Vicia faba L. in the Bejaia region of Algeria is nodulated by Rhizobium leguminosarum sv. viciae, Rhizobium laguerreae and two new genospecies

Fifty-eight rhizobial strains were isolated from root nodules of Vicia faba cv. Equina and Vicia faba cv. Minor by the host-trapping method in soils collected from eleven sites in Bejaia, Eastern Algeria. Eleven genotypic groups were distinguished based on the combined PCR/RFLP of 16S rRNA, 16S–23S rRNA intergenic spacer and symbiotic (nodC and nodD-F) genes and further confirmed by multilocus sequence analysis (MLSA) of three housekeeping genes (recA, atpD and rpoB), the 16S rRNA gene and the nodulation genes nodC and nodD. Of the 11 genotypes, 5 were dominant and 2 were the most represented. Most of the strains shared high nodD gene sequence similarity with Rhizobium leguminosarum sv. viciae; their nodC sequences were similar to both Rhizobium leguminosarum and Rhizobium laguerreae. Sequence analyses of the 16S–23S rRNA intergenic spacer showed that all the new strains were phylogenetically related to those described from Vicia sativa and V. faba in several African, European, American and Asian countries, with which they form a group related to Rhizobium leguminosarum. Phylogenetic analysis based on MLSA of 16S rRNA, recA, atpD and rpoB genes allowed the affiliations of strain AM11R to Rhizobium leguminosarum sv. viciae and of strains EB1 and ES8 to Rhizobium laguerreae. In addition, two separate clades with <97% similarity may represent two novel genospecies within the genus Rhizobium.     

Rhizobium pisi sv. trifolii K3.22 harboring nod genes of the Rhizobium leguminosarum sv. trifolii cluster

The taxonomic status of the Rhizobium sp. K3.22 clover nodule isolate was studied by multilocus sequence analysis (MLSA) of 16S rRNA and six housekeeping chromosomal genes, as well as by a subsequent phylogenic analysis. The results revealed full congruence with the Rhizobium pisi DSM 30132^T core genes, thus supporting the same taxonomic position for both strains. However, the K3.22 plasmid symbiosis nod genes demonstrated high sequence similarity to Rhizobium leguminosarum sv. trifolii, whereas the R. pisi DSM 30132^Tnod genes were most similar to R. leguminosarum sv. viciae. The strains differed in the host range nodulation specificity, since strain K3.22 effectively nodulated red and white clover but not vetch, in contrast to R. pisi DSM 30132^T, which effectively nodulated vetch but was not able to nodulate clover. Both strains had the ability to form nodules on pea and bean but they differed in bean cultivar specificity. The R. pisi K3.22 and DSM 30132^T strains might provide evidence for the transfer of R. leguminosarum sv. trifolii and sv. viciae symbiotic plasmids occurring in natural soil populations.     

Genomic insight into the taxonomy of Rhizobium genospecies that nodulate Phaseolus vulgaris

Due to the wide cultivation of bean (Phaseolus vulgaris L.), rhizobia associated with this plant have been isolated from many different geographical regions. In order to investigate the species diversity of bean rhizobia, comparative genome sequence analysis was performed in the present study for 69 Rhizobium strains mainly isolated from root nodules of bean and clover (Trifolium spp.). Based on genome average nucleotide identity, digital DNA:DNA hybridization, and phylogenetic analysis of 1,458 single-copy core genes, these strains were classified into 28 clusters, consistent with their species definition based on multilocus sequence analysis (MLSA) of atpD, glnII, and recA. The bean rhizobia were found in 16 defined species and nine putative novel species; in addition, 35 strains previously described as Rhizobium etli, Rhizobium phaseoli, Rhizobium vallis, Rhizobium gallicum, Rhizobium leguminosarum and Rhizobium spp. should be renamed. The phylogenetic patterns of symbiotic genes nodC and nifH were highly host-specific and inconsistent with the genomic phylogeny. Multiple symbiovars (sv.) within the Rhizobium species were found as a common feature: sv. phaseoli, sv. trifolii and sv. viciae in Rhizobium anhuiense; sv. phaseoli and sv. mimosae in Rhizobium sophoriradicis/R. etli/Rhizobium sp. III; sv. phaseoli and sv. trifolii in Rhizobium hidalgonense/Rhizobium acidisoli; sv. phaseoli and sv. viciae in R. leguminosarum/Rhizobium sp. IX; sv. trifolii and sv. viciae in Rhizobium laguerreae. Thus, genomic comparison revealed great species diversity in bean rhizobia, corrected the species definition of some previously misnamed strains, and demonstrated the MLSA a valuable and simple method for defining Rhizobium species.     

