Effect of Streptomyces roseolus Cell-Free Supernatants on the Fungal Development, Transcriptome, and Aflatoxin B1 Production of Aspergillus flavus.

Crop contamination by aflatoxin B1 (AFB1), an Aspergillus-flavus-produced toxin, is frequently observed in tropical and subtropical regions. This phenomenon is emerging in Europe, most likely as a result of climate change. Alternative methods, such as biocontrol agents (BCAs), are currently being developed to reduce the use of chemicals in the prevention of mycotoxin contamination. Actinobacteria are known to produce many bioactive compounds, and some of them can reduce in vitro AFB1 concentration. In this context, the present study aims to analyze the effect of a cell-free supernatant (CFS) from Streptomyces roseolus culture on the development of A. flavus, as well as on its transcriptome profile using microarray assay and its impact on AFB1 concentration. Results demonstrated that in vitro, the S. roseolus CFS reduced the dry weight and conidiation of A. flavus from 77% and 43%, respectively, and was therefore associated with a reduction in AFB1 concentration reduction to levels under the limit of quantification. The transcriptomic data analysis revealed that 5198 genes were differentially expressed in response to the CFS exposure and among them 5169 were downregulated including most of the genes involved in biosynthetic gene clusters. The aflatoxins' gene cluster was the most downregulated. Other gene clusters, such as the aspergillic acid, aspirochlorine, and ustiloxin B gene clusters, were also downregulated and associated with a variation in their concentration, confirmed by LC-HRMS.

Influence of the culture conditions on the production of NGPs by Aspergillus tubingensis.

The filamentous fungus Aspergillus tubingensis that belongs to the black Aspergillus section has the capacity to produce high-value metabolites, for instance, Naphtho-Gamma-Pyrones (NGPs). For these fungal secondary metabolites, numerous biological properties of industrial interest have been demonstrated, such as antimicrobial, antioxidant and anti-cancer capacities. It has been observed that these secondary metabolites production is linked with the fungal sporulation. The aim of this research was to apply environmental stresses to trigger the production of NGPs in liquid cultures with CYB (Czapek Dox Broth): osmotic and oxidative stresses. In addition, numerous parameters were tested during the experiments, such as pH value, incubation time, container geometry, and static and agitation conditions. Results demonstrate that the produced amount of NGPs can be enhanced by decreasing the water activity (aw) or by adding an oxidative stress factor. In conclusion, this study can contribute to our knowledge regarding A. tubingensis to present an effective method to increase NGPs's production, which may support the development of current industrial processes.

Quantitative Characterization of the Growth of Deinococcus geothermalis DSM-11302: Effect of Inoculum Size, Growth Medium and Culture Conditions.

Due to their remarkable resistance to extreme conditions, Deinococcaceae strains are of great interest to biotechnological prospects. However, the physiology of the extremophile strain Deinococcus geothermalis has scarcely been studied and is not well understood. The physiological behaviour was then studied in well-controlled conditions in flask and bioreactor cultures. The growth of D. geothermalis type strains was compared. Among the strains tested, the strain from the German Collection of Microorganisms (Deutsche Sammlung von Mikroorganismen DSM) DSM-11302 was found to give the highest biomass concentration and growth rate: in a complex medium with glucose, the growth rate reached 0.75 h(-1) at 45 °C. Yeast extract concentration in the medium had significant constitutive and catalytic effects. Furthermore, the results showed that the physiological descriptors were not affected by the inoculum preparation steps. A batch culture of D. geothermalis DSM-11302 on defined medium was carried out: cells grew exponentially with a maximal growth rate of 0.28 h(-1) and D. geothermalis DSM-11302 biomass reached 1.4 g·L(-1) in 20 h. Then, 1.4 gDryCellWeight of biomass (X) was obtained from 5.6 g glucose (Glc) consumed as carbon source, corresponding to a yield of 0.3 CmolX·CmolGlc(-1); cell specific oxygen uptake and carbon dioxide production rates reached 216 and 226 mmol.CmolX(-1)·h(-1), respectively, and the respiratory quotient (QR) value varied from 1.1 to 1.7. This is the first time that kinetic parameters and yields are reported for D. geothermalis DSM-11302 grown on a mineral medium in well-controlled batch culture.

Experimental and statistical analysis of nutritional requirements for the growth of the extremophile Deinococcus geothermalis DSM 11300.

Few studies concerning the nutritional requirements of Deinococcus geothermalis DSM 11300 have been conducted to date. Three defined media compositions have been published for the growth of this strain but they were found to be inadequate to achieve growth without limitation. Furthermore, growth curves, biomass concentration and growth rates were generally not available. Analysis in Principal Components was used in this work to compare and consequently to highlight the main compounds which differ between published chemically defined media. When available, biomass concentration, and/or growth rate were superimposed to the PCA analysis. The formulations of the media were collected from existing literature; media compositions designed for the growth of several strains of Deinococcaceae or Micrococcaceae were included. The results showed that a defined medium adapted from Holland et al. (Appl Microbiol Biotechnol 72:1074-1082, 2006) was the best basal medium and was chosen for further studies. A growth rate of 0.03 h(-1) and a final OD600nm of 0.55 were obtained, but the growth was linear. Then, the effects of several medium components on oxygen uptake and biomass production by Deinococcus geothermalis DSM 11300 were studied using a respirometry-based method, to search for the nutritional limitation. The results revealed that the whole yeast extract in the medium with glucose is necessary to obtain a non-limiting growth of Deinococcus geothermalis DSM 11300 at a maximum growth rate of 0.64 h(-1) at 45 °C.

Growth of the extremophilic Deinococcus geothermalis DSM 11302 using co-substrate fed-batch culture.

Deinococcus geothermalis metabolism has been scarcely studied to date, although new developments on its utilization for bioremediation have been carried out. So, large-scale production of this strain and a better understanding of its physiology are required. A fed-batch experiment was conducted to achieve a high cell density non-limiting culture of D. geothermalis DSM 11302. A co-substrate nutritional strategy using glucose and yeast extract was carried out in a 20-L bioreactor in order to maintain a non-limited growth at a maximal growth rate of 1 h(-1) at 45 °C. Substrate supplies were adjusted by monitoring online culture parameters and physiological data (dissolved oxygen, gas analyses, respiratory quotient, biomass concentration). The results showed that yeast extract could serve as both carbon and nitrogen sources, although glucose and ammonia were consumed too. Yeast extract carbon-specific uptake rate reached a value 4.5 times higher than glucose carbon-specific uptake rate. Cell concentration of 9.6 g L(-1) dry cell weight corresponding to 99 g of biomass was obtained using glucose and yeast extract as carbon and nitrogen sources.