Maintenance and preservation of ectomycorrhizal and arbuscular mycorrhizal fungi

The Current and Future Role of Microbial Culture Collections in Food Security Worldwide

Food security is the pillar of nutritional wellbeing for food availability, and is necessary to satisfy all physiological needs to thus maintain the general wellbeing of populations. However, global agricultural deficiencies occur due to rapid population growth, causing an increase in competition for resources; such as water, land, and energy, leading to the overexploitation of agro-ecosystems, and the inability to produce a suitable quantity of efficient food. Therefore, the development of sustainable agro-biotechnologies is vital to increase crop yield and quality, reducing the negative impacts caused by intensive non-sustainable agricultural practices. In this way, the genetic and metabolic diversity of soil and plant microbiota in agro-ecosystems are a current and promising alternative to ensure global food security. Microbial communities play an important role in the improvement of soil fertility and plant development by enhancing plant growth and health through several direct and/or indirect mechanisms. Thus, the bio-augmentation of beneficial microbes into agro-ecosystems not only generates an increase in food production but also mitigates the economic, social, and environmental issues of intensive non-sustainable agriculture. In this way, the isolation, characterization, and exploitation of preserved beneficial microbes in microbial culture collections (MCC) is crucial for the ex situ maintenance of native soil microbial ecology focused on driving sustainable food production. This review aims to provide a critical analysis of the current and future role of global MCC on sustainable food security, as providers of a large number of beneficial microbial strains with multiple metabolic and genetic traits.

From field sampling to pneumatic bioreactor mycelia production of the ectomycorrhizal mushroom Laccaria trichodermophora

In order to increase survival rates of greenhouse seedlings destined for restoration and conservation programs, successful mycorrhization of the seedlings is necessary. To reforest forest ecosystems, host trees must be inoculated with ectomycorrhizal fungi and, in order to guarantee a sufficient supply of ectomycorrhizal inoculum, it is necessary to develop technologies for the mass production of ectomycorrhizal fungi mycelia. We selected the ectomycorrhizal fungus Laccaria trichodermophora, due to its ecological traits and feasible mycelia production in asymbiotic conditions. Here, we report the field sampling of genetic resources, as well as the highly productive nutritional media and cultivation parameters in solid cultures. Furthermore, in order to achieve high mycelial production, we used strain screening and evaluated pH, carbon source concentration, and culture conditions of submerged cultures in normal and baffled shake flasks. The higher productivity culture conditions in shake flasks were selected for evaluation in a pneumatic bioreactor, using modified BAF media with a 10 g/L glucose, pH 5.5, 25 °C, and a volumetric oxygen transfer coefficient (K_La) of 36 h^-1. Under those conditions less biomass (12-37 %) was produced in the pneumatic bioreactor compared with the baffled shake flasks. This approach shows that L. trichodermophora can generate a large biomass concentration and constitute the biotechnological foundation of its mycelia mass production.

PCR-denaturing Gradient Gel Electrophoresis as a Simple Identification Tool of Arbuscular Mycorrhizal Fungal Isolates

Due to their obligate symbiotic nature and lack of long-term storage methods, the strain collection of arbuscular mycorrhizal (AM) fungi requires periodic proliferation using a pot culture with host plants. Therefore, a method to evaluate the purity of proliferated AM fungal cultures is critical for the quality control of their collection. In a simple evaluation of the purity and identity of a proliferated AM fungal culture, DNA extracted from the culture was amplified using AM fungi-specific PCR followed by an analysis with denaturing gradient gel electrophoresis (PCR-DGGE). The present results showed that the DGGE band patterns of AM fungal strains differed according to their phylogenetic positions, allowing for the rapid and easy identification of the proliferated AM fungal strains. When a culture was contaminated with another AM fungal strain, the DGGE pattern became a mixture of those strains. A contaminant strain was detectable even when its ratio was 1/9 of the main strain. It was also possible to confirm the purity of the culture by comparing whether the DGGE band pattern of the proliferated culture was identical to that obtained from single spores isolated from the culture. Therefore, PCR-DGGE is useful as a quality control tool for maintaining culture collections of AM fungi.

Fungal biological resources to support international development: challenges and opportunities

Exploitation of microbes, especially fungi, has the potential to help humankind meet the UN's sustainable development goals, help feed the worlds growing population and improve bioeconomies of poorer nations. The majority of the world's fungal genetic resources are held in collections in developed countries, primarily within the USA, Europe and Japan. Very little capacity exists in low to middle income countries, which are often rich in biodiversity but lack resources to be able to conserve and exploit their own microbial resources. In this paper we review the current challenges facing culture collections and the challenges of integrating new approaches, the worth of collaborative networks, and the importance of technology, taxonomy and data handling. We address the need to underpin research and development in developing countries through the need to build 'in country' infrastructure to address these challenges, whilst tackling the global challenges to meet the requirements of the research community through the impacts of legislation and the Nagoya protocol on access to biological resources.

