Lifespan and functionality of mycorrhizal fungal mycelium are uncoupled from host plant lifespan

Arbuscular mycorrhizal fungi (AMF) are obligate symbionts, living in associations with the roots of most land plants. AMF produce wide networks of extraradical mycelium (ERM) of indeterminate length, spreading from host roots into the surrounding soil and establishing belowground interconnections among plants belonging to the same or to different taxa. Whether their lifespan and functionality are limited by host plant viability or can be extended beyond this limit is unknown. To address this issue, we performed time-course studies to investigate viability and functionality of ERM produced in an in vivo whole-plant system by Funneliformis mosseae and Rhizoglomus irregulare, after shoot detachment. Our data revealed that viability and functionality of F. mosseae and R. irregulare extraradical hyphae were uncoupled from host plant lifespan. Indeed, ERM spreading from roots of intact or shootless plants showed comparable levels of viability, similar structural traits and ability to establish mycorrhizal symbioses with new plants, as long as five months after shoot removal. Our findings expand the current knowledge on AMF biology and life cycle, providing data on ERM long-term survival in the soil of two Glomeracean species, functional to the prompt establishment of mycorrhizal symbioses and to the maintenance of soil biological fertility

Different levels of hyphal self-incompatibility modulate interconnectedness of mycorrhizal networks in three arbuscular mycorrhizal fungi within the Glomeraceae

Arbuscular mycorrhizal fungi (AMF) live in symbiosis with most plant species and produce underground extraradical hyphal networks functional in the uptake and translocation of mineral nutrients from the soil to host plants. This work investigated whether fungal genotype can affect patterns of interconnections and structural traits of extraradical mycelium (ERM), by comparing three Glomeraceae species growing in symbiosis with five plant hosts. An isolate of Funneliformis coronatus consistently showed low ability to form interconnected ERM and self-incompatibility that represented up to 21 % of hyphal contacts. The frequency of post-fusion self-incompatible interactions, never detected before in AMF extraradical networks, was 8.9 %. In F. coronatus ERM, the percentage of hyphal contacts leading to perfect hyphal fusions was 1.2–7.7, while it ranged from 25.8–48 to 35.6–53.6 in Rhizophagus intraradices and Funneliformis mosseae, respectively. Low interconnectedness of F. coronatus ERM resulted also from a very high number of non-interacting contacts (83.2 %). Such findings show that AMF genotypes in Glomeraceae can differ significantly in anastomosis behaviour and that ERM interconnectedness is modulated by the fungal symbiont, as F. coronatus consistently formed poorly interconnected networks when growing in symbiosis with five different host plants and in the asymbiotic stage. Structural traits, such as extent, density and hyphal self-compatibility/incompatibility, may represent key factors for the differential performance of AMF, by affecting fungal absorbing surface and foraging ability and thus nutrient flow from soil to host roots

Belowground environmental effects of transgenic crops: a soil microbial perspective

Experimental studies investigated the effects of transgenic crops on the structure, function and diversity of soil and rhizosphere microbial communities playing key roles in belowground environments. Here we review available data on direct, indirect and pleiotropic effects of engineered plants on soil microbiota, considering both the technology and the genetic construct utilized. Plants modified to express phyto-pathogen/phytoparasite resistance, or traits beneficial to food industries and consumers, differentially affected soil microorganisms depending on transformation events, experimental conditions and taxa analyzed. Future studies should address the development of harmonized methodologies by taking into account the complex interactions governing soil lif

Identification and characterization of lactic acid bacteria and yeasts of PDO Tuscan bread sourdough by culture dependent and independent methods

