Predominant Colonizers Research Articles

Investigating into microbiota in the uterine cavity of the unexplained recurrent pregnancy loss patients in early pregnancy

IntroductionThe majority of unexplained recurrent pregnancy loss (URPL) cases have been attributed to immune abnormalities. Inappropriate changes in microbiota could lead to immune disorders. However, the specific role of uterine cavity microbiota in URPL remains unclear, and only a limited number of related studies are available for reference. MethodsWe utilized double-lumen embryo transfer tubes to collect uterine cavity fluid samples from pregnant women in their first trimester. Subsequently, we conducted 16S rRNA sequencing to analyze the composition and abundance of the microbiota in these samples. ResultsFor this study, we enlisted 10 cases of URPL and 28 cases of induced miscarriages during early pregnancy. Microbial communities were detected in all samples of the URPL group (100 %, n = 10), whereas none were found in the control group (0 %, n = 28). Among the identified microbes, Lactobacillus and Curvibacter were the two most dominant species. The abundance of Curvibacter is correlated with the number of NK cells in peripheral blood (r = −0.759, P = 0.018). DiscussionThis study revealed that during early pregnancy, Lactobacillus and Curvibacter were the predominant colonizers in the uterine cavity of URPL patients and were associated with URPL. Consequently, alterations in the dominant microbiota may lead to adverse pregnancy outcomes.

Bioactivity and antibacterial properties of calcium- and silver-doped coatings on 3D printed titanium scaffolds

One of the major problems faced by metallic implants is the high probability of bacterial infections, with significant consequences for the patient. In this work, a thermochemical treatment is proposed to obtain silver-doped calcium titanate coatings on the Ti surface to improve the bioactivity of porous 3D-printed Ti structures and simultaneously provide them with antibacterial properties. A complete characterization of the new coating, the study of the ion release and the analysis of its cytotoxicity were carried out together with evaluation of the natural apatite forming in simulated body fluid (SBF). Moreover, the antibacterial properties of the coatings were assessed against Pseudomona aeruginosa and Escherichia coli as gram-negative and Staphylococcus aureus and Staphylococcus epidermidis as gram-positive bacterial strains. Ag ions were integrated into the Ca titanate layer and Ag nanoparticles were formed within the entire 3D Ti surface. Ca and Ag ions were released from both porous and solid samples into the Hanks' solution for 48 h. The treated surfaces showed no cytotoxicity and an apatite layer precipitated on the entire porous surface when the samples were immersed in SBF. The release of Ag from the surface had a strong antibacterial effect and prevented bacterial adhesion and proliferation on the surface. Moreover, the nanostructured topography of the coating resulted also in a reduction of bacterial adhesion and proliferation, even in absence of Ag. In conclusion, the cost-effective approach here reported provided protection against the most predominant bacterial colonizers to the Ti porous implants, while maintaining their bioactivity.

Structure and evolution of the bifidobacterial carbohydrate metabolism proteins and enzymes.

Bifidobacteria have attracted significant attention because they provide health-promoting effects in the human gut. In this review, we present a current overview of the three-dimensional structures of bifidobacterial proteins involved in carbohydrate uptake, degradation, and metabolism. As predominant early colonizers of the infant's gut, distinct bifidobacterial species are equipped with a panel of transporters and enzymes specific for human milk oligosaccharides (HMOs). Interestingly, Bifidobacterium bifidum and Bifidobacterium longum possess lacto-N-biosidases with unrelated structural folds to release the disaccharide lacto-N-biose from HMOs, suggesting the convergent evolution of this activity from different ancestral proteins. The crystal structures of enzymes that confer the degradation of glycans from the mucin glycoprotein layer provide a structural basis for the utilization of this sustainable nutrient in the gastrointestinal tract. The utilization of several plant dietary oligosaccharides has been studied in detail, and the prime importance of oligosaccharide-specific ATP-binding cassette (ABC) transporters in glycan utilisations by bifidobacteria has been revealed. The structural elements underpinning the high selectivity and roles of ABC transporter binding proteins in establishing competitive growth on preferred oligosaccharides are discussed. Distinct ABC transporters are conserved across several bifidobacterial species, e.g. those targeting arabinoxylooligosaccharide and α-1,6-galactosides/glucosides. Less prevalent transporters, e.g. targeting β-mannooligosaccharides, may contribute to the metabolic specialisation within Bifidobacterium. Some bifidobacterial species have established symbiotic relationships with humans. Structural studies of carbohydrate-utilizing systems in Bifidobacterium have revealed the interesting history of molecular coevolution with the host, as highlighted by the early selection of bifidobacteria by mucin and breast milk glycans.