Genetic diversity of root-nodulating bacteria isolated from pea (<Emphasis Type="Italic">Pisum sativum</Emphasis>) in subtropical regions of China

Diversity of 42 isolates from effective nodules of Pisum sativum in different geographical regions of China were studied using 16S rRNA gene RFLP patterns, 16S rRNA sequencing, 16S–23S rRNA intergenic spacer (IGS) region RFLP patterns and G-C rich random amplified polymorphic DNA (RAPD). The isolates were distributed in two groups on the basis of their 16S rRNA gene RFLP patterns. The 16S rRNA gene sequences of strains from 16S rRNA gene RFLP patterns group I were very closely related (identities higher than 99.5%) to Rhizobium leguminosarum USDA 2370. Group II consisting of WzP3 and WzP15 was closely related to Rhizobium etli CFN42. The analysis of the 16S-23S IGS RFLP patterns divided the isolates into 18 genotypes and four groups. Group I was clustered with R. leguminosarum USDA2370. Group II consisted of YcP2, YcP3 and CqP7. The strains of group III were distributed abroad. Group IV consisted of WzP3, WzP15 and R. etli CFN42. RAPD divided the isolates into nine clusters in which group IV only consisted of YcP2 and the strains of group V and IX were from Wenzhou and Xiantao, respectively. This assay demonstrated the geographical effect on genetic diversity of pea rhizobia.     

Sequence Analysis of Hypothetical Lysine Exporter Genes of Rhizobium leguminosarum bv. trifolii from Calamine Old Waste Heaps and Their Evolutionary History

The aim of this study was to identify heavy metal detoxification system in Rhizobium leguminosarum bv. trifolii isolated from Trifolium repens inhabiting old (70–100 years) Zn–Pb waste heaps in Poland by PCR reaction with czcD1 and czcD2 primers. By sequence analysis, four different genotypes of obtained amplicons were identified among eight examined isolates. Their sequence similarity ranged 91–99 %. They indicated the highest sequence identity to the hypothetical lysine exporter gene of R. leguminosarum bv. trifolii WSM1325 (91–97 %) and 76–81 % sequence similarity to hypothetical lysine exporter genes of R. leguminosarum bv. trifolii WSM2304 and R. etli CFN42 and CIAT652. On phylogenetic tree of obtained amplicons, all four studied R. leguminosarum bv. trifolii genotypes formed common monophyletic cluster with R. leguminosarum bv. trifolii WSM1325 at 100 % bootstrap support showing that all four amplicons obtained in PCR with czcD1 and czcD2 primers are fragments of hypothetical lysine exporter gene (lysE). We also suggest that Lys efflux exporter may participate in heavy metal transport out of R. leguminosarum bv. trifolii cells.     

