Interactions Between Facultative Symbionts Hamiltonella and Cardinium in Bemisia tabaci (Hemiptera: Aleyrodoidea): Cooperation or Conflict?

Maternally-inherited facultative symbionts are widespread in most insect species, and it is common that several symbionts coexist in the same host individual. Hence, the symbionts may compete or share for the limited resources and space in the host. The whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodoidea), harbors a diverse array of facultative symbionts, among which Hamiltonella sp. and Cardinium sp. are abundant species. Hamiltonella alone increases host fitness, while Cardinium alone confers lower fitness. Locking those different partners together creates ideal situations for the evolution of interactions between symbionts. In this study, we compared the fitness effects of whiteflies infected with only Hamiltonella to Hamiltonella-Cardnium co-infected whiteflies and measured the density of Hamiltonella and Cardinium during host aging, aiming to explore Hamiltonella-Cardinium interactions in B. tabaci. Our results illustrated that Hamiltonella-Cardinium coinfection induced lower fecundity, egg hatchability and number of female offspring, leading to a male-biased sex ratio in offspring, while there is no evidence for reproductive incompatibility between the infections. We also found an antagonistic interaction between Hamiltonella and Cardinium given that the density of the latter increased across time and led to a decrease of Hamiltonella density, which may be the underlying causes of the fitness cost in double-infected B. tabaci. Exploring the ecological consequences of co-infections of these different symbionts helps us to understand the nature of host-symbiont interactions in this species and potential for evolutionary conflict.

Bacteroidales recruit IL-6-producing intraepithelial lymphocytes in the colon to promote barrier integrity

Interactions between the microbiota and distal gut are important for the maintenance of a healthy intestinal barrier; dysbiosis of intestinal microbial communities has emerged as a likely contributor to diseases that arise at the level of the mucosa. Intraepithelial lymphocytes (IELs) are positioned within the epithelial barrier, and in the small intestine they function to maintain epithelial homeostasis. We hypothesized that colon IELs promote epithelial barrier function through the expression of cytokines in response to interactions with commensal bacteria. Profiling of bacterial 16S ribosomal RNA revealed that candidate bacteria in the order Bacteroidales are sufficient to promote IEL presence in the colon that in turn produce interleukin-6 (IL-6) in a MyD88 (myeloid differentiation primary response 88)-dependent manner. IEL-derived IL-6 is functionally important in the maintenance of the epithelial barrier as IL-6-/- mice were noted to have increased paracellular permeability, decreased claudin-1 expression, and a thinner mucus gel layer, all of which were reversed by transfer of IL-6+/+ IELs, leading to protection of mice in response to Citrobacter rodentium infection. Therefore, we conclude that microbiota provide a homeostatic role for epithelial barrier function through regulation of IEL-derived IL-6.

Colonisation of gingival epithelia by subgingival biofilms in vitro: role of "red complex" bacteria

OBJECTIVES

Biofilm formation on tooth surface results in colonisation and invasion of the juxtaposed gingival tissue, eliciting strong inflammatory responses that lead to periodontal disease. This in vitro study investigated the colonisation of human gingival multi-layered epithelium by multi-species subgingival biofilms, and evaluated the relative effects of the "red complex" species (Porphyromonas gingivalis, Tannerella forsythia and Treponema denticola).

METHODS

The grown biofilm consisted of Fusobacterium nucleatum, Campylobacter rectus, Veillonella dispar, P. gingivalis, Prevotella intermedia, T. forsythia, T. denticola, Actinomyces oris, Streptococcus anginosus and Streptococcus oralis, or its variant lacking the "red complex". After 48h in co-culture with the gingival epithelia, the bacterial species in the biofilm were quantified, whereas their localisation on the cell surface was investigated by combining confocal-laser scanning microscopy (CLSM) and fluorescence in situ hybridisation (FISH), as well as by scanning electron microscopy (SEM).

RESULTS

Exclusion of the "red complex" quantitatively affected S. oralis, but not other species. The "red-complex" species were all able to colonise the gingival epithelial cells. A co-localisation trend was observed between P. gingivalis and T. denticola, as determined by FISH. However, in the absence of all three "red complex" bacteria from the biofilm, an immense colonisation of streptococci (potentially S. oralis) was observed on the gingival epithelia, as confirmed by both CLSM and SEM.