An Analysis of Forensically Important Insects Associated with Human Remains in Indiana, U.S.A.

Research documenting insect colonization of human remains is limited in North America, and currently nonexistent for the American Midwest. Such research is essential for forensic entomologists to identify species of research interest in a region. In this study, we collected insects from human remains in 24 cases across Indiana from June 2016 through September 2018. We analyzed species composition across scene type and season. Eight species of blow flies were collected as larvae from human remains, with Phormia regina and Lucilia sericata as the two predominant colonizers. Phormia regina was the most numerous species collected from outdoor scenes (73.6% of total collections) while L.sericata was the most numerous from the indoor scenes (60.4% of total collections). With scene types pooled, Calliphora vicina and Cochliomya macellaria were the predominant species in the fall (55.6% and 42.2%, respectively); P.regina was the dominant colonizer in the spring (68.6%); and P.regina and L.sericata were the predominant colonizers (46.5% and 44.4%, respectively) in the summer. In addition to these findings, we confirmed the first record of Lucilia cuprina colonizing human remains in Indiana having collected this species from three cases. A single adult Chrysomya megacephala was collected from an indoor scene in southern Indiana, which represents its second collection in the state. Beetles belonging to the families Staphylinidae, Silphidae, Histeridae, Cleridae, Trogidae, Dermestdae, and Nitidulidae were also collected from two outdoor scenes. This study provides important baseline data for forensic entomologists in Indiana, as well as surrounding states with similar environments.

Diversity and Tissue Preference of Osmotolerant Bacterial Endophytes Associated with Pearl Millet Genotypes Having Differential Drought Susceptibilities.

Genetic and functional diversity of osmotolerant bacterial endophytes colonizing the root, stem, and leaf tissues of pearl millet genotypes differing in their drought susceptibility was assessed. Two genotypes of pearl millet, viz., the drought tolerant genotype TT-1 and the drought susceptible genotype PPMI-69, were used in the present study. Diazotrophs were found to be the predominant colonizers, followed by the Gram positive bacteria in most of the tissues of both the genotypes. Higher proportion of bacterial endophytes obtained from the drought tolerant genotype was found to be osmotolerant. Results of 16S rRNA gene-ARDRA analysis grouped 50 of the highly osmotolerant isolates into 16 clusters, out of which nine clusters had only one isolate each, indicating their uniqueness. One cluster had 21 isolates and remaining clusters were represented by isolates ranging from two to four. The representative isolates from each cluster were identified, and Bacillus was found to be the most prevalent osmotolerant genera with many different species. Other endophytic bacteria belonged to Pseudomonas sp., Stenotrophomonas sp., and Macrococcus caseolyticus. High phylogenetic diversity was observed in the roots of the drought tolerant genotype while different tissues of the drought susceptible genotype showed less diversity. Isolates of Bacillus axarquiensis were present in all the tissues of both the genotypes of pearl millet. However, most of the other endophytic bacteria showed tissue/genotype specificity. With the exception of B. axarquiensis and B. thuringiensis, rest all the species of Bacillus were found colonizing only the drought-tolerant genotype; while M. caseolyticus colonized all the tissues of only the drought susceptible genotype. There was high incidence of IAA producers and low incidence of ACC deaminase producers among the isolates from the root tissues of the drought-tolerant genotype while reverse was the case for the drought-susceptible genotype. Thus, host played an important role in the selection of endophytes based on both phylogenetic and functional traits.

Spatial Distribution of Benthic Macroinvertebrate Assemblages in Relation to Environmental Variables in Korean Nationwide Streams

Conserving and enhancing freshwater biodiversity are global issues to ensure ecosystem integrity and sustainability. To meet this, it is critical to understand how the biological assemblages are determined by environmental gradients in different spatial scales. Nevertheless, information on their large-scale environmental relationships remains scarce in Korea. We aimed to understand nationwide spatial distribution patterns of benthic macroinvertebrates and important environmental factors affecting their distribution in 388 streams and rivers across Korea. A total of 340 taxa, belonging to 113 families in 23 orders of five phyla, were identified. Assemblage composition in most Korean streams included a few predominant colonizers and a majority of rare taxa. Cluster analysis based on benthic macroinvertebrates classified a total of 720 sampling sites into five clusters according to the pollution levels from fast-flowing less polluted streams with low electrical conductivity to moderately or severely polluted streams with high electrical conductivity and slow water velocity. Canonical correspondence analysis revealed that altitude, water velocity and streambed composition were the most important determinants, rather than watershed and water chemistry variables, for explaining the variation in macroinvertebrate assemblage patterns. The results provide basic information for establishing the conservation and restoration strategies of macroinvertebrate biodiversity against anthropogenic disturbances and developing more confident bio-assessment tools for diagnosing stream ecosystem integrity.

