Bacteroides stercorirosoris sp. nov. and Bacteroides faecichinchillae sp. nov., isolated from chinchilla (Chinchilla lanigera) faeces

The roles of different Bacteroides uniformis strains in alleviating DSS-induced ulcerative colitis and related functional genes

Bacteroides is a common intestinal bacterium closely associated with host colitis. However, relevant studies have been focused on the genus level, which could not identify the major Bacteroides species associated with intestinal disease. Thus, we have evaluated the Bacteroides species structure in healthy people and mouse intestinal tracts and explored the change in major Bacteroides species during colitis development. The results demonstrated that B. uniformis with a high abundance in the intestinal tract of healthy people and mice may be a core species that contributes to colitis remission. The results of animal experiments reported that B. uniformis FNMHLBE1K1 (1K1) could alleviate the severity of colitis and enhance the expression of the tight junction protein occludin by regulating gut microbiota. Notably, the protective roles of 1K1 may be attributed to some specific genes. This study revealed that B. uniformis is a key microbe influencing the occurrence and development of colitis and it provides a scientific basis for screening the next generation of probiotics.

Influence of the densities and nutritional components of bacterial colonies on the culture-enriched gut bacterial community structure

Isolating relevant microorganisms is still a substantial challenge that limits the use of bacteria in the maintenance of human health. To confirm which media and which bacterial colony densities can enrich certain kinds of bacteria, we selected eight common media and used them to enrich the gut microorganisms on agar plates. Then, we calculated the numbers of bacterial colonies and collected the bacterial culture mixtures from each kind of medium. Using the Illumina HiSeq platform, we analyzed the composition and diversity of the culture-enriched gut bacterial community. Our data suggested that medium supplemented with blood could increase the diversity of the bacterial community. In addition, beef powder and peptone could significantly change the culture-enriched bacterial community. A moderate density (100-150 colony-forming units per plate) was optimal for obtaining the highest diversity on the agar. Similarly, membrane transport was significantly enriched in the moderate-density group, which indicated a more active metabolism in this density range. Overall, these results reveal the optimal culture conditions, including the densities of colonies and nutritional components for various gut bacteria, that provide a novel strategy for isolating bacteria in a way that is targeted and avoids blinded and repetitive work.

Roles of intestinal bacteroides in human health and diseases

Bacteroides, an abundant genus in the intestines of mammals, has been recently considered as the next generation probiotics (NGP) candidate due to its potential role in promoting host health. However, the role of Bacteroides in the development of intestinal dysfunctions such as diarrhea, inflammatory bowel disease, and colorectal cancer should not be overlooked. In the present study, we focused on nine most widely occurred and abundant Bacteroides species and discussed their roles in host immunity, glucose and lipid metabolism and the prevention or induction of diseases. Besides, we also discussed the current methods used in the safety evaluation of Bacteroides species and key opinions about the concerns of these strains for the future use.

Bacteroides faecalis sp. nov., isolated from human faeces

A novel Gram-stain-negative and strictly anaerobic bacterial strain, designated KGMB02408^T, was isolated from faeces of a healthy human in the Republic of Korea. The isolate was characterized as non-motile, non-spore-forming and rod-shaped (variable in length). The results of phylogenetic analysis based on 16S rRNA gene sequences revealed that strain KGMB02408^T belonged to the genus Bacteroides and was most closely related to Bacteroides faecichinchillae JCM 17102^T (=KCTC 15666^T; 96.5 %). Based on its whole-genome sequence, the DNA G+C content of the isolate was 39.5 mol%. The average nucleotide identity value between strain KGMB02408^T and related species, B. faecichinchillae JCM 17102^T, was 93.8 %. The major cellular fatty acids (>10 %) of the isolate were anteiso-C_15 : 0, iso-C_17 : 0-OH, summed feature 11 (iso-C_17 : 0-OH and/or C_18 : 2 DMA) and C_16 : 0. Menaquinone-8 (28.6 %) and menaquinone-10 (47.1 %) were detected as the major respiratory quinones in the isolate. The major end products of glucose fermentation produced by strain KGMB02408^T were lactic acid, acetic acid and formic acid. Based on its phylogenetic, phenotypic and chemotaxonomic characteristics, strain KGMB02408^T represents a novel species of the genus Bacteroides in the family Bacteroidaceae. The type strain is KGMB02408^T (=KCTC 15687^T=DSM 107828^T).

