Effects of microbial diversity on nitrite concentration in pao cai, a naturally fermented cabbage product from China

Pao cai is a spontaneously fermented cabbage where native bacteria may have an important influence on nitrite content during fermentation. In this research, we used metagenomic-based 16S rRNA gene amplicon sequencing to analyze differences in bacterial composition of pao cai from Hohhot City (northern China) and Guiyang City (southern China). Alongside this, metagenome functional features from the 16S rRNA genes of the microbiome were predicted and correlated with the nitrite content of pao cai. Nitrite-reducing bacterial genera were identified including Lactobacillus (73.37%), Pediococcus (0.93%), Acinetobacter (0.74%), Leuconostoc (0.31%), Weissella (0.14%), Streptococcus (0.09%), Megamonas (0.08%), Enterococcus (0.07%), and Alistipes (0.06%). Lactobacillus was the predominant genus in both the northern and the southern pao cai samples and was significantly negatively correlated with nitrite content; it was more abundant in southern samples than northern samples. Based on determination of alpha and beta diversities of the microbiome in samples, differences in the microbiome of northern and southern pao cai were demonstrated that may influence nitrogen metabolism. This research suggests that 16S rRNA gene amplicon sequencing is an effective way to comprehensively study the microbes with potential nitrite formation or decomposition ability instead of investigating the individual bacterial genera.