Trans-ethnic gut microbial signatures of prediabetic subjects from India and Denmark
Authors: Pinna Nishal Kumar , Anjana Ranjit Mohan , Saxena Shruti , Dutta Anirban , Gnanaprakash Visvanathan , Rameshkumar Gnanavadivel , Aswath Sukumaran , Raghavan Srividhya , Rani Coimbatore Subramanian Shanthi , Radha Venkatesan , Balasubramanyam Muthuswamy , Pant Archana , Nielsen Trine , Jørgensen Torben , Færch Kristine , Kashani Alireza , Silva Maria Camila Alvarez , Vestergaard Henrik , Hansen Tue Haldor , Hansen Torben , Arumugam Manimozhiyan , Nair Gopinath Balakrish , Das Bhabatosh , Pedersen Oluf , Mohan Viswanathan , Mande Sharmila Shekhar 
Published: March 2021

Abstract
Background
Recent studies have indicated an association of gut microbiota and microbial metabolites with type 2 diabetes mellitus (T2D). However, large-scale investigation of the gut microbiota of “prediabetic” (PD) subjects has not been reported. Identifying robust gut microbiome signatures of prediabetes and characterizing early prediabetic stages is important for the understanding of disease development and could be crucial in early diagnosis and prevention.

Methods
The current study performed amplification and sequencing on the variable regions (V1–V5) of the 16S rRNA genes to profile and compare gut microbiota of prediabetic individuals (N = 262) with normoglycemic individuals (N = 275) from two cohorts in India and Denmark. Similarly, fasting serum inflammatory biomarkers were profiled from the study participants.

Results
After correcting for strong country-specific cohort effect, 16 operational taxonomic units (OTUs) including members from the genera Prevotella9, Phascolarctobacterium, Barnesiella, Flavonifractor, Tyzzerella_4, Bacteroides, Faecalibacterium, and Agathobacter were identified as enriched in normoglycaemic subjects with respect to the subjects with prediabetes using a negative binomial Wald test. We also identified 144 OTUs enriched in the prediabetic subjects, which included members from the genera Megasphaera, Streptococcus, Prevotella9, Alistipes, Mitsuokella, Escherichia/Shigella, Prevotella2, Vibrio, Lactobacillus, Alloprevotella, Rhodococcus, and Klebsiella. Comparative analyses of relative abundance of bacterial taxa revealed that the Streptococcus, Escherichia/Shigella, Prevotella2, Vibrio, and Alloprevotella OTUs exhibited more than fourfold enrichment in the gut microbiota of prediabetic subjects. When considering subjects from the two geographies separately, we were able to identify additional gut microbiome signatures of prediabetes. The study reports a probable association of Megasphaera OTU(s) with impaired glucose tolerance, which is significantly pronounced in Indian subjects. While the overall results confirm a state of proinflammation as early as in prediabetes, the Indian cohort exhibited a characteristic pattern of abundance of inflammatory markers indicating low-grade intestinal inflammation at an overall population level, irrespective of glycemic status.

Conclusions
The results present trans-ethnic gut microbiome and inflammation signatures associated with prediabetes, in Indian and Danish populations. The identified associations may be explored further as potential early indicators for individuals at risk of dysglycemia.