Differentiation of Lactobacillus plantarum, L. pentosus, and L. paraplantarum by recA gene sequence analysis and multiplex PCR assay with recA gene-derived primers

In this study, we succeeded in differentiating Lactobacillus plantarum, Lactobacillus pentosus, and Lactobacillus paraplantarum by means of recA gene sequence comparison. Short homologous regions of about 360 bp were amplified by PCR with degenerate consensus primers, sequenced, and analyzed, and 322 bp were considered for the inference of phylogenetic trees. Phylograms, obtained by parsimony, maximum likelihood, and analysis of data matrices with the neighbor-joining model, were coherent and clearly separated the three species. The validity of the recA gene and RecA protein as phylogenetic markers is discussed. Based on the same sequences, species-specific primers were designed, and a multiplex PCR protocol for the simultaneous distinction of these bacteria was optimized. The sizes of the amplicons were 318 bp for L. plantarum, 218 bp for L. pentosus, and 107 bp for L. paraplantarum. This strategy permitted the unambiguous identification of strains belonging to L. plantarum, L. pentosus, and L. paraplantarum in a single reaction, indicating its applicability to the speciation of isolates of the L. plantarum group.

Bacterial composition of commercial probiotic products as evaluated by PCR-DGGE analysis

The use of Polymerase Chain Reaction-Denaturing Gradient Gel Electrophoresis (PCR-DGGE) technique in identifying the microorganisms present in commercial probiotic yoghurts and lyophilised products was evaluated. Two reference ladders were assembled constituted by PCR-amplified V2-V3 regions of 16S rDNA from bacterial species generally used as probiotics. Identification was achieved comparing the PCR-DGGE patterns obtained from the analysed products with the ladder bands. Bands from members of the same species showed the same migration distance in denaturing gel, hence supporting the identificative value of the method. The validity of the technique was also proven confirming the PCR-DGGE identification results by sequence data analysis and by species-specific PCR. General congruence between microorganisms declared on the label and those revealed by PCR-DGGE was found for probiotic yoghurts. Conversely, some discrepancies were observed for probiotic lyophilised preparations, i.e. the incorrect identification of some Bifidobacterium and Bacillus species and the presence of not declared microorganisms. PCR-DGGE turned out to be an appropriate culture-independent approach for a rapid detection of the predominant species in mixed probiotic cultures.

Proposal to reclassify Leuconostoc oenos as Oenococcus oeni [corrig.] gen. nov., comb. nov

Wine strains belonging to the genus Leuconostoc were classified as Leuconostoc oenos by Garvie in 1967, and this name was confirmed on the Approved Lists of Bacterial Names in 1980. L. oenos is distinguished from other Leuconostoc spp. by its growth in acidic media, by its requirement for a growth factor in tomato juice, and by a number of carbohydrate fermentation characteristics. In addition, the results of a total soluble cell protein analysis, an electrophoretic analysis of NAD-dependent D-(-)-lactate dehydrogenase, 6-phosphogluconate dehydrogenase, and alcohol dehydrogenase, and an analysis of cross-reactivity with anti-glucose-6-phosphate dehydrogenase and anti-NAD-dependent D-(-)-lactate dehydrogenase performed with other Leuconostoc spp. clearly indicated that L. oenos should be distinguished from the other Leuconostoc species. Phylogenetic studies, in particular 16S and 23S rRNA sequencing studies, have revealed that L. oenos represents a distinct subline that is separate from other Leuconostoc spp. and lactic acid bacteria. In view of the phenotypic and phylogenetic distinctiveness of L. oenos, we propose that this species should be assigned to a new genus as Oenococcus oeni [corrig.] gen. nov., comb. nov. The type strain of O. oeni is NCDO 1674 (= ATCC 23179).

