Bacterial diversity associated with the Brazilian endemic reef coral Mussismilia braziliensis

Aims:  We performed the first characterization of the microbiota associated with the reef coral Mussismilia braziliensis by means of a culture-independent approach.
Methods and Results:  The main groups were Proteobacteria , Cyanobacteria and unclassified bacteria according to the 16S rDNA libraries. Most of the sequences of the mucus of healthy and diseased M. braziliensis did not find close matches in GenBank (i.e. >97% 16S rDNA similarity). Most of the sequences of seawater and mucus of healthy coral fell into tight clusters (17 and 15 clusters respectively). In contrast, most of the sequences of mucus of diseased coral did not form clusters. The rarefaction curves indicate saturation in the recovery of higher taxa (approximately 40 phyla). However, the number of species in the coral mucus ( n  = 130–170) and seawater ( n  = 170) did not reach a plateau.
Conclusions:  The coral microbiota encompasses several potentially novel species and higher taxa. The microbiota of M. braziliensis appears to be species-specific. Diseased coral may have provided a suitable place for colonization by opportunistic bacteria, resulting in a greater bacterial diversity.
Significance and Impact of the Study:  The first study on the diversity of the microbiota of the endemic and endangered of extinction coral M. braziliensis .     

Vibrios dominate as culturable nitrogen-fixing bacteria of the Brazilian coral Mussismilia hispida

Taxonomic characterization was performed on the putative N₂-fixing microbiota associated with the coral species Mussismilia hispida, and with its sympatric species Palythoa caribaeorum, P. variabilis, and Zoanthus solanderi, off the coast of São Sebastião (São Paulo State, Brazil). The 95 isolates belonged to the Gammaproteobacteria according to the 16S rDNA gene sequences. In order to identify the isolates unambiguously, pyrH gene sequencing was carried out. The majority of the isolates (n=76) fell within the Vibrio core group, with the highest gene sequence similarity being towards Vibrio harveyi and Vibrio alginolyticus. Nineteen representative isolates belonging to V. harveyi (n=7), V. alginolyticus (n=8), V. campbellii (n=3), and V. parahaemolyticus (n=1) were capable of growing six successive times in nitrogen-free medium and some of them showed strong nitrogenase activity by means of the acetylene reduction assay (ARA). It was concluded that nitrogen fixation is a common phenotypic trait among Vibrio species of the core group. The fact that different Vibrio species can fix N₂ might explain why they are so abundant in the mucus of different coral species.     

Distribution and Abundance of Fauna on Living Tissues of Two Brazilian Hermatypic Corals (Mussismilia hispida (Verril 1902) and Siderastrea stellata Verril, 1868)

This study describes the distribution and abundance patterns of the associate fauna on the living surface of the corals Siderastrea stellata Verril, 1868 and Mussismilia hispida (Verril 1902) using a non-destructive method, on the northern coast of Rio de Janeiro State. For each coral species, infestation density and proportions of infested colonies, colonies attached and unattached to the substrate were estimated. A total of 474 colonies of S. stellata and 452 colonies of M. hispida were examined. The barnacle Ceratoconcha floridana (Pilsbry, 1931) was the dominant coral associate found, followed by gall-crabs of the family Cryptochiridae Paulson, 1875 and the bivalve Lithophaga bisulcata (d’Orbigny, 1842). Both coral species presented similar patterns of infestation dominance. S. stellata colonies were more commonly infested and showed a greater mean infestation density of 0.62 ind/cm² at Armação dos Búzios, whereas M. hispida colonies had infestation densities of only 0.20 ind/cm². Infestation density does not appear to impact negatively on corals of Armação dos Búzios. A clear negative relationship between the number of associates in the coral colony and coral size was found. Evidently abundance and frequency of occurrence of associated fauna is highly related to coral community structure and composition and the results highlight the importance of local scale studies.     