Distributional patterns of freshwater ascomycetes communities along an Andes to Amazon elevational gradient in Peru

Freshwater ascomycetes are the predominant fungal colonizers of ligno-cellulosic substrates submerged in freshwater habitats. Although considered important decomposers and a food resource in freshwater food webs, little is known about the influence of environmental factors on their geographical distribution patterns, species richness and community structure. We undertook a study of the distribution of freshwater lignolytic ascomycetes in the Madre de Dios River basin in Peru along an elevational gradient from the headwater regions dominated by the Inambari and Araza Rivers to the lowlands of the Madre de Dios River. The gradient extended from 218 to 3870 m; collections were made at low ( 1000 m) elevations. Three separate collecting trips were conducted during the dry seasons over 3 years. Samples of submerged woody debris were returned to the University of Illinois where they were incubated in moist chambers and examined for the presence of sexual and asexual reproductive structures, which were used for identification. GPS location, altitude, water temperature and pH were measured at the time of collection. A total of 2187 vouchered fungal collections representing 268 fungal taxa were collected. One hundred and fifty-nine taxa were collected at low elevations, 201 at middle elevations and 56 at high elevations. Only 33 of 268 taxa occurred at all three elevational ranges. Canonical analyses of principal coordinates and Sorensons Similarity Index of species based on presence/absence data revealed different structuring of freshwater fungal communities at low, middle, and high elevations, indicating a change in species composition along the Andes to Amazon elevation gradient. Mantel’s tests demonstrated that beta diversity is strongly impacted by both elevation and pH as rapid taxonomic turnover was associated with both these factors. Of 140 species found in their sexual reproductive state, only ten occurred at all three elevational ranges. The most commonly occurring species was Annulatascus velatisporus, a species with a worldwide distribution. Of 128 taxa found in their asexual reproductive state, 23 occurred at all three elevational ranges. The most commonly collected species was Candelabrum broccchiatum, also a species with a worldwide distribution. Most of the taxa reported from Peru have been reported previously from Asian and/or Australian freshwater tropical habitats. One hundred and three species are new records for South America and 137 species are new records for Peru. About 80 species found in Peru have a pan-tropical distribution. Whether these distribution patterns exist due to vicariance or geodispersal remains to be determined. This study indicates that the composition of fungal communities in mountainous areas is influenced by elevation and has implications for the effects of global warming.

Fluorescence in situ hybridization probing of protozoal Entodinium spp. and their methanogenic colonizers in the rumen of cattle fed alfalfa hay or triticale straw

To develop and test a fluorescence in situ hybridization (FISH) based technique and to identify and quantify simultaneously those methanogenic populations colonizing Entodinium spp. in the rumen of cows fed different forages. New FISH probes targeting protozoal Entodinium spp. were designed and used together with FISH probes for methanogens in the cow rumen. The composition and relative abundance of methanogenic populations colonizing Entodinium simplex-, E. caudaum- and Entodinium furca-related populations were similar. Methanogens including Methanobrevibacter thaueri, Methanobrevibacter millerae and Methanobrevibacter smithii, and members of Methanomicrobium and Methanosphaera were generally the predominant colonizers of protozoa, regardless of the forage fed to cattle. Individual animals appeared to differ in which ruminal methanogenic populations colonized each of the individual Entodinium spp. Simultaneous FISH probing is shown here to be a reliable and effective approach to investigate the dynamics of symbiotic relationships between ruminal protozoa and methanogens at a single cell level. Phylogenetically closely related Entodinium spp. were colonized by similar methanogenic populations regardless of the forage fed. This is the first report of the methanogenic archaeal populations that specifically colonize Entodinium spp. as identified using simultaneous FISH probing.

