Mixed biofilms formed by C. albicans and non-albicans species: a study of microbial interactions

Abstract Most Candida infections are related to microbial biofilms often formed by the association of different species. The objective of this study was to evaluate the interactions between Candida albicans and non-albicans species in biofilms formed in vitro. The non-albicans species studied were:Candida tropicalis, Candida glabrata andCandida krusei. Single and mixed biofilms (formed by clinical isolates of C. albicans and non-albicans species) were developed from standardized suspensions of each strain (107 cells/mL), on flat-bottom 96-well microtiter plates for 48 hour. These biofilms were analyzed by counting colony-forming units (CFU/mL) in Candida HiChrome agar and by determining cell viability, using the XTT 2,3-bis (2-methoxy-4-nitro-5-sulphophenyl)-5-[(phenylamino) carbonyl]-2H-tetrazolium hydroxide colorimetric assay. The results for both the CFU/mL count and the XTT colorimetric assay showed that all the species studied were capable of forming high levels of in vitro biofilm. The number of CFU/mL and the metabolic activity of C. albicans were reduced in mixed biofilms with non-albicans species, as compared with a singleC. albicans biofilm. Among the species tested, C. krusei exerted the highest inhibitory action against C. albicans. In conclusion, C. albicans established antagonistic interactions with non-albicans Candida species in mixed biofilms.

El impacto de la hidroquinona usada como un modelo de efector redox sobre la desnitrificación potencial, la actividad microbiana y las condiciones redox de un suelo cultivable / Impact of hydroquinone used as a redox effector model on potential denitrification, microbial activity and redox condition of a cultivable soil

In this microcosm study, we analyzed the effect produced by hydroquinone on the expression of soil biological denitrification, in relation to the redox state of the soil, both in terms of intensity factor (Eh′) and capacity factor (amount of oxidized or reduced compounds). The supplementation of an Argiudoll soil with hydroquinone decreased the soil apparent reduction potential (Eh′) and soil dehydrogenase activity (formazan production from tetrazolium chloride reduction; redox capacity factor), the relationship between both factors being highly significative, r = 0.99 (p < 0.001). The bacterial population (measured by colony forming units) increased, and the production of N2O was greater (p < 0.001) at 200 and 400 μg/g dry soil doses. Furthermore, there was an inverse relationship between soil dehydrogenase activity and the number of bacteria (r = −0.82; p < 0.05), increased denitrification activity and changes in the CO2/N2O ratio value. These results suggest that hydroquinone at supplemented doses modified the soil redox state and the functional structure of the microbial population. Acetate supplementation on soil with hydroquinone, to ensure the availability of an energy source for microbial development, confirmed the tendency of the results obtained with the supplementation of hydroquinone alone. The differences observed at increased doses of hydroquinone might be explained by differences on the hydroquinone redox species between treatments.

En este trabajo estudiamos, en condiciones de microcosmos, el efecto que produce la hidroquinona sobre la expresión de la desnitrificación en relación con el estado de óxido-reducción del suelo, en términos de factor de intensidad (Eh′) y de factor de capacidad (cantidad de compuestos oxidados o reducidos). La suplementación de un suelo argiudol con hidroquinona disminuyó el potencial de reducción aparente (Eh′) y la actividad deshidrogenasa (producción de formazán a partir de la reducción de cloruro de tetrazolio; factor de capacidad redox), la relación entre ambos factores fue altamente significativa, r = 0,99 (p < 0,001). La población bacteriana heterotrófica (medida como unidades formadoras de colonias) aumentó y la producción de N2O fue mayor (p < 0,001) con las dosis de 200 y 400 μg/g de suelo seco. Además se observó una relación inversa entre la producción de formazán y el número de bacterias (r = −0,82; p < 0,05), la actividad desnitrificadora aumentó y se produjeron cambios en el valor del cociente CO2/N2O. Estos resultados sugieren que la hidroquinona, en las dosis empleadas, modificó el estado redox del suelo y la estructura funcional de la población microbiana. La suplementación con acetato en el suelo con hidroquinona, a fin de asegurar la disponibilidad de una fuente de energía para el desarrollo bacteriano, confirmó la tendencia de los resultados obtenidos con la suplementación con hidroquinona solamente. Las diferencias observadas con el incremento en la dosis de hidroquinona podrían explicarse por las diferencias sobre las especies redox de la hidroquinona entre los tratamientos.