Responses of coral‐associated bacterial communities to heat stress differ with Symbiodinium type on the same coral host

This study compared the effect of heat stress on coral‐associated bacterial communities among juveniles of the coral, Acropora tenuis, hosting different Symbiodinium types. In comparison to a control temperature treatment (28 °C), we documented dramatic changes in bacterial associates on juvenile corals harbouring ITS 1 type D Symbiodinium when placed in a high (32 °C) temperature treatment. In particular, there was a marked increase in the number of retrieved Vibrio affiliated sequences, which coincided with a 44% decline in the photochemical efficiency of the D‐juveniles. Interestingly, these Vibrio sequences affiliated most closely with the coral pathogen, Vibrio coralliilyticus, which has been implicated in some coral disease outbreaks. In contrast, A. tenuis hosting ITS 1 type C1 Symbiodinium did not exhibit major bacterial shifts in the elevated temperature treatment, indicating a more stable bacterial community during thermal stress; concomitantly a decline (10%) in photochemical efficiency was minimal for this group. D juveniles that had been exposed to moderately elevated sea temperatures (30 °C) in the field before being placed in the control temperature treatment displayed a decrease in the number of Vibrio affiliated sequences and bacterial profiles shifted to become more similar to profiles of corals harbouring type C1 Symbiodinium. In combination, these results demonstrate that thermal stress can result in shifts in coral‐associated bacterial communities, which may lead to deteriorating coral health. The lower resilience of A. tenuis to thermal stress when harbouring Symbiodinium D highlights the importance of inter‐kingdom interactions among the coral host, dinoflagellate endosymbiont and bacterial associates for coral health and resilience.     

Associated community with the zoanthid <Emphasis Type="Italic">Palythoa caribaeorum</Emphasis> (Duchassaing &; Michelotti, 1860) (Cnidaria,Anthozoa) from littoral of Pernambuco,Brazil

The community associated with the zoanthid Palythoa caribaeorum on shores (Porto de Galinhas and Guadalupe) in northeastern Brazil were analysed. Seasonal samples (dry and wet) were made in both beaches throughout one year. This preliminary study identified 28 taxa and recognized two modes of existence, endobionts (three taxa) and hypobionts (25 taxa). Among hypobionts two patterns of ecological relationships were found: those fixed to the rocky substrata or on the base of the zoanthid colony (11 taxa) and the free-living (14 taxa). In some of these relationships, the organisms observed (Carijoa riisei and barnacles), were under the mat as victims of the zoanthid overgrowth (spatial competition). The more abundant taxa were: Mollusca (28%), Crustacea (25%), Nematoda (24%) and Polychaeta (16%). Among all samples species richness, abundance, similarity and diversity were different, especially the dry season of Porto de Galinhas. Porto de Galinhas in the dry season showed the lowest diversity with only one record. After evaluating the different ecological parameters of the P. caribaeorum-associated community, we conclude that the Guadalupe shore maintains annual homogeneity, while Porto de Galinhas shore is notably different during the year. The only environmental difference between them seems to be the effect of human activity from tourism (reef walkers, fishery and diving), that could be directly and indirectly affecting some ecological parameters of this zoanthid-associated community, such as abundance, richness and diversity of species.     

Symbiont footprints highlight the diversity of scleractinian‐associated Zanclea hydrozoans (Cnidaria,Hydrozoa)

Hydrozoans of the genus Zanclea have been acknowledged only recently as a fundamental component of the highly diverse fauna associated with reef‐building scleractinian corals. Although widely distributed in coral reefs and demonstrated to be important in protecting corals from predation and diseases, the biodiversity of these hydrozoans remains enigmatic due to the paucity of available morphological characters, incomplete morphological characterisations and the possible existence of cryptic species. Recently, molecular techniques have revealed the existence of multiple hidden genetic lineages not yet supported by diagnostic morphological characters. In this work, we further explore the morpho‐diversity of three genetic lineages, namely Zanclea associated with the coral genera Goniastrea (clade I), Porites (clade II) and Pavona (clade VI). Aside from providing a complete classical characterisation of the polyp and medusa stage of each clade, we searched for new potential taxonomic indicators either on symbiotic hydroids or on host corals. On the hydroids, statistical analyses on almost 7,000 nematocyst capsules revealed a significant difference in terms of nematocyst size among the three Zanclea clades investigated. On each host coral genus, we identified peculiar skeletal modifications related to the presence of Zanclea symbionts. Lastly, we discussed the potential diagnostic value of these footprints in the characterisation of Zanclea–scleractinian associations.     

