Degradation profile of nixtamalized maize pericarp by the action of the microbial consortium PM-06.

The nixtamalized maize pericarp (NMP) is a plentiful by-product of the tortilla industry and an important source of fermentable sugars. The aim of this study was to describe the degradation profile of NMP by the action of a consortium (PM-06) obtained from the native microbial community of this residue. The degradation was analyzed in terms of the changes in the community dynamics, production of enzymes (endo-xylanase and endo-cellulase), physicochemical parameters, and substrate chemical and microstructural characteristics, to understand the mechanisms behind the process. The consortium PM-06 degraded 86.8 ± 3.3% of NMP after 192 h of growth. Scanning electron microscopy images, and the composition and weight of the residual solids, showed that degradation was sequential starting with the consumption of hemicellulose. Xylanase was the highest enzyme activity produced, with a maximum value of 12.45 ± 0.03 U mL-1. There were fluctuations in the pH during the NMP degradation, starting with the acidification of the culture media and finishing with a pH close to 8.5. The most abundant species in the consortium, at the moment of maximum degradation activity, were Aneurinibacillus migulanus, Paenibacillus macerans, Bacillus coagulans, Microbacterium sp. LCT-H2, and Bacillus thuringiensis. The diversity of PM-06 provided metabolic abilities that in combination helped to produce an efficient process. The consortium PM-06 generated a set of different tools that worked coordinated to increase the substrate availability through the solubilization of components and elimination of structural diffusion barriers. This is the first report about the degradation of NMP using a microbial consortium.

[Microbiological analysis of red octopus in fishing ports of Campeche, Mexico]. / Análisis microbiológicodel pulpo rojo en puertos pesqueros de Campeche, México.

OBJECTIVE: In this work we studied the microbiological quality of the red octopus given its important economic and social impact on the region South-Southeast of Mexico. MATERIALS AND METHODS: Samples were taken in different areas of capture of the species and analyzed with biochemical tests described in the Mexican official standards, identifying strains belonging to the genus Vibrio, Salmonella and faecal coliforms, and E. coli O157: H7. We used the BAx System for the identification of microorganisms through their bacterial DNA. The results obtained in biochemical and molecular methods were confirmed. RESULTS: Bland-Altman statistical method pointed out that both techniques can be used interchangeably. McNemar test showed that both methods have the same efficacy for the identification of pathogens (value X2=0.5 ρ=0.4795). CONCLUSION: The microbiological quality of the octopus in the South-Southeast region of Mexico is deficient due to the presence of pathogenic intestinal flora that might represent an epidemiological risk. The indexes established by the regulations suggest the need to apply effective and rapid identification technologies, such as the BAx System.This alternative method of analysis can contribute to the implementation of effective strategies that allow compliance with the minimal sanitary specifications during the processing of fishing products, thus strengthening the control systems to decrease the risks of epidemiological outbreaks in the region.

Análisis microbiológicodel pulpo rojo en puertos pesqueros de Campeche, México / Microbiological analysis of red octopus in fishing ports of Campeche, Mexico

Resumen: Objetivo: Estudiar la calidad microbiológica del pulpo rojo dado su importante impacto económico y social en la región sur-sureste de México. Material y métodos: Se tomaron muestras en diversas zonas de captura de la especie y se analizaron con pruebas bioquímicas descritas en las normas oficiales mexicanas. Se identificaron cepas pertenecientes al género Vibrio, Salmonella, coliformes fecales y E. coli O157:H7. Con el empleo del Sistema BAx, se logró la identificación de microorganismos a través de su ADN bacteriano. Los resultados obtenidos en los métodos bioquímicos y moleculares fueron contrastados. Resultados: El método estadístico de Bland-Altman indicó que ambas técnicas pueden usarse indistintamente. La prueba de McNemar demostró que ambos métodos cuentan con la misma eficacia para la identificación de patógenos (valor X2=0.5 ρ=0.4795). Conclusión: La calidad microbiológica del pulpo en la región sur-sureste de México es deficiente debido a la presencia de flora bacteriana patógena que podría representar un riesgo epidemiológico. Los índices establecidos por las normas sugieren la necesidad de aplicar técnicas de identificación eficaces y rápidas como el Sistema BAx. Este método alternativo de análisis puede coadyuvar a la implementación de estrategias efectivas que permitan cumplir con especificaciones mínimas sanitarias durante el procesamiento de los productos pesqueros, y así elevar los sistemas de control para disminuir los riesgos de brotes epidemiológicos en la región.

Abstract: Objective: In this work we studied the microbiological quality of the red octopus given its important economic and social impact on the region South-Southeast of Mexico. Materials and methods: Samples were taken in different areas of capture of the species and analyzed with biochemical tests described in the Mexican official standards, identifying strains belonging to the genus Vibrio, Salmonella and faecal coliforms, and E. coli O157: H7. We used the BAx System for the identification of microorganisms through their bacterial DNA. The results obtained in biochemical and molecular methods were confirmed. Results: Bland-Altman statistical method pointed out that both techniques can be used interchangeably. McNemar test showed that both methods have the same efficacy for the identification of pathogens (value X2=0.5 ρ=0.4795). Conclusion: The microbiological quality of the octopus in the South-Southeast region of Mexico is deficient due to the presence of pathogenic intestinal flora that might represent an epidemiological risk. The indexes established by the regulations suggest the need to apply effective and rapid identification technologies, such as the BAx System.This alternative method of analysis can contribute to the implementation of effective strategies that allow compliance with the minimal sanitary specifications during the processing of fishing products, thus strengthening the control systems to decrease the risks of epidemiological outbreaks in the region.

Nitrogen fixation in transposon mutants from Bradyrhizobium japonicum USDA 110 impaired in nitrate reductase.

Tn5 transposon mutagenesis was carried out in Bradyrhizobium japonicum strain USDA 110 to produce defective mutants. From over one thousand clones expressing low levels of nitrate reductase activity as free-living bacteria, approximately five percent had significantly different ratios of nodulation, N2 fixation or nitrate reductase activity compared to the wild strain when determined in bacteroids from soybean nodules. Tn5 insertions were checked previously and mutants were arranged into four different groups. Only one of these groups, designated AN, was less effective at N2 fixation than the wild strain, suggesting a mutation in a domain shared by nitrogenase and NR. The remaining groups of insertions successfully nodulated and were as effective at N2 fixation as the wild strain, but showed diminished ability to reduce nitrate both in nodules and in the isolated bacteroids when assayed in vitro with NADH or methyl viologen as electron donors. PCR amplification demonstrated that Tn5 insertions took place in different genes on each mutant group and the type of mutant (CC) expressing almost no nitrate reductase activity under all treatments seemed to possess transposable elements in two genes. Induction of nitrate reductase activity by nitrate was observed only in those clones expressing a low constitutive activity (AN and AE). Nitrate reductase activity in bacteroids along nodule growth decreased in all groups including the ineffective AN group, whose nodulation was highly inhibited by nitrate at 5 mmol/L N. Host-cultivar interaction seemed to influence the regulation of nitrate reductase activity in bacteroids. Total or partial repression of nitrate reductase activity in bacteroids unaffected by N2 fixation (CC, AJ and AE groups) improved nodule resistance to nitrate and N yields of shoots over those of the wild strain. These observations may suggest that some of the energy supplied to bacteroids was wasted by its constitutive NRA.