Analysis of 1,000 Type-Strain Genomes Improves Taxonomic Classification of Bacteroidetes

Although considerable progress has been made in recent years regarding the classification of bacteria assigned to the phylum Bacteroidetes, there remains a need to further clarify taxonomic relationships within a diverse assemblage that includes organisms of clinical, piscicultural, and ecological importance. Bacteroidetes classification has proved to be difficult, not least when taxonomic decisions rested heavily on interpretation of poorly resolved 16S rRNA gene trees and a limited number of phenotypic features. Here, draft genome sequences of a greatly enlarged collection of genomes of more than 1,000 Bacteroidetes and outgroup type strains were used to infer phylogenetic trees from genome-scale data using the principles drawn from phylogenetic systematics. The majority of taxa were found to be monophyletic but several orders, families and genera, including taxa proposed long ago such as Bacteroides, Cytophaga, and Flavobacterium but also quite recent taxa, as well as a few species were shown to be in need of revision. According proposals are made for the recognition of new orders, families and genera, as well as the transfer of a variety of species to other genera. In addition, emended descriptions are given for many species mainly involving information on DNA G+C content and (approximate) genome size, both of which can be considered valuable taxonomic markers. We detected many incongruities when comparing the results of the present study with existing classifications, which appear to be caused by insufficiently resolved 16S rRNA gene trees or incomplete taxon sampling. The few significant incongruities found between 16S rRNA gene and whole genome trees underline the pitfalls inherent in phylogenies based upon single gene sequences and the impediment in using ordinary bootstrapping in phylogenomic studies, particularly when combined with too narrow gene selections. While a significant degree of phylogenetic conservation was detected in all phenotypic characters investigated, the overall fit to the tree varied considerably, which is one of the probable causes of misclassifications in the past, much like the use of plesiomorphic character states as diagnostic features.

Intra-Genomic Heterogeneity in 16S rRNA Genes in Strictly Anaerobic Clinical Isolates from Periodontal Abscesses

BACKGROUND

Members of the genera Prevotella, Veillonella and Fusobacterium are the predominant culturable obligate anaerobic bacteria isolated from periodontal abscesses. When determining the cumulative number of clinical anaerobic isolates from periodontal abscesses, ambiguous or overlapping signals were frequently encountered in 16S rRNA gene sequencing chromatograms, resulting in ambiguous identifications. With the exception of the genus Veillonella, the high intra-chromosomal heterogeneity of rrs genes has not been reported.

METHODS

The 16S rRNA genes of 138 clinical, strictly anaerobic isolates and one reference strain were directly sequenced, and the chromatograms were carefully examined. Gene cloning was performed for 22 typical isolates with doublet sequencing signals for the 16S rRNA genes, and four copies of the rrs-ITS genes of 9 Prevotella intermedia isolates were separately amplified by PCR, sequenced and compared. Five conserved housekeeping genes, hsp60, recA, dnaJ, gyrB1 and rpoB from 89 clinical isolates of Prevotella were also amplified by PCR and sequenced for identification and phylogenetic analysis along with 18 Prevotella reference strains.

RESULTS

Heterogeneity of 16S rRNA genes was apparent in clinical, strictly anaerobic oral bacteria, particularly in the genera Prevotella and Veillonella. One hundred out of 138 anaerobic strains (72%) had intragenomic nucleotide polymorphisms (SNPs) in multiple locations, and 13 strains (9.4%) had intragenomic insertions or deletions in the 16S rRNA gene. In the genera Prevotella and Veillonella, 75% (67/89) and 100% (19/19) of the strains had SNPs in the 16S rRNA gene, respectively. Gene cloning and separate amplifications of four copies of the rrs-ITS genes confirmed that 2 to 4 heterogeneous 16S rRNA copies existed.