Identity and diversity of coral endosymbionts (zooxanthellae) from three Palauan reefs with contrasting bleaching, temperature and shading histories

The potential of corals to associate with more temperature-tolerant strains of algae (zooxanthellae, Symbiodinium) can have important implications for the future of coral reefs in an era of global climate change. In this study, the genetic identity and diversity of zooxanthellae was investigated at three reefs with contrasting histories of bleaching mortality, water temperature and shading, in the Republic of Palau (Micronesia). Single-stranded conformation polymorphism and sequence analysis of the ribosomal DNA internal transcribed spacer (ITS)1 region was used for genotyping. A chronically warm but partly shaded coral reef in a marine lake that is hydrographically well connected to the surrounding waters harboured only two single-stranded conformation polymorphism profiles (i.e. zooxanthella communities). It consisted only of Symbiodinium D in all 13 nonporitid species and two Porites species investigated, with the remaining five Porites harbouring C*. Despite the high temperature in this lake (> 0.5 degrees above ambient), this reef did not suffer coral mortality during the (1998) bleaching event, however, no bleaching-sensitive coral families and genera occur in the coral community. This setting contrasts strongly with two other reefs with generally lower temperatures, in which 10 and 12 zooxanthella communities with moderate to low proportions of clade D zooxanthellae were found. The data indicate that whole coral assemblages, when growing in elevated seawater temperatures and at reduced irradiance, can be composed of colonies associated with the more thermo-tolerant clade D zooxanthellae. Future increases in seawater temperature might, therefore, result in an increasing prevalence of Symbiodinium phylotype D in scleractinian corals, possibly associated with a loss of diversity in both zooxanthellae and corals.     

Genetic diversity in and phylogenetic relationships of the Brazilian endemic cotton,Gossypium mustelinum (Malvaceae)

Gossypium mustelinum, one of five tetraploid species in the cotton genus, is geographically restricted to a few states in NE Brazil. Allozyme analysis was used to assess levels and patterns of genetic diversity inG. mustelinum and its relationship to the other tetraploid species. Genetic variation was low, with only 6 of 50 loci examined being polymorphic, a mean of 1.14 alleles per locus and a mean panmictic heterozygosity of 0.08. These estimates are low relative to other tetraploid cotton species, but are typical of island endemics. Interpopulational genetic identities were uniformly high, lending support to the concept of there being only one wild species of Brazilian cotton. The limited allelic diversity observed was correlated with geographical distribution, although variability is so limited in the species that geographically marginal populations are electrophoretically ordinary. Phylogenetic and phenetic analyses demonstrate thatG. mustelinum is isolated among polyploid cotton species, occupying one of the three basal clades resulting from an early radiation of polyploid taxa subsequent to polyploid formation. We suggest thatG. mustelinum represents a paleoendemic that presently exists as a series of widely scattered, relictual populations. Despite several centuries of sympatric cultivation ofG. barbadense andG. hirsutum, there was little evidence of interspecific introgression of alleles from cultivated cottons intoG. mustelinum.     

Patterns of Symbiodinium (Dinophyceae) diversity and assemblages among diverse hosts and the coral reef environment of Lizard Island,Australia

Large‐scale environmental disturbances may impact both partners in coral host–Symbiodinium systems. Elucidation of the assembly patterns in such complex and interdependent communities may enable better prediction of environmental impacts across coral reef ecosystems. In this study, we investigated how the community composition and diversity of dinoflagellate symbionts in the genus Symbiodinium were distributed among 12 host species from six taxonomic orders (Actinaria, Alcyonacea, Miliolida, Porifera, Rhizostoma, Scleractinia) and in the reef water and sediments at Lizard Island, Great Barrier Reef before the 3rd Global Coral Bleaching Event. 454 pyrosequencing of the ITS2 region of Symbiodinium yielded 83 operational taxonomic units (OTUs) at a 97% similarity cut‐off. Approximately half of the Symbiodinium OTUs from reef water or sediments were also present in symbio. OTUs belonged to six clades (A‐D, F‐G), but community structure was uneven. The two most abundant OTUs (100% matches to types C1 and A3) comprised 91% of reads and OTU C1 was shared by all species. However, sequence‐based analysis of these dominant OTUs revealed host species specificity, suggesting that genetic similarity cut‐offs of Symbiodinium ITS2 data sets need careful evaluation. Of the less abundant OTUs, roughly half occurred at only one site or in one species and the background Symbiodinium communities were distinct between individual samples. We conclude that sampling multiple host taxa with differing life history traits will be critical to fully understand the symbiont diversity of a given system and to predict coral ecosystem responses to environmental change and disturbance considering the differential stress response of the taxa within.     

