Diauxic growth of Geotrichum candidum and Penicillium camembertii on amino acids and glucose

Microbiome and Metabiotic Properties of Kefir Grains and Kefirs Based on Them

The analysis of the literature on the microbiome composition and metabolic properties of kefir available at the RSCI and Web of Science was carried out. Kefir has been used by humans for centuries. It is a useful product of mixed lactic and alcoholic fermentation, produced using evolutionally established associative cultures, collected in an aggregated state termed kefir grains. General characterization of kefir grains from the territorial zones of different continents (Russia, Europe, Asia, and America) is provided. The methods for differentiation and identification of individual species are described, as well as their interactions within the community. The diversity of microbial composition of kefir grains depending on local cultivation conditions and storage processes is shown. The microorganisms present in kefir have a number of properties that determine their metabolism, interaction in the community, beneficial effects on human health and immune system, which is important for the prevention and control of bacterial and viral infections, especially during the COVID-19 pandemic.

Growth dynamics of lactic acid bacteria and dairy microscopic fungus Geotrichum candidum during their co-cultivation in milk

Production of high-quality and microbiologically safe fermented dairy products requires controlled growth and microbial interactions between lactic acid bacteria and microscopic fungi. For this purpose, detailed knowledge of their growth characteristics is needed. Therefore, the objective of this study was to analyse the growth dynamics of lactic acid bacteria of commercial DVS® FRESCO® 1000NG culture and dairy isolate of microscopic fungus Geotrichum candidum during their co-cultivation in milk. The growth dynamics of microorganisms was studied in dependence on their initial counts at 12, 15, 18, 21 and 30 °C. Growth parameters were calculated by two primary predictive models, model of Baranyi and Roberts and Huang's model. Both models showed good ability to describe the growth dynamics of studied microorganisms, as it was confirmed by low values of RMSE index. Both microbial cultures, Fresco culture and Geotrichum candidum, showed good growth ability in milk since they reached the average maximum density of 9.50 ± 0.13 log CFU/mL and 5.85 ± 0.69 log CFU/mL (n = 45), in order. Maximum density of studied microorganisms was not affected by their initial counts or incubation temperature. On the other hand, effect of mutual ratio of microbial initial counts and increasing temperature had a significant impact on growth dynamics.

Enhanced bio-recovery of aluminum from low-grade bauxite using adapted fungal strains

Filamentous fungi have been proved to have a pronounced capability to recover metals from mineral ores. However, the metal recovery yield is reduced due to toxic effects triggered by various heavy metals present in the ore. The current study highlights the fungal adaptations to the toxic effects of metals at higher pulp densities for the enhanced bio-recovery of aluminum from low-grade bauxite. In the previous studies, a drastic decrease in the aluminum dissolution was observed when the bauxite pulp density was increased from 1 to 10% (w/v) due to the high metal toxicity and low tolerance of Aspergillus niger and Penicillium simplicissium to heavy metals. These fungi were adapted in order to increase heavy metal tolerance of these fungal strains and also to get maximum Al dissolution. A novel approach was employed for the adaptation of fungal strains using a liquid growth medium containing 5% bauxite pulp density supplemented with molasses as an energy source. The mycelia of adapted strains were harvested and subsequently cultured in a low-cost oat-agar medium. Batch experiments were performed to compare the aluminum leaching efficiencies in the direct one-step and the direct two-step bioleaching processes. FE-SEM analysis revealed the direct destructive and corrosive action by the bauxite-tolerant strains due to the extension and penetration of the vegetative mycelium filaments into the bauxite matrix. XRD analysis of the bioleached bauxite samples showed a considerable decline in oxide minerals such as corundum and gibbsite. Results showed a high amount of total Al (≥ 98%) was successfully bioleached and solubilized from low-grade bauxite by the adapted fungal strains grown in the presence of 5% pulp density and molasses as a low-cost substrate. Graphical abstract.

ACTIVIDAD BIOCONTROLADORA IN VITRO DE MACROHONGOS CONTRA DIFERENTES HONGOS FITOPATÓGENOS

Las enfermedades causadas por hongos en las plantas son una gran preocupación en la producción agrícola. Los macromicetos son una fuente potencial de compuestos antifúngicos que podrían usarse para controlar estas enfermedades. El objetivo de este estudio fue evaluar la actividad biocontroladora in vitro de cuatro macromicetos de los géneros Xylaria, Agrocybe, Psilocybe y Stereum sobre diferentes hongos fitopatógenos. Para ello, se determinó la curva de crecimiento de los macrohongos en dos medios: papa dextrosa (PDA) y salvado de trigo (ST) y se caracterizaron las interacciones y la inhibición in vitro de hongos fitopatógenos. Se realizó la extracción y caracterización de metabolitos secundarios de la biomasa, el medio extracelular y del homogeneizado del micelio y caldo en los hongos con mayor porcentaje de inhibición. Finalmente, se evaluó la actividad antifúngica in vitro de estos extractos. Las curvas de crecimiento cambiaron con la fuente de carbono, tres de cuatro macrohongos mostraron una mayor acumulación de biomasa en PDA que en ST. Las interacciones de Xylaria se clasificaron principalmente como reemplazo, obteniendo el mayor nivel de antagonismo en PDADos de los tres extractos evaluados mostraron actividad antifúngica contra los tres patógenos aislados en concentraciones de 18 μg/ml para extractos metanólicos de biomasa y 2,5 % para el filtrado de homogeneizado con inhibiciones de 10 % a 80 %.  La caracterización de los metabolitos de Xylaria mostró como posibles compuestos responsables de la actividad a los ácidos grasos. Este trabajo mostró el potencial de estos hongos para el control de enfermedades fúngicas.

Evaluation of aluminium mobilization from its soil mineral pools by simultaneous effect of Aspergillus strains' acidic and chelating exometabolites

This contribution investigates aluminium mobilization from main aluminium pools in soils, phyllosilicates and oxyhydroxides, by acidic and chelating exometabolites of common soil fungi Aspergillus niger and A. clavatus. Their exometabolites' acidity as well as their ability to extract aluminium from solid mineral phases differed significantly during incubation. While both strains are able to mobilize aluminium from boehmite and aluminium oxide mixture to some extent, A. clavatus struggles to mobilize any aluminium from gibbsite. Furthermore, passive and active fungal uptake of aluminium enhances its mobilization from boehmite, especially in later growth phase, with strong linear correlation between aluminium bioaccumulated fraction and increasing culture medium pH. We also provide data on concentrations of oxalate, citrate and gluconate which are synthesized by A. niger and contribute to aluminium mobilization. Compared to boehmite-free treatment, fungus reduces oxalate production significantly in boehmite presence to restrict aluminium extraction efficiency. However, in presence of high phyllosilicates' dosages, aluminium is released to an extent that acetate and citrate is overproduced by fungus. Our results also highlight fungal capability to significantly enhance iron and silicon mobility as these elements are extracted from mineral lattice of phyllosilicates by fungal exometabolites alongside aluminium.