Nitrogen balance and supply in Australasian mushroom composts

Mushrooms are an important source of protein in the human diet. They are increasingly viewed as a sustainable meat replacement in an era of growing populations, with button mushrooms (Agaricus bisporus) the most popular and economically important mushroom in Europe, Australia and North America. Button mushrooms are cultivated on a defined, straw-derived compost, and the nitrogen (N) required to grow these high-protein foods is provided mainly by the addition of poultry manure and horse manure. Using the correct balance of carbon (C) and N sources to produce mushroom compost is critically important in achieving maximum mushroom yields. Changes in the amount and form of N added, the rate and timing of N addition and the other compost components used can dramatically change the proportion of added N recovered in the mushroom caps, the yield and quality of the mushrooms and the loss of N as ammonia and nitrogen oxide gases during composting. This review examines how N supply for mushroom production can be optimised by the use of a broad range of inorganic and organic N sources for mushroom composting, together with the use of recycled compost leachate, gypsum and protein-rich supplements. Integrating this knowledge into our current molecular understanding of mushroom compost biology will provide a pathway for the development of sustainable solutions in mushroom production that will contribute strongly to the circular economy. KEY POINTS: • Nitrogen for production of mushroom compost can be provided as a much wider range of organic feedstocks or inorganic compounds than currently used • Most of the nitrogen used in production of mushroom compost is not recovered as protein in the mushroom crop • The sustainability of mushroom cropping would be increased through alternative nitrogen management during composting and cropping.

Dynamics of microbial community and enzyme activities during preparation of Agaricus bisporus compost substrate

Button mushrooms (Agaricus bisporus) are grown commercially on a specialized substrate that is usually prepared from wheat straw and poultry manure in a microbially-mediated composting process. The quality and yield of the mushroom crop depends critically on the quality of this composted substrate, but details of the microbial community responsible for compost production have only emerged recently. Here we report a detailed study of microbial succession during mushroom compost production (wetting, thermophilic, pasteurization/conditioning, spawn run). The wetting and thermophilic phases were characterized by a rapid succession of bacterial and fungal communities, with maximum diversity at the high heat stage. Pasteurization/conditioning selected for a more stable community dominated by the thermophilic actinomycete Mycothermus thermophilus and a range of bacterial taxa including Pseudoxanthomonas taiwanensis and other Proteobacteria. These taxa decreased during spawn run and may be acting as a direct source of nutrition for the proliferating Agaricus mycelium, which has previously been shown to use microbial biomass in the compost for growth. Comparison of bacterial communities at five geographically separated composting yards in south-eastern Australia revealed similarities in microbial succession during composting, although the dominant bacterial taxa varied among sites. This suggests that specific microbial taxa or combinations of taxa may provide useful biomarkers of compost quality and may be applied as predictive markers of mushroom crop yield and quality.

[AORTOENTERIC FISTULA, A POOR PROGNOSIS FINDING]

We report the case of a patient admitted with upper gastrointestinal bleeding. The CT scan revealed an aorto-duodenal fistula. This case highlights the progression of radiological imaging in parallel with the clinical course. We take this opportunity to write a brief literature review mainly focused on the description and diagnostic modalities of aortoenteric fistulas.