Phylogenetic characterization of culturable bacterial diversity associated with the mucus and tissue of the coral Acropora digitifera from the Gulf of Mannar

Corals, considered the rainforests of the oceans, harbour an abundance of different bacterial populations throughout the coral structure. In the present study we attempted to characterize the cultivable bacterial population associated within the mucus and tissue of the coral Acropora digitifera from the Gulf of Mannar. 16S rRNA gene was amplified from the cultured mucus and tissue isolates. Amplified ribosomal DNA restriction analysis, performed with a combination of restriction enzymes to determine the polymorphic groups of bacteria, generated 19 distinct groups in the coral mucus and 17 distinct groups in the coral tissue. Phylogenetic analyses based on the full-length sequences of 16S rRNA gene sequences showed that the majority of bacterial isolates belonged to the group Firmicutes , followed by Gammaproteobacteria and Actinobacteria . On investigating their antimicrobial activity, mucus isolates showed about 25% activity and tissue isolates showed 48% activity. This study revealed the presence of actinomycetes in both the coral mucus and the coral tissue, which had high activity against pathogens. This study, for the first time, demonstrates that actinomycetes existing within corals also have potential antibacterial activity. This has been overlooked so far, and indicates that, in addition to mucus, bacteria within the tissue of corals might defend the coral host against pathogens.     

Production of D-amino acid oxidase (DAO) of Trigonopsis variabilis in Schizosaccharomyces pombe and the characterization of biocatalysts prepared with recombinant cells

The cDNA of D-amino acid oxidase (DAO) gene isolated from Trigonopsis variabilis was expressed in Schizosaccharomyces pombe. A clone, ASP327-10, transformed with plasmid vector, pTL2M5DAO, expressed catalytically active DAO in the presence of G418, and converted Cephalosprin C to alpha-ketoadipyl-7-cephalosporanic acid (KA-7-ACA) and glutaryl-7-aminocephalosporanic acid (GL-7-ACA). Biocatalysts were prepared using ASP327-10 and T. variabilis, and evaluated to demonstrate the feasibility of recombinant S. pombe for industrial application. The cells were immobilized by crosslinking polyethylene imine after glutardialdehyde (GDA) fixation and permeabilization by alkaline treatment. Although the biocatalyst prepared from ASP327-10 exhibited DAO activity, catalase activity still remained fully even after permeabilization, under which condition, the catalase activity of T. variabilis decreased to 20-30%. Heat treatment was required before cell fixation by GDA to inactivate the catalase in S. pombe. This improved the efficiency of bioconversion to GL-7-ACA, but caused poor mechanical strength in the biocatalyst of S. pombe. To overcome this weakness, a catalase-deficient host strain was obtained by ethylmethansulfate mutagenesis. Moreover, taking economics into consideration, the integrative vector, pTL2M5DAO-8XL, with multi-copies of expression cassette was constructed to express DAO in S. pombe even in the absence of G418. The newly established integrant, ASP417-7, did not exhibit any catalase activity so that heat treatment was not required. The obtained integrant and its biocatalyst were significantly improved in GL-7ACA conversion ability and mechanical strength. This study demonstrates that the established integrant is a potential candidate as an alternative source of DAO enzyme.     

Genomic signatures of host‐associated divergence and adaptation in a coral‐eating snail,Coralliophila violacea (Kiener, 1836)

The fluid nature of the ocean, combined with planktonic dispersal of marine larvae, lowers physical barriers to gene flow. However, divergence can still occur despite gene flow if strong selection acts on populations occupying different ecological niches. Here, we examined the population genomics of an ectoparasitic snail, Coralliophila violacea (Kiener 1836), that specializes on Porites corals in the Indo‐Pacific. Previous genetic analyses revealed two sympatric lineages associated with different coral hosts. In this study, we examined the mechanisms promoting and maintaining the snails’ adaptation to their coral hosts. Genome‐wide single nucleotide polymorphism (SNP) data from type II restriction site‐associated DNA (2b‐RAD) sequencing revealed two differentiated clusters of C. violacea that were largely concordant with coral host, consistent with previous genetic results. However, the presence of some admixed genotypes indicates gene flow from one lineage to the other. Combined, these results suggest that differentiation between host‐associated lineages of C. violacea is occurring in the face of ongoing gene flow, requiring strong selection. Indeed, 2.7% of all SNP loci were outlier loci (73/2,718), indicative of divergence with gene flow, driven by adaptation of each C. violacea lineage to their specific coral hosts.     