Genista tinctoria microsymbionts from Poland are new members of Bradyrhizobium japonicum bv. genistearum

The phylogeny and taxonomic position of slow-growing Genista tinctoria rhizobia from Poland, Ukraine and England were estimated by comparative 16S rDNA, atpD, and dnaK sequence analyses, PCR-RFLP of 16S rDNA, DNA G + C content, and DNA–DNA hybridization. Each core gene studied placed the G. tinctoria rhizobia in the genus Bradyrhizobium cluster with unequivocal bootstrap support. G. tinctoria symbionts and bradyrhizobial strains shared 96–99% similarity in 16S rDNA sequences. Their similarity for atpD and dnaK sequences was 93–99% and 89–99%, respectively. These data clearly showed that G. tinctoria rhizobia belonged to the genus Bradyrhizobium. 16S rDNA sequence analysis was in good agreement with the results of the PCR-RFLP of the 16S rRNA gene. Although the tested strains formed separate lineages to the reference bradyrhizobia their RFLP 16S rDNA patterns were quite similar. The genomic DNA G + C content of three G. tinctoria rhizobia was in the range from 60.64 to 62.83 mol%. Data for species identification were obtained from DNA–DNA hybridization experiments. G. tinctoria microsymbionts from Poland were classified within Bradyrhizobium japonicum genomospecies based on 56–82% DNA–DNA similarity.     

Genetic diversity of common bean (Phaseolus vulgaris L.) nodulating rhizobia in Nepal

Background and Aims

This study was conducted to reveal the genetic diversity of common bean (Phaseolus vulgaris L.) nodulating rhizobia in various agroecological regions in Nepal.

Method

A total of 63 strains were isolated from common bean grown in the soils collected from seven bean fields in Nepal and characterized based on the partial sequences of 16S–23S internal transcribed spacer (ITS) regions, 16S rDNA, nodC, and nifH. Symbiotic properties of some representative strains with host plants were examined to elucidate their characteristics in relation to genotype and their origin.

Results

The isolated strains belonged to Rhizobium leguminosarum, Rhizobium etli, Rhizobium phaseoli, and one unknown Rhizobium lineage, all belonging to a common symbiovar (sv.) phaseoli. Nine ITS genotypes were detected mainly corresponding to a single site, including a dominant group at three sites harboring highly diverse multiple ITS sequences. Three symbiotic genotypes corresponded to a geographical region, not to the ribosomal DNA group, suggesting horizontal transfer of symbiotic genes separately in each region. Great differences in nitrogenase activity and nodule forming ability among the strains irrespective of their species and origin were observed.

Conclusions

Nepalese Himalaya harbor phylogenetically highly diverse and site-specific strains of common bean rhizobia, some of which could have high potential of symbiotic nitrogen fixation.     

Bradyrhizobium arachidis sp. nov., isolated from effective nodules of Arachis hypogaea grown in China

Twenty-three bacterial strains isolated from root nodules of Arachis hypogaea and Lablab purpureus grown in five provinces of China were classified as a novel group within the genus Bradyrhizobium by analyses of PCR-based RFLP of the 16S rRNA gene and 16S–23S IGS. To determine their taxonomic position, four representative strains were further characterized. The comparative sequence analyses of 16S rRNA and six housekeeping genes clustered the four strains into a distinctive group closely related to the defined species Bradyrhizobium liaoningense, Bradyrhizobium yuanmingense, Bradyrhizobium huanghuaihaiense, Bradyrhizobium japonicum and Bradyrhizobium daqingense. The DNA–DNA relatedness between the reference strain of the novel group, CCBAU 051107^T, and the corresponding type strains of the five mentioned species varied between 46.05% and 13.64%. The nodC and nifH genes of CCBAU 051107^T were phylogenetically divergent from those of the reference strains for the related species. The four representative strains could nodulate with A. hypogaea and L. purpureus. In addition, some phenotypic features differentiated the novel group from the related species. Based on all the results, we propose a new species Bradyrhizobium arachidis sp. nov. and designate CCBAU 051107^T (=CGMCC 1.12100^T = HAMBI 3281^T = LMG 26795^T) as the type strain, which was isolated from a root nodule of A. hypogaea and had a DNA G + C mol% of 60.1 (Tm).     

