Germination test for the evaluation of plant-growth promoting microorganisms.

There is an increased interest for finding strains able to contribute to plant nutrition and health, since these are desirable for the formulation of agricultural bioinoculants. Obtaining a safe and efficient product requires exhaustive evaluations from which most methods used for this purpose involve the use of substrates or are established under uncontrolled conditions, so that various factors can mask the results of the plant-microorganism interaction. In vitro methods mostly involve the use of Petri Dishes (PD) but limit the results to seed germination. Other methods of germination involve the use of acrylic boxes (GB) allowing for better plant development, but are little known. Methods such as ISTA are widely used to evaluate the physiological quality of seeds in productive terms. Despite their efficiency, these methods have not been previously used to evaluate the effect of plant-microorganism interaction on crops. In the present study, modifications were made to the germination between paper of ISTA (BP) method, and were compared to the PD anf GB methods to evaluate the impact of the bacterium Serratia liquefaciens 385 and the yeast Clavispora lusitaniae Y35 on maize, bean and squash. Through the evaluation of physiological parameters in seed and seedling, the results clearly showed the superiority of the BP method to evaluate the effect of microorganisms since it allows observing a better development in the seedlings in terms of growth of the plumule, a better architecture of the radical system in which the emergence of adventitious secondary roots and differentiated radical hairs is observed in comparison with seedlings obtained under the other methods. Similarly, it was possible to observe the different effects on each of the three crops with respect to the inoculation of the bacteria and yeast. These results were significantly better in seedlings obtained in the BP method independently of the type of crop evaluated, considering the BP method suitable to be applied in large-scale bioprospecting plant-growth-promoting microorganism studies.

Hibiscus Acid from Hibiscus sabdariffa L. Inhibits Flagellar Motility and Cell Invasion in Salmonella enterica.

Extracts of Hibiscus sabdariffa L. (commonly called Rosselle or "Jamaica flower" in Mexico) have been shown to have antibiotic and antivirulence properties in several bacteria. Here, an organic extract of H. sabdariffa L. is shown to inhibit motility in Salmonella enterica serovars Typhi and Typhimurium. The compound responsible for this effect was purified and found to be the hibiscus acid. When tested, this compound also inhibited motility and reduced the secretion of both flagellin and type III secretion effectors. Purified hibiscus acid was not toxic in tissue-cultured eukaryotic cells, and it was able to reduce the invasion of Salmonella Typhimurium in epithelial cells. Initial steps to understand its mode of action showed it might affect membrane proton balance.

Antagonistic Interaction of Staphylococcus aureus Toward Candida glabrata During in vitro Biofilm Formation Is Caused by an Apoptotic Mechanism.

Background: Infections caused by Candida species and Staphylococcus aureus are associated with biofilm formation. C. albicans-S. aureus interactions are synergistic due to the significant increase in mixed biofilms and improved resistance to vancomycin of S. aureus. C. glabrata and S. aureus both are nosocomial pathogens that cause opportunistic infections in similar host niches. However, there is scarce information concerning the interaction between these last microorganisms. Results: The relationship between C. glabrata and S. aureus was evaluated by estimating the viability of both microorganisms in co-culture of planktonic cells and in single and mixed biofilms. An antagonistic behavior of S. aureus and their cell-free bacterial supernatant (CFBS) toward C. glabrata, both in planktonic form and in biofilms, was demonstrated. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and confocal laser scanning microscopy (CLSM) images showed yeast cells surrounded by bacteria, alterations in intracytoplasmic membranes, and non-viable blastoconidia with intact cell walls. Concomitantly, S. aureus cells remained viable and unaltered. The antagonistic activity of S. aureus toward C. glabrata was not due to cell-to-cell contact but the presence of CFBS, which causes a significant decrement in yeast viability and the formation of numerous lipid droplets (LDs), reactive oxygen species (ROS) accumulation, as well as nuclear alterations, and DNA fragmentation indicating the induction of an apoptotic mechanism. Conclusion: Our results demonstrate that the S. aureus CFBS causes cell death in C. glabrata by an apoptotic mechanism.