CONCLUSION

Sequence alignment of five housekeeping genes revealed that intra-species nucleotide similarities were very high in the genera Prevotella, ranging from 94.3-100%. However, the inter-species similarities were relatively low, ranging from 68.7-97.9%. The housekeeping genes rpoB and gyrB1 were demonstrated to be alternative classification markers to the species level based on intra- and inter-species comparisons, whereas based on phylogenetic tree rpoB proved to be reliable phylogenetic marker for the genus Prevotella.

Draconibacterium orientale gen. nov., sp. nov., isolated from two distinct marine environments, and proposal of Draconibacteriaceae fam. nov

The taxonomic characteristics of two bacterial strains, FH5T and SS4, isolated from enrichment cultures obtained from two distinct marine environments, were determined. These bacteria were Gram-stain-negative, facultatively anaerobic rods. Growth occurred at 20–40 °C (optimum, 28–32 °C), pH 5.5–9.0 (optimum, pH 7.0–7.5) and in the presence of 1–7 % NaCl (optimum, 2–4 %). The major cellular fatty acids were anteiso-C15 : 0 and iso-C15 : 0. Menaquinone 7 (MK-7) was the sole respiratory quinone. The major polar lipids were phosphatidylethanolamine, an unkown phospholipid and an unknown lipid. The DNA G+C contents of strains FH5T and SS4 were both determined to be 42.0 mol%. The results of DNA–DNA hybridization studies indicated that the FH5T and SS4 genomes share greater than 95 % relatedness. The strains formed a distinct phyletic line within the class Bacteroidia , with less than 89.4 % sequence similarity to their closest relatives with validly published names. On the basis of physiological and biochemical characteristics, 16S rRNA gene sequences and chemical properties, a novel genus and species, Draconibacterium orientale gen. nov., sp. nov., within the class Bacteroidia , are proposed, with strain FH5T ( = DSM 25947T = CICC 10585T) as the type strain. In addition, a new family, Draconibacteriaceae fam. nov., is proposed to accommodate Draconibacterium gen. nov.

Parabacteroides chinchillae sp. nov., isolated from chinchilla (Chincilla lanigera) faeces

Strains of Gram-stain-negative, anaerobic, rod-shaped bacteria were isolated from chinchilla (Chinchilla lanigera) faeces, and strain ST166(T) was investigated taxonomically. Phylogenetic analyses of 16S rRNA gene sequences revealed that strain ST166(T) belonged to the genus Parabacteroides. Strain ST166(T) formed a distinct line of descent, and the highest sequence similarity to ST166(T) was found with Parabacteroides merdae JCM 9497(T) (95.6%) and Parabacteroides johnsonii JCM 13406(T) (95.0%). Analysis of hsp60 gene sequences also supported these relationships. Based on the phenotypic and phylogenetic characteristics, the novel species Parabacteroides chinchillae sp. nov. is proposed. The type strain of P. chinchillae sp. nov. is ST166(T) ( = JCM 17104(T) =CCUG 62154(T)).

Reclassification of Xylanibacter oryzae Ueki et al. 2006 as Prevotella oryzae comb. nov., with an emended description of the genus Prevotella

16S rRNA gene sequence information has indicated that Xylanibacter oryzae has a close relationship with the genus Prevotella. To clarify the taxonomic position of X. oryzae, we determined the sequence of hsp60 as it represents an alternative phylogenetic marker for identification and classification of Gram-negative anaerobic rods. On the basis of hsp60 sequences, X. oryzae was located within the genus Prevotella, indicating that the species does not represent a distinct taxon at the genus level. Statistical tests (the Shimodaira-Hasegawa test and the approximately unbiased test) supported the finding that X. oryzae is monophyletic with members of the genus Prevotella and thus belongs to the genus. On the basis of the phylogenetic findings, we propose that X. oryzae should be reclassified as Prevotella oryzae comb. nov.; the type strain is KB3(T) (=JCM 13648(T) =DSM 17970(T)). An emended description of the genus Prevotella is also provided.