The excessive use of synthetic pesticides for plant pathogens control could cause possible harmful side-effects to humans and animals, environmental pollution, residual toxicity, affects soil characteristics or induce the development of fungal resistance. Alternative ways for fungal contamination control involve natural products, based on microorganisms, many of them being already available for use. The selection and characterization of new biological agents useful for plant pathogens control are permanent goals for plant protection researches. In the last decade, several studies revealed that Streptomyces species are promising biocontrol agents against a wide range of phytopathogenic fungi, including Fusarium spp., one of the most important wheat pathogens. In our study, 60 strains of Streptomyces spp. were isolated from soil or compost and evaluated for in vitro antifungal abilities by dual confrontation method. At least 30% of the isolates presented inhibitory activity against F. culmorum and F. graminearum. The bacterial strains were also tested for their ability to produce various bioactive compounds, possible involved in fungal inhibition. The capacity of some of the bacterial isolates to produce cellulases, amylases, lipases and volatile metabolites was proved. In addition, a new screening method for chitinases production was developed, based on the use of a combination of Congo red and Lugol solutions, which allowed the detection of chitinases in several Streptomyces spp. strains. Moreover, the reduction of the level of some Fusarium mycotoxins was detected by HPTLC analysis. As a conclusion, antagonistic interactions between Streptomyces isolates and fusaria could involve antibiosis, competition and parasitism and suggested that at least some of the selected isolates could be used in obtaining biological control products.
Ana Valentina Ardelean, Ioan I. Ardelean, Oana Alina Sicuia-Boiu and Petruţa Cornea
In the last decade there is an increased interest in selecting photosynthetic microorganisms with higher lipid content useful for biotechnological applications. In this paper we present our original results concerning: i) the selection of naturally occurring photosynthetic microorganisms with higher lipid content; ii) the use of these isolates as biological material subject of randomly induced mutagenesis; iii) selection by iodine vapour method of clones with decreased polysaccharides content and expected higher lipid content) as well as iv) genetic analysis of most promising strains in order to check the if they are true mutants or not. The results thus obtained argue the importance of the selection of naturally occurring photosynthetic microorganisms with higher lipid content as well as the use of random mutagenesis as a valuable tool to improve the genetic diversity of photosynthetic microorganisms in order to increase their ability to synthesize lipids for further biodiesel production and/or omega 3 or 6 production.