Geomycology

Improving the nutritional value and digestibility of wheat straw, rice straw, and corn cob through solid state fermentation using different Pleurotus species

BACKGROUND

The growing food-feed-fuel competition, declining availability of traditional feeds, higher prices, and the urgent need to provide long-term sustainability for animal production have all triggered global research into the optimum extraction of energy and nutrients from lignin-rich plant biomass. Recent studies have shown that the Pleurotus species of white rot fungus can selectively degrade lignin in lignin-rich plant biomass; however, its effectiveness in selectively degrading lignin depends on the type of substrate and species of fungus. This study was therefore designed to treat wheat straw, rice straw, and corn cob, with Pleurotus eryngii, P. ostreatus, and P. florida for 30 days under solid-state fermentation, to identify a promising fungus-substrate combination for the selective degradation of lignin and optimal improvement in the nutritional value and digestibility of each substrate.

RESULTS

The type of fungus strongly influenced (P < 0.01) selectivity in lignin degradation, and the level of improvement in crude protein (CP), in vitro dry matter digestibility (IVDMD), and in vitro gas production (IVGP), in wheat straw, rice straw, and corn cob. Fungus-substrate interaction data revealed that P. ostreatus caused maximum (P < 0.05) degradation of lignin, and greater (P < 0.05) improvement in CP, IVDMD, and IVGP in wheat straw and rice straw. The lowest (P < 0.05) degradation of lignin and improvement in CP, IVDMD, and IVGP was caused by P. eryngii in corn cob. Among the fungi, the maximum (P < 0.05) degradation of lignin, and greater (P < 0.05) improvement in CP, IVDMD, and IVGP were caused by P. florida as compared with those of P. ostreatus and P. eryngii.

CONCLUSION

The results highlight significant influence of fungus-substrate combination for selective lignin degradability and the consequent improvement in the nutritional value of the substrates. Maximum selective lignin degradability and improvement in nutritional value and digestibility was caused by P. ostreatus in wheat straw and in rice straw, and by P. florida in corn cob. © 2021 Society of Chemical Industry.

Unveiling microbial preservation under hyperacidic and oxidizing conditions in the Oligocene Rio Tinto deposit

The preservation of biosignatures on Mars is largely associated with extensive deposits of clays formed under mild early Noachian conditions (> 3.9 Ga). They were followed by widespread precipitation of acidic sulfates considered adverse for biomolecule preservation. In this paper, an exhaustive mass spectrometry investigation of ferric subsurface materials in the Rio Tinto gossan deposit (~ 25 Ma) provides evidence of well-preserved molecular biosignatures under oxidative and acidic conditions. Time of flight secondary ion mass spectrometry (ToF–SIMS) analysis shows a direct association between physical-templating biological structures and molecular biosignatures. This relation implies that the quality of molecular preservation is exceptional and provides information on microbial life formerly operating in the shallow regions of the Rio Tinto subsurface. Consequently, low-pH oxidative environments on Mars could also record molecular information about ancient life in the same way as the Noachian clay-rich deposits.

Microbial biofilm community structure and composition on the lithic substrates of Herculaneum Suburban Baths

In this work, we want to investigate the impact of different substrates and different environmental condition on the biofilm communities growing on plaster, marble, and mortar substrates inside the Herculaneum Suburban Baths. To do so, we measured environmental conditions and sampled biofilm communities along the walls of the baths and used culture-dependent and -independent molecular techniques (DGGE) to identify the species at each sampling sites. We used the species pool to infer structure and richness of communities within each site in each substrate, and confocal light scanning microscopy to assess the three-dimensional structure of the sampled biofilms. To gather further insights, we built a meta-community network and used its local realizations to analyze co-occurrence patterns of species. We found that light is a limiting factor in the baths environment, that moving along sites equals moving along an irradiation gradient, and that such gradient shapes the community structure, de facto separating a dark community, rich in Bacteria, Fungi and cyanobacteria, from two dim communities, rich in Chlorophyta. Almost all sites are dominated by photoautotrophs, with Fungi and Bacteria relegated to the role of rare species., and structural properties of biofilms are not consistent within the same substrate. We conclude that the Herculaneum suburban baths are an environment-shaped community, where one dark community (plaster) and one dim community (mortar) provides species to a “midway” community (marble).

Fungal Bioweathering of Mimetite and a General Geomycological Model for Lead Apatite Mineral Biotransformations

Fungi play important roles in biogeochemical processes such as organic matter decomposition, bioweathering of minerals and rocks, and metal transformations and therefore influence elemental cycles for essential and potentially toxic elements, e.g., P, S, Pb, and As. Arsenic is a potentially toxic metalloid for most organisms and naturally occurs in trace quantities in soil, rocks, water, air, and living organisms. Among more than 300 arsenic minerals occurring in nature, mimetite [Pb5(AsO4)3Cl] is the most stable lead arsenate and holds considerable promise in metal stabilization for in situ and ex situ sequestration and remediation through precipitation, as do other insoluble lead apatites, such as pyromorphite [Pb5(PO4)3Cl] and vanadinite [Pb5(VO4)3Cl]. Despite the insolubility of mimetite, the organic acid-producing soil fungus Aspergillus niger was able to solubilize mimetite with simultaneous precipitation of lead oxalate as a new mycogenic biomineral. Since fungal biotransformation of both pyromorphite and vanadinite has been previously documented, a new biogeochemical model for the biogenic transformation of lead apatites (mimetite, pyromorphite, and vanadinite) by fungi is hypothesized in this study by application of geochemical modeling together with experimental data. The models closely agreed with experimental data and provided accurate simulation of As and Pb complexation and biomineral formation dependent on, e.g., pH, cation-anion composition, and concentration. A general pattern for fungal biotransformation of lead apatite minerals is proposed, proving new understanding of ecological implications of the biogeochemical cycling of component elements as well as industrial applications in metal stabilization, bioremediation, and biorecovery.

