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Biosurfactants are metabolites produced by microorganisms during their growth and reproduction. They are amphiphilic molecules capable of modifying surface and interfacial tension. A petrophilic, nitrogen-fixing, phosphorus-solubilizing, and biosurfactant-producing bacterial strain was isolated and characterized. The isolated strain was cultivated in Kim medium with a C:N ratio of 2:1, from which its growth kinetics was determined. Samples of the culture broth were taken at different times and the collapsed drop, oil dispersion and emulsification index tests were performed. Maximum culture growth occurred at 72 h. The biosurfactant was extracted from the crude cell-free broth using a mixture of solvents and a yield of 2.21 g/L was obtained. Thin-layer chromatography and FT-IR analyzes revealed the presence of a lipopeptide biosurfactant. Tensiometry tests showed that the biosurfactant was able to lower the surface tension of water from 72 mN/m to 40 mN/m and the critical micelle concentration was 0.058 (w/w). Probit analysis for toxicity determination showed that there was no weight loss in Eisenia foetida specimens in a range between 10000 and 50000 ppm. [ABSTRACT FROM AUTHOR]

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Degradation processes of the soil, water erosion and loss of organic matter lead to a violation of its physical, chemical and biological properties. To combat these processes, the application of anti-erosion technologies on sloping agricultural lands is imperative. The present study is on the number of different groups of soil microorganisms under the influence of traditionally applied anti-erosion technologies for growing wheat on sloping terrain. The research was conducted in the period 2017 − 2019 in the experimental field of Experimental Station for fighting erosion village Trastenik IPAZR "N. Pushkarov" АA-Sofia. A field experiment with wheat was performed using a block method in four replications. The obtained results show a positive influence of the applied soil protection technologies on the number of saprophytic bacteria, mold fungi, actinomycetes, nitrogen-fixing and cellulose-degrading microorganisms. In variant e3 with applied advanced soil protection technologies, the total number of saprophytic bacteria was within the limits of 609.15x106 CFU/g before sowing, 1427.43x106 CFU/g during maximum growth and 546.07x106 CFU/g after harvesting. Oligotrophs have high values in variants e2 and e3, where soil protection technologies are applied, and are 295.44x106 CFU/g and 293.74x106 CFU/g, respectively. Nitrogen-fixing bacteria in variant e3 had the highest values, ranging from 4.18x106 CFU/g at maximum plant growth to 9.66x106 CFU/g after harvest. Variant e3 has the lowest values of spore-forming microorganisms before sowing - 332.88x106 CFU/g. The highest amount of cellulosedegrading microorganisms was found in the soil samples of variants e2 (before sowing 4.79x106 CFU/g; maximum growth -3.89x106 CFU/g and 2.44x106 CFU/g after harvesting) and e3 (6.55x106 CFU /g, 2.87x106 CFU/g and 3.64x106 CFU/g). The analysis for mold fungi shows that variant e2 obtained the highest values - 0.00587x106 CFU/g. The stimulation of the soil microbiota leads to more intensive biochemical processes in the soil and to an increase in soil fertility. [ABSTRACT FROM AUTHOR]

Nitrogen (N2) is an essential nutrient for plant growth; however, roots can only assimilate the reduced form of this element. Specific bacterial communities, known as nitrogen-fixing bacteria, can synthesize a nitrogenase enzyme complex, which converts N2 into plant-assimilable molecules, such as nitrates (NO3) and ammonium (NH4+); nifH gene encodes a highly conserved subunit of the bacterial nitrogenase complex. In the present work, bioinformatic analyses of primers targeting bacterial nifH genes were performed. Nitrogenase complex subunit encoded by the nifH gene was identified in Uniprot database, this protein sequence was aligned against nucleotide sequences using the BLAST (tblastn) tool. A total of 4,693 nucleotide sequences were obtained and aligned using MEGA11. Aligned sequences were subjected to an in-silico PCR assay using primer pairs identified in previous studies. These analyses allowed us to identify that primer pair (nifH2/nifH1) had the highest coverage percentage (80%). Results of this study will allow us to detect and quantify the presence of bacterial nifH genes in soil and root samples using PCR assays. [ABSTRACT FROM AUTHOR]

Symbiotic nitrogen fixation is critical for high soybean (Glycine max L. Merril) yields with protection to the environment. This paper describes a procedure for massive production of Bradyrhizobium japonicum in an orbital multi-platform shaker and the use of the bacterial culture for seed inoculation in soybean areas under mechanized sowing. The B. japonicum strain was selected based on its highly efficient symbiotic interaction with major soybean varieties cropped in Cuba. Optimization of the growth medium and the use of serial and scaled inoculations allowed maintaining the cultures in continuous logarithmic phase while increasing its volume 100-fold in 7 days. The final culture having average cell viability of 5 x 1010 f.u.c/mL and high exopolysaccharides content does not require additives and can be stably stored for at least 8 months at 4 °C. Soybean seeds were sprayed with the inoculant at equivalent dose of 150 mL/ha and sowed mechanically in production fields of Ciego de Avila province during the campaigns 2010-2013. The plants showed abundant nodulation and a proper nutritional state during the whole cycle. The bacterium strain was reisolated from root nodules of inoculated plants and its identity was confirmed by phenotype characterization. The high-cell density liquid inoculant rich in polysaccharides produced in this work is compatible with mechanized seed sowing, favors the bacterium survival in soil, and promotes the establishment of an efficient symbiotic interaction with the host plant. [ABSTRACT FROM AUTHOR]