Description of a new Brazilian species of Mycodrosophila (Diptera,Drosophilidae) with emphasis on the morphology of phallic sclerites

Mycodrosophila is a cosmopolitan genus of Drosophilidae that comprises approximately 130 species with mycophagous habitats. In this study, we described a new species of Mycodrosophila based on morphological traits and included details of the male terminalia. The holotype is from Eugênio Lefévre, locality in Campos do Jordão municipality, SP, Brazil, located in the Atlantic rainforest biome and was sampled in the 1930s.     

Morphology and sedimentology of (clustered) cold-water coral mounds at the south Rockall Trough margins,NE Atlantic Ocean

Cold-water coral mounds on both margins of the Rockall Trough (NE Atlantic Ocean) have a strongly different morphology. Single, isolated mounds occur on the SE margin and are mainly found on the upper slope between 900 and 650 m water depth, while large mound clusters are found on the SW margin in water depths between 600 and 1,000 m, in a narrow zone almost parallel to the slope. Sedimentation rates on the mounds are higher than on the surrounding seabed as a result of baffling of biogenic carbonate debris and siliciclastic particles by the coral framework covering the mounds. This is confirmed by ²¹⁰Pb measurements. The individual coral growth rate can be three times higher then the vertical growth rate of the coral cover (±10 mm year⁻¹) which in turn is more than an order of magnitude higher then the present-day overall mound growth rate (±0.25 mm year⁻¹). The presence of extensive hardgrounds and firmgrounds and the three-dimensional coral framework are considered to be responsible for the stability of the relatively steep slopes of the mounds. High current velocities in the intramound areas result in local non-sedimentation and erosion, as is shown by the presence of IRD (ice-rafted debris) lag deposits on the seabed and moats around some of the mounds. The morphology and sedimentology of cold-water coral-covered (mainly Lophelia pertusa and Madrepora oculata) mounds on the southern Rockall Trough margins (NE Atlantic Ocean) is discussed and a model describing the development of these mounds is presented.     

The diversity, antimicrobial and anticancer activity of endophytic fungi associated with the medicinal plant Stryphnodendron adstringens (Mart.) Coville (Fabaceae) from the Brazilian savannah

The diversity and biological activities of the endophytic fungi associated with the Brazilian medicinal plant Stryphnodendron adstringens were studied. A total of 320 fungal isolates were obtained, and 66 phylotypes comprising 25 genera were identified. The fungal community of S. adstringens displayed high richness, diversity and low dominance indices. The most abundant phylotypes were closely related to Diaporthe phaseolorum, Guignardia camelliae, and Preussia pseudominima. Sixteen fungal extracts displayed biological activities when screened against bacteria, fungi, cancer cell lines, and amastigote forms of Leishmania amazonensis. The extract of phylotype Nigrospora cf. oryzae exhibited a selective antifungal activity and inhibited the growth of Candida albicans and Cladosporium sphaerospermum. The extracts of Diaporthe cf. phaseolorum and Xylaria sp. phylotypes displayed anticancer activities. Our results indicate that the endophytes associate with this medicinal plant may be a source for novel drugs.     

Characterization of the bacterial community associated with the surface and mucus layer of whiting (Merlangius merlangus)

The bacterial community inhabiting the mucus layer and surface of whiting was examined to determine whether the bacteria present are a reflection of the surrounding water or an indigenous bacterial flora is present. The outer mucus, mouth mucus and gut of four whiting harvested from a site in the Irish Sea and the surrounding water were examined by terminal restriction fragment length polymorphism (tRFLP) analysis of the 16S rRNA gene and clone library construction. The water community was the most diverse, with only a small number of shared water-mucus phylotypes present. The bacterial flora associated with the outer mucus layer were more diverse than that of the mouth mucus and gut. All three mucus layers were characterized by the presence of a dominant phylotype, identified as clone wom-1, highly similar to Photobacterium iliopiscarium. In addition to other Photobacterium phylotypes, members of the CFB and Clostridia groups were also detected. Subsequently, whiting from 11 different sites along the east and south coast of Ireland were compared by tRFLP analysis. Strikingly, the mucus layer of whiting at all sites was characterized by the presence and dominance of a TRF corresponding to the clone wom-1 which was virtually absent from the water column.     