Adaptation and interaction of saxicolous crustose lichens with metals

One of the most successful mechanisms enabling fungi to survive in extreme subaerial environments is by formation of mutualistic symbioses with algae and/or cyanobacteria as lichens. Collections, field and mineral weathering studies and developments in modern instrumental and analytical techniques have considerably advanced knowledge in understanding tolerance mechanisms to stress, environmental adaptation, species concepts and evolutionary processes in lichens colonising metalliferous habitats. This review focuses on the predominantly saxicolous, crustose, taxonomically notoriously challenging Acarospora sens. lat. Pioneering studies investigating element and substance localization in Acarospora sens. lat. in different geological terrains led to the discovery of novel fixation mechanisms, new minerals and substances associated with lichens, and new taxa and evolutionary lineages. Acarospora sens. lat. are generally under-represented in collections. Systematic sampling of Acarospora sens. lat. and other saxicolous lichens, in different mineralogical environments is now required, a priority being those occurring in extreme habitats at risk from climatic and other environmental changes. The potential for the discovery of new lichen and mineral species associated with Acarospora and other saxicolous crustose lichens, is high. These may represent special mechanisms to tolerate metal toxicity and other forms of environmental stress, including photoprotection.

Transformation of vanadinite [Pb5 (VO4 )3 Cl] by fungi

Saprotrophic fungi were investigated for their bioweathering effects on the vanadium- and lead-containing insoluble apatite group mineral, vanadinite [Pb5 (VO4 )3 Cl]. Despite the insolubility of vanadinite, fungi exerted both biochemical and biophysical effects on the mineral including etching, penetration and formation of new biominerals. Lead oxalate was precipitated by Aspergillus niger during bioleaching of natural and synthetic vanadinite. Some calcium oxalate monohydrate (whewellite) was formed with natural vanadinite because of the presence of associated ankerite [Ca(Fe(2+) ,Mg)(CO3 )2 ]. Aspergillus niger also precipitated lead oxalate during growth in the presence of lead carbonate, vanadium(V) oxide and ammonium metavanadate, while abiotic tests confirmed the efficacy of oxalic acid in solubilizing vanadinite and precipitating lead as oxalate. Geochemical modelling confirmed the complexity of vanadium speciation, and the significant effect of oxalate. Oxalate-vanadium complexes markedly reduced the vanadinite stability field, with cationic lead(II) and lead oxalate also occurring. In all treatments and geochemical simulations, no other lead vanadate, or vanadium minerals were detected. This research highlights the importance of oxalate in vanadinite bioweathering and suggests a general fungal transformation of lead-containing apatite group minerals (e.g. vanadinite, pyromorphite, mimetite) by this mechanism. The findings are also relevant to remedial treatments for lead/vanadium contamination, and novel approaches for vanadium recovery.

Geomycology: metals, actinides and biominerals

Geomycology can be simply defined as 'the scientific study of the roles of fungi in processes of fundamental importance to geology' and the biogeochemical importance of fungi is significant in several key areas. These include nutrient and element cycling, rock and mineral transformations, bioweathering, mycogenic biomineral formation and interactions of fungi with clay minerals and metals. Such processes can occur in aquatic and terrestrial habitats, but it is in the terrestrial environment where fungi probably have the greatest geochemical influence. Of special significance are the mutualistic relationships with phototrophic organisms, lichens (algae, cyanobacteria) and mycorrhizas (plants). Central to many geomycological processes are transformations of metals and minerals, and fungi possess a variety of properties that can effect changes in metal speciation, toxicity and mobility, as well as mineral formation or mineral dissolution or deterioration. Some fungal transformations have beneficial applications in environmental biotechnology, e.g. in metal and radionuclide leaching, recovery, detoxification and bioremediation, and in the production or deposition of biominerals or metallic elements with catalytic or other properties. Metal and mineral transformations may also result in adverse effects when these processes result in spoilage and destruction of natural and synthetic materials, rock and mineral-based building materials (e.g. concrete), acid mine drainage and associated metal pollution, biocorrosion of metals, alloys and related substances, and adverse effects on radionuclide speciation, mobility and containment. The ubiquity and importance of fungi in biosphere processes underlines the importance of geomycology as an interdisciplinary subject area within microbiology and mycology.

Biotransformation of manganese oxides by fungi: solubilization and production of manganese oxalate biominerals

The ability of the soil fungi Aspergillus niger and Serpula himantioides to tolerate and solubilize manganese oxides, including a fungal-produced manganese oxide and birnessite, was investigated. Aspergillus niger and S. himantioides were capable of solubilizing all the insoluble oxides when incorporated into solid medium: MnO(2) and Mn(2) O(3) , mycogenic manganese oxide (MnO(x) ) and birnessite [(Na(0.3) Ca(0.1) K(0.1) )(Mn(4+) ,Mn(3+) )(2) O(4) ·1.5H(2) O]. Manganese oxides were of low toxicity and A. niger and S. himantioides were able to grow on 0.5% (w/v) of all the test compounds, with accompanying acidification of the media. Precipitation of insoluble manganese and calcium oxalate occurred under colonies growing on agar amended with all the test manganese oxides after growth of A. niger and S. himantioides at 25°C. The formation of manganese oxalate trihydrate was detected after growth of S. himantioides with birnessite which subsequently was transformed to manganese oxalate dihydrate. Our results represent a novel addition to our knowledge of the biogeochemical cycle of manganese, and the roles of fungi in effecting transformations of insoluble metal-containing compounds in the environment.