin-producer strain and a bacteriocin-sensitive strain of G. diazotrophicus. In these experiments, both in the rhizosphere as well as inside the roots, the bacteriocin-sensitive population decreased drastically. In addition, this study shows that inside the plants there may exist antagonistic interactions among endophytic bacteria like to those described among the rhizospheric community.
    FEMS Microbiology Ecology 10/2005; 54(1):57-66. · 3.56 Impact Factor
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    Jesús Muñoz Rojas
    Elementos : Ciencia y cultura. 01/2005;
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    Jesús Muñoz-Rojas
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    ABSTRACT: Los microorganismos poseen distintas formas para competir en su ambiente, una de ellas es la producción de sustancias antagónicas. Entre estas se incluyen antibióticos clásicos, algunos productos del metabolismo, agentes líticos, numerosos tipos de exotoxinas proteicas y bacteriocinas. La diversidad de estas sustancias inhibitorias es muy grande y muchas bacteriocinas han sido identificadas. No obstante, los orígenes evolutivos y la función que desempeñan en la mediación de las interacciones microbianas son aun pocos conocidos. En esta revisión pretendemos dar un panorama global del conocimiento que se tiene sobre las bacteriocinas abarcando su purificación, diversidad, ecología, evolución y aplicaciones. Estas sustancias antagónicas son producidas tanto por bacterias como por arqueas y solo presentan capacidad antibiótica contra miembros de la misma especie que la produjo o especies muy relacionadas.
    01/2004: pages 1-20;
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    J Muñoz-Rojas, J Caballero-Mellado
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    ABSTRACT: Different experiments have estimated that the contribution of biological nitrogen fixation (BNF) is largely variable among sugarcane cultivars. Which bacteria are the most important in sugarcane-associated BNF is unknown. However, Gluconacetobacter diazotrophicus has been suggested as a strong candidate responsible for the BNF observed. In the present study, bacteria-free micropropagated plantlets of five sugarcane cultivars were inoculated with three G. diazotrophicus strains belonging to different genotypes. Bacterial colonization was monitored under different nitrogen fertilization levels and at different stages of plant growth. Analysis of the population dynamics of G. diazotrophicus strains in the different sugarcane varieties showed that the bacterial populations decreased drastically in relation to plant age, regardless of the nitrogen fertilization level, bacterial genotype or sugarcane cultivars. However, the persistence of the three strains was significantly longer in some cultivars (e.g., MEX 57-473) than in others (e.g., MY 55-14). In addition, some strains (e.g., PAl 5(T)) persisted for longer periods in higher numbers than other strains (e.g., PAl 3) inside plants of all the cultivars tested. Indeed, the study showed that the inoculation of G. diazotrophicus may be beneficial for sugarcane plant growth, but this response is dependent both on the G. diazotrophicus genotype and the sugarcane variety. The most positive response to inoculation was observed with the combination of strain PAl 5(T) and the variety MEX 57-473. Although the positive effect on sugarcane growth apparently occurred by mechanisms other than nitrogen fixation, the results show the importance of the sugarcane variety for the persistence of the plant-bacteria interaction, and it could explain the different rates of BNF estimated among sugarcane cultivars.
    Microbial Ecology 12/2003; 46(4):454-64. · 3.28 Impact Factor

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