Reclassification of Lactobacillus casei subsp. casei ATCC 393 and Lactobacillus rhamnosus ATCC 15820 as Lactobacillus zeae nom. rev., designation of ATCC 334 as the neotype of L. casei subsp. casei, and rejection of the name Lactobacillus paracasei

The type strain of Lactobacillus casei subsp. casei (ATCC 393) exhibits low levels of DNA homology with other strains of L. casei subsp. casei (8 to 46%) and strains of Lactobacillus paracasei (30 to 50%), but exhibits a level of DNA similarity of 80% with Lactobacillus rhamnosus ATCC 15820, the original type strain of "Lactobacterium zeae" Kuznetsov 1959. Strains ATCC 393T (T = type strain) and ATCC 15820T are members of one protein profile cluster that is separate from the other Lactobacillus spp. The randomly amplified polymorphic DNA PCR profile of strain ATCC 393T is also different from the profiles obtained for the other species. L. casei ATCC 334T is genetically closely related to L. casei subsp. casei strains (71 to 97%) and L. paracasei strains (71 to 91%), is a member of the same protein profile cluster as these organisms, and shares several DNA amplicons with L. paracasei strains. On the basis of these results, we propose that L. casei subsp. casei ATCC 393T and L. rhamnosus ATCC 15820 should be reclassified as members of Lactobacillus zeae nom. rev. (type strain, ATCC 15820), that strain ATCC 334 should be designated the neotype strain of L. casei subsp. casei, and that the name L. paracasei should be rejected.

Analysis of bifidobacterial evolution using a multilocus approach

Bifidobacteria represent one of the most numerous groups of bacteria found in the gastrointestinal tract of humans and animals. In man, gastrointestinal bifidobacteria are associated with health effects and for this reason they are often used as functional ingredients in food and pharmaceutical products. Such applications may benefit from or require a clear and reliable bifidobacterial species identification. The increasing number of available bacterial genome sequences has provided a large amount of housekeeping gene sequences that can be used both for identification of bifidobacterial species as well as for understanding bifidobacterial evolution. In order to assess their relative positions in the evolutionary process, fragments from seven conserved genes, clpC, dnaB, dnaG, dnaJ1, purF, rpoC and xfp, were sequenced from each of the currently described type strains of the genus Bifidobacterium. The results demonstrate that the concatenation of these seven gene sequences for phylogenetic purposes allows a significant increase in the discriminatory power between taxa.

Development of reverse transcription (RT)-PCR and real-time RT-PCR assays for rapid detection and quantification of viable yeasts and molds contaminating yogurts and pasteurized food products

Reverse transcriptase PCR (RT-PCR) and real-time RT-PCR assays have been used to detect and quantify actin mRNA from yeasts and molds. Universal primers were designed based on the available fungal actin sequences, and by RT-PCR they amplified a specific 353-bp fragment from fungal species involved in food spoilage. From experiments on heat-treated cells, actin mRNA was a good indicator of cell viability: viable cells and cells in a nonculturable state were detected, while no signal was observed from dead cells. The optimized RT-PCR assay was able to detect 10 CFU of fungi ml(-1) in pure culture and 10(3) and 10(2) CFU ml(-1) in artificially contaminated yogurts and pasteurized fruit-derived products, respectively. Real-time RT-PCR, performed on a range of spoiled commercial food products, validated the suitability of actin mRNA detection for the quantification of naturally contaminating fungi. The specificity and sensitivity of the procedure, combined with its speed, its reliability, and the potential automation of the technique, offer several advantages to routine analysis programs that assess the presence and viability of fungi in food commodities.

Differences in faecal bacterial communities in coeliac and healthy children as detected by PCR and denaturing gradient gel electrophoresis

Coeliac disease (CD) is a chronic inflammatory disorder of the small intestinal mucosa. Scientific evidence supports a role of the gut microbiota in chronic inflammatory disorders; yet information is not specifically available for CD. In this study, a comparative denaturing gradient gel electrophoresis analysis of faecal samples from coeliac children and age-matched controls was carried out. The diversity of the faecal microbiota was significantly higher in coeliac children than in healthy controls. The presence of the species Lactobacillus curvatus, Leuconostoc mesenteroides and Leuconostoc carnosum was characteristic of coeliac patients, while that of the Lactobacillus casei group was characteristic of healthy controls. The Bifidobacterium population showed a significantly higher species diversity in healthy children than in coeliacs. In healthy children, this population was characterized by the presence of Bifidobacterium adolescentis. Overall, the results highlighted the need for further characterization of the microbiota in coeliac patients, and suggested a potential role of probiotics and/or prebiotics in restoring their gut microbial balance.

