Table 4.

Key findings from selected studies.

Key Findings from the Studies
Diversity
Altered in males but not in females (Cui M, 2017) [20] Decreased (Sittipo P, 2020) [21] Decreased at eclosion day in the irradiated gut males (Ben Ami, 2020) [44] Decreased (Casero D, 2017) [26] Significant increase at 1 DPE (Cai Z, 2018) [43] Increased (Woruba DN) [45] Macaques: not significantly affected (Carbonero F, 2018) [41]
ACE index	Unaltered (Li Y, 2020) [17] Significantly higher (Cai Z, 2018) [43]
α diversity
Decreased p < 0.05 (Lu L, 2019) [25] Decreased slightly on day 6 (Li Y, 2020) [17] Did not cause significant changes 12 Gy dose (Goudarzi M, 2016) [19] No significant differences (Wang W, 2020) [30] No significant difference (Tong, 2022) [34] Unchanged (Raber J, 2020) [33] Marked increase 30 days (Casero D, 2017) [26]
Shannon index	Decreased, no statical differences (p = 0.055) (Lu L, 2019) [25] Decreased. Recovers 30 days after. (Goudarzi M, 2016) [19] Unaltered (Wang M, 2020) [28] Decreased significantly; (p < 0.05) (Liu X, 2019) [23] Decreased p = 0.97 (Sittipo P, 2020) [21] Decreased significantly; p = 0.03 (Zhao Y, 2019) [31] Remarkably decreased p < 0.0001 (Li Yiyi, 2020) [32] Unaltered (Tong, 2022) [34] Macaques: no significant effect/Minipigs: decreased (Carbonero F, 2018) [40] Increased (60% significantly) (Cai Z, 2018) [43] No major difference between pre- and post-irradiation (Kalkeri, 2021) [42] No significant difference (Lavrinienko, 2020) [39] Increased in small intestine and no significant differences in large intestine (Kim YS, 2015) [27]
Simpson diversity index	Significantly greater p = 0.0440 (Zhao Z, 2020) [29] No significant difference (Wang M, 2020) [28] Increased significantly (Liu X, 2019) [23] Unaltered (Tong, 2022) [34]
Chao1 index	Lower, no statically different p = 0.069 (Lu L, 2019) [25] Significant lower p = 0.0120 (Zhao Z, 2020) [29] Decreased on day 3. Recovered 30 days after. (Goudarzi M, 2016) [19] No significant difference (Wang M, 2020) [28] Decreased p = 0.015 (Sittipo P, 2020) [21] Unaltered (Li Y, 2020) [17] Unaltered 10 months after p = 0.64 (Zhao Y, 2019) [31] Unaltered (Tong, 2022) [34] Increased (Cai Z, 2018) [43] Increased in small intestine and no significant differences in large intestine (Kim YS, 2015) [27]
Beta diversity
Changed (Li Y, 2020) [17] Significantly different in the LT10 (Liu X, 2019) [23] Differences (Kalkeri, 2021) [42] Significant differences (p = 0.001) (Lavrinienko A, 2018) [38] Significant difference p < 0.001 (Casero D, 2017) [26] Unchanged p = 0.12 (Zhao Y, 2019) [31]
Richness
Number of OTUs/Taxa number	Significantly lower (Zhao Z, 2020) [29] Decreased significantly as LDR exposure time increased. However, no difference was found among groups LT1, LT5, and LT10 (p < 0.05). (Liu X, 2019) [23] Diversity decreased—OTUs estimated by richness analysis (p = 0.009) (Sittipo P, 2020) [21] Different OTUs after (Goudarzi M, 2016) [19] Remarkably decreased (Li Y, 2020) [32] Decreased species number significantly (p < 0.05). (Liu X, 2019) [23] Increased bacterial load (Woruba DN, 2019) [45] Decreased by 40% at 1 DPE (Cai Z, 2018) [43] No significant differences (p > 0.05) (Lavrinienko A, 2018) [38] Higher in small intestine and no significant differences in large intestine (Kim YS, 2015) [27]
Altered composition/Dysbiosis