The paleosymbiosis hypothesis: host plants can be colonised by root symbionts that have been inactive for centuries to millenia

Paleoecologists have speculated that post-glacial migration of tree species could have been facilitated by mycorrhizal symbionts surviving glaciation as resistant propagules belowground. The general premise of this idea, which we call the 'paleosymbiosis hypothesis', is that host plants can access and be colonised by fungal root symbionts that have been inactive for millennia. Here, we explore the plausibility of this hypothesis by synthesising relevant findings from a diverse literature. For example, the paleoecology literature provided evidence of modern roots penetrating paleosols containing ancient (>6000 years) fungal propagules, though these were of unknown condition. With respect to propagule longevity, the available evidence is of mixed quality, but includes convincing examples consistent with the paleosymbiosis hypothesis (i.e. >1000 years viable propagules). We describe symbiont traits and environmental conditions that should favour the development and preservation of an ancient propagule bank, and discuss the implications for our understanding of soil symbiont diversity and ecosystem functioning. We conclude that the paleosymbiosis hypothesis is plausible in locations where propagule deposition and preservation conditions are favourable (e.g. permafrost regions). We encourage future belowground research to consider and explore the potential temporal origins of root symbioses.

Genetic stability of ectomycorrhizal fungi is not affected by cryopreservation at -130 °C or cold storage with repeated sub-cultivations over a period of 2 years

Cryopreservation is considered the most reliable method for storage of filamentous fungi including ectomycorrhizal (ECM) fungi. A number of studies, however, have reported genetic changes in fungus cultures following cryopreservation. In the present study, the genetic stability of six ECM fungus isolates was analyzed using amplified fragment length polymorphism (AFLP). The isolates were preserved for 2 years either by cryopreservation (at -130 °C) or by storage at 4 °C with regular sub-cultivation. A third preservation treatment consisting of isolates maintained on Petri dishes at 22-23 °C for 2 years (i.e., without any sub-cultivation) was included and used as a control. The differences observed in AFLP patterns between the three preservation methods remained within the range of the total error generated by the AFLP procedure (6.85%). Therefore, cryopreservation at -130 °C and cold storage with regular sub-cultivation did not affect the genetic stability of the ECM fungus isolates, and both methods can be used for the routine storage of ECM fungus isolates over a period of 2 years.

Potential application of glycerol in the production of plant beneficial microorganisms

This review highlights the importance of research for development of biofertilizer and biocontrol products based on the use of glycerol for further process scale-up to industrial microbiology. Glycerol can be used successfully in all stages of production of plant beneficial microorganisms. It serves as an excellent substrate in both submerged and solid-state fermentation processes with free and immobilized microbial cells. Glycerol is also one of the most attractive formulation agents that ensures high cell density and viability including in harsh environmental conditions. Future research is discussed to make this inexpensive material a base for industrial production of plant beneficial microorganisms.

Arctic arbuscular mycorrhizal spore community and viability after storage in cold conditions

Arbuscular mycorrhizal fungi (AMF) form probably the most widespread symbiosis on earth and are found across all ecosystems including the Arctic regions. In the Arctic, the prevalent harsh cold conditions experienced by both host plants and fungi may have selected for AMF species with long-surviving spores, the principal means for dispersal and survival. However, basic knowledge about their viability is lacking. AMF spore assembly from two Arctic sites was examined in soil samples collected across an 11-year period and stored at -20 °C for up to 10 years. AMF spore viability and ability to colonize plants were investigated in the greenhouse using Plantago lanceolata. It was predicted that Arctic AMF spores would survive in cold conditions for several years, with an expected decrease in viability over time as suggested by other experiments with temperate material. Results show that even though the two study sites differed in AMF spore density, the relative abundance of spore morphotypes was rather similar across sites and years. Furthermore, spore viability over time was site-dependent as it decreased only in one site. Although spores were viable, only a very small proportion of hosts and roots became colonized in the greenhouse even 21 months after inoculation. Taken together, these results suggest a certain site-dependent variability in AMF spore communities and the ability of Arctic AMF spores to remain viable after a long-term storage in cold conditions. The lack of host colonization in the greenhouse may be related to the inability to overcome spore dormancy under these conditions.

Nutrients responses of Pleurotus ostreatus to slow frozen storage in the short term

This paper improves the understanding of changes happening with nutraceuticals in slow freezingPleurotus ostreatusduring short-term storage.