Identification of a functional capsule locus in Streptococcus mitis

The polysaccharide capsule of Streptococcus pneumoniae is a hallmark for virulence in humans. In its close relative Streptococcus mitis, a common human commensal, analysis of the sequenced genomes of six strains revealed the presence of a putative capsule locus in four of them. We constructed an isogenic S.mitis mutant from the type strain that lacked the 19 open reading frames in the capsule locus (Δcps mutant), using a deletion strategy similar to previous capsule functional studies in S.pneumoniae. Transmission electron microscopy and atomic force microscopy revealed a capsule-like structure in the S.mitis type strain that was absent or reduced in the Δcps mutant. Since S.mitis are predominant oral colonizers of tooth surfaces, we addressed the relevance of the capsule locus for the S.mitis overall surface properties, autoaggregation and biofilm formation. The capsule deletion resulted in a mutant with approximately two-fold increase in hydrophobicity. Binding to the Stains-all cationic dye was reduced by 40%, suggesting a reduction in the overall negative surface charge of the mutant. The mutant exhibited also increased autoaggregation in coaggregation buffer, and up to six-fold increase in biofilm levels. The results suggested that the capsule locus is associated with production of a capsule-like structure in S.mitis and indicated that the S.mitis capsule-like structure may confer surface attributes similar to those associated with the capsule in S.pneumoniae.

Evaluation of the Ugandan sorghum accessions for grain mold and anthracnose resistance

Sorghum accessions from Uganda were evaluated for grain mold and anthracnose resistance during the 2005 and 2006 growing seasons at the Texas A&M University Research Farm, near College Station, TX. Accession PI534117 and SC719-11E exhibited the lowest grain mold severities of 2.4, whereas, accessions PI534117, PI534144, PI576337, PI297199, PI533833, and PI297210, with SC748-5 were highly resistant to anthracnose in both years. Accessions PI534117, PI297134, PI297156 exhibited low grain mold severities in 2006. Significant negative correlation was recorded between grain mold and percent germination and high temperature in both years. In 2006, daily precipitation recorded significant positive correlation with grain mold. The seed mycoflora was analyzed across sorghum lines and treatments. In 2005, Curvularia lunata and Fusarium thapsinum were the most frequently recovered fungal species with 31 and 21% incidence, respectively, followed by Alternaria spp. (19%) and F. semitectum (13%). In 2006, predominant colonizers were F. thapsinum (58%), followed by Alternaria and F. semitectum with 15 and 10, percent respectively, while C. lunata had a 6% incidence. In this study, PI534117 holds promise for multiple disease resistance, as it had the lowest disease severity of grain mold and was highly resistant to anthracnose in both years. It also has a high germination rate, a high seed weight, and its short stature is more advantageous for the new A-line conversion program.

In vitro and in planta assays for biological control of Fusarium root rot disease of vanilla

Rhizosphere and phyllosphere organisms isolated from vanilla consisted of predominant colonizers such as Fusarium sp. (24 isolates) and Colletotrichum sp. (20 isolates). Other organisms were Rhizoctonia sp. (two isolates), Trichoderma spp. (seven isolates), Paecilomyces sp. (one isolate), Mucor sp. (three isolates), non-sporulating fungal species (10 isolates) and Pseudomonas fluorescens (three isolates). When tested in vitro, six isolates showed more than 50% inhibition of Fusarium oxysporum f. sp. vanillae. These were two isolates of Trichoderma sp. (53.30-70.58), one isolate of Paecilomyces sp. (65.00%) and two isolates of P. fluorescens (59.15- 62.50%) that were antagonistic to the pathogen. None of the non-pathogenic Fusarium species tested showed promising inhibitory effect on F. oxysporum f. sp. vanillae. The five promising isolates were tested in planta by challenge inoculation. Paecilomyces sp. provided 100 per cent protection against root rot. T. harzianum and P. fluorescens provided 40% protection. Thus the present study indicated the possibility of using Paecilomyces sp. as a potential antagonist for F. oxysporum f. sp. vanillae .