Feasibility of biohydrogen production from industrial wastes using defined microbial co-culture

BACKGROUND: The development of clean or novel alternative energy has become a global trend that will shape the future of energy. In the present study, 3 microbial strains with different oxygen requirements, including Clostridium acetobutylicum ATCC 824, Enterobacter cloacae ATCC 13047 and Kluyveromyces marxianus 15D, were used to construct a hydrogen production system that was composed of a mixed aerobic-facultative anaerobic-anaerobic consortium. The effects of metal ions, organic acids and carbohydrate substrates on this system were analyzed and compared using electrochemical and kinetic assays. It was then tested using small-scale experiments to evaluate its ability to convert starch in 5 L of organic wastewater into hydrogen. For the one-step biohydrogen production experiment, H1 medium (nutrient broth and potato dextrose broth) was mixed directly with GAM broth to generate H2 medium (H1 medium and GAM broth). Finally, Clostridium acetobutylicum ATCC 824, Enterobacter cloacae ATCC 13047 and Kluyveromyces marxianus 15D of three species microbial co-culture to produce hydrogen under anaerobic conditions. For the two-step biohydrogen production experiment, the H1 medium, after cultured the microbial strains Enterobacter cloacae ATCC 13047 and Kluyveromyces marxianus 15D, was centrifuged to remove the microbial cells and then mixed with GAM broth (H2 medium). Afterward, the bacterial strain Clostridium acetobutylicum ATCC 824 was inoculated into the H2 medium to produce hydrogen by anaerobic fermentation. RESULTS: The experimental results demonstrated that the optimum conditions for the small-scale fermentative hydrogen production system were at pH 7.0, 35°C, a mixed medium, including H1 medium and H2 medium with 0.50 mol/L ferrous chloride, 0.50 mol/L magnesium sulfate, 0.50 mol/L potassium chloride, 1% w/v citric acid, 5% w/v fructose and 5% w/v glucose. The overall hydrogen production efficiency in the shake flask fermentation group was 33.7 mL/h-1.L-1, and those the two-step and the one-step processes of the small-scale fermentative hydrogen production system were 41.2 mLVh-1.L-1 and 35.1 mL/h-1.L-1, respectively. CONCLUSION: Therefore, the results indicate that the hydrogen production efficiency of the two-step process is higher than that of the one-step process.

Comportamento de cepas distintas de Lactobacillus acidophilus em queijo petit-suisse

O objetivo do presente trabalho foi avaliar as características de físico-químicas e microbiológicas de queijo petit-suisse processado com a adição de duas cepas de Lactobacillus acidophilus: LA-14 (potencialmente probiótica) e La-5 (comprovadamente probiótica), utilizando Streptococcus thermophilus TA040 como cultura starter. Três queijos petit-suisse foram preparados: Q1 (controle:TA040), Q2 (TA040 + LA-14) e Q3 (TA040 +La-5). Foram realizadas análises microbiológicas (determinação das populações dos microrganismos La-5, La-14 e TA040) e físico-químicas (umidade e pH) após 1, 7, 14, 21 e 28 dias de armazenamento dos produtos a 4±1°C. As populações de L. acidophilus oscilaram entre 7,46 e 7,62 log UFC g -1 para La-5 e entre 6,39 e 6,83 log UFC g -1 para LA-14, evidenciando que a sobrevivência de L. acidophilus no produto depende de características particulares da cepa. Populações superiores da cultura starter foram observadas para Q2 (9,58 - 9,68 log UFC g -1 ) e Q3 (9,42 - 9,79 log UFC g -1 ), quando comparadas a Q1 (9,11 - 9,23 log UFC g -1 ), sugerindo sinergismo entre L. acidophilus e o starter. A umidade e o pH permaneceram estáveis e não diferiram entre os queijos após o 1º dia de armazenamento (p>0,05). As características peculiares das cepas de L. acidophilus determinaram os comportamentos distintos observados nos queijos petitsuisse, sendo possível detectar a melhor adaptação da cepa La-5 ao produto, o que resultou em populações significativamente superiores quando comparada a LA-14.

Particular behavior of different Lactobacillus acidophilus strains in petit-suisse cheese. The objective of this study was to evaluate the physico-chemical andmicrobiological characteristics of petit-suisse cheeses manufactured with the addition of two Lactobacillus acidophilus strains: LA-14 (potentially probiotic) and La-5 (probiotic culture), using Streptococcus thermophilus TA040 as starter culture. Three cheese-making trials were prepared: Q1 (control: with TA040), Q2 (with TA040 + LA-14), and Q3 (with TA040 + La-5). Parameters analyzed included microbial counts of probiotic, potentially probiotic and starter microorganisms, and physico-chemical parameters (pH and moisture) after 1, 7, 14, 21, and 28 days of storage of the product at 4±1°C. Viable counts of L. acidophilus remained between 7.46 and 7.62 log CFU g -1 for La-5, and between 6.39 and 6.83 log CFU g -1 for LA-14. As for the starter, higher populations were observed for Q2 (9.58 - 9.68 log CFU g -1 ) and Q3 (9.42 - 9.79 log CFU g -1 ), when compared to Q1, which suggests synergism between L. acidophilus and the starter culture. Moisture and pH values remained stable for cheeses Q1, Q2, and Q3, and no significant differences were detected between cheeses after the first day of storage (p>0.05). Particular features of both L. acidophilus strains determined different behavior in petit-suisse cheese, and the better adaptation of the La-5 to the product environment was perceptible, since higher populations were observed when compared to LA-14.