This review focuses on interactions among plants, mycorrhizal fungi, and bacteria, testing the hypothesis whether mycorrhizas can be defined as tripartite associations. After summarizing the main biological features of mycorrhizas, we illustrate the different types of interaction occurring between mycorrhizal fungi and bacteria, from loosely associated microbes to endobacteria. We then discuss, in the context of nutritional strategies, the mechanisms that operate among members of the consortium and that often promote plant growth. Release of active molecules, including volatiles, and physical contact among the partners seem important for the establishment of the bacteria/mycorrhizal fungus/plant network. The potential involvement of quorum sensing and Type III secretion systems is discussed, even if the exact nature of the complex interspecies/interphylum interactions remains unclear.

Plants, mycorrhizal fungi, and bacteria: a network of interactions.

Bacteria and fungi can form a range of physical associations that depend on various modes of molecular communication for their development and functioning. These bacterial-fungal interactions often result in changes to the pathogenicity or the nutritional influence of one or both partners toward plants or animals (including humans). They can also result in unique contributions to biogeochemical cycles and biotechnological processes. Thus, the interactions between bacteria and fungi are of central importance to numerous biological questions in agriculture, forestry, environmental science, food production, and medicine. Here we present a structured review of bacterial-fungal interactions, illustrated by examples sourced from many diverse scientific fields. We consider the general and specific properties of these interactions, providing a global perspective across this emerging multidisciplinary research area. We show that in many cases, parallels can be drawn between different scenarios in which bacterial-fungal interactions are important. Finally, we discuss how new avenues of investigation may enhance our ability to combat, manipulate, or exploit bacterial-fungal complexes for the economic and practical benefit of humanity as well as reshape our current understanding of bacterial and fungal ecology.

Bacterial-Fungal Interactions: Hyphens between Agricultural, Clinical, Environmental, and Food Microbiologists

The fungal symbionts forming ectomycorrhizas, as well as their associated bacteria, benefit forest trees in a number of ways although the most important is enhancing soil nutrient mobilization and uptake This is reciprocated by the allocation of carbohydrates by the tree to the fungus through the root interface, making the relationship a mutualistic association Many field observations suggest that ectomycorrhizal fungi contribute to a number of key ecosystem functions such as carbon cycling, nutrient mobilization from soil organic matter, nutrient mobilization from soil minerals, and linking trees through common mycorrhizal networks Until now, it has been very difficult to study trees and their fungal associates in forest ecosystems and most of the work on ECM functioning has been done in laboratory or nursery conditions In this review with discuss the possibility of working at another scale, in forest settings Numerous new techniques are emerging that makes possible the in situ study of the functional diversity of ectomycorrhizal communities This approach should help to integrate developing research on the functional ecology of ectomycorrhizas and their associated bacteria with the potential implications of such research for managing the effects of climate change on forests (C) 2010 Elsevier Ltd All rights reserved

The role of ectomycorrhizal communities in forest ecosystem processes: new perspectives and emerging concepts.

Hydrophobic interaction chromatography of proteins.

Is mitochondrial DNA content a potential biomarker of mitochondrial dysfunction

Tuber magnatum, an ascomycetous fungus and obligate ectomycorrhizal symbiont, forms hypogeous fruit bodies, commonly called Italian white truffles. The diversity of bacterial communities associated with T. magnatum truffles was investigated using culture-independent and -dependent 16S rRNA gene-based approaches. Eighteen truffles were classified in three groups, representing different degrees of ascocarp maturation, based on the percentage of asci containing mature spores. The culturable bacterial fraction was (4.17 +/- 1.61) x 10(7), (2.60 +/- 1.22) x 10(7) and (1.86 +/- 1.32) x 10(6) cfu g(-1) for immature, intermediate and mature ascocarps respectively. The total of bacteria count was two orders of magnitude higher than the cfu g(-1) count. Sequencing results from the clone library showed a significant presence of alpha-Proteobacteria (634 of the 771 total clones screened, c. 82%) affiliated with Sinorhizobium, Rhizobium and Bradyrhizobium spp. The bacterial culturable fraction was generally represented by gamma-Proteobacteria (210 of the 384 total strains isolated, c. 55%), which were mostly fluorescent pseudomonads. Fluorescent in situ hybridization confirmed that alpha-Proteobacteria (85.8%) were the predominant components of truffle bacterial communities with beta-Proteobacteria (1.5%), gamma-Proteobacteria (1.9%), Bacteroidetes (2.1%), Firmicutes (2.4%) and Actinobacteria (3%) only poorly represented. Molecular approaches made it possible to identify alpha-Proteobacteria as major constituents of a bacterial component associated with T. magnatum ascoma, independently from the degree of maturation.

Occurrence and diversity of bacterial communities in Tuber magnatum during truffle maturation.

The microbial community associated with ascocarps of the ectomycorrhizal fungus Tuber borchii Vittad. was studied by both cultivation and direct extraction of bacterial 16S rRNA gene (rDNA) sequence approaches. The inner part of six T. borchii ascoma collected in North-Central Italy was used to establish a bacterial culture collection and to extract the total genomic DNA to obtain a library of 16S rDNAs representative of the truffle bacterial community. Most of the isolates were affiliated to the gamma-Proteobacteria, mainly Fluorescent pseudomonads; some isolates were members of the Bacteroidetes group and Gram-positive bacteria, mostly Bacillaceae. The majority of the clones from the library were alpha-Proteobacteria showing significant similarity values, of greater than 97%, with members of the Sinorhizobium/Ensifer Group, Rhizobium and Bradyrhizobium spp. not previously identified as Tuber-associated bacteria. Only a few bacterial strains belonging to this bacterial subclass were found in the culture collection and isolated on a medium specific for Rhizobium-like organisms. A few clones were members of the beta- and gamma-Proteobacteria; as well as low and high G+C Gram-positive bacteria. Our findings clearly indicate that a dual approach increases the information obtained on the structural composition of a truffle bacterial community as compared to that derived via cultivation or direct recovery of 16S rDNA sequences alone.

Paola Ceccaroli

Papers

Occurrence and diversity of bacterial communities in Tuber magnatum during truffle maturation.

New evidence for bacterial diversity in the ascoma of the ectomycorrhizal fungus Tuber borchii Vittad.

Biochemical characterisation and antioxidant activity of mycelium of Ganoderma lucidum from Central Italy

New evidence for nitrogen fixation within the Italian white truffle Tuber magnatum.

Effect of storage on biochemical and microbiological parameters of edible truffle species.