Different species and symbiotic genotypes of field rhizobia can nodulate Phaseolus vulgaris in Tunisian soils

A collection of 160 isolates of rhizobia nodulating Phaseolus vulgaris in three geographical regions in Tunisia was characterized by restriction fragment length polymorphism analysis of polymerase chain reaction (PCR)-amplified 16S rDNA, nifH and nodC genes. Nine groups of rhizobia were delineated: Rhizobium gallicum biovar (bv.) gallicum, Rhizobium leguminosarum bv. phaseoli and bv. viciae, Rhizobium etli bv. phaseoli, Rhizobium giardinii bv. giardinii, and four groups related to species of the genus Sinorhizobium, Sinorhizobium meliloti, Sinorhizobium medicae and Sinorhizobium fredii. The most abundant rhizobial species were R. gallicum, R. etli, and R. leguminosarum encompassing 29–20% of the isolates each. Among the isolates assigned to R. leguminosarum, two-thirds were ineffective in nitrogen fixation with P. vulgaris and harbored a symbiotic gene typical of the biovar viciae. The S. fredii-like isolates did not nodulate soybean plants but formed numerous effective nodules on P. vulgaris. Comparison of nodC gene sequences showed that their symbiotic genotype was not related to that of S. fredii, but to that of the S. fredii-like reference strain GR-06, which was isolated from a bean plant grown in a Spanish soil. An additional genotype including 16% of isolates was found to be closely related to species of the genus Agrobacterium. However, when re-examined, these isolates did not nodulate their original host.     

Conservation of Plasmid-Encoded Traits among Bean-Nodulating Rhizobium Species

Rhizobium etli type strain CFN42 contains six plasmids. We analyzed the distribution of genetic markers from some of these plasmids in bean-nodulating strains belonging to different species (Rhizobium etli, Rhizobium gallicum, Rhizobium giardinii, Rhizobium leguminosarum, and Sinorhizobium fredii). Our results indicate that independent of geographic origin, R. etli strains usually share not only the pSym plasmid but also other plasmids containing symbiosis-related genes, with a similar organization. In contrast, strains belonging to other bean-nodulating species seem to have acquired only the pSym plasmid from R. etli.     

Genetic diversity of rhizobia nodulating common bean (Phaseolus vulgaris L.) in the Central Black Sea Region of Turkey

We have analyzed 30 rhizobial isolates obtained from common bean (Phaseolus vulgaris L.) root nodules grown in the Middle Blacksea Region of Turkey, using ARDRA and nucleotide sequence data. ARDRA analysis with enzymes CfoI, HinfI, NdeII, MspI and PstI revealed three patterns. Based on sequence data from 16S rDNA, the patterns were identified as, Rhizobium leguminosarum bv. phaseoli (n = 16), R. etli bv. phaseoli (n = 8) and R. phaseoli (n = 6). On the other hand, nucleotide sequence phylogenies of housekeeping genes (recA, atpD and glnII) selected to confirm the 16S rDNA phylogeny revealed different evolutionary relationships. These results suggested the possibility of lateral transfers of these genes amongst different rhizobial species (including R. leguminosarum, R. etli and R. phaseoli) sharing the same ecological niche (nodulating P. vulgaris) which also indicates that there may be no true genetic barier among these species. Phylogenetic analysis based on DNA sequence data from the nodA and nifH genes showed that all rhizobial species obtained in this study were carrying nodA and nifH haplotypes which were the same or similar to those of CFN42 (R. etli type strain), suggesting a further support for the lateral transfer of CFN42 Sym plasmid, p42, amongst Turkish common bean nodulating rhizobial isolates.     

Genetic diversity and symbiotic evolution of rhizobia from root nodules of Coronilla varia

Ninety symbiotic rhizobial isolates from root nodules of Coronilla varia growing in the Shaanxi province of China were characterized. Combined with the results of RFLP patterns, six genotypes were defined among the rhizobial strains and they were divided into three genomic genera. These included Mesorhizobium sp., M. alhagi, M. amorphae, M. metallidurans/M. gobiense as the dominant group (86.7%), and Rhizobium yanglingense and Agrobacterium tumefaciens as the minor groups, according to analysis of the corresponding 16S rRNA, nodC and nifH genes. Five nodC types, which mainly grouped into the Mesorhizobium genus, were obtained from all the isolates examined, implying that nodC genes probably occurred from the native habitat through lateral transfer and long-term adaptation, finally evolving toward M. alhagi. Four different nifH types, displaying obvious differences compared to those of 16S rRNA and nodC, implied that possible lateral transfer of the symbiotic genes occurred between different genera. The association between soil components and the genetic diversity of the rhizobial population demonstrated that combined genotypes were positively correlated with the pH of soil samples.     

