Fungal and bacterial community composition and structure in fermented
‘hairy’ tofu (Mao tofu)
Abstract
The process of fermenting tofu extends thousands of years. Despite a
resurgent interest in microbial communities and fermented foods, little
knowledge exists concerning microbial diversity of communities of
fermented ‘hairy’ tofu known in China as Mao tofu. We used
high-throughput metagenomic sequencing of the ITS, LSU and 16S rDNA
marker genes to disentangle the Mao tofu fungal and bacterial community
composition and diversity across the four most important markets in the
Yunnan region of China. We show that hairy tofu in this region consists
of around 170 fungal and 365 bacterial taxa. Significant differences in
community structure were found between markets and niches. Machine
learning random forest models were able to accurately classify both
market and niche of sample origin. An over-abundance of yeast taxa were
detected, and Geotrichum were the most abundant fungal taxa, followed by
Torulaspora, Trichosporon, and Pichia. Mucor (Mucormycota) was also
abundant in the LSU data and especially in the outside niche (rind),
which consists of the visible ‘hairy’ mycelium. The majority of the
bacterial OTUs belonged to Proteobacteria, Firmicutes, and Bacteroidota,
with Acinetobacter, Lactobacillus, Sphingobacterium and Flavobacterium
the most abundant members. Of interest, putative fungal pathogens of
plants (e.g. Cercospora, Diaporthe, Fusarium) and animal (e.g.
Metarhizium, Entomomortierella, Pyxidiophora, Candida, Clavispora), as
well as bacterial (e.g. Legionella) pathogens, were detected. Non-target
eukaryotic taxa detected in by LSU amplicon sequencing included soybean
(Glycine max), Protozoa, Metazoa (e.g. Nematoda and Platyhelminthes),
Rhizaria and Chromista, providing evidence of additional biocomplexity
and diversity in the tofu microbiome.