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  • Author: Sorin Matei x
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Abstract

Lactic acid bacteria are frequently utilized in food industry and they are also recognized as antimicrobial agents due to their capability to produce metabolites such as: organic acids, biosurfactants, bacteriocins, hydrogen peroxide, cyclic dipeptides, exopolysaccharides. The main goal of this paper was to present the results of the research carried out on the strain LCM2 of lactic acid bacteria isolated from brined cucumbers, for production of biosurfactants and to assess its antifungal properties. The emulsification capacity of biosurfactant was measured using kerosene as the hydrophobic substrate. The value of emulsification index E24 was 89.04% showing a high emulsification activity of the biosurfactant. The structural characterization of biosurfactant by TLC revealed its glycolipidic nature. Assay of the ionic charge established the anionic charge of the biosurfactant revealed by the presence of precipitation lines towards the cationic surfactant dodecyl-dimethyl-ammonium chloride. The biosurfactant presented antibiofilm activity with low adherence capacity, structural damages of the hyphal net, conidiophores and delays or lack of sporulation and decreased biomass accumulation in four mycotoxigenic Penicillium and Aspergillus isolates. Results of in vitro assays recommend the biosurfactant produced by the new lactic acid bacteria strain LCM2 for biotechnological purposes, as alternative antifungal agent in food industry.

Abstract

In forests, edaphic microbial communities are involved in litter decomposition and soil forming processes, with major contribution to humification, especially bacteria and fungi being responsible for the main ecosystem services fulfilled by the soil. Research has been carried out aiming to characterize the structure and diversity of microbial communities in the Rendzic Leptosols (WRB) under natural deciduous forest from Visterna, Babadag Plateau and to assess their contribution to ecosystem services provided by soil. The paper presents the results of quantitative estimations and taxonomic composition of soil and litter communities of heterotrophic bacteria and fungi, identification of cellulolytic species, as well as the microbial biomass and global physiological activities expressed as soil respiration potential. More than a half of bacterial species were common in litter and soil (SI=57.14%) and were represented by dominant species of fluorescent or non-fluorescent pseudomonads and Bacillus subtilis but no similarity was found between the two fungal communities. Fungal populations included cosmopolitan species, such as antagonists and strong cellulolytic representatives of genera Penicillium, Trichoderma, Mortierella, Chaetomium, Epicoccum, Aspergillus. Microbial density and microbial biomass presented the highest values in the litter (684 mg C x kg-1 d.s.) and in surface horizon Am1 of soil profile than in the bottom layers. The highest diversity was found in Am1 horizon (0-5 cm) H’=1.983 bits and ε=0.869 for cellulolytic community. Soil respiration reflected the intense physiological activity of microbiome, with high values associated to numerous effectives of bacteria and fungi especially in surface horizon. Microorganisms identified contribute to formation of soil by recycling of nutrients, cellulose decomposition, the synthesis of stable organic matter (humic acids), aggregation of soil particles, biological control of pathogens by antagonistic activity. They improve plant uptake of water and nutrients by forming symbioses (ectomycorrhizae), thus modelling the structure of vegetation.

Abstract

The soil degraded and changed by the anthropic activity must be monitored and the awareness of the intrinsic processes will allow a pertinent analysis of the effects of the application of the new technologies on the management and the sustainability of the soil.

Two natural and anthropic Phaeozems were analyzed from the point of view of chemical, microbiological characteristics, quality and composition of organic compounds.

Total values of microbial biomass and bacterial and fungal counts were generally twice higher in Calcaric Phaeozems than in Verti-Stagnic Phaeozems.

The content of humic precursors in Calcaric Phaeozems was quantitatively higher than that determined in Verti-stagnic Phaeozems, with a total content of phenols of 14.6mgGAExg−1d.m., polysaccharides and proteins of 97mgxg−1, respectivelly 16.6mgxl−1.

The ascending chromatograms showed specific distribution and higher density of the organic compounds in the CAFT sub-fraction of the Verti-stagnic Phaeozems. Pfeiffer specific chromatograms revealed an enzyme activity much higher than average at the Verti-stagnic Phaeozems, with a well-characterized functional diversity. The nutritional reserve appeared increased but poorly diversified in the Calcaric Phaeozems. Humification processes are intense, colloidal substances are present, the mineral component is very well integrated in the organic material at the Verti-stagnic Phaeozems and complex protein content is well revealed especially in the Calcaric Phaeozems.

Capillary dynamolysis reflected a characteristic pattern of Phaeozems soils, with particularities for each soil type, represented by colors, contours and particular forms of the specific structures developed.

Both soils presented good conditions for sustaining vegetation either natural or cultivated but results indicated that anthropic intervention determined a more dynamic mineralization of organic matter. Further monitoring of soil organic matter dynamics is needed and adjusting management practices for conservation of biodiversity and global ecosystem protection against the effect of anthropic intervention.

Abstract

Soils from rural zones with high natural value (HNV) agriculture systems are an important source of beneficial microbial species that can be useful for various biotechnological purposes, such as transfer of suppressiveness against plant pathogens from suppressive to disease-inducing soils by using inoculation with antagonistic selected strains.

The main goal of the paper was to present the results of the research carried out on strains isolated from soil microbial populations in HNV agriculture system (Mureș county, Romania) responsible for specific suppressiveness against soil-borne phytopathogens. The dual culture method was used for assessing the mechanisms involved in antagonism against a plant pathogenic strain from genus Fusarium.

