Dynamic succession of microbial compost communities and functions during Pleurotus ostreatus mushroom cropping on a short composting substrate

Antifungal, growth-promoting, and lignocellulose degrading-bacteria from compost and casing soil of button mushroom (Agaricus bisporus)

Eleven dominant mesophilic and thermophilic bacteria were identified from the phase-1 compost and casing of button mushroom (Agaricus bisporus). During phase 1 (at 45-48 °C), Bacillus subtilis (BSB1, BSB3, BSB5, and BSB13), Paenibacillus polymyxa (PPB6), Bacillus sp. (BB7), B. cereus (BCB8 and BCB12), and Acinetobacter johnsonii (AJB15/B) were identified as useful bacterial species by 16S rRNA sequencing. Whereas, in casing soil (at 22-25 °C) Alcaligenes faecalis (AFB11) and Pseudomonas aeruginosa (PAB16/P) were identified as useful mesophiles. PAB16/P showed the strongest antagonistic activities against M. perniciosa (wet bubble disease) with the highest mycelial growth inhibition (91.89%), followed by BB-7 (76.39%). The other isolates, BSB1, BSB3, BSB5, PPB6, BCB8, and BSB13, also inhibited the growth of M. perniciosa by 61.11 to 72.55%. The degradation of wheat straw via six microbe complexes (MC-1 to MC-6) was monitored based on CO2 release. The highest CO2 release (174666.70 ppm) was recorded in MC-3 (a combination of PAB16/P, AJB15/B, AFB11, and BSB5) compared with the lowest in control (43166.60 ppm). Compost inoculated with MC-3 produced the highest crop yield (16.20 kg/100 kg substrate) whereas lowest in control (12.84 kg/100 kg substrate). MC-3 may be recommended for button mushroom compost, to manage wet bubble disease and increase crop yield.

The Mechanism of Ammonia-Assimilating Bacteria Promoting the Growth of Oyster Mushrooms (Pleurotus ostreatus)

Oyster mushrooms (Pleurotus ostreatus) are one of the most commonly grown edible mushrooms using compost, which contains high concentrations of ammonia. In this study, inoculation of the oyster mushroom culture substrate with ammonia-assimilating bacterium Enterobacter sp. B12, either before or after composting, reduced the ammonia nitrogen content, increased the total nitrogen content of the compost, and enhanced the mushroom yield. Co-cultivation with P. ostreatus mycelia on potato dextrose agar (PDA) plates containing 200 mM NH4+, B12 reduced reactive oxygen species (ROS) accumulation in the mycelia and downregulated the expression of the ROS-generating enzymes NADPH oxidase A (NOXA) and the stress hormone ethylene synthase 1-aminocyclopropane-1-carboxylate oxidase (ACO). It also downregulated the expression of the ammonia-assimilating related genes in the mycelia, such as glutamate dehydrogenase (GDH), glutamate synthase (GOGAT), glutamine synthetase (GS), ammonia transporter protein (AMT), and amino acid transporter protein (AAT), while upregulating its own ammonia-assimilation genes. These findings suggest that the mechanism by which B12 promoted oyster mushroom growth was that B12 assimilated ammonia, alleviated ammonia stress, mitigated ROS accumulation in the mycelia, and supplied ammonia and amino acids to the mycelia. To our knowledge, ammonia-assimilating bacteria are a novel type of mushroom growth promoter (MGP).

Ammonia-Assimilating Bacteria Promote Wheat (Triticum aestivum) Growth and Nitrogen Utilization

Nitrogen fertilizers in agriculture often suffer losses. Ammonia-assimilating bacteria can immobilize ammonia and reduce these losses, but they have not been used in agriculture. This study identified an ammonia-assimilating strain, Enterobacter sp. B12, which assimilated ammonia via the glutamate dehydrogenase (GDH) pathway at low levels (5 mM) and the glutamine synthetase (GS)-glutamine-2-oxoglutarate aminotransferase (GOGAT) pathway at high levels (10 mM). Inoculating wheat with B12 increased seedling dry weight, nitrogen accumulation, rhizosphere soil nitrogen content, and root enzyme activities, including GDH, superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD), under both conditions. However, root GS, GOGAT enzyme activities, and ammonia assimilation-related gene expressions were lower than the controls. The results suggest that the ammonia-assimilating bacterium promotes wheat growth, nitrogen accumulation, and soil nitrogen immobilization by establishing an ammonia and amino acid exchange with roots and enhancing root antioxidant capacity, making it a potential plant growth-promoting rhizobacteria (PGPR).

