Table 2.
Longitudinal studies examining effects of military-relevant stressors on human gut microbiota composition and metabolites.
| Reference | Design | Microbiota method | Results- Microbiota | Results- Microbiota metabolites |
|---|---|---|---|---|
| Military training | ||||
| Karl et al., 2017a | n = 26M; Norwegian soldiers before and after 4-day arctic military training | 16S rRNA gene sequencing | Changes in relative abundance of 58% of genera (e.g., ↑Peptostreptococcus. Christensenella, Staphylococcus, Bulleidia, Peptoniphilus, Acidaminococcus, Fusobacterium; ↓Faecalibacterium, Roseburia, Bacteroides, Collinsella) ↑Diversity due to increased abundance of less dominant taxa | Fecal metabolome: Changes in microbiota linked to changes in 69 metabolites affected by training; e.g., ↓secondary bile acids, amino acid fermentation metabolites; ↑p-cresol |
| Plasma metabolome:Changes in microbiota linked to changes in 30 metabolites affected by training; e.g., ↑amino acid fermentation metabolites; ↓benzoate metabolites; ↑↓secondary bile acids | ||||
| Psychological stress | ||||
| Knowles et al., 2008 | n = 23 (7M); measured before and during exams | Targeted; culture | ↓Lactic acid bacteria post-exam | NA |
| Kato-Kataoka et al., 2016 | n = 46 (25M); measured before and during medical exams, randomized to placebo or probiotic | 16S rRNA gene sequencing | No reported effects of stress | NA |
| Circadian disruption/Sleep restriction | ||||
| Benedict et al., 2016 | n = 9M; 2 nights 4.25 h SO vs. 2 nights 8.5 h SO | 16S rRNA gene sequencing | ↓Tenericutes | ↔Fecal SCFA, BCFA |
| ↑Firmicutes:Bacteroidetes ratio, Coriobacteriaceae, Erysipelotrichaceae | ||||
| Zhang et al., 2017 | n = 11 (6M); 5 nights of 4 h SO followed by 2–5 nights of 12 h SO | 16S rRNA gene sequencing | No effects | NA |
| High Altitude | ||||
| Kleessen et al., 2005 | n = 7 (5M); 47 days expedition to 6677 m | Targeted; FISH | ↑Gammaproteobacteria, Enterobacteriaceae ↓Bifidobacterium, Atopobium/Coriobacterium/Eggerthella lenta ↔Total bacteria, C. coccoides/E. rectale, Lactobacillus/Enterococcus, C. hitolyticum, Bacteroides, F. prausnitzii | NA |
| Adak et al., 2013 | n = 15M; 15 days at 3505 m | Targeted; culture | ↑Total anaerobes, Escherichia coli, Bacteroides, C. perfringens, Bifidobacterium, Lactobacillus, Peptostreptococcus, proteinase producers, amylase producers, tannase producers | ↓Fecal α-amylase activity↑Fecal proteinase, β-gluronidase, alakaline phosphatase activity |
| ↓Total aerobes, phosphatase producers | ||||
| Sket et al., 2017a,b, 2018 | n = 11M; 21 days bed rest at normobaric hypoxia (∼4000 m) vs. 21 days bed rest at normoxia | Targeted; qPCR 16S rRNA gene sequencing; SM | ↑Bacteroides spp.; ↔Roseburia/E. rectale, F. prausnitzii, butyrate producing communities | ↔Fecal pH, SCFA, BCFA, fecal metabolome |
| Heat and cold: No human studies | ||||
| Toxicants/pollutants: No human studies | ||||
| Noise: No human studies | ||||
| Travelers’ diarrhea | ||||
| Kampmann et al., 2016 | n = 13 (3M) adults testing positive for Campylobacter jejuni or Salmonella enterica after traveling to high risk region for 1–3 weeks; no Abx use | 16S rRNA gene sequencing | No changes in relative abundance of any taxa over time | NA |
| Pop et al., 2016 | n = 12 (7M) adults challenged with ETEC + ciprofloxacin who developed diarrhea (n = 5) or did not (n = 7) | 16S rRNA gene sequencing | Diarrhea vs. no-diarrhea post infection: Transient ↓diversity; ↑Escherichia (largely attributed to the challenge strain); within diarrhea group post-infection community similar to pre-treatment community by day 28 | NA |
| Physical activity | ||||
| Allen et al., 2018b | n = 32 (12M; 14 obese); 3 days/week moderate exercise for 6 weeks then sedentary washout for 6 weeks | 16S rRNA gene sequencing | Lean-exercise: ↓Bacteroides; ↑Faecalibacterium, Lachnospira, SCFA-regulating genes | Lean-exercise: ↑Fecal acetate, propionate, butyrate |
| Lean-washout: ↑Collinsella, Dorea; ↓Faecalibacterium, Lachnospira, SCFA-regulating genes | Lean-washout: ↓Fecal propionate, butyrate | |||
| Obese-exercise: ↑Bacteroides, Collinsella; ↓Faecalibacterium; ↔relative abundance of SCFA-regulating genes | Obese-exercise: ↔Fecal acetate, butyrate, propionate | |||
| Obese-washout: ↓Collinsella, Dorea, SCFA-regulating genes; ↑Faecalibacterium, Lachnospira | Obese-washout: ↔Fecal acetate, butyrate, propionate | |||
Abx, antibiotics; BCFA, branched-chain fatty acids; ETEC, enterotoxigenic Escherichia coli; FISH, fluorescence in-situ hybridization; M, men; SCFA, short-chain fatty acids; SM, shotgun metagenomics; SO, sleep opportunity; ↑, increase/higher; ↓, decrease/lower; ↔, no change/no difference. Genus abbreviations: C., Clostridium; E., Eubacterium; F; Faecalibacterium.