CONCLUSIONS

While the "red complex" species synergise in colonizing gingival epithelia, their absence from the biofilm enhances streptococcal colonisation. This antagonism with streptococci reveals that the "red complex" may regulate biofilm virulence, with potential implications in periodontal pathogenesis.

Endosymbiotic Bacteroidales bacteria of the flagellated protist Pseudotrichonympha grassii in the gut of the termite Coptotermes formosanus

A unique lineage of bacteria belonging to the order Bacteroidales was identified as an intracellular endosymbiont of the protist Pseudotrichonympha grassii (Parabasalia, Hypermastigea) in the gut of the termite Coptotermes formosanus. We identified the 16S rRNA, gyrB, elongation factor Tu, and groEL gene sequences in the endosymbiont and detected a very low level of sequence divergence (<0.9% of the nucleotides) in the endosymbiont population within and among protist cells. The Bacteroidales endosymbiont sequence was affiliated with a cluster comprising only sequences from termite gut bacteria and was not closely related to sequences identified for members of the Bacteroidales attached to the cell surfaces of other gut protists. Transmission electron microscopy showed that there were numerous rod-shaped bacteria in the cytoplasm of the host protist, and we detected the endosymbiont by fluorescence in situ hybridization (FISH) with an oligonucleotide probe specific for the 16S rRNA gene identified. Quantification of the abundance of the Bacteroidales endosymbiont by sequence-specific cleavage of rRNA with RNase H and FISH cell counting revealed, surprisingly, that the endosymbiont accounted for 82% of the total bacterial rRNA and 71% of the total bacterial cells in the gut community. The genetically nearly homogeneous endosymbionts of Pseudotrichonympha were very abundant in the gut symbiotic community of the termite.

A bacterial symbiont in the Bacteroidetes induces cytoplasmic incompatibility in the parasitoid wasp Encarsia pergandiella

Vertically transmitted symbionts of arthropods have been implicated in several reproductive manipulations of their hosts. These include cytoplasmic incompatibility (CI), parthenogenesis induction in haplodiploid species (PI), feminization and male killing. One symbiont lineage in the alpha-Proteobacteria, Wolbachia, is the only bacterium known to cause all of these effects, and has been thought to be unique in causing CI, in which the fecundity of uninfected females is reduced after mating with infected males. Here, we provide evidence that an undescribed symbiont in the Bacteroidetes group causes CI in a sexual population of the parasitic wasp Encarsia pergandiella. Wasps were crossed in all four possible combinations of infected and uninfected individuals. In the cross predicted to be incompatible, infected (I) males x uninfected (U) females, progeny production was severely reduced, with these females producing only 12.6% of the number of progeny in other crosses. The incompatibility observed in this haplodiploid species was the female mortality type; dissections showed that most progeny from the incompatible cross died as eggs. The 16S rDNA sequence of this symbiont is 99% identical to a parthenogenesis-inducing symbiont in other Encarsia, and 96% identical to a feminizing symbiont in haplodiploid Brevipalpus mites. Thus, this recently discovered symbiont lineage is capable of inducing three of the four principal manipulations of host reproduction known to be caused by Wolbachia.

Roles of mucosal bacteria and succinic acid in colitis caused by dextran sulfate sodium in mice

Intestines of mice with colitis caused by dextran sulfate sodium (DSS) contain more Bacteroidaceae cells than untreated controls. We investigated the roles of intestinal bacteria and succinic acid, a by-product of Bacteroidaceae metabolism, in this model of colitis. CBA/J mice were given 3% DSS in water for 14 days. After mice were anesthetized and killed, concentrations of organic acids in stools from the cecum and colon were measured. The resected rectum and colon were washed with sterile saline; some specimens were incubated with imipenem in saline for 1 h to kill bacteria on the surfaces and others were not. Their homogenates were cultured anaerobically and aerobically. Separately, 1 mL of 20 mM succinic acid was infused into the rectum of mice, whose anal verge was glued. Animals were anesthetized and killed the next day. The rectum and colon were examined histologically. Concentrations of succinate were higher everywhere in the colon of mice with colitis than in controls. Mice with colitis had more Bacteroidaceae cells, especially B. caccae, than controls. Mice given succinate enemas had focal erosions of the mucosa and edema of the submucosa. Succinic acid, produced abundantly by members of the family Bacteroidaceae, especially B. caccae, may be the ulcerogenic agent in DSS colitis.