A new genus of soft coral of the family Alcyoniidae (Cnidaria, Octocorallia) with re-description of a new combination and description of a new species

A new genus, Aldersladum (family Alcyoniidae), is established to accommodate a previously described species, Efflatounaria sodwanae Benayahu, 1993 (family Xeniidae) from Sodwana Bay, South Africa that was wrongly assigned to the latter genus. This species is redescribed and a second new species, Aldersladum jengi from Penghu Is., Taiwan, is described. The diagnostic features of the new genus include the presence of only figure-eight shaped platelets in all parts of the colony, thus differentiating it from all known genera of the Alcyoniidae. Based on examination of additional material from other localities, the zoogeographical distribution of the genus is confirmed to include the coral reefs of South Africa, Kenya, Gulf of Oman, Taiwan and Japan. Phylogenetic analyses of two mitochondrial genes strongly support its placement in the family Alcyoniidae.     

Hepatic Coccidiosis in Triportheus angulatus Spix & Agassiz, 1829 (Characiformes: Triportheidae), a Tropical Fish from the Eastern Brazilian Amazon,with the Description of a New Species of Calyptospora (Apicomplexa: Calyptosporidae)

Hepatic infection involving a parasite of the family Calyptosporidae was recorded in characiform fish from the Tocantins river in the Brazilian Amazon region. In the present study, an integrated comparative analysis of morphological characteristics, histological and structural traits, and the sequence of a partial fragment of the SSUrRNA gene provides support for the identification of a new calyptosporid species, found parasitising the hepatic tissue of the fish Triportheus angulatus, collected from the Tocantins River. This new species was named Calyptospora gonzaguensis n. sp. and had ovoid oocysts with a diameter of 19.6 ± 1.4 μm and four peripheral sporocysts, 9.2 ± 0.6 μm long and 3.9 ± 0.2 μm wide, enveloped individually in fine adhesive membrane, composed of an ellipsoid body and posterior extension, with a mean length of 2.2 ± 0.4 μm.     

Site fidelity and movements of humpback whales (Megaptera novaeangliae) on the Brazilian breeding ground,southwestern Atlantic

Site fidelity and movements were studied for humpback whales photo-identified from 1989 to 2006 in the Abrolhos Bank, southwestern Atlantic, Brazil. A total of 2,612 individuals were identified, 374 of which were observed on more than one occasion. The cumulative number of identified whales has increased since 1989. Recapture rate was low and varied among different years. A total of 33 whales was observed using the Abrolhos Bank for longer than 10 yr, up to a maximum of 16 yr. Our data suggest that different whales show distinct movement rates. Some whales used a large extent of the Abrolhos Bank region. Opportunistic photo-identification data (on the scale of the Brazilian coast from 4° to 23°S) revealed important information about stock identity. The longest distance between within-season resightings was over 600 km, while one whale was observed in two locations separated by more than 1,400 km in different years. Long-range movements within and between seasons support the single stock hypothesis for humpback whales wintering off the Brazilian coast.     

Molecular diversity of bacterial endosymbionts associated with dagger nematodes of the genus Xiphinema (Nematoda: Longidoridae) reveals a high degree of phylogenetic congruence with their host

Bacterial endosymbionts have been detected in some groups of plant‐parasitic nematodes, but few cases have been reported compared to other groups in the phylum Nematoda, such as animal‐parasitic or free‐living nematodes. This study was performed on a wide variety of plant‐parasitic nematode families and species from different host plants and nematode populations. A total of 124 nematode populations (previously identified morphologically and molecularly) were screened for the presence of potential bacterial endosymbionts using the partial 16S rRNA gene and fluorescence in situ hybridization (FISH) and confocal microscopy. Potential bacterial endosymbionts were only detected in nematode species belonging to the genus Xiphinema and specifically in the X. americanum group. Fifty‐seven partial 16S rRNA sequences were obtained from bacterial endosymbionts in this study. One group of sequences was closely related to the genus ‘Candidatus Xiphinematobacter’ (19 bacterial endosymbiont sequences were associated with seven nematode host species, including two that have already been described and three unknown bacterial endosymbionts). The second bacterial endosymbiont group (38 bacterial endosymbiont sequences associated with six nematode species) was related to the family Burkholderiaceae, which includes fungal and soil–plant bacterial endosymbionts. These endosymbionts were reported for the first time in the phylum Nematoda. Our findings suggest that there is a highly specific symbiotic relationship between nematode host and bacterial endosymbionts. Overall, these results were corroborated by a phylogeny of nematode host and bacterial endosymbionts that suggested that there was a high degree of phylogenetic congruence and long‐term evolutionary persistence between hosts and endosymbionts.