Sourdough fermentation has been increasingly used worldwide, in accordance with the demand of consumers for tasty, natural and healthy food. The high diversity of lactic acid bacteria (LAB) and yeast species, detected in sourdoughs all over the world, may affect nutritional, organoleptic and technological traits of leavened baked goods. A wide regional variety of traditional sourdough breads, over 200 types, has been recorded in Italy, including special types selected as worthy of either Protected Geographical Indication (PGI) or Protected Designation of Origin (PDO), whose sourdough microbiota has been functionally and molecularly characterized. As, due to the very recent designation, the microbiota of Tuscan bread sourdough has not been investigated so far, the aim of the present work was to isolate and characterize the species composition of LAB and yeasts of PDO Tuscan bread sourdough by culture-independent and dependent methods. A total of 130 yeasts from WLN medium and 193 LAB from both mMRS and SDB media were isolated and maintained to constitute the germplasm bank of PDO Tuscan bread. Ninety six LAB from mMRS medium and 68 yeasts from WLN medium were randomly selected and molecularly identified by ARDRA (Amplified Ribosomal DNA Restriction Analysis) and PCR-RFLP analysis of the ITS region, respectively, and sequencing. The yeast identity was confirmed by 26S D1/D2 sequencing. All bacterial isolates showed 99% identity with Lactobacillus sanfranciscensis, 65 yeast isolates were identified as Candida milleri, and 3 as Saccharomyces cerevisiae. Molecular characterization of PDO Tuscan bread sourdough by PCR-DGGE confirmed such data. The distinctive tripartite species association, detected as the microbiota characterizing the sourdough used to produce PDO Tuscan bread, encompassed a large number of L. sanfranciscensis and C. milleri strains, along with a few of S. cerevisiae. The relative composition and specific physiological characteristics of such microbiota could potentially affect the nutritional features of PDO Tuscan bread, as suggested by the qualitative functional characterization of the isolates. Investigations on the differential functional traits of such LAB and yeast isolates could lead to the selection of the most effective single strains and of the best performing strain combinations to be used as starters for the production of baked goods

Rhizoglomus venetianum, a new arbuscular mycorrhizal fungal species from a heavy metal-contaminated site, downtown Venice in Italy

Rhizoglomus venetianum, a new arbuscular mycorrhizal fungal species, has been isolated and propagated from a heavy metal-contaminated site in Sacca San Biagio island, downtown Venice, Italy. Interestingly, under the high levels of heavy metals occurring in the site, the new fungus was able to grow only intraradically. In greenhouse trap and single species cultures under low heavy metal levels, the fungus produced innumerous spores, clusters, and sporocarps extraradically, which were formed terminally on subtending hyphae either singly, in small spore clusters, or, preferably, in loose to compact non-organized sporocarps up to 2500 × 2000 × 2000 μm. Spores are golden-yellow to bright yellow brown, globose to subglobose to rarely oblong, 75–145 × 72–140 μm in diameter, and have four spore wall layers. Morphologically, the new fungus is similar to R. intraradices, and phylogenetically, it forms a monophyletic clade next to R. irregulare, which generally forms irregular spores and lacks, like R. intraradices, the flexible innermost wall layer beneath the structural/persistent third wall layer. A key for the species identification is presented comprising all 18 Rhizoglomus species, so far described or newly combined

Characterisation of arbuscular mycorrhizal fungi in roots by means of epifluorescence microscopy and molecular methods

In this work we characterised different species of the arbuscular mycorrhizal (AM) fungal genusGlomus by using Restriction Fragment Length Polymorphisms (RFLPs), combining epifluorescence microscopy and nested PCR, for the easy retrieval of AM fungal DNAin planta. Epifluorescence microscopy allowed us to select highly colonised root segments for DNA extraction, enhancing the chance of fungal DNA amplification by PCR. The primer pair used in nested PCR after a first reaction performed by using NS31/AM1 primers, showed a high specificity forGlomus DNA amplification and yielded enough fungal DNA for RFLP analyses. RFLP patterns of PCR products from colonised roots matched with reference profiles obtained from spores and discriminated the fourGlomus species tested. The method described may be useful for checking the establishment of mycorrhizal colonisation by the inoculated fungal species in controlled experimental conditions

Multifunctionality and diversity of culturable bacterial communities strictly associated with spores of the plant beneficial symbiont Rhizophagus intraradices

Arbuscular Mycorrhizal Fungi (AMF) live in symbiosis with most crop plants and represent essentialelements of soil fertility and plant nutrition and productivity, facilitating soil mineral nutrient uptakeand protecting plants from biotic and abiotic stresses. These beneficial services may be mediated bythe dense and active spore-associated bacterial communities, which sustain diverse functions, such asthe promotion of mycorrhizal activity, biological control of soilborne diseases, nitrogen fixation, and the supply of nutrients and growth factors. In this work, we utilised culture-dependent methods to isolate and functionally characterize the microbiota strictly associated to Rhizophagus intraradices spores,and molecularly identified the strains with best potential plant growth promoting (PGP) activities by16S rDNA sequence analysis. We isolated in pure culture 374 bacterial strains belonging to different functional groups—actinobacteria, spore-forming, chitinolytic and N2-fixing bacteria—and screened 122 strains for their potential PGP activities. The most common PGP trait was represented by P solubilization from phytate (69.7%), followed by siderophore production (65.6%), mineral P solubilization (49.2%) and IAA production (42.6%). About 76% of actinobacteria and 65% of chitinolytic bacteria displayed multiple PGP activities. Nineteen strains with best potential PGP activities, assigned to Sinorhizobium meliloti, Streptomyces spp., Arthrobacter phenanthrenivorans, Nocardiodes albus, Bacillus sp. pumilus group, Fictibacillus barbaricus and Lysinibacillus fusiformis, showed the ability to produce IAA and siderophores and to solubilize P from mineral phosphate and phytate, representing suitable candidates as biocontrol agents,biofertilisers and bioenhancers, in the perspective of targeted management of beneficial symbionts and their associated bacteria in sustainable food production systems