Marked dysbiosis (Lu L, 2019) [25] Intestinal bacterial flora substantially shifted (Li Y, 2020) [17] Altered composition of enteric bacteria in males but not in females (Cui M, 2017) [20] Significant shift in post-radiation gut microbial composition (Gerassy-Vainberg, 2018) [22] Not changed significantly 7 days after, with obvious changes 30 days after (Wang W, 2020) [30] Significant shift in microbial composition (Li Yiyi, 2020) [32] Composition associated with radiation dose (p = 0.0002) (Raber J, 2020) [33]
Anaerobic counts
	Significant decreases 2 and 6 h p <0.05 compared to 24 h. No significant differences 24 h after (Johnson, 2004) [24]
Aerobic counts
	Significantly decreased; p <0.05. Compared to the 24 h levels, significant decreases at 2 h p < 0.05 (Johnson, 2004) [24]
Phylum
Ratio Firmicutes/Bacteroidetes	Decreased (Sittipo P, 2020) [21] Decreased (Wang M, 2020) [28] Decreased (Lavrinienko A, 2018) [38] Increased, without significance (Tong, 2022) [34] Altered (Cheema, 2021) [35] Decreased (Kalkeri, 2021) [42]
Actinobacteria	Smaller increase (Lu L, 2019) [25] Decreased in large intestine (Kim YS, 2015) [27] Decreased 1 week after, increased 6 weeks after (Li Yiyi, 2020) [32] Decreased (Carbonero F, 2018) [41]
Bacteroidetes	Increased in the large intestine by 4 percentage points (Kim YS, 2015) [27] Decreased (Wang M, 2020) [28] Decreased in minipigs (Carbonero F, 2018) [41] Significantly decreased in a time-dependent manner (Liu X, 2019) [23] Decreased (Li Yiyi, 2020) [32] Unchanged (Rentea RM, 2016) [36] Less affected (Lam Vy, 2012) [37]
Epsilonbacteraeota	Decreased 1 and 6 weeks after (Li Yiyi, 2020) [32]
Firmicutes	Decreased at D1; recovered at later (D3 and D10) (Sittipo P, 2020) [21] Decreased (Lu L, 2019) [25] Decreased (Goudarzi M, 2016) [19] Decreased (Rentea RM, 2016) [36] Decreased—large intestine. Increased—small intestine (Kim YS, 2015) [27] Significantly decreased (p < 0.01). (Gerassy-Vainberg, 2018) [22] Decreased 30 day after (Wang W, 2020) [30] Decreased 1 week after, increased 6 weeks after (Li Yiyi, 2020) [32] Decrease in Macaques and Increased minipigs (Carbonero F, 2018) [41]
Proteobacteria	Increased (Lu L, 2019) [25] Significantly increased (Zhao Z, 2020) [29] Increased (Kim YS, 2015) [27] Increased (Wang M, 2020) [28] Increased (Liu X, 2019) [23] Increased (Rentea RM, 2016) [36] Significant change in abundance. (Gerassy-Vainberg, 2018) [22] Increased 1 week after, but no alteration 6 weeks after (Li Yiyi, 2020) [32] Increased 4 days after, then returned to control values. (Lam Vy, 2012) [37] Macaques—Increases/Minipigs—decreases (Carbonero F, 2018) [41]
Verrucomicrobia	Decreased (Zhao Z, 2020) [29] Increased. Recovered by day 30 (Goudarzi M, 2016) [19] Identified in the irradiated samples but not in the control samples. (Kim YS, 2015) [27] Akkermansia spp. (p < 0.01)—significant change. (Gerassy-Vainberg, 2018) [22] Increased (Wang W, 2020) [30] Increased minipigs and macaques (Carbonero F, 2018) [40] Increased minipigs (Carbonero F, 2018) [41] Increased (Casero D, 2017) [26]
Spirochaetes	Increases (Carbonero F, 2018) [41]
Class
Clostridia	Increased (Liu X, 2019) [23] Decreased (Zhao Y, 2019) [31] Less affected (Lam Vy, 2012) [37]
Bacteroida	Significantly decreased in LT10 (Liu X, 2019) [23] Increased (Zhao Y, 2019) [31]
Betaproteobacteria	Increased (Zhao Y, 2019) [31]
Unidentified_Saccharibacteria	Decreased (Zhao Y, 2019) [31]
Epsilonproteobacteria	Increased (Zhao Y, 2019) [31]
Deltaproteobacteria	Decreased (Zhao Y, 2019) [31]
Erysipelotrichia	Increased (Zhao Y, 2019) [31]
Order
Clostridiales	Increased in the LT10 group (Liu X, 2019) [23] Increased (Carbonero F, 2018) [40]
