Carbohydrate utilization and metabolism is highly differentiated in Agaricus bisporus

Abstract

BackgroundAgaricus bisporus is commercially grown on compost, in which the available carbon sources consist mainly of plant-derived polysaccharides that are built out of various different constituent monosaccharides. The major constituent monosaccharides of these polysaccharides are glucose, xylose, and arabinose, while smaller amounts of galactose, glucuronic acid, rhamnose and mannose are also present.ResultsIn this study, genes encoding putative enzymes from carbon metabolism were identified and their expression was studied in different growth stages of A. bisporus. We correlated the expression of genes encoding plant and fungal polysaccharide modifying enzymes identified in the A. bisporus genome to the soluble carbohydrates and the composition of mycelium grown compost, casing layer and fruiting bodies.ConclusionsThe compost grown vegetative mycelium of A. bisporus consumes a wide variety of monosaccharides. However, in fruiting bodies only hexose catabolism occurs, and no accumulation of other sugars was observed. This suggests that only hexoses or their conversion products are transported from the vegetative mycelium to the fruiting body, while the other sugars likely provide energy for growth and maintenance of the vegetative mycelium. Clear correlations were found between expression of the genes and composition of carbohydrates. Genes encoding plant cell wall polysaccharide degrading enzymes were mainly expressed in compost-grown mycelium, and largely absent in fruiting bodies. In contrast, genes encoding fungal cell wall polysaccharide modifying enzymes were expressed in both fruiting bodies and vegetative mycelium, but different gene sets were expressed in these samples.

Accumulation of recalcitrant xylan in mushroom-compost is due to a lack of xylan substituent removing enzyme activities of Agaricus bisporus

“…As expected, a decrease in total carbohydrate content (30% w/w based on dry matter (DM)), both xylan (40% w/w) and glucan (23% w/w), was observed in compost from Filling to 2 nd flush, indicating that carbohydrates were metabolized during the fruiting of A. bisporus. These results were in agreement with gene expression levels of A. bisporus during fruiting body formation showing that both the hexose and pentose catabolic pathway were upregulated (Patyshakuliyeva et al, 2013). Previously, it was reported that if compost of PII was compared with 1 st flush of mushrooms, which also includes carbohydrate consumption during mycelium growth (16 days (PIII)), a decrease of 50% (w/w DM) of carbohydrates was reported (Iiyama et al, 1994).…”

“…Apparently, A. bisporus did not degrade these remaining substituted xylan fragments. That conclusion was supported by the result that the two genes annotated as putative ␣-glucuronidases (both GH115, Patyshakuliyeva et al, 2013Patyshakuliyeva et al, , 2015 were not expressed in the same compost samples as used to analyze the resistant substituted xylans. In addition, A. bisporus genes from family GH43 were assessed for similarity to two genes known to encode biochemically characterized AXH-d3 activity featuring the release of arabinose from xylosyl residues doubly substituted with arabinosyl residues.…”

“…The A. bisporus genome contains two genes from family GH115, which are expected to encode ␣-glucuronidases able to remove (4-O-methyl-)glucuronic acid from xylans (Patyshakuliyeva et al, 2013)). However, expression analysis demonstrated no-to verylow expression of these genes (Fig.…”

“…The WSS constituted mainly of glucosyl 20-33 mol%), mannosyl (18-25 mol%) and xylosyl (12-19 mol%) residues. High mannose content is expected to originate from mannitol produced by A. bisporus mycelium (Patyshakuliyeva et al, 2013). The 1 M and 4 M KOHss were enriched in xylosyl (Xyl) residues, 60-74 mol% and 40-55 mol%, respectively, next to 7-10 mol% arabinosyl (Ara) and 7-11 mol% uronyl (UA) residues.…”

“…Genes encoding for (putative) enzymes from the carbon metabolism of A. bisporus were recently identified. It was shown that in compost during 1 st flush, A. bisporus mycelium expresses a variety of genes known to be involved in the degradation of both xylan and cellulose (Patyshakuliyeva et al, 2013). However, the expression of genes encoding for (putative) enzymes degrading xylan substituents was not analyzed in detail, and only analyzed for the compost obtained at 1 st flush.…”