Co-inoculation of Glomus intraradices and Trichoderma atroviride acts as a biostimulant to promote growth, yield and nutrient uptake of vegetable crops.

BACKGROUND: The application of beneficial microorganisms at transplanting can promote rapid transplant establishment (starter effect) for achieving early and high yields. The aim of this study was to evaluate the biostimulant effects of Glomus intraradices BEG72 (G) and Trichoderma atroviride MUCL 45632 (T) alone or in combination on plant growth parameters, yield, chlorophyll index (SPAD), chlorophyll fluorescence and mineral composition of several vegetable crops. RESULTS: The T. atroviride strain was capable of producing siderophores and auxin-like compounds under a wide range of substrate pH conditions (5.5-8.0). The highest shoot, root dry weight, SPAD and chlorophyll fluorescence in lettuce, tomato and zucchini was observed in the G + T combination, followed by a single inoculation of G or T, whereas the lowest values were recorded in the uninoculated plants. Under greenhouse conditions, the shoot dry weight was significantly increased by 167%, 56%, 115%, 68% and 58% in lettuce, melon, pepper, tomato and zucchini, respectively, when supplied with both beneficial microorganisms in comparison with the control. This increase in root and shoot weight was associated with an increased level of nutrient uptake (e.g. P, Mg, Fe, Zn and B). Under open field conditions, the lettuce shoot and root dry weight increased by 61% and 57%, respectively, with biostimulant microorganism application in field conditions. For zucchini, early and total yields were significantly increased by 59% and 15%, respectively, when plants were inoculated with both microorganisms. CONCLUSION: The application of the biostimulant tablet containing both G and T can promote transplant establishment and vegetable crop productivity in a sustainable way.

Alteration of bacterial communities and organic matter in microbial fuel cells (MFCs) supplied with soil and organic fertilizer.

The alteration of the organic matter (OM) and the composition of bacterial community in microbial fuel cells (MFCs) supplied with soil (S) and a composted organic fertilizer (A) was examined at the beginning and at the end of 3 weeks of incubation under current-producing as well as no-current-producing conditions. Denaturing gradient gel electrophoresis revealed a significant alteration of the microbial community structure in MFCs generating electricity as compared with no-current-producing MFCs. The genetic diversity of cultivable bacterial communities was assessed by random amplified polymorphic DNA (RAPD) analysis of 106 bacterial isolates obtained by using both generic and elective media. Sequencing of the 16S rRNA genes of the more representative RAPD groups indicated that over 50.4% of the isolates from MFCs fed with S were Proteobacteria, 25.1% Firmicutes, and 24.5% Actinobacteria, whereas in MFCs supplied with A 100% of the dominant species belonged to γ-Proteobacteria. The chemical analysis performed by fractioning the OM and using thermal analysis showed that the amount of total organic carbon contained in the soluble phase of the electrochemically active chambers significantly decreased as compared to the no-current-producing systems, whereas the OM of the solid phase became more humified and aromatic along with electricity generation, suggesting a significant stimulation of a humification process of the OM. These findings demonstrated that electroactive bacteria are commonly present in aerobic organic substrates such as soil or a fertilizer and that MFCs could represent a powerful tool for exploring the mineralization and humification processes of the soil OM.

Screening of Bifidobacterium strains isolated from human faeces for antagonistic activities against potentially bacterial pathogens.

As probiotic bacteria, strains belonging to the genus Bifidobacterium colonise the gastro-intestinal tract of humans and animals at the time of birth, and they are found in young as well as in adult individuals in great numbers. Moreover, they can interact with the development of enteric infections by the production of antimicrobial metabolites. In this work 281 strains of bifidobacteria were anaerobically isolated from human faecal samples, supplied by volunteers of different ages (youngs, adults, elders), and preliminarly described by microscopic observation. All strains were screened by the fructose 6-phosphate phosphoketolase (F6PPK) test in order to confirm their classification within the genus Bifidobacterium. Selected strains were used to evaluate their antagonistic activities against Escherichia coli, Salmonella thyphimurium, Staphylococcus lentus, Enterococcus faecalis, Acinetobacter calcoaceticus, Sphingomonas paucimobilis, Listeria monocytogenes, Yersinia enterocolitica, Bacillus cereus, Clostridium sporogenes. Experiments were performed in vitro by different methods based on the observation of growth inhibition in Petri dishes. The strains that showed the highest inhibiting activities were compared by SDS-PAGE for total cell proteins, using type strains of human origin as references. Representative isolates were metabolically characterised by the BIOLOG system; a specific database was created with strains obtained from our collection and a statistical evaluation for metabolic patterns was carried out.

Influence of substrate composition and flow rate on growth of Azospirillum brasilense Cd in a co-culture with 3 sorghum rhizobacteria.

The ability of Azospirillum brasilense Cd to colonize the niche occupied by 3 bacterial strains previously isolated from sorghum rhizosphere was studied by means of the Biolog system. The isolates were identified by different methods as strains belonging to Pseudomonas putida, Stenotrophomonas maltophilia, and Klebsiella terrigena species. Several C sources, also chosen among the constituents of sorghum root exudates, were used to evaluate the metabolic profiles of Azospirillum and the sorghum rhizobacteria. Azospirillum brasilense Cd exploited the same class of C compounds as the sorghum rhizobacteria and overlapped in their niche requirements. Since structure and functioning of a microbial community are largely affected by the flow rate of nutrient supply, the competitive behavior of A. brasilense Cd was studied in a chemostat mixed culture under C-limited conditions using disodium succinate as C source. Only at high growth rates, i.e., when the C source was highly supplied, A. brasilense Cd appeared to be a good competitor and it became the dominant species, whereas at low growth rates, it was outnumbered by the other species. However, the coexistence of all the strains was always maintained, thus suggesting that interactions other than competition or a potential cross-feeding might occur within the mixed culture.