Use of PCR-based methods for rapid differentiation of Lactobacillus delbrueckii subsp. bulgaricus and L. delbrueckii subsp. lactis

Two PCR-based methods, specific PCR and randomly amplified polymorphic DNA PCR (RAPD-PCR), were used for rapid and reliable differentiation of Lactobacillus delbrueckii subsp. bulgaricus and L. delbrueckii subsp. lactis. PCR with a single combination of primers which targeted the proline iminopeptidase (pepIP) gene of L. delbrueckii subsp. bulgaricus allowed amplification of genomic fragments specific for the two subspecies when either DNA from a single colony or cells extracted from dairy products were used. A numerical analysis of the RAPD-PCR patterns obtained with primer M13 gave results that were consistent with the results of specific PCR for all strains except L. delbrueckii subsp. delbrueckii LMG 6412(T), which clustered with L. delbrueckii subsp. lactis strains. In addition, RAPD-PCR performed with primer 1254 provided highly polymorphic profiles and thus was superior for distinguishing individual L. delbrueckii strains.

Phenotypic and genetic diversity of enterococci isolated from Italian cheeses

In the present study, 124 enterococcal strains, isolated from traditional Italian cow, goat and buffalo cheeses, were characterized using phenotypic features and randomly amplified polymorphic DNA polymerase chain reaction (RAPD-PCR). The RAPD-PCR profiles obtained with four primers and five different amplification conditions were compared by numerical analysis and allowed an inter- and intraspecific differentiation of the isolates. Whole cell protein analysis by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) was used as a reference method for species identification. The strains were identified as Enterococcus faecalis (82 strains), E. faecium (27 strains), E. durans (nine strains), E. gallinarum (four strains) and E. hirae (two strains). Species recognition by means of RAPD-PCR was in agreement with the SDS-PAGE results except for eight strains of E. faecium that clustered in separated groups. On the other hand, phenotypic identification based on carbohydrate fermentation profiles, using the rapid ID 32 STREP galleries, gave different results from SDS-PAGE in 12.1% of the cases. The majority of the strains had weak acidifying and proteolytic activities in milk. One E. faecium strain showed vanA (vancomycin resistance) genotype while four strains showed a beta-haemolytic reaction on human blood. Several strains showed antagonistic activity towards indicator strains of Listeria innocua, Clostridium tyrobutyricam and Propionibacterium freudenreichii subsp. shermanii.

The status of the species Lactobacillus casei (Orla-Jensen 1916) Hansen and Lessel 1971 and Lactobacillus paracasei Collins et al. 1989. Request for an opinion

On the basis of considerable published evidence, it is concluded that the species Lactobacillus casei is not correctly represented by the strain actually designated as the type strain ATCC 393. It is proposed that the Judicial Commission consider: (1) that ATCC 393T is scientifically unsuitable as the type strain of Lactobacillus casei and should be reclassified as Lactobacillus zeae; (2) that Lactobacillus casei ATCC 334 and Lactobacillus paracasei strains are members of the same taxon and therefore can be united within the name Lactobacillus casei (Rules 42 and 23a), the name Lactobacillus paracasei being rejected; and (3) designating ATCC 334 as the neotype strain for the species

Comparative sequence analysis of a recA gene fragment brings new evidence for a change in the taxonomy of the Lactobacillus casei group

The taxonomic positions of species of the Lactobacillus casei group have been evaluated by sequencing and phylogenetic analysis of a 277 bp recA gene fragment. High sequence similarity between strain ATCC 393T, currently designated as the type strain of L. casei, and the type strain of Lactobacillus zeae, LMG 17315T, has been established, while L. casei ATCC 334 and Lactobacillus paracasei NCDO 151T form a single phylogenetic group. The taxonomic status of species and strains at issue is discussed.

Genomic DNA fingerprinting of Oenococcus oeni strains by pulsed-field gel electrophoresis and randomly amplified polymorphic DNA-PCR

Genetic diversity of 60 Oenococcus oeni strains from different wines was evaluated by numerical analysis of (i) pulsed-field gel electrophoresis (PFGE) patterns with endonuclease ApaI and (ii) randomly amplified polymorphic DNA (RAPD)-PCR fingerprints with four oligonucleotide primers. Sixty-two percent of the strains could be distinguished by PFGE, whereas most strains were identified by distinct RAPD-PCR profiles and associated according to the geographical origin. Because of its rapidity and reliability, RAPD-PCR appeared to be a suitable method for typing and monitoring O. oeni strains in winemaking.

