Plant growth promoting rhizobacteria is a beneficial microbe colonizing plant roots, which enhances crop productivity and offers an attractive way to replace chemical fertilizers, pesticides, and supplements. In Mexico, the corn (Zea mays L.) is an important annual gramineae crop with a high volume of global production because of the favorable environmental and socioeconomic situation. In this study the isolation of new strains of bacteria under different environmental conditions will enable further research avenues to better use the capacities of root-colonizing bacteria in agricultural production systems. The strains isolates were analyzed for five plant-growth-promoting attributes: N fixation, solubilization of phosphate, production of auxins, siderophores and gibberellins. The identification of bacterial isolates was determined by biochemical assays and VITEK2 Compact (bioMérieux). A total of 143 morphologically distinct rhizobacteria from corn crops of three communities of Guerrero, Mexico, were isolated, and 54 effective multi trait rhizobacteria were found. It was determined that the bacterial isolates are related to Pseudomonas, Enterobacter, Serratia, Pantoea, Staphylococcus, Klebsiella, Burkholderia, Salmonella, Proteus, Acinetobacter, Citrobacter and Streptoccoccus genus. This collection represents the first bank of multi trait activity in Mexico, and it will contribute to future studies as biomolecules for promoting early emergence and growth of the seeds.Palabras clave: maíz, biofertilizante, rizobacteria, rizosfera 2017 DOI: 10.20937/RICA.2017 J. Toribio-Jiménez et al.Rev. Int. Contam. Ambie. 33 (Especial Biotecnología e ingeniería ambiental) 143-150, 144 RESUMENLas rizobacterias promotoras del crecimiento vegetal, son microorganismos benéficos que colonizan las raíces de las plantas para mejorar la productividad de los cultivos y ofrecen una forma atractiva para reemplazar los fertilizantes químicos, plaguicidas y suplementos. En México, el maíz (Zea mays L) es un importante cultivo de gramínea anual con grandes volúmenes de producción global debido a las condiciones ambientales y socioeconómicas favorables . En este trabajo se aislaron nuevas cepas de bacterias bajo diferentes condiciones ambientales que permitirán investigaciones futuras sobre el uso de las capacidades de las bacterias que colonizan la raíz en los sistemas de producción agrícola. A las cepas aisladas se les analizaron cinco capacidades de promoción del crecimiento vegetal: fijación de nitrógeno, solubilización de fosfatos, producción de auxinas, sideróforos y giberelinas. La identificación de las bacterias aisladas se hizo por pruebas bioquímicas y el sistema VITEK2 (bioMérieux). Un total de 143 rizobacterias morfológicamente distintas se aislaron de cultivos de maíz de tres comunidades de Guerrero, México y se encontraron 54 de ellas con múltiples capacidades. Se determinó que los aislados bacterianos se relacionan con los géneros Pseudomonas, Enterobacter, Serratia, Pantoea, Staphylococcus, Klebsiella, Burkholderia...

Bacillus licheniformis M2-7 is a heat-resistant bacterium able to biotransform polycyclic aromatic hydrocarbons. It can transform a wide range of these compounds as naphthalene, phenanthrene, pyrene and benzo[a]pyrene. Benzo[a]pyrene is a polycyclic aromatic hydrocarbon of high molecular weight considered as potentially toxic and carcinogenic for humans. Aiming to discover the genes involved in the biotransformation of benzo[a]pyrene, we made a B. licheniformis M2-7 genomic library in E. coli. We isolated two E. coli strains that were able to grow in minimal salt medium supplemented with benzo[a]pyrene. From the analysis of the DNA fragments in the clones H23 and H38, we identified open reading frames coding for 5 possible genes, among them pobA and fabHB, which products are the enzymes 4hydroxybenzoate 3-monooxygenase and the ketoacyl-ACP synthase Genetics and Molecular Research 17 (2): gmr16039916 III, respectively. To evaluate the role of these genes in the metabolism of benzo[a]pyrene in B. licheniformis M2-7, we estimated their relative expression through reverse transcription quantitative PCR. Finally, we observed that the genes pobA and fabHB were overexpressed after 3 h under induction with benzo[a]pyrene, suggesting that this strain could use these genes during the metabolism of this PAH, plus it does it in a faster time than that reported for other bacterial genera

Petroleum derivates used in energy production are gravely pollutants for the ecosystem, especially for aquatic environments and human health. This study aimed to isolate hydrocarbons-degrading bacteria from hot springs. Three strains of hydrocarbondegrading bacteria strains, belonging to the Bacillus and one of the genus Lysinibacillus were isolated. These strains tolerate temperatures from 65 to 100 ºC and were able to degrade and grow on BH medium supplemented with gasoline and diesel. Strain M2-7 shared 100 % 16S rRNA identity with Bacillus licheniformis and was the only able to degrade pyrene and benzopyrene among these isolated strains. The results indicate that B. licheniformis M2-7 could degrade a wider range of hydrocarbons and some recalcitrant hydrocarbon components, which could be particularly helpful for the treatment and bioremediation of hydrocarbon-polluted systems.

Benzopyrene is a high molecular weight polycyclic aromatic hydrocarbon with highly recalcitrant and develops carcinogenic effects. CsrA is a conserved regulatory protein, which controls the translation and stability of its target transcripts, having negative or positive effects depending on the target mRNAs. It is known that Bacillus licheniformis M2-7 has the ability to grow and survive in concentrations of hydrocarbons as benzopyrene, which prompted in part by CsrA, as it occurs in the presence of gasoline.However, there are a few studies that reveal the genes involved in that process. In order to know the involved genes in the Bacillus licheniformis M2-7 degradation pathway, the plasmid pCAT-sp containing a mutation in the catEgen was constructed and used to transform B. licheniformis M2-7 and generate the CAT1 strain. We determined the capacity of the mutant B. licheniformis(CAT1) to grow in the presence of glucose and benzopyrene as a carbon source. We observed that CAT1 strain presented an increase in growth in the presence of glucose, but a statistically considerable decrease in the presence of benzopyrene with respect to the wild strain M2-7. Also we demonstrated that the Csr system regulates its expression positively since it was observed that the expression of the gene in the mutant strain LYA12 (M2-7 csrA:: Sp, SpR) decreased considerably with respect to the wild strain. This allowed to characterize the metabolic pathway that Bacillus licheniformis M2-7 implements in the presence of benzopyrene.

The biological control using organisms that inhibit growth or the appearance of pests or diseases has proven to be a successful alternative for mango disease control. In this work, in vitro analyses were carried out with Bacillus licheniformis M2–7 and B. licheniformis LYA12 strain derived from M2–7 against the phytopathogenic fungi Aspergillus oryzae, Colletotrichum sp., and Aspergillus niger. Besides, the effect of bacteria on the micellar structure of phytopathogenic fungi was observed and evaluated through real-time PCR, the expression of two main metacaspases (casA and casB) that triggers the process of programmed cell death in fungi. The results obtained showed that both bacterial species inhibited by 45, 40, and 35 % the fungal growth of Aspergillus oryzae , Colletotrichum sp., and Aspergillus niger, respectively. The bacteria presence affected the mycelial appearance of the fungi because they presented fragmentation of the hyphae with intracellular inclusion bodies, swellings, malformations and scarce growth of the hyphae. The gene expression results conclude that the LYA12 and M2-7 strains against A. oryzae and A. niger have a fungicidal effect; therefore, the bacterial strains could be used in disease control in mango.