Diverse bacterial communities are recruited on spores of different arbuscular mycorrhizal fungal isolates

Arbuscular mycorrhizal fungi (AMF) establish mutualistic symbioses with the roots of most food crops, playing a key role in soil fertility and plant nutrition and health. The beneficial activity of AMF may be positively affected by bacterial communities living associated with mycorrhizal roots, spores and extraradical hyphae. Here, we investigated the diversity of bacterial communities associated with the spores of six AMF isolates, belonging to different genera and species and maintained for several generations in pot cultures with the same host plant, under the same environmental conditions and with the same soil. The occurrence of large bacterial communities intimately associated with spores of the AMF isolates was revealed by PCR denaturing gradient gel electrophoresis (DGGE) analysis and sequencing of DGGE bands. Cluster and canonical correspondence analysis showed that the six AMF isolates displayed diverse bacterial community profiles unrelated with their taxonomic position, suggesting that each AMF isolate recruits on its spores a different microbiota. The 48 sequenced fragments were affiliated with Actinomycetales, Bacillales, Pseudomonadales, Burkholderiales, Rhizobiales and with Mollicutes-related endobacteria (Mre). For the first time, we report the occurrence of Mre in Funneliformis coronatum and Rhizophagus intraradices and sequences related to endobacteria of Mortierella elongata in F. coronatum and Funneliformis mosseae. The bacterial species identified are known to possess diverse and specific physiological characteristics and may play multifunctional roles affecting the differential performance of AMF isolates, in terms of infectivity and efficiency

Valorizzazione dei prodotti alimentari del territorio attraverso la loro caratterizzazione salutistica

Valorisation of local food products by the characterization of their health-promoting properties. Typical local food products play a very important economic role, in particular in Italy, where food processes and products are highly diversified, not only at the regional scale, but also within the same province and municipality. The valorisation of such processes and products, often obtained by quality marks, i.e. PDO, PGI, TSG, TAP, can be further prosecuted through their nutritional and nutraceutical characterization. Knowledge of the heath-promoting features of peculiar local foods can be utilized for its diversification and marketing. Tuscany is rich in local and traditional food products, from PDO pecorino cheese to PDO Lunigiana honey, from PDO Garfagnana and Lunigiana chesnut flour to PGI Garfagnana spelt flour IGP, from PGI Sorana bean to Pratomagno “zolfino” bean, from mountain blueberry to white truffle, from PDO Tuscan bread to different PDO extra-virgin olive oils. Here, we discuss the available means for their further characterization from a health-promoting point of view, aimed at pursuing their diversification and valorisation

Facilitation of phosphorus uptake in maize plants by mycorrhizosphere bacteria

A major challenge for agriculture is to provide sufficient plant nutrients such as phosphorus (P) to meet the global food demand. The sufficiency of P is a concern because of it’s essential role in plant growth, the finite availability of P-rock for fertilizer production and the poor plant availability of soil P. This study investigated whether biofertilizers and bioenhancers, such as arbuscular mycorrhizal fungi (AMF) and their associated bacteria could enhance growth and P uptake in maize. Plants were grown with or without mycorrhizas in compartmented pots with radioactive P tracers and were inoculated with each of 10 selected bacteria isolated from AMF spores. Root colonization by AMF produced large plant growth responses, while seven bacterial strains further facilitated root growth and P uptake by promoting the development of AMF extraradical mycelium. Among the tested strains, Streptomyces sp. W94 produced the largest increases in uptake and translocation of 33P, while Streptomyces sp. W77 highly enhanced hyphal length specific uptake of 33P. The positive relationship between AMF-mediated P absorption and shoot P content was significantly influenced by the bacteria inoculants and such results emphasize the potential importance of managing both AMF and their microbiota for improving P acquisition by crops