Bifidobacteriales	Significant perturbation (Casero D, 2017) [26]
Coriobacteriales	Significant perturbation (Casero D, 2017) [26]
Verrucomicrobiales	Significant perturbation (Casero D, 2017) [26]
Lactobacillales	Significant perturbation (Casero D, 2017) [26]
Bacteroidales	Increased (Lam Vy, 2012) [37]
Family
Desulfovibrionaceae	Increased (Li Y, 2020) [17] Increased (Lavrinienko A, 2020) [39] Some members tolerate high radiation levels (Lavrinienko A, 2018) [38]
Staphylococcaceae	Increased (Goudarzi M, 2016) [19]
Lactobacillacea	Increased (Goudarzi M, 2016) [19] Decreased (Li Y, 2020) [17]
Prevotellacea	Unaltered (Lu L, 2019) [25]
Clostridiaceae	Irradiation-resistant bacteria (Sittipo P, 2020) [21] Decreased (Goudarzi M, 2016) [19] Clostridiaceae_1—increased p = 0.042 (Zhao Y, 2019) [31] Increased (Cai Z, 2018) [43] Unchanged abundance. 47 separate Clostridiaceae OTUs with decreased expression (Lam Vy, 2012) [37]
Lachnospiracea	Irradiation-resistant bacteria (Sittipo P, 2020) [21] Decreased (Lu L, 2019) [25] Decreased (Goudarzi M, 2016) [19] Increased (Liu X, 2019) [23] Increased (Tong, 2022) [34] Increased (Lavrinienko A, 2020) [39] Significant changes 1 week post-radiation compared with unirradiated group (p <0.05). Largely reversed in chronic phase (p < 0.05) (Li Yiyi, 2020) [32] Lachnospiraceae_NK4A136—Decreased (Wang M, 2020) [28] uncultured_bacterium_f_Lachnospiraceae—decreased (Wang M, 2020) [28] Minipigs—unclassified Lachnospiraceae—significantly decreased. Macaques—Increased(Carbonero F, 2018) [40]
Moraxellaceae	Decreased (Tong, 2022) [34]
Ruminococcaceae	Irradiation-resistant bacteria (Sittipo P, 2020) [21] Decreased (Lu L, 2019) [25] Decreased. Two members of the Ruminococcaceae family increased (Goudarzi M, 2016) [19] Increased in the LT10 group (Liu X, 2019) [23] Increase (p < 0.05) (Lavrinienko A, 2020) [39]
Porphyromonadaceae	Significant decrease (Liu X, 2019) [23]
Rikenellaceae	Significant changes in 1 week post-radiation (p < 0.05). Largely reversed in chronic phase of the disease (p < 0.05) (Li Yiyi, 2020) [32]
Eggerthellaceae	Significant changes in 1 week post-radiation (p < 0.05). (Li Yiyi, 2020) [32]
Enterobacteriaceae	Decreased 2 h after and significantly decreased 16 h after p < 0.05. No significant differences 24 h after. (Johnson, 2004) [24] Decreased (Tong, 2022) [34] Decreased (Cai Z, 2018) [43]
Flavobacteriaceae	Increased significantly (Cai Z, 2018) [43]
Muribaculaceae S24-7 family	Significant changes in 1 week post-radiation (p < 0.05). Largely reversed in chronic phase (p < 0.05) (Li Yiyi, 2020) [32] Bacteroidales_S24-7_group increased (Wang W, 2020) [30] uncultured_ bacterium_f_Bacteroidales_S24-7_group –increased 30 days after (Wang W, 2020) [30] Enrichment of members. In second capture—CL: decrease in abundance of members (>10% reduction) (Lavrinienko A, 2020) [39]
Bacillaceae	Increased significantly (Cai Z, 2018) [43]
Xanthomonadaceae	Increased significantly (Cai Z, 2018) [43]
Sphingobacteriaceae	Increased significantly (Cai Z, 2018) [43]
Aeromonadacea	Increased significantly (Cai Z, 2018) [43]
Peptostreptococcaceae	Unchanged (Lam Vy, 2012) [37]
Veillonellaceae	Macaques—Increased (Carbonero F, 2018) [40]
Genus
Acinetobacter	Decreased (Kalkeri, 2021) [42]
Aerococcus	Decreased (Kalkeri, 2021) [42]
Actinobacillus	Significantly increased (Kalkeri, 2021) [42]
Actinobacteria major genera	Decreased (Carbonero F, 2018) [41]