Mycobiota of the Takamatsuzuka and Kitora Tumuli in Japan, focusing on the molecular phylogenetic diversity of Fusarium and Trichoderma

In an effort to clarify the cause of the deterioration of the colorfully painted murals that adorn the inner walls of the small stone chambers in the Takamatsuzuka and Kitora Tumuli in Japan, we enumerated the fungi that were isolated from moldy spots on the plaster walls collected between May 2004 and April 2005. The 262 fungal isolates from 79 samples of both tumuli were identified as approximately 100 species based on their phenotypic characters. Fusarium, Trichoderma, and Penicillium species were the predominant colonizers in the stone chamber interior and adjacent areas of both tumuli. In addition to the 28S phylogeny, neighbor-joining and Bayesian phylogenies of partial EF-1-alpha gene sequences revealed 24 genetically diverse fusaria in the Takamatsuzuka and Kitora Tumuli. Most of the fusaria were nested in clade 3 of the Fusarium solani species complex (FSSC); however, a few isolates were members of the F. oxysporum species complex (FOSC) clade or the F. avenaceum/F. tricinctum species complex clade. The FSSC isolates were compared with those detected in the Lascaux cave in France. In addition, a partial EF-1α gene phylogeny indicated that 13 Trichoderma isolates clustered in the Harzianum-Virens clade and 5 isolates in the Viride clade or Trichoderma sect. Longibrachiatum. Our analyses suggest that most of the fungi recovered from both tumuli are typically soil dwellers.

Mycobiota of the Takamatsuzuka and Kitora Tumuli in Japan, focusing on the molecular phylogenetic diversity of <i>Fusarium</i> and <i>Trichoderma</i>

In an effort to clarify the cause of the deterioration of the colorfully painted murals that adorn the inner walls of the small stone chambers in the Takamatsuzuka and Kitora Tumuli in Japan, we enumerated the fungi that were isolated from moldy spots on the plaster walls collected between May 2004 and April 2005. The 262 fungal isolates from 79 samples of both tumuli were identified as approximately 100 species based on their phenotypic characters. Fusarium, Trichoderma, and Penicillium species were the predominant colonizers in the stone chamber interior and adjacent areas of both tumuli. In addition to the 28S phylogeny, neighbor-joining and Bayesian phylogenies of partial EF-1-alpha gene sequences revealed 24 genetically diverse fusaria in the Takamatsuzuka and Kitora Tumuli. Most of the fusaria were nested in clade 3 of the Fusarium solani species complex (FSSC); however, a few isolates were members of the F. oxysporum species complex (FOSC) clade or the F. avenaceum/F. tricinctum species complex clade. The FSSC isolates were compared with those detected in the Lascaux cave in France. In addition, a partial EF-1α gene phylogeny indicated that 13 Trichoderma isolates clustered in the Harzianum-Virens clade and 5 isolates in the Viride clade or Trichoderma sect. Longibrachiatum. Our analyses suggest that most of the fungi recovered from both tumuli are typically soil dwellers.

Identification of early microbial colonizers in human dental biofilm

To elucidate the first colonizers within in vivo dental biofilm and to establish potential population shifts that occur during the early phases of biofilm formation. A 'checkerboard' DNA-DNA hybridization assay was employed to identify 40 different bacterial strains. Dental biofilm samples were collected from 15 healthy subjects, 0, 2, 4 and 6 h after tooth cleaning and the composition of these samples was compared with that of whole saliva collected from the same individuals. The bacterial distribution in biofilm samples was distinct from that in saliva, confirming the selectivity of the adhesion process. In the very early stages, the predominant tooth colonizers were found to be Actinomyces species. The relative proportion of streptococci, in particular Streptococcus mitis and S. oralis, increased at the expense of Actinomyces species between 2 and 6 h while the absolute level of Actinomyces remained unaltered. Periodontal pathogens such as Tannerella forsythensis(Bacteroides forsythus), Porphyromonas gingivalis and Treponema denticola as well as Actinobacillus actinomycetemcomitans were present in extremely low levels at all the examined time intervals in this healthy group of subjects. The data provide a detailed insight into the bacterial population shifts occurring within the first few hours of biofilm formation and show that the early colonizers of the tooth surface predominantly consist of beneficial micro-organisms. The early colonizers of dental plaque are of great importance in the succession stages of biofilm formation and its overall effect on the oral health of the host.