Lactobacillus plantarum subsp. argentoratensis subsp. nov., isolated from vegetable matrices

Fourteen strains isolated from vegetable sources and identified as belonging to Lactobacillus plantarum presented an atypical pattern of amplification with a species-specific multiplex-PCR assay. Phylogenetic analysis of two protein-encoding genes, recA (encoding the recombinase A protein) and cpn60 (encoding the GroEL chaperonin), as well as phenotypic and genomic traits revealed a homogeneous group of very closely related strains for which subspecies status is proposed, with the name Lactobacillus plantarum subsp. argentoratensis. The type strain is DKO 22T (=CIP 108320T=DSM 16365T).

Intraspecies genomic groups in Enterococcus faecium and their correlation with origin and pathogenicity

Seventy-eight Enterococcus faecium strains from various sources were characterized by random amplified polymorphic DNA (RAPD)-PCR, amplified fragment length polymorphism (AFLP), and pulsed-field gel electrophoresis (PFGE) analysis of SmaI restriction patterns. Two main genomic groups (I and II) were obtained in both RAPD-PCR and AFLP analyses. DNA-DNA hybridization values between representative strains of both groups demonstrated a mean DNA-DNA reassociation level of 71%. PFGE analysis revealed high genetic strain diversity within the two genomic groups. Only group I contained strains originating from human clinical samples or strains that were vancomycin-resistant or beta-hemolytic. No differentiating phenotypic features between groups I and II were found using the rapid ID 32 STREP system. The two groups could be further subdivided into, respectively, four and three subclusters in both RAPD-PCR and AFLP analyses, and a high correlation was seen between the subclusters generated by these two methods. Subclusters of group I were to some extent correlated with origin, pathogenicity, and bacteriocinogeny of the strains. Host specificity of E. faecium strains was not confirmed.

Design and evaluation of malolactic enzyme gene targeted primers for rapid identification and detection of Oenococcus oeni in wine

Rapid identification and detection of Oenococcus oeni was achieved by species-specific PCR. Two primers flanking a 1025 bp region of the O. oeni gene encoding the malolactic enzyme were designed. The expected DNA amplificate was obtained only when purified DNA from O. oeni was used. The identity of PCR product was confirmed by nested PCR and restriction analysis. Within 8 h, 10(3) cfu ml-1 of oenococci were detected in fermenting grape must containing 10(7) yeast cells, whereas the detection limit in wine was 10(4) cfu ml-1. The rapidity and reliability of the PCR procedure established suggests that the method may be profitably applied in winery laboratories for quality control.

Characterization of sourdough lactic acid bacteria based on genotypic and cell-wall protein analyses

AIMS

To evaluate the effectiveness of two independent methods in differentiating a large population of lactic acid bacteria (LAB) isolated from wheat flours and sourdoughs and to correlate eventual differences/similarities among strains with their geographical origin and/or process parameters.

METHODS AND RESULTS

One hundred fifty strains belonging to Lactobacillus spp. and Weissella spp., plus eight type strains, one for each species, and two unidentified isolates, were characterized by randomly amplified polymorphic DNA (RAPD) and SDS-PAGE of cell-wall proteins. The RAPD analysis separated the eight type strains but did not always assign all the strains of a species to the same group, while SDS-PAGE cell-wall protein profiles were species-specific. Frequently, strains isolated from sourdoughs of the same geographical origin or produced by similar raw material/process parameters showed similar RAPD and/or cell-wall profiles.

CONCLUSIONS

The combined use of the RAPD and cell-wall protein analysis represents a useful tool to classify large adventitious microbial populations and to discriminate the diversity of the strains.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study represents a typing of a large collection of flour/sourdough LAB and provides evidence of the advantage of using two independent methods in the classification and traceability of microorganisms.

Lactobacillus curvatus subsp. curvatus subsp. nov. and Lactobacillus curvatus subsp. melibiosus subsp. nov. and Lactobacillus sake subsp. sake subsp. nov. and Lactobacillus sake subsp. carnosus subsp. nov., new subspecies of Lactobacillus curvatus Abo-Elnaga and Kandler 1965 and Lactobacillus sake Katagiri, Kitahara, and Fukami 1934 (Klein et al. 1996, emended descriptions), respectively

