Cultivating Lentinula edodes on Substrate Containing Composted Sawdust Affects the Expression of Carbohydrate and Aromatic Amino Acid Metabolism-Related Genes

Cysteine and thiosulfate promoted cadmium immobilization in strain G303 by the formation of extracellular CdS

Bacteria have evolved a variety of strategies to defend themselves against cadmium toxicity, however, the specific mechanisms involved in the enhancement of bacterial cadmium resistance by sulfur sources are unclear. In this study, a novel cadmium (Cd)-tolerant bacterium, Stenotrophomonas geniculata G303, was isolated from activated sludge. The growth of strain G303 under diverse Cd concentrations was investigated, and the minimum inhibitory concentration of Cd was found to be 1 mM. Strain G303 effectively remove 94.7 % of Cd after 96 h of culture. Extracellular CdS was detected using multiple methods, with the CdS formed being aggregated in the biofilm. The addition of cysteine and thiosulfate to the medium significantly enhanced the Cd resistance and removal capacity of strain G303. Integrated genomic and proteomic analyses revealed that heavy metal transporters cooperate to resist Cd stress. Cysteine and thiosulfate improved Cd tolerance in strain G303 by upregulating nitrogen and energy metabolism. Proteins associated with nitrate reduction likely played a pivotal role in cysteine and thiosulfate metabolism. Notably, cysteine synthase and the SUF system played crucial roles in CdS formation. This study systematically explored the impact of cysteine and thiosulfate on the Cd resistance of strain G303, deepening our understanding of the microbial response mechanism to heavy metals.

Effects of Different Nitrogen Levels on Lignocellulolytic Enzyme Production and Gene Expression under Straw-State Cultivation in Stropharia rugosoannulata

Stropharia rugosoannulata has been used in environmental engineering to degrade straw in China. The nitrogen and carbon metabolisms are the most important factors affecting mushroom growth, and the aim of this study was to understand the effects of different nitrogen levels on carbon metabolism in S. rugosoannulata using transcriptome analysis. The mycelia were highly branched and elongated rapidly in A3 (1.37% nitrogen). GO and KEGG enrichment analyses revealed that the differentially expressed genes (DEGs) were mainly involved in starch and sucrose metabolism; nitrogen metabolism; glycine, serine and threonine metabolism; the MAPK signaling pathway; hydrolase activity on glycosyl bonds; and hemicellulose metabolic processes. The activities of nitrogen metabolic enzymes were highest in A1 (0.39% nitrogen) during the three nitrogen levels (A1, A2 and A3). However, the activities of cellulose enzymes were highest in A3, while the hemicellulase xylanase activity was highest in A1. The DEGs associated with CAZymes, starch and sucrose metabolism and the MAPK signaling pathway were also most highly expressed in A3. These results suggested that increased nitrogen levels can upregulate carbon metabolism in S. rugosoannulata. This study could increase knowledge of the lignocellulose bioconversion pathways and improve biodegradation efficiency in Basidiomycetes.

A Comparative Analysis of Biodegradation and Bioconversion of Lentinula edodes and Other Exotic Mushrooms

Mushrooms are capable of bioconverting organic residues into food. Understanding the relationship between high-quality yields and substrate biomass from these residues is critical for mushroom farms when choosing new strains. The objective of this exploratory study was, therefore, to analyze whether exotic mushrooms, namely, Pleurotus eryngii, Flammulina velutipes, and Agrocybe aegerita, could biologically convert the substrate into edible mushrooms as effectively as Lentinula edodes (baseline). Five experiments were carried out. Biological efficiency, biodegradability coefficient, mass balance and chemical characterization of the substrate were evaluated. Strategically hydrating the sawdust enabled L. edodes to achieve the greatest biodegradability and biological efficiency of 0.5 and 94.2 kg dt−1, respectively. The values for L. edodes on wheat straw without hydration were 0.2 and 68.8 kg dt−1, respectively. From 1000 kg of fresh substrate, P. eryngii produced 150.1 kg of edible mushrooms, making it technically competitive with L. edodes on wheat straw (195.9 kg). Hence, P. eryngii was the most reliable option for scaling among the exotic mushrooms. The analytical insights from our study provide further knowledge to advance the field’s prominence in high-throughput mushroom-producing systems, particularly for exotic mushrooms.