Direct detection of cell surface interactive forces of sessile, fimbriated and non-fimbriated Actinomyces spp. using atomic force microscopy

Actinomyces species are predominant early colonizers of the oral cavity and prime mediators of inter-bacterial adhesion and coaggregation. Previous workers have evaluated the adhesion of Actinomyces spp. by quantitative assessment of sessile, as opposed to planktonic cells attached to substrates, but did not quantify the cell surface interactive forces. Therefore we used atomic force microscopy to directly detect the interactive force between an approaching silicon tip and sessile Actinomyces spp. adhering to a substrate, at nanonewton (nN) range force levels. A total of eight strains each belonging to fimbriated and non-fimbriated Actinomyces species were employed, namely A. bovis, A. gerencseriae, A. israelii, A. meyeri, A. naeslundii genospecies 1 and 2, A. odontolyticus and A. viscosus. The sterile mica discs, used as the adhesion substrate, were immersed in mono-species bacterial suspensions for five days to obtain a thin bacterial biofilm. Interactive forces were measured using a silicon nitride cantilever attached to a Nanoscope IIIA atomic force microscope. The interactive forces between the approaching silicon nitride tip and bacterial biofilm surfaces were randomly quantified at three different locations on each cell; namely, the cell surface proper, the periphery of the cell and the substrate and, the interface between two cells. When the interactive forces at these locations of the same species were compared, significantly higher force levels at the cell–cell interface than the other two locations were noted with A. gerencseriae ( P < 0.001), A. viscosus ( P < 0.01) and A. israelii ( P < 0.05). When the interactive forces of different Actinomyces spp. at an identical location were compared, fimbriated A. naeslundii genospecies 2 showed the greatest interactive force at the cell surface proper (−32.6 ± 8.7 nN, P < 0.01). A. naeslundii genospecies 1, 2 and A. viscosus demonstrated greater interactive force at the cell-mica periphery than the other five species ( P < 0.05); A. viscosus (−34.6 ± 10.5 nN) displayed greater interactive force at the cell–cell interface than the others ( P < 0.01), except for A. gerencseriae ( P > 0.05). These data indicate that fimbriated Actinomyces spp., including A. naeslundii genospecies 1, 2 and A. viscosus exert higher cell surface interactive forces than those devoid of fimbriae and, such variable force levels may modulate their adhesion and coaggregation during biofilm formation.

Population dynamics of the sympagic amphipods Gammarus wilkitzkii and Apherusa glacialis in sea ice north of Svalbard

The population structure and production of the two autochthonous sympagic amphipods, Gammarus wilkitzkii and Apherusa glacialis, collected in different categories of sea ice north of Svalbard and in the Fram Strait, were examined. A longevity of 6 years for male G. wilkitzkii and 5–6 years for females was indicated, using a Mixture distribution analysis technique. Growth is best described by the Gompertz growth function. The theoretical maximum body length was estimated to be 53.2 and 45.3 mm, and the corresponding maximum age was estimated to be 7.5 and 6.3 years for males and females, respectively. Juveniles of age classes 0+ and 1+ of G. wilkitzkii were most abundant in first-year ice and were regarded as predominant colonizers of new ice habitats. It is unclear whether juveniles have colonized the ice independently or been released there by females colonizing the new ice. Age classes 2+ and 3+ were numerous in multi-year ice. The growth rate for G. wilkitzkii was low, and lower for females than for males. Highest growth rates were found in an area dominated by old ice. A mean production of 0.0237 g ash-free dry weight year–1 m–2 and a somatic P/B ratio (productivity) of 0.255 year–1 were calculated for the entire set of data. Individuals of age class 4+ were the most productive within the population, while juveniles have little influence on the annual productivity. A. glacialis reached a maximum age of 2 years and age class 0+ was about tenfold more abundant compared to age class 1+, indicating a high mortality rate during the 1st year of life. The population structure seems to be more affected by ice conditions (e.g. floe size) than by the age of the ice.

Colonization of a dynamic substrate: factors influencing recruitment of the wood-boring isopod, Sphaeroma terebrans, onto red mangrove (Rhizophora mangle) prop roots.

The isopod Sphaeroma terebrans, which bores into the prop roots of the red mangrove, Rhizophora mangle, can cause death and subsequent breakage of the inhabited root and, debatably, may reduce the support system of the tree. We examined whether different characteristics of a root or its physical setting, both of which may relate to habitat quality, influence the colonization of S. terebrans. A series of in situ experimental manipulations were conducted over 2years. The first experimental protocol examined colonization of intact root substratum. Free-hanging aerial prop roots which were previously unsubmerged were bent down and anchored underwater at high tide after which the colonization of S. terebrans was monitored. A second manipulation was performed to evaluate the relative roles of submergence depth and plant anatomy in isopod colonization preference. Detached aerial prop roots were oriented either with the root tip directed downward, or upside down with the root tip directed upward but at a constant water depth. Additionally, detached aerial prop roots were oriented so that their tips were in contact with the sediment surface in order to investigate whether colonization on grounded roots was prevented by benthic predators. For all experiments, colonization began within 24h; juveniles were the predominant colonizers. The submergence depth of a prop root, a characteristic of a root's physical setting, was consistently the strongest component correlated with the abundance of colonizing S. terebrans. The root-quality feature of root diameter was also found to play a significant role in colonization. Biotic influences, such as predation, however, did not influence recruitment of the isopod onto a root. Additionally, the absence of burrowing on grounded roots appeared to be related to intrinsic plant features. Along a root there was a strong preference by S. terebrans to colonize the root tip region (i.e., youngest part of the root) especially when these roots were also the deepest. The results of our experimental manipulation using natural root substratum are the first to identify physical setting as an important feature of habitat suitability for S. terebrans.