Lactobacillus curvatus and Lactobacillus sake are each genetically homogeneous species, as indicated by the high levels of DNA homology (> or = 76%) exhibited by strains of these taxa. However, the results of a numerical analysis of total soluble cell protein patterns and biochemical test data revealed that there are two phenotypic subgroups within L, curvatus and two phenotypic subgroups within L. sake. The overall randomly amplified polymorphic DNA (RAPD)-PCR band patterns obtained for the majority of L. curvatus strains corresponded well to the pattern obtained for the type strain of L. curvatus (strain DSM 20019). However, six strains of L. curvatus had different, but similar, RAPD-PCR profiles and grouped in a separate genetic cluster, which was linked to one of the clusters of L. sake strains. On the basis of these results, differences in biochemical and physiological characteristics, and total soluble cell protein profiles, we describe the subspecies L. curvatus subsp. curvatus subsp. nov. and L. curvatus subsp. melibiosus subsp. nov. for L. curvatus Abo-Elnaga and Kandler 1965 (Klein et al. 1996, emended description). Strains of L. sake grouped in two RAPD-PCR clusters, which was consistent with previous reports of phenotypic heterogeneity. Strains of Lactobacillus bavaricus, including type strain LMG 9844, clustered with the type strain of L. sake (strain NCFB 2714), indicating that these organisms belong to the same genetic group. We propose that strains of L. sake Katagiri, Kitahara, and Fukami 1934 (Klein et al. 1996, emended description) should be reclassified as members of L. sake subsp. sake subsp. nov. and L. sake subsp. carnosus subsp. nov. Strains of L. bavaricus are reclassified as members of L. sake subsp. sake, and the name L. bavaricus Stetter and Stetter 1980 is rejected.

Lactobacillus rossii sp. nov., isolated from wheat sourdough

Screening of sourdough lactic acid bacteria for bacteriocin production resulted in the isolation of a Gram-positive, catalase-negative, non-spore-forming, non-motile rod bacterium (strain CS1T) that could not be associated with any previously described species. Comparative 16S rRNA gene sequence analysis recognized strain CS1T as a distinct member of the genus Lactobacillus. By a species-specific PCR strategy, five additional strains previously isolated from sourdoughs were found to belong to the same species as strain CS1T, as confirmed by 16S rRNA gene sequence analysis. The closest related species were Lactobacillus durianis, Lactobacillus malefermentans and Lactobacillus suebicus, with which strain CS1T shared 93 % sequence similarity. For a further characterization of strain CS1T, physiological (growth temperature, CO2 production, hydrolysis of arginine, isomeric type of lactate, sugar fermentation) and chemotaxonomic (G+C content and peptidoglycan structure) properties were determined. Phenotypic characterization showed that strain CS1T was a member of the obligately heterofermentative group of the genus Lactobacillus. The DNA G+C content was 44.6 mol%. The peptidoglycan was of the A3alpha (L-Lys-L-Ser-L-Ala2) type. Physiological, biochemical and genotypic data, as well as results of DNA-DNA hybridization of genomic DNA with one of the closest phylogenetic relatives, L. durianis (34.3 %), indicated that strain CS1T represents a novel species of the genus Lactobacillus for which the name Lactobacillus rossii sp. nov. is proposed. The type strain of this species is CS1T (=ATCC BAA-822T=DSM 15814T).

Differentiation of Lactobacillus plantarum, L. pentosus and L. paraplantarum species by RAPD-PCR and AFLP

Two high-resolution genotypic techniques (RAPD-PCR and AFLP) were evaluated for their possibility to discriminate the species Lactobacillus plantarum, Lactobacillus pentosus and Lactobacillus paraplantarum and to type these taxa at the infra-species level. In total 23 strains of L. plantarum, three strains of L. pentosus, two strains of L. paraplantarum and two related strains for which the species assignment was not clear, were studied. For RAPD-PCR, suitable oligonucleotides and amplification conditions were selected and tested. For AFLP, a double digest of total genomic DNA was used and a subset of restriction fragments was selectively amplified and visualised using different primer combinations. Both methodologies generated, species-specific electrophoretic profiles. Moreover, the presence of distinct subgroups was revealed within the species L. plantarum.

