Insights into the taxonomy, genetics and physiology of bifidobacteria

Despite the generally accepted importance of bifidobacteria as probiotic components of the human intestinal microflora and their use in health promoting foods, there is only limited information about their phylogenetic position, physiology and underlying genetics. In the last few years numerous molecular approaches have emerged for the identification and characterization of bifidobacterial strains. Their use, in conjunction with traditional culturing methods, has led to a polyphasic taxonomy which has significantly enhanced our knowledge of the role played by these bacteria in the human intestinal ecosystem. The recent adaptation of culture-independent molecular tools to the fingerprinting of intestinal and food communities offers an exciting opportunity for revealing a more detailed picture of the true complexity of these environments. Furthermore, the availability of bifidobacterial genome sequences has advanced knowledge on the genetics of bifidobacteria and the effects of their metabolic activities on the intestinal ecosystem. The release of a complete Bifidobacterium longum genome sequence and the recent initiative to sequence additional strains are expected to open up a new era of comparative genomics in bifidobacterial biology. Moreover, the use of genomotyping allows a global comparative analysis of gene content between different bifidobacterial isolates of a given species without the necessity of sequencing many strains. Genomotyping provides useful information about the degree of relatedness among various strains of Bifidobacterium species and consequently can be used in a polyphasic identification approach. This review will deal mainly with the molecular tools described for bifidobacterial identification and the first insights into the underlying genetics involved in bifidobacterial physiology as well as genome variability.     

Pollen morphology of the Thymelaeaceae in relation to its taxonomy

 Pollen morphology of the four subfamilies of Thymelaeaceae sensu Domke (1934) was examined using LM, SEM and TEM. The variation of the exine architecture allows to distinguish four pollen types and three subtypes. Distribution of pollen types proves to be widely correlated with the occurrence of characters from wood anatomy and flower morphology. If pollen types are connected with subfamilies sensu Domke (1934), Gonystyloideae, Thymelaeoideae and Synandrodaphnoideae are stenopalynous, whereas Aquilarioideae are eurypalynous. Based on pollen morphology as well as on other characters it is evident that Aquilarioideae are not monophyletic. Its genera Aquilaria and Gyrinops are more closely related to Thymelaeoideae and Synandrodaphnoideae than to other genera of Aquilarioideae sensu Domke (1934). The remaining genera of Aquilarioideae Deltaria, Solmsia and Lethedon are most similar to Gonystyloideae and therefore are included in this subfamily, as it was suggested by Airy Shaw (1979). Furthermore, palynological and other characters favour the transfer of Octolepis from Aquilarioideae to Gonystyloideae. The re-circumscribed Aquilarioideae together with Thymelaeoideae and Synandrodaphnoideae are shown to form a monophyletic group. Received August 8, 2001 Accepted December 7, 2001     

Mechanism of the variation of the acetate/lactate/ratio during glucose fermentation by bifidobacteria (author's transl)]

It is demonstrated that most strains of bifidobacteria form much more acetate and less lactic acid from glucose than is to be expected according to the breakdown of glucose via the "bifidoshunt". The analysis of isotope distribution among the fermentation products of glucose labeled in different positions showed that the excess of acetate is the result of the phosphoroclastic splitting of a part of the pyruvate arising from carbons 4, 5, and 6 of glucose. In addition to acetate (carbons 5 and 6), formate is formed from carbon 4 and some acetate is reduced to ethanol. The formation of "extra" acetate occurs mainly during the log phase and is less pronounced in resting cells. The extent of the phosphoroclastic splitting of pyruvate varies considerably among different strains even among those from the same species.     

