Discoveries in non-symbiotic environments: Dynamic changes and potential contributions of arbuscular mycorrhizal fungi in cigar tobacco fermentation

Arbuscular mycorrhizal fungi (AMF) are key species in plant-microbe interactions, and this study is the first to suggest their dynamic survival in the fermentation system of cigar tobacco. To explore the functional significance of AMF in cigar tobacco fermentation, this study focused on the Yunxue variety of cigar tobacco. We combined multi-time point sampling over a 35-day fermentation process and used Internal Transcribed Spacer (ITS) gene high-throughput sequencing to analyze the AMF community structure in the fermenting material. Diversity indices, species correlation networks, and Mantel tests were employed to explore the relationship between AMF and chemical components. The results showed a significant dynamic succession in AMF OTUs within the fermenting material throughout the fermentation process, identifying 22 species (comprising 524 OTUs), with <i>Paraglomus</i> being the predominant species. Core functional flora included OTU217 and OTU88, whose abundance variations aligned with the generation of volatile flavor compounds. AMF diversity peaked during the mid-fermentation stage and exhibited a negative correlation with total nitrogen, total sulfur, and reducing sugars, indicating that sugar and nitrogen metabolism were driving factors in the reorganization of the AMF community. The observations suggest that us to propose that <i>Glomus</i>-group-B-<i>Glomus-lamellosu</i>-VTX00193 may have a marked increase in abundance towards the end of fermentation, suggesting its crucial role in the degradation of complex organic compounds. Analysis specific to different tobacco varieties revealed a significant increase in the number of OTUs unique to Yunxue 6, with fluctuations in total acidity content significantly associated with changes in AMF abundance. The findings suggest a the regulatory role of AMF in modulating the chemical composition of cigar tobacco leaves through carbon and nitrogen metabolism, with <i>Paraglomu</i>s and <i>Glomus</i> identified as core functional funga. These results suggests the importance of further research on confirmation of AMF, if any, in the tobacco fermenting process.