Molecular and genetic analyses of Actinomyces spp.

Members of the genus Actinomyces are predominant primary colonizers of the oral cavity and play an important role in initiating plaque development. These bacteria have evolved unique mechanisms that favor colonization and persistence in this micro-environment. The expression of cell-surface fimbriae is correlated with the ability of these bacteria to adhere to specific receptors on the tooth and mucosal surfaces, and to interact with other plaque bacteria. The elaboration of sialidase is thought to enhance fimbriae-mediated adherence by unmasking the fimbrial receptors on mammalian cells. The presence of certain cell-associated or extracellular enzymes, including those involved in sucrose or urea metabolism, may provide the means for these bacteria to thrive under conditions when other growth nutrients are not available. Moreover, these enzyme activities may influence the distribution of other plaque bacteria and promote selection for Actinomyces spp. in certain ecological niches. The recent development of a genetic transfer system for Actinomyces spp. has allowed for studies the results of which demonstrate the existence of multiple genes involved in fimbriae synthesis and function, and facilitated the construction of allelic replacement mutants at each gene locus. Analyses of these mutants have revealed a direct correlation between the synthesis of assembled fimbriae and the observed adherence properties. Further genetic analysis of the various enzyme activities detected from strains of Actinomyces should allow for an assessment of the role of these components in microbial ecology, and their contribution to the overall success of Actinomyces spp. as a primary colonizer and a key player in oral health and disease.

Bacterial endosymbionts in the gills of the deep-sea wood-boring bivalves Xylophaga atlantica and Xylophaga washingtona.

Bacterial endosymbionts found in gill tissues in several bivalve families convert otherwise unavailable energy sources (sulfide, methane, or cellulose) to forms readily metabolized by their hosts. We investigated the existence of such a symbiosis in two species of Xylophaga (family Pholadidae). The genus Xylophaga includes opportunistic species that are the predominant colonizers of wood at depths greater than 150 m. It has been hypothesized that, like their shallow-water counterparts the shipworms (family Teredinidae), species of Xylophaga utilize wood for nutrition. Results from transmission and scanning electron microscopy of X. atlantica and X. washingtona clearly demonstrate the presence of endosymbionts that resemble the shipworm endosymbionts both morphologically and in their anatomical location within the gills. Xylophaga and the teredinids both have a caecum packed with wood chips but lack the dense populations of microorganisms associated with cellulose digestion in termites or ruminants. These observations suggest that Xylophaga has evolved a symbiotic solution to wood digestion similar to that seen in shipworms. Hence, the Xylophaga symbiosis suggests a mechanism for the conversion of terrestrially derived cellulosic carbon from wood into animal biomass in the deep sea.

On the composition of the intestinal microbiota of Fridericia hegemon (Enchytraeidae)

A computer-aided numerical taxonomic analysis on selected representative bacterial and actinomycete strains isolated from fresh faecal pellets of Fridericia Hegemon (Enchytraeidae) revealed that pseudomonads, belonging to a particular variety of Pseudomonas aureofaciens, are the predominant gut colonizers of this worm. These, together with nocardioform actinomycetes, among them “Non Motile Oerskovia-like Organisms” (NMOs: Type-B), Micrococcus spp and undetermined Gram-positive, nonfermenting rods constitute the larger fraction of the intestinal microbial population. The faecal bacteria of F. hegemon are mostly Gram-negative, non-fermenting, developing well at 5°C but, apart from a few strains, not multiplying at 38°C, actively producing H 2S, growing quickly at high pH values. chitinase-negative and phosphatase-positive organisms, which can grow on simple synthetic media.