Akkermansia	Increased (Kim YS, 2015) [27] Significant change in abundance. (Gerassy-Vainberg, 2018) [22] Increased (Wang W, 2020) [30] Significantly increased (p < 0.05). (Li Yiyi, 2020) [32]
Alloprevotella	Decreased (Wang W, 2020) [30] Increased (Cheema, 2021) [35] Significant changes in 1 week (p < 0.05). Largely reversed in chronic phase (p < 0.05) (Li Yiyi, 2020) [32]
Alistipes	Decreased (Lu L, 2019) [25] Increased in large intestine (>5%). Small intestine—decreased (Kim YS, 2015) [27] Increased (Wang M, 2020) [28] Increased (Carbonero F, 2018) [41] Increased 7 days after and reversed 30 days after (Wang W, 2020) [30] Significant changes in 1 week post-radiation (p < 0.05). Largely reversed in chronic phase (p < 0.05) (Li Yiyi, 2020) [32]
Anaerotruncus	Increased (Li Y, 2020) [17]
Bacteroides	Decreased (Kim YS, 2015) [27] Increased (Wang M, 2020) [28] Increased (Cheema, 2021) [35] Decreased LT10 group (Liu X, 2019) [23] Decreased—(Wang W, 2020) [30] Significant changes in 1 week post-radiation (p < 0.05). Largely reversed in chronic phase (p < 0.05) (Li Yiyi, 2020) [32] Significantly increased (Kalkeri, 2021) [42] Minipigs—decreased (Carbonero F, 2018) [40] Minipigs—All radiation levels led to significant decreases (Carbonero F, 2018) [41] Macaques—High radiation levels—increase (Carbonero F, 2018) [41]
Barnesiella	Decreased (Kim YS, 2015) [27] Decreased (Liu X, 2019) [23]
Betaproteobacteria members (Desulfovibrio and Bilophila)	Macaques—Irradiation at all levels significantly decreases/At day 3 were also increased at all radiation levels (Carbonero F, 2018) [41]
Bacillus spp.	Decreased (Raber J, 2020) [33] Decreased (Ben Ami, 2020) [44]
Bifidobacterium	Decreased in 2. However, in the 4 Gy–irradiated group increased ~10 times after 48 h and reached 28 times after 72 h. (Yamanouchi K, 2019) [18] Decreased (Carbonero F, 2018) [41] Decreased 30 days after exposure compared to their 10-day (Casero D, 2017) [26]
Butyricimonas	Decreased (Carbonero F, 2018) [41]
Blautia	Minipigs and Macaques—increases (Carbonero F, 2018) [41] Minipigs—Increased (Carbonero F, 2018) [40]
Citrobacter sp.	Decreased (Ben Ami, 2020) [44]
Collinsella	Decreased (Carbonero F, 2018) [41]
Coprococcus_1	Increased (Li Y, 2020) [17]
Corynebacterium	Increase (Kim YS, 2015) [27]
Clostridium	Significantly increased in a time-dependent manner (Lu L, 2019) [25] Minipigs—All radiation—Significant decreases; Macaques—increases in High levels (Carbonero F, 2018) [41]
Clostridium cluster IV, XIVa and XIVb	Minipigs and Macaques—High radiation level increases (Carbonero F, 2018) [41] Clostridium XIVa Significant positive correlations (Carbonero F, 2018) [41]
Dubosiella	Significant changes in 1 week post-radiation (p < 0.05). Largely reversed in chronic phase (p < 0.05) (Li Yiyi, 2020) [32]
Elusimicrobium	Significant decreases (Carbonero F, 2018) [41]
Enterobacter sp.	Increased (Ben Ami, 2020) [44]
Enterococcus	Significant changes in 1 week post-radiation (p < 0.05). Largely reversed in chronic phase (p < 0.05) (Li Yiyi, 2020) [32]
Escherichia-Shigella	Increased (Lu L, 2019) [25] Significant changes in 1 week post-radiation (p < 0.05). Largely reversed in chronic phase (p < 0.05) (Li Yiyi, 2020) [32]
Eubacterium_coprostanoligenes_group	Decreased (Wang W, 2020) [30]
Faecalibacterium	Decreases (Carbonero F, 2018) [41]
Helicobacter	Significantly increased (Lu L, 2019) [25] Decreased (Carbonero F, 2018) [41] Minipigs and Macaques—Increased (Carbonero F, 2018) [40]
Klebsiella sp.	Decreased (Ben Ami, 2020) [44]