Melanin Production by Rhizobium Strains

Different Rhizobium and Bradyrhizobium strains were screened for their ability to produce melanin. Pigment producers (Mel⁺) were found among strains of R. leguminosarum biovars viceae, trifolii, and phaseoli, R. meliloti, and R. fredii; none of 19 Bradyrhizobium strains examined gave a positive response. Melanin production and nod genes were plasmid borne in R. leguminosarum biovar trifolii RS24. In R. leguminosarum biovar phaseoli CFN42 and R. meliloti GR015, mel genes were located in the respective symbiotic plasmids. In R. fredii USDA 205, melanin production correlated with the presence of its smallest indigenous plasmid.     

Rhizobium sophorae is the dominant rhizobial symbiont of Vicia faba L. In North China

Faba bean (Vicia faba L.) is a major introduced grain-legume crop cultivated in China. In this study, rhizobia that nodulated faba bean grown in soils from three sites in North China (Hebei Province) were isolated and characterized. Firstly, isolates were categorized into genotypes by ribosomal IGS PCR-RFLP analysis, then representatives of the different IGS genotypes were further identified by phylogenetic analyses of 16S rRNA, housekeeping (atpD, recA) and nodulation (nodC) gene sequences. Rhizobial distribution based on the IGS genotype was related to the different soil physicochemical features by redundancy analysis. IGS typing and phylogenetic analyses of 16S rRNA and concatenated housekeeping gene sequences affiliated the 103 rhizobial strains isolated into four Rhizobium species/genospecies. A total of 69 strains of 3 IGS types were assigned to R. sophorae, 20 isolates of 5 IGS types to R. changzhiense and 9 isolates of 3 IGS types to R. indicum. The representative strain of the five remaining isolates (1 IGS type) was clearly separated from all Rhizobium type strains and was most closely related to defined genospecies according to the recently described R. leguminosarum species complex. Rhizobium sophorae strains (67% of total isolates) were common in all sites and shared an identical nodC sequence typical of faba bean symbionts belonging to symbiovar viciae. In this first study of rhizobia nodulating faba bean in Hebei Province, China, R. sophorae was found to be the dominant symbiont in contrast to other countries.     

Association between osteoporosis and polymorphisms of the bone Gla protein, estrogen receptor 1, collagen 1-A1 and calcitonin receptor genes in Turkish postmenopausal women

In this study, we have investigated the association between osteoporosis and osteocalcin (BGLAP) − 298 C>T, estrogen receptor 1 (ER1) 397 T>C, collagen type1 alpha 1 (Col1A1) 2046 G>T and calcitonin receptor (CALCR) 1340 T>C polymorphisms. Genomic DNA was obtained from 266 persons (158 osteoporotic and 108 healthy controls). Genomic DNA was extracted from EDTA-preserved peripheral venous blood of patients and controls by a salting-out method and analyzed by PCR-RFLP. As a result, there was no statistically significant difference in the genotype and allele frequencies of patients and controls for BGLAP − 298 C>T, Col1A1 2046 G>T, ER1 397 T>C and CALCR 1340 T>C polymorphisms. However, ER1 CC genotype compared with TT + TC genotypes was found to increase the two fold the risk of osteoporosis [p = 0.039, OR = 2.156, 95% CI (1.083–4.293)] and CALCR CC genotype compared with TT + TC genotypes was found to have protective effect against osteoporosis [p = 0.045, OR = 0.471, 95% CI (0.237–0.9372)]. In the combined genotype analysis, ER1/CALCR TCCC combined genotype was estimated to have protective effect against osteoporosis [p = 0.0125, OR = 0.323, 95% CI (0.1383–0.755)] whereas BGLAP/Col1A1 CCTT and ER1/CALCR CCTT combined genotypes were estimated as risk factors for osteoporosis in Turkish population (p = 0.027, p = 0.009 respectively).     