Long-call structure and its relation to taxonomy in lion tamarins

Recent evidence on craniodental morphology suggests the acceptance of three species of lion tamarins (Leontopithecus). Confirmatory evidence is presented here using the morphology of long-call vocalizations recorded from several individuals of each type of lion tamarin. Recordings were made of Leontopicthecus rosalia, Leontopithecus chrysopygus, and Leontopithecus chrysomelas at the Centro de Primatologia do Rio de Janeiro (FEEMA) and of L. rosalia at Monkey Jungle in Florida. Thirty separate parameters were measured, and 17 of them differed significantly between populations. In general, L. chrysomelas had higher pitched calls with shorter note duration, while L. chrysopygus, the larger of the animals, had lower pitched calls with longer note duration. L. rosalia was either intermediate to the other two populations or resembled L. chrysopygus. Thus, the results from the analysis of vocal structures closely paralleled the results obtained with more traditional taxonomic methods and suggests that the quantitative analysis of vocal strucures can be a useful adjunct in taxonomy.     

Pollen morphology in theBoragineae (Boraginaceae) in relation to the taxonomy of the tribe

The results of a comparative survey on pollen morphology in theBoragineae by means of light, scanning and transmission electron microscopy are presented and discussed in relation to the taxonomy of the tribe. Multivariate analyses lead to the recognition of 15 pollen morphotypes for which a discriminant key is proposed. The discriminatory characters concern mainly the stereostructural and ultrastructural features of the grains, such as tectum sculpture and aperture morphology, while the number of apertures appears variable within genera and even single species. Seven out of the 12 investigated genera, as currently circumscribed, are matched by palynological data:Anchusella, Borago, Brunnera, Elizaldia, Lithodora, Symphytum andTrachystemon. On account of aperture shape,Lithodora is however closer to theLithospermeae than to theBoragineae. Other genera, and in particularNonea, show a wide variation in tectum ornamentation, shape of grains and number of apertures. Palynological data do not support a broad concept of the genusAnchusa, and point to the autonomy of the satellite generaHormuzakia, Gastrocotyle, Phyllocara, Pentaglottis andCynoglottis.     

Distribution of carotenoids and sterols in relation to the taxonomy of Taphrina and Protomyces

Species of the genera Taphrina Fr. and Protomyces Unger were screened for the presence of carotenoid pigments and the sterols ergosterol and brassicasterol. All strains produced carotenoids in variable amounts: Taphrina: 0.3–39 g/g dry weight; Protomyces: 65–99 g/g dry weight. It was concluded that the tow genera cannot be separated on the basis of presence or absence of carotenoids. Thirty strains (24 species) of Taphrina produced brassicasterol as the principal sterol; twenty-one strains (17 species) did not form ergosterol. Only four isolates (4 species) produced ergosterol without formation of brassicasterol. Brassicasterol was the major sterol in 3 species of Protomyces, whereas ergosterol was absent. Brassicasterol is a rather unique sterol within the fungal kingdom and has hitherto not been found in the red yeasts. Therefore, this sterol is of taxonomic significance in contrast with ergosterol, which is widespread among fungi.     

Continuous fermentation of high-strength glucose feeds to ethanol

Summary Aqueous feeds of 413 and 495 g/L glucose were fermented to ethanol at 90–95% conversion in a continuous flow extractive fermentation system with cell recycle. Compared to the continuous conventional fermentation of a 195 g/L glucose medium, the volumetric productivity was more than doubled in extractive mode, with no deleterious effects on cell viability, specific glucose consumption rate or ethanol yield. The use of an effective, biocompatible and stable in situ extractant with flash vaporization can also produce a concentrated ethanol vapour stream, reducing distillation costs of the product.     

Fine structure ofMicrococcus denitrificans andM. halodenitrificans in relation to their taxonomy

A study of ultrathin sections ofMicrococcus denitrificans andM.halodenitrificans has shown similar cell structures. The cell wall consists of several layers corresponding to those of the cell wall of gram-negative bacteria. The thickness of the cell wall is 250 – 350 Å; that of the cytoplasmic membrane 70 Å. The cytoplasm in both species contains ribosomes and inclusions of polymetaphosphate. Comparison with ultrathin sections ofThiobacillus novellus shows too much difference to consider the former two species to be identical with the latter one. The taxonomic position ofM.denitrificans andM.halodenitrificans is discussed.Deceased 3 July 1967.     