Lactobacillus	No significant changes (Lu L, 2019) [25] Decreased D1, recovered at D3 and D10 (Sittipo P, 2020) [21] Decreased from 6 h to 12 h and then recovered to baseline. (Yamanouchi K, 2019) [18] Increased in the large intestine (>5%) (Kim YS, 2015) [27] Decreased (Wang M, 2020) [28] Decreased 2 h after and significant decrease after sixteen p < 0.05. No significant differences 24 h after. (Johnson, 2004) [24] Decreased (Cheema, 2021) [35] Significantly increased (p < 0.05) (Li Yiyi, 2020) [32] Minipigs—Increased (Carbonero F, 2018) [40] Minipigs—Correlate negatively; Macaques—sharp increase of only immediately after irradiation/correlate negatively (Carbonero F, 2018) [41]
Mucispirilum	Decreased (Kim YS, 2015) [27]
Olsenella	Increases High radiation levels (Carbonero F, 2018) [41]
Oscillibacter	Decreased (Kim YS, 2015) [27] Significantly increased (Lu L, 2019) [25] Minipigs—Increased (Carbonero F, 2018) [40]
Parabacteroides	Increased (Wang M, 2020) [28] Increased (Carbonero F, 2018) [41]
Paraprevotella	Macaques—Increased (Carbonero F, 2018) [41] Minipigs—Decreased (Carbonero F, 2018) [40]
Pseudomonas sp.	Increased (Ben Ami, 2020) [44]
Pseudoflavonifractor	Reduced the proportions (Kim YS, 2015) [27]
Prevotella	Decreased (Kim YS, 2015) [27] Minipigs and Macaques—significantly decreased (Carbonero F, 2018) [41] Significantly increased (Kalkeri, 2021) [42]
Providencia sp.	Decreased (Ben Ami, 2020) [44]
Quinella	Decreased significantly; p = 0.029 (Zhao Y, 2019) [31]
Ralstonia sp.	Decreased (Ben Ami, 2020) [44]
Roseburia	Decreased (Lu L, 2019) [25] Increased (Casero D, 2017) [26] Minipigs—Significant decreased (Carbonero F, 2018) [40]
Ruminococcus	Significant positive correlations (Carbonero F, 2018) [41] Minipigs—Significant decreased (Carbonero F, 2018) [40]
Slackia	Macaques—decrease higher radiation levels (Carbonero F, 2018) [41]
Streptococcus	Minipigs: Significant increased/Macaques: Sharp decrease (Carbonero F, 2018) [41] Minipigs—Increased (Carbonero F, 2018) [40]
Suterella spp.	Significant change (Gerassy-Vainberg, 2018) [22]
Treponema	Macaques—significant decreases in all radiation levels/Higher radiation levels induced immediate increase. On day 3, members increased at all radiation levels (Carbonero F, 2018) [41] Macaques and Minipigs—Increased (Carbonero F, 2018) [40]
Veillonella	Significantly increased (Kalkeri, 2021) [42]
Species
Adlercreutzia unclassified	Decrease 30 days after (Casero D, 2017)[26]
Akkermansia muciniphila	Increase (Casero D, 2017) [26]
Clostridiaceae species	Decrease 30 days after (Casero D, 2017) [26]
Eubacterium biforme	Decrease (Goudarzi M, 2016) [19]
Mollicutes species (Tenericutes phylum)	Extinguish after exposure to 0.25 Gy of 16O (Casero D, 2017) [26]
Prevotellaceae_UCG-001	Decreased (Wang M, 2020) [28] Decreased (Wang W, 2020) [30]
Ruminococcaceae_UCG-014	Increased relative abundance (Wang M, 2020) [28] Increased 7 days after and decreased 30 days after (Wang W, 2020) [30]
Ruminococcus gnavus	Declined significantly (Goudarzi M, 2016) [19] Increased (Casero D, 2017) [26]
S24–7 unclassified species	Decrease 30 days after exposure (Casero D, 2017) [26]
Unclassified Lactobacillus	Decrease 30 days after (Casero D, 2017) [34]
uncultured_bacterium_g_Acinetobacter,	Decreased (Tong, 2022) [34]
uncultured_bacterium_o_, Mollicutes_RF39,	Decreased (Tong, 2022) [34]
uncultured_bacterium_g_Citrobacter,	Decreased (Tong, 2022) [34]
uncultured_bacterium_g_Lactococcus—decreased	Decreased (Tong, 2022) [34]
Streptococcus_gallolyticus	Decrease significantly; p = 0.034 (Zhao Y, 2019) [31]