The global microbial activity measured as soil respiration was intense. Total counts of bacteria and fungi estimated by dilution plate were also high.

The community of heterotrophic aerobic bacteria included 13 species. Associations of fluorescent pseudomonads and actinomycetes were dominant and presented antagonistic activity against Fusarium.

Twenty fungal species presented cellulolytic capability evidenced by growth on culture media with cellulose as sole source of carbon. Over cellulolytic capacity, the selected isolate of Trichoderma viride presented antagonistic activity against pathogenic Fusarium strain. Both biochemical mechanism and hyperparasitism were evidenced as involved in its antifungal activity.

Abstract

Silver nanoparticles (AgNPs) are nanomaterials obtained by nanotechnology and due to their antimicrobial properties have a major importance in the control of various species of bacteria, fungi and viruses, with applications in medicine, cosmetics or food industry. The goal of the paper was to present the results of the research carried out on rapid extracellular biosynthesis of silver nanoparticles mediated by culture filtrate of lactic acid bacteria Lactobacillus sp. strain LCM5 and to assess the antimicrobial activity. Analysis of transmission electron microscopy (TEM) micrographs evidenced that the size of AgNPs synthesized using culture filtrates of lactic acid bacteria strain LCM5 ranged between 3 and 35 nm diameter, with an average particle size of 13.84±4.56 nm. AgNPs presented a good dispersion, approximately spherical shape, with parallel stripes certifying crystal structure. Frequency distribution revealed that preponderant dimensions of biosynthesized AgNPs were below 20 nm (94%). Antimicrobial activity of AgNPs was variable depending on both species and group of test microorganisms (bacteria or fungi) involved. Diameter of growth inhibition zone of Aspergillus flavus and Aspergillus ochraceus caused by silver nanoparticles synthesized by lactic acid bacteria strain LCM5 were similar (12.39 ± 0.61mm and 12.86 ± 0.78 mm) but significant stronger inhibition was registered against Penicillium expansum (15.87 ± 1.01mm). The effectiveness of biosynthesized silver nanoparticles was more pronounced against Gram-negative bacteria Chromobacterium violaceum with larger zone of inhibition (18 ± 0.69 mm diameter) when compared to those from fungi. Results recommend the silver nanoparticles biosynthesized using culture filtrate of the lactic acid bacteria Lactobacillus sp. strain LCM5 for biotechnological purposes, as promising antimicrobial agents.

Abstract

The presence of oil hydrocarbons and salts in soils has as consequence the poor growth of plants due to the low availability of nutrients caused by unappropriate water regime, increased soil toxicity and the deterioration of soil structure. The present research has as main purpose the improvement of the bean plants (cultivar UNIDOR) growth and to stimulate microbial activity in rhizosphere using various natural stimulators and fertilizers (AMALGEROL,VERMIPLANT, POCO, IGUANA and FORMULEX) in greenhouse experiments on oil-polluted soil from Icoana farm, Olt county. The total counts of microorganisms (heterotrophic aerobic bacteria and filamentous fungi) were estimated by dilution plate method. The global microbial activity was measured as soil respiration by substrate-induced respiration method. Total bean plants biomass accumulation significantly increased under the influence of natural stimulators and fertilizers added (excepting IGUANA) when compared to untreated control. The best results were recorded for VERMIPLANT. Natural products induced activation of physiological activities of soil microbiota reflected in increased values of CO2 released by respiration, lower levels of colonization with phytopathogenic species, the domination of fluorescent pseudomonads, actinomycetes and cellulolytic fungi, too. The particular aspect of paper circular chromatograms reflected qualitative differences between rhizosphere soils determined by the effect of treatments with natural stimulators and fertilizers.

Abstract

As low-input environmentally friendly agricultural practices are currently associated with the delivery of a wide range of public goods and socioeconomic benefits, the strategy of European Union in mitigating climate change effects, protecting environment and ensuring public health has, among others, focused around preserving the High Natural Value (HNV) areas. About a quarter of the land in Romania is potentially covered by HNV farming and eligible for associated support payments, mostly along the chain of the Carpathian Mountains. Since soil systematic data on HNV area are scarce, recent research developments currently undertake to build up a first national HNV soil data base.

Soil fertility state in a HNV payment eligible area of south-eastern Transylvania was studied in seven in-depth dug profiles and seven additional shallow dug profiles. Soil samples were taken by genetic horizons as well as agrochemical samples from the upper soil layers (0-20 cm). Physical, chemical, and microbiological analyses revealed that the studied soils have a medium clayey loamy texture, good fertility and are subject to an adequate HNV management in the area, as the analytical values mostly range in favorable intervals for plant growth and nutrition. Thus, soil reaction is moderately acid up to slightly alkaline in the presence of carbonates, the soil organic matter, generally well mineralized, reaches fair levels and the high and very high cation exchange capacity ensure good conditions for plants growth and nutrition whilst nitrogen and potassium supply is adequate. Phosphorus is the only element in short supply – a situation often encountered in Romania unfertilized soils. Soil bulk density and total porosity are also favorable for root growth and spreading and plant nutrition. Microorganisms’ activity is diverse and is also adequate for plant nutrition.