Salt-tolerant rhizobia isolated from a Tunisian oasis that are highly effective for symbiotic N2-fixation with Phaseolus vulgaris constitute a novel biovar (bv. mediterranense) of Sinorhizobium meliloti

Nodulation of common bean was explored in six oases in the south of Tunisia. Nineteen isolates were characterized by PCR–RFLP of 16S rDNA. Three species of rhizobia were identified, Rhizobium etli, Rhizobium gallicum and Sinorhizobium meliloti. The diversity of the symbiotic genes was then assessed by PCR–RFLP of nodC and nifH genes. The majority of the symbiotic genotypes were conserved between oases and other soils of the north of the country. Sinorhizobia isolated from bean were then compared with isolates from Medicago truncatula plants grown in the oases soils. All the nodC types except for nodC type p that was specific to common bean isolates were shared by both hosts. The four isolates with nodC type p induced N₂-fixing effective nodules on common bean but did not nodulate M. truncatula and Medicago sativa. The phylogenetic analysis of nifH and nodC genes showed that these isolates carry symbiotic genes different from those previously characterized among Medicago and bean symbionts, but closely related to those of S. fredii Spanish and Tunisian isolates effective in symbiosis with common bean but unable to nodulate soybean. The creation of a novel biovar shared by S. meliloti and S. fredii, bv. mediterranense, was proposed.     

Phylogenetic multilocus sequence analysis of native rhizobia nodulating faba bean (Vicia faba L.) in Egypt

The taxonomic diversity of forty-two Rhizobium strains, isolated from nodules of faba bean grown in Egypt, was studied using 16S rRNA sequencing, multilocus sequence analyses (MLSA) of three chromosomal housekeeping loci and one nodulation gene (nodA). Based on the 16S rRNA gene sequences, most of the strains were related to Rhizobium leguminosarum, Rhizobium etli, and Rhizobium radiobacter (syn. Agrobacterium tumefaciens). A maximum likelihood (ML) tree built from the concatenated sequences of housekeeping proteins encoded by glnA, gyrB and recA, revealed the existence of three distinct genospecies (I, II and III) affiliated to the defined species within the genus Rhizobium/Agrobacterium. Seventeen strains in genospecies I could be classified as R. leguminosarum sv. viciae. Whereas, a single strain of genospecies II was linked to R. etli. Interestingly, twenty-four strains of genospecies III were identified as A. tumefaciens. Strains of R. etli and A. tumefaciens have been shown to harbor the nodA gene and formed effective symbioses with faba bean plants in Leonard jar assemblies. In the nodA tree, strains belonging to the putative genospecies were closely related to each other and were clustered tightly to R. leguminosarum sv. viciae, supporting the hypothesis that symbiotic and core genome of the species have different evolutionary histories and indicative of horizontal gene transfer among these rhizobia.     

Prevalence of the Rhizobium etli-Like Allele in Genes Coding for 16S rRNA among the Indigenous Rhizobial Populations Found Associated with Wild Beans from the Southern Andes in Argentina

A collection of rhizobial isolates from nodules of wild beans, Phaseolus vulgaris var. aborigineus, found growing in virgin lands in 17 geographically separate sites in northwest Argentina was characterized on the basis of host range, growth, hybridization to a nifH probe, analysis of genes coding for 16S rRNA (16S rDNA), DNA fingerprinting, and plasmid profiles. Nodules in field-collected wild bean plants were largely dominated by rhizobia carrying the 16S rDNA allele of Rhizobium etli. A similar prevalence of the R. etli allele was observed among rhizobia trapped from nearby soil. Intragroup diversity of wild bean isolates with either R. etli-like or Rhizobium leguminosarum bv. phaseoli-like alleles was generally found across northwest Argentina. The predominance of the R. etli allele suggests that in this center of origin of P. vulgaris the coevolution of Rhizobium spp. and primitive beans has resulted in this preferential symbiotic association.     