Pollen morphology in relation to the taxonomy and phylogeny of some native Greek Aegilops species

The pollen morphology of some native Greek Aegilops species is investigated in LM (quantitative pollen characters) and SEM (exine sculpture) using acetolysed material. Furthermore, quantitative data are subjected to a multivariate analysis. The tetraploid Ae. cylindrica and its diploid parent Ae. caudata show a distinct morphological affinity as regards their quantitative pollen profile and the features of the exine sculpture. The tetraploid Ae. triuncialis is morphologically divergent from both its parents Ae. caudata and Ae. umbellulata due to the very large values of its quantitative pollen characters. However, the SEM survey of the exine sculpture indicates a rather high degree of similarity between Ae. triuncialis and Ae. umbellulata. No significant differences have been found between the two varieties of Ae. caudata (caudata and polyathera) concerning the quantitative pollen characters as a total or the morphology of the exine sculpture. The resultant clustering of the taxa on the basis of the quantitative pollen characters as well as the recorded similarities of their exine pattern are related to their sectional classification based on cytogenetical and morphological data.     

The chromosomes of mantids (Orthoptera; Manteidae) in relation to taxonomy

Summary The distinguishing cytological characters, including chromosome number and sex chromosome mechanism, have been tabulated for all mantids thus far studied cytologically—including 16 species (starred in Table 1) not hitherto examined. Data on 46 species in 17 subfamilies are reviewed.The XO—XX sex chromosome mechanism represents the ancestral condition for the family and has been retained in 14 of the subfamilies sampled.The distribution of the X¹X²Y—X¹X¹X²X² mechanism, previously known in the subfamilies Manteinae and Choeradodinae, is extended to include Mellierinae, Acromantinae and Vatinae.Cytological evidence indicates a monophyletic origin of the compound sex chromosomes and necessitates a reconsideration of the taxonomic association of XO and X¹X²Y forms in the same subfamily, specifically of Miomantis and Callimantis with the other Manteinae, and Aethalocroa with Vates and Phyllovates in the Vatinae.The pre-metaphase stretch is established as a regular stage in male meiosis in 14—and is absent in 3—of the species checked for this character. It should prove of taxonomic value when a wider sampling of the lower categories is available.The prolongation of parallel pairing of homologous chromosomes in male meiosis appears to be characteristic of the Manteidae as a whole. No correlation is apparent between the degree of its expression and taxonomic category. Since it provides a mechanism, additional or alternative to chiasmata, for the post-pachytene association of homologues, its establishment permits the evolution of non-chiasmate meiosis in the group.Two structural types of bivalents—one with, one without chiasmata—are found. Present evidence favors the multiple origin of the non-chiasmate type within the family, and since both types may coexist in the karyotype of the same sex of a single species, presence or absence of chiasmata cannot be considered a valid taxonomic criterion.     

Influence of oral glucose load upon blood glucose level in relation to the time of day

Blood glucose levels were estimated at different times of day in fasted rats and after 30, 60,90 and 120 min, since oral glucose load. Circadian variations in basal glucose levels and in the levels after glucose load were observed with the highest values noted between 11 a.m. and 7 p.m., and the lowest ones about midnight. These variations were most prominent when the measurements were performed 60 min after glucose load. Circadian variation in glucose tolerance was also revealed with the best tolerance at about midnight while the worst one was noted at noon and in the afternoon.     

Susceptibility of bifidobacteria to nisin

A collection of 17 bifidobacteria was tested for sensitivity or resistance to lantibiotic nisin. Minimal inhibitory concentration of the strain tested was highly variable, ranging from 4·88 to 10 000 IU ml⁻¹. In general, strains isolated from faecal samples were more resistant than those purchased from culture collections. These results could be useful in the production of foods containing both bifidobacteria and nisin.