Contribution of enterococci to the spread of antibiotic resistance in the production chain of swine meat commodities

Thirty-six samples, including fecal specimens, dry feedstuffs, raw and processed pork meat products, and dry fermented sausages, were collected from two production chains of swine meat commodities and analyzed for the presence of 11 antibiotic resistance (AR) genes. Specific PCR assays carried out on DNA extracted directly from the samples revealed a high incidence of the genes tet(K) (80.5%), ermB (66.7%), and tet(M) (66.7%). Feces and feedstuffs gave the largest number of positive amplifications. To elucidate the contribution of enterococci to the occurrence and spread of AR, 146 resistant enterococci were isolated, and their identity, genetic fingerprints, and AR gene profiles were determined by means of molecular techniques. Enterococcus faecalis and Enterococcus faecium were the predominant isolated species (43.8 and 38.4%, respectively); Other Enterococcus species identified were E. durans (8.9%), E. hirae (2.7%), E. gallinarum (2.1%), E. mundtii (2.1%), and E. casseliflavus (2.1%). A number of isolates displayed a complex AR gene profile comprising up to four different resistance determinants. The genes tet(M) and ermB were highly diffused, being present in 86.9 and 84.9%, respectively, of the isolates. The application of amplified fragment length polymorphism fingerprinting was particularly valuable to monitor the resistant enterococcal isolates along the production chain and to individuate steps in which contamination might occur. In fact, isolates of E. faecalis and E. faecium showing the same amplified fragment length polymorphism profile and AR gene pattern were detected in samples taken at different steps of the food chain suggesting three cases of bacterial clonal spread.

Evolution of the bacterial species Lactobacillus delbrueckii: a partial genomic study with reflections on prokaryotic species concept

The species Lactobacillus delbrueckii consists at present of three subspecies, delbrueckii, lactis and bulgaricus, showing a high level of DNA-DNA hybridization similarity but presenting markedly different traits related to distinct ecological adaptation. The internal genetic heterogeneity of the bacterial species L. delbrueckii was analyzed. Phenotypic and several genetic traits were investigated for 61 strains belonging to this species. These included 16S rDNA sequence mutations, expression of beta-galactosidase and of the cell wall-anchored protease, the characterization of the lactose operon locus and of the sequence of lacR gene, galactose metabolism, and the distribution of insertion sequences. The high genetic heterogeneity of taxa was confirmed by every trait investigated: the lac operon was completely deleted in the subsp. delbrueckii, different mutation events in the repressor gene of the operon led to a constitutive expression of lacZ in the subsp. bulgaricus. Structural differences in the same genetic locus were probably due to the presence of different IS elements in the flanking regions. The different expression of the cell wall-anchored protease, constitutive in the subsp. bulgaricus, inducible in the subsp. lactis, and absent in the subsp. delbrueckii was also a consequence of mutations at the gene level. The galT gene for galactose metabolism was found only in the subsp. lactis, while no specific amplification product was detected in the other two subspecies. All these data, together with the absence of a specific IS element, ISL6, from the major number of strains belonging to the subsp. bulgaricus, confirmed a deep internal heterogeneity among the three subspecies. Moreover, this evidence and the directional mutations found in the 16S rDNA sequences suggested that, of the three subspecies, L. delbrueckii subsp. lactis is the taxon closer to the ancestor. Limitations of the current prokaryotic species definition were also discussed, based on presented evidences. Our results indicate the need for an accurate investigation of internal heterogeneity of bacterial species. This study has consequences on the prokaryotic species concept, since genomic flexibility of prokaryotes collides with a stable classification, necessary from a scientific and applied point of view.

Description of Gluconacetobacter swingsii sp. nov. and Gluconacetobacter rhaeticus sp. nov., isolated from Italian apple fruit

Two Gram-negative, rod-shaped, non-spore-forming bacteria (DST GL01T and DST GL02T) were isolated from apple fruit juice in the region of the Italian Alps. On the basis of 16S rRNA gene sequence similarities, strains DST GL01T and DST GL02T were shown to belong to the α-subclass of the Proteobacteria, and, in particular, to the genus Gluconacetobacter, in the Gluconacetobacter xylinus branch (98·5–100 %). Chemotaxonomic data (major ubiquinone, Q10; predominant fatty acid, C18 : 1ω7c , accounting for approximately 50 % of the fatty acid content) support the affiliation of both strains to the genus Gluconacetobacter. The results of DNA–DNA hybridizations, together with physiological and biochemical data, allowed genotypic and phenotypic differentiation between strains DST GL01T and DST GL02T and from the 11 validly published Gluconacetobacter species. They therefore represent two new species, for which the names Gluconacetobacter swingsii sp. nov. and Gluconacetobacter rhaeticus sp. nov. are proposed, with the type strains DST GL01T (=LMG 22125T=DSM 16373T) and DST GL02T (=LMG 22126T=DSM 16663T), respectively.