Adherence of oral microorganisms to guided tissue membranes: an in vitro study

Microorganisms can adhere and colonize on an exposed guided tissue regeneration (GTR) membrane thus developing a nidus of infection. The purpose of this study was to compare early bacterial adhesion to three different GTR membranes. Expanded polytetrafluoroethylene, polyglactin 910, and collagen were used as the test membranes. In part I of this study 15 different oral microbes were used to compare their relative ability to adhere to the membranes. Six of the most strongly adherent bacteria (Actinomyces viscosus, Actinobacillus actinomycetemcomitans, Porphyromonas gingivalis, Streptococcus mutans, Fusobacterium nucleatum, and Selenomonas sputigena) were selected for part II of this study. The membranes were placed in tubes containing broth cultures containing identical concentrations (1 x 10(8) cells/ml) of these bacteria at 37 degrees C. Membranes were placed in tubes of media without bacteria as controls. At 4, 6, 12, and 24 hours, the bacterial cultures were decanted and the membranes in the tubes were agitated gently in reduced transfer fluid (RTF) 4 times to remove non-adherent bacteria. Each tube was then sonicated for 30 seconds in 10 ml RTF to detach adherent bacteria. The detached adherent bacteria were counted using a Petroff-Hausser chamber. Data were analyzed by using the SAS program. Analysis of variance was used to test for differences between multiple means. Results showed S. mutans had the strongest attachment to the collagen membrane at 4 and 6 hours. Selenomonas sputigena had the lowest adherence capability to all test membranes. Polyglactin 910 had significantly (P < 0.05) lower S. mutants adherence than either the ePTFE or the collagen membrane at 4 and 6 hours.(ABSTRACT TRUNCATED AT 250 WORDS)

The surface structure of Leptotrichia buccalis

Leptotrichia buccalis shows a mosaic of surface structure on its outer membrane consisting of curved ridges 35 mm high and 22 nm apart, and erect on that surface. Fimbriae (common pili) are not present and nor is an S layer. The flap-like ridges consist of strings of macromolecules radiating from the cell surface. This ridge structure is not soluble in any of the usual chaotropes and can only be released when the outer membrane has been damaged or dispersed by extracting envelope preparations with 0.5% SDS at room temperature. The ridge is then found to be attached firmly to the peptidoglycan sacculus, which may be the point of origin of the structure. When so prepared the macromolecules forming the ridge can be removed from the sacculus by treatment with 6 M guanidine HCl, and SDS-PAGE analysis of the extract reveals a 210-kDa polypeptide as a major component and a 15-kDa minor component. The latter is probably a peptidoglycan-associated protein and much of it remains with the sacculus. Each string forming the ridge is of a volume consistent with being made of three elongated 210-kDa molecules, which are united in series by strong hydrophobic association and laterally with neighboring strings by slightly weaker forces. We confirm that L. buccalis causes haemagglutination and the bacteria are known to attach to various tissue cells. Human group A red blood corpuscles remove both of the proteins from solution, which supports the hypothesis that the ridges are adhesin structures. It is likely but not proven that the 210-kDa molecule is the adhesin.

[Recent bacteriologic data: from physiopathology to treatment]

