TABLE 2.

Animal studies assessing the association between vitamin B-12 and the gut microbiome¹

First author, year (ref)	Animal model	n	B12 intervention or exposure	Specimen	DNA extraction	Sequencing	Multiple comparison method
Murine models
Kelly, 2019 (25)	C57BL/6 mice age 8–16 wk	24 (n = 12 baseline, n = 12 endline)	2 groups receiving CC in drinking water (3.94 μg/mL) for 16 d or a control group	Fecal pellets and cecum contents	Power Fecal DNA Isolation Kit (MO BIO Laboratories)	V3–V4 16S rRNA region, Illumina MiSeq platform	Tukey's and Dunnett's multiple comparison test and Bonferroni correction
Lurz, 2020 (27)	C57BL/6 mice age 3 wk, with induced acute colitis [via 5% (wt:vol) DSS] after day 28	24	3 noncolitis groups receiving the following diets for 28 d: deficient (0 mg/kg), medium (50 mg/kg), or high (200 mg/kg) dose of CC	Fecal pellets	FastDNA spin kit for soil (MP Biomedicals)	V3 16S rRNA region, Ilumina MiSeq platform	FDR
Park, 2019 (28)	Male Sprague Dawley rats, with amyloid-β infused in hippocampus, a cannula inserted in hippocampus, being fed a high-fat diet	50	5 groups receiving the following diets for 8 wk: control diet (25 μg/kg B12 and 2.5 mg/kg folate), B12 deficient (2.5 mg/kg folate), folate deficient (25 μg/kg B12), folate and B12 and folate deficient (no supplementation), sham operated on the control diet	Fecal pellets	Power Water DNA Isolation Kit (Qiagen)	Metagenome, Illumina MiSeq platform	Tukey's multiple comparison test
Siddharth, 2017 (29)	Wistar rats, 8–24 mo old: 8 mo (adults), 18 mo (pre-sarcopenic), and 24 mo (sarcopenic)	30	Serum B12 concentrations	Fecal pellets	PowerMag DNA extraction kit (MO BIO)	V4–V6 rRNA region, Illumina MiSeq platform	FDR
Zhu, 2019 (26)	Male C57BL/6 mice (10 wk old) with and without induced acute colitis [via 5% (wt:vol) DSS]	36 without colitis (n = 6 per group)	3 noncolitis groups receiving the following in drinking water for 3 d: CC (1.25 mg/L), MC (1.25 mg/L), control (no supplementation)	Feces washed out from colon with saline	MicroElute Genomic DNA kit (Omega Bio-tek, Inc.)	V3–V4 16S rRNA region, Illumina MiSeq	Duncan's multiple range test
Non–murine models
Cheng, 2018 (30)	Wulong geese, 1-day-old	72 (n = 2 per replicate, 6 replicates)	2 × 3 factorial design with groups receiving either low (0.55 mg/kg) or high (2.50 mg/kg) dose of folic acid, and either low (0.009 mg/kg), medium (0.018 mg/kg), or high (0.036 mg/kg) dose of B12 added to feed for 4 wk	Cecum contents	Genomic DNA kit (Tiangen Biochemical Technology Co., Ltd.)	V3–V4 16S rRNA region, PCR	Not specified
Long, 2018 (31)	Wulong geese, 4 weeks old	72 (n = 2 per replicate, 6 replicates)	6 groups receiving the following doses of B12 for 11 wk: 1) 0.000 mg/kg, 2) 0.005 mg/kg, 3) 0.010 mg/kg, 4) 0.015 mg/kg, 5) 0.020 mg/kg, 6) 0.025 mg/kg	Cecum contents	Genomic DNA kit (Tiangen Biochemical Technology Co., Ltd.)	V3–V4 16S rRNA region, PCR	Not specified
Duan, 2021 (32)	Healthy Litopenaeus vannamei (Pacific white shrimp); 4 groups receiving various stress tests (i.e., thermal stress, ammonia stress, ammonia and thermal stress)	200	Methylmalonic acid concentrations in hemolymph (i.e., invertebrate equivalent of blood)	Intestines without feces	TAB/SDS method	V4 16S rRNA region, PCR	Tukey's multiple comparison test

¹B12, vitamin B-12; CC, cyanocobalamin; DSS, dextran sulfate soldium; FDR, false discovery rate; MC, methylcobalamin; ref, reference; rRNA, ribosomal RNA; TAB/SDS, trimethyl ammonium bromide/sodium dodecyl sulphate; V, hypervariable region.