Multi-metal tolerant Porostereum umbrinoalutaceum isolated from Pleurotus ostreatus fruit body showing root colonization, growth promotion of chilli (Capsicum annuum L.) plant and antagonism against fungal pathogens

Mushroom associated microbes could be utilized to improve crop productivity providing nutrients, plant growth promoting substances, production of hydrolytic enzymes and protecting plant from biotic and abiotic stress. An endophyte designated as KUFC101 was isolated from fruit body of Pleurotus ostreatus and identified as Porostereum umbrinoalutaceum based on nuclear-rRNA gene sequence analysis. Growth in different culture media, metal tolerance, biochemical characterization and effect on chilli plant growth promotion were studied. The isolate showed best growth in Malt extract medium and least growth in synthetic media. It could tolerate toxic metals (Mg, Ca, Fe, Cu, Mn, Zn and Cd each at 100 ppm concentration). It produced amylase, cellulase, chitinase, pectinase, catecholate type of siderophore and indole acetic acid, and inhibited growth of Alternaria solani and Penicillium citrinum. It could colonize in the rhizosphere of chilli plant and influence growth of chilli plant by improving biomass and metabolite content. Porostereum umbrinoalutaceum KUFC101 could be utilized in formulation of biofertiliser under sustainable agricultural system.

Microbial Inoculation during the Short-Term Composting Process Enhances the Nutritional and Functional Properties of Oyster Mushrooms (Pleurotus ostreatus)

In recent years, short-term composting techniques have been widely applied in oyster mushroom cultivation, but there is still a lack of systematic research on their impact on the nutritional and functional properties of fruiting bodies. In this study, the microbial inoculant Streptomyces thermoviolaceus BUA-FM01 (ST) was applied in the short-term composting process for oyster mushroom cultivation. The agronomic traits, nutritional composition, flavor compounds, and antioxidant activity of fruiting bodies from the first three flushes were evaluated. The results show that microbial inoculation significantly (p < 0.05) reduced the total carbon content and C/N ratio of the composted substrates and, furthermore, increased the total yield of the fruiting bodies. Moreover, microbial inoculation significantly (p < 0.05) increased the crude protein, crude polysaccharide, total amino acid, and essential amino acid contents of the fruiting bodies. The fruiting bodies of the first flush of ST treatment possessed the highest umami amino acid content and equivalent umami concentration value. Furthermore, microbial inoculation significantly (p < 0.05) enhanced the scavenging ability of crude polysaccharides toward free radicals. The results indicate that microbial inoculation has many benefits for the composting cultivating process of oyster mushrooms and good application prospects.

Bacterial communities during composting cultivation of oyster mushroom Pleurotus floridanus using broken eggs as the nitrogen source and study of agronomic and nutritional properties

Introduction

Broken eggs are a byproduct of the poultry industry and a potential nitrogen source for mushroom cultivation. However, its feasibility needs to be evaluated experimentally.

Methods

In this study, a series of different addition amounts (0, 1.8, 3.6, 5.3 and 8.5%, w/w) of broken egg mixture (BEM) were applied in the composting cultivation process of oyster mushroom. The physicochemical properties and bacterial communities of composting substrate, and agronomic and nutritional properties of fruiting bodies were determined.

Results and discussion

The results showed that the BEM addition significantly (P < 0.05) increased the total nitrogen content in the composted substrate, and the contents of crude protein, total amino acids and essential amino acids of mushrooms. The P3 treatment (initial C/N of 26:1) showed the highest biological efficiency (BE) of 100.19% and a low contamination rate (CR) of 7.00%, while the higher dosage of BEM (P4 and P5) led to a sharp decrease in BE and a sharp increase in CR. High throughput sequencing revealed that the addition of BEM significantly (P < 0.05) changed the bacterial communities in the substrate at the beginning of composting. Streptococcus and Lactococcus were predominant bacterial genera in BEM treatments at the beginning stage of composting, while Acinetobacter became predominant at the ending stage. The co-occurrence network analysis showed that the P3 treatment demonstrated a much more complex bacterial community. The structural equation model analysis indicated that the addition of BEM affected the bacterial communities and nitrogen metabolism during composting, which further affected agronomic and nutritional properties of oyster mushrooms. An appropriate amount of BEM combined with composting processes can significantly improve the yield and quality of oyster mushroom, providing a new way for efficient utilization of BEM.