Bacterial vaginosis is characterized by a change in the vaginal ecosystem in which Lactobacillus spp, the dominant members of the normal flora, are replaced by an association of various bacterial species including Gardnerella vaginalis, anaerobes (Bacteroides spp, Prevotella spp, Porphyromonas spp, Peptostreptococcus spp and Mobiluncus spp) and Mycoplasma hominis. The reasons for this imbalance are unknown, although the loss of lactobacilli that produce hydrogen peroxide (which is toxic for G. vaginalis and numerous anaerobes) may be an essential element. The introduction of one or several of these species into the vagina (they can occasionally be isolated in small numbers even in the absence of vaginosis) following intercourse or from the intestinal tract may also play a role. G. vaginalis itself is not considered to cause vaginosis, but is almost always present and multiplies rapidly; in addition, it has a high capacity for adherence to epithelial cells both in vivo and in vitro. It is now agreed that the concomitant growth of one or several anaerobic species is required for bacterial vaginosis to develop. Our knowledge of the bacteriology of bacterial vaginosis has implications for diagnosis and treatment. It is now possible to obtain a precise bacteriologic diagnosis, not by culturing G. vaginalis (a costly and low-yield procedure), but by direct examination of the vaginal flora after Gram staining, which shows the replacement of lactobacilli by a characteristic polymorphic flora. Therapy is based on the use of antibiotics such as the imidazoles, which are active against G. vaginalis and anaerobes, but not against the commensal lactobacilli.(ABSTRACT TRUNCATED AT 250 WORDS)

Antimicrobial activities of black-pigmented gram-negative anaerobes

The antimicrobial activities of Prevotella intermedia and Porphyromonas gingivalis isolates were tested against other species of Gram-positive and Gram-negative anaerobes as well as against each other. Generally, Pr. intermedia possessed significantly higher antimicrobial activity than P. gingivalis. The strongest activity of P. gingivalis towards Gram-negative anaerobes was directed against Pr. intermedia. Cross-sensitivity between both species was observed with strains from different lesions. Antimicrobial activity towards strains of the same species was detected only with Pr. intermedia. No correlations were found between plasmid content and antimicrobial activity. It was concluded that the inhibitory potency of Pr. intermedia could be one reason for the high proportion of black-pigmented Gram-negative anaerobes in the subgingival flora of periodontitis lesions.

DNA base composition, aerotolerance and enzyme patterns of Leptotrichia buccalis

The guanine plus cytosine content of the DNA of Leptotrichia buccalis varied from 28.4 to 29.5 mol% (three strains). Eleven strains examined grew well under anaerobic and microaerobic conditions, but slowly in air in the presence of CO2. When examined for preformed enzymes in the APIZYM Complete Research Kit, positive reactions were obtained for several glucosidases and carboxylic ester hydrolases, and for a few peptidases.

Antagonistic effect exerted by three strictly anaerobic strains against various strains of Clostridium perfringens in gnotobiotic rodent intestines

Our purpose was to study bacterial antagonism between a limited number of strictly anaerobic strains and Clostridium perfringens in the intestinal tract of gnotobiotic rodents. Gnotobiotic mice harboring a Bacteroides thetaiotaomicron, a Fusobacterium necrogenes, and a Clostridium sp. strain were protected against pathogenic B, C, and D C. perfringens serotypes. A drastic antagonistic effect of this three-strain association was also observed against a nonpathogenic C. perfringens serotype A (CpA). It was less efficient in gnotobiotic rats than in mice and less efficient in gnotobiotic mice fed an autoclaved diet than in mice fed the same diet sterilized by irradiation. No diffusible inhibitory substances against CpA were detected in feces of gnotobiotic mice harboring the three antagonistic strains, and no nutrient depletion was demonstrated in filtrates prepared from 10-fold diluted feces of these mice. In vitro mixed cultures of the three antagonistic strains failed to inhibit growth of CpA, whereas CpA did not multiply in a 10-fold diluted feces from gnotobiotic mice. A reverse correlation between the initial number of antagonistic strains and the division number of CpA was determined using serially diluted fecal suspensions. Thus, large numbers of viable cells of both antagonistic strains were required to inhibit the target strain in fecal suspensions as was also found in gnotobiotic mice intestines. However, no diffusible inhibitory substance was detectable nor could depletion of growth factors be identified as causing antagonism. Whatever factors that may be responsible for antagonism were found to be influenced by the host and its diet.