Rhizobium etli cycHJKL gene locus involved in c-type cytochrome biogenesis: sequence analysis and characterization of two cycH mutants

The cycHJKL gene locus was cloned from Rhizobium etli by the rescue of a Tn5mob insertion of a mutant (IFC01) which was affected in the production of c-type cytochromes. The cycH, cycJ, cycK and cycL genes are proposed to code for different subunits of a haem lyase complex involved in the attachment of haem to cytochrome c apoproteins. CycH of 365 aa shared 27, 36, 47 and 63% identity with CycH from Paracoccus denitrificans, Bradyrhizobium japonicum, R. meliloti , and R. leguminosarum, respectively. CycJ of 153 aa shared 52, 71, and 85% identity to the cycJ gene product of B. japonicum, R. meliloti, R. leguminosarum, respectively. CycK of 666 aa shared 62, 73, and 90% homology with CycK from B. japonicum, R. meliloti , and R. leguminosarum, respectively, while CycL of 151 aa shared 57, 67 and 86% homology with CycL from the abovementioned species. The Tn5mob insertion present in the IFC01 strain was located in the cycH gene. This strain was able to infect bean plants, but unable to fix nitrogen during symbiosis. A previously described R. etli cytochrome c-deficient MuD1lac-induced mutant (CFN4202) that induced empty nodules on Phaseolus vulgaris, also have lesions in cycH. Complementation analysis suggested that the MuD1lac insertion of the CFN4202 strain was polar on expression of genes downstream of cycH in contrast with the Tn5mob insertion present in IFC01, which showed no polarity on cycJKL. Our data suggest that CycH may not be essential for the infection process, but is necessary for nitrogen fixation.     

Null genotypes of GSTM1 and GSTT1 contribute to increased risk of diabetes mellitus: A meta-analysis

Diabetes mellitus (DM) is a common disease which results from various causes including genetic and environmental factors. Glutathione S-Transferase M1 (GSTM1) and Glutathione S-Transferase T1 (GSTT1) genes are polymorphic in human and the null genotypes lead to the absence of enzyme function. Many studies assessed the associations between GSTM1/GSTT1 null genotypes and DM risk but reported conflicting results. In order to get a more precise estimate of the associations of GSTM1/GSTT1 null genotypes with DM risk, we performed this meta-analysis. Published literature from PubMed, Embase and China Biology Medicine (CBM) databases was searched for eligible studies. Pooled odds ratios (OR) and corresponding 95% confidence intervals (95%CI) were calculated using a fixed- or random-effects model. 11 publications (a total of 2577 cases and 4572 controls) were finally included into this meta-analysis. Meta-analyses indicated that null genotypes of GSTM1/GSTT1 and dual null genotype of GSTM1–GSTT1 were all associated with increased risk of DM (GSTM1: OR _{random-effects} = 1.60, 95%CI 1.10–2.34, P_OR = 0.014; GSTT1: OR _{random-effects} = 1.47, 95%CI 1.12–1.92, P_OR = 0.005; GSTM1–GSTT1: OR _{fixed-effects} = 1.83, 95%CI 1.30–2.59, P_OR = 0.001). Subgroup by ethnicity suggested significant associations between null genotypes of GSTM1 and GSTT1 and DM risk among Asians (GSTM1: OR _{random-effects} = 1.77, 95%CI 1.24–2.53, P_OR = 0.002; GSTT1: OR _{random-effects} = 1.58, 95%CI 1.09–2.27, P_OR = 0.015). This meta-analysis suggests null genotypes of GSTM1/GSTT1 and dual null genotype of GSTM1–GSTT1 are all associated with increased risk of DM, and null genotypes of GSTM1/GSTT1 and dual null genotype of GSTM1–GSTT1 are potential biomarkers of DM.