Role of encapsulated anaerobic bacteria in synergistic infections

The effect of encapsulation on the virulence, survival, and protection of anaerobic bacteria from phagocytosis is reviewed. Support for the importance of encapsulated Bacteroides sp. and anaerobic and facultative Gram-positive cocci (AFGPC) was provided by their higher recovery rate in oropharyngeal infections, compared to their number in the normal oral flora. Studies of the pathogenicity of anaerobic bacteria of the Bacteroides, Fusobacterium, and Clostridium genera and AFGPC are also presented. The organisms were inoculated into mice and their ability to induce subcutaneous abscesses was determined. Encapsulated Bacteroides, Fusobacteria, and AFGPC generally induced abscesses, whereas unencapsulated organisms did not. However, many of the strains that had only a minimal number of encapsulated organisms (less than 1%) survived in the abscess, and became heavily encapsulated when inoculated with other viable or nonviable encapsulated bacteria. These strains were thereafter able to induce abscesses when injected alone. Encapsulated Bacteroides sp. and anaerobic cocci induced bacteremia and translocation, and increased the mortality of the infected animals more often than did the unencapsulated form of the same strains. The relative importance of encapsulated anaerobes in relation to their aerobic and facultative counterparts in mixed infection was studied, using selective antimicrobial therapy and quantitative cultures of abscesses induced in mice. With few exceptions, possession of a capsule made Bacteroides sp. more important than their aerobic counterparts. Synergistic potentials were seen between encapsulated Bacteroides sp. and all tested aerobic bacteria and most AFGPC, and between most AFGPC and Pseudomonas aeruginosa or Staphylococcus aureus. These studies demonstrated the importance of encapsulated anaerobes in mixed infections.

Modulation of the rats' immune status by monoassociation with anaerobic bacteria

The capacity of a pure culture of anaerobic intestinal bacteria to influence the host's cellular and humoral immune systems was investigated with germfree, monoassociated, and conventionally reared rats. Monoassociation of germfree rats with Bacteroides fragilis stimulated the production of serum gamma globulin, agglutinating antibodies, and an apparent IgG (immunoelectrophoresis) band. A comparison of the in vitro blastogenic potential of lymphocytes (spleen cells and mesenteric lymph node cells) from germfree, monoassociated, and conventionally reared rats indicated the following: (1) the microbial flora had no obvious effect on the capacity of nonstimulated lymphocytes to incorporate [3H]thymidine; (2) spleen cells from conventionally reared rats responded to phytohemagglutinin, concanavalin A, or pokeweed mitogen better than splenocytes from germfree rats; (3) colonization of germfree rats with Fusobacterium necrophorum increased the responsiveness of splenocytes to photohemagglutinin and concanavalin A; and (4) monoassociation of germfree rats with B. fragilis, but not with F. necrophorum or propionibacterium acnes, increased splenocyte blastogenesis to homologous (i.e., colonizing) bacterial antigens. This study indicated that some intestinal bacteria can modulate the immune status of the host; the extent and nature of this modulation depended on the particular species of colonizing bacteria.

A scheme for the identification of clinical isolates of Gram-negative anaerobic bacilli by conventional bacteriological tests

More than 1000 strains of gram-negative anaerobic bacilli, including reference strains, clinical isolates, and members of the normal flora of the mouth, lower gastro-intestinal tract and vagina of healthy human subjects, were studied by conventional bacteriological methods and by gas-liquid chromatographic analysis of metabolic products in a series of investigations. A short combined set of tests with particular discriminant value was selected, and a scheme for the identification of the species and subspecies encountered in the diagnostic bacteriological laboratory was based upon our composite results. The tests are: antibiotic-disk resistance tests with neomycin 1000 micrograms, kanamycin 1000 micrograms, penicillin 2 units and rifampicin 15 micrograms per disk; tolerance tests with sodium taurocholate, Victoria blue 4R and gentian violet; and tests for pigment production, indole production, aesculin hydrolysis and the fermentation of glucose, lactose, sucrose, rhamnose, trehalose, mannitol and xylose. Gram-negative anaerobic bacilli are divided into four groups: (1) the fragilis group with nine species, which include the five subgroups previously classified as subspecies of B. fragilis; (2) the melaninogenicus-oralis group, which includes the three saccharolytic subspecies (ss.) of B. melaninogenicus--ss. melaninogenicus, ss. intermedius and ss. levii--and four non-pigmented species; (3) the asaccharolytic group, which comprises B. asaccharolyticus (formerly B. melaninogenicus ss. asaccharolyticus), B. corrodens and other non-pigmented non-saccharolytic strains, and (4) the fusobacteria.