De Clerck, Olivier

Hollants, Joke

Leliaert, Frédérik

Willems, Anne

English

Ghent University Academic Bibliography

Endosymbiotic Bacteria within Bryopsis species (Bryopsidales, Chlorophyta): Naming the Actors  HOLLANTS Joke 1,2, LELIAERT Frederik2, DE CLERCK Olivier2, and WILLEMS Anne1  1 Laboratory of Microbiology, Department of Biochemistry and Microbiology, Ghent University, Ledeganckstraat 35, 9000 Ghent, Belgium. Joke.Hollants@UGent.be  2 Phycology Research Group, Department of Biology, Ghent University, Krijgslaan 281 (S8), 9000 Ghent, Belgium.   Microbial symbionts have been well documented in animals and plants, but they are also commonly found in association with various algal groups. In the marine green alga Bryopsis the endosymbiotic bacteria even seem to be present in every stage of the life cycle, suggesting vertical transmission of the endosymbionts1. This indicates an ancient association among host and symbiont, rather than a recent opportunistic and non-specific relationship. Although this remarkable algal-bacterial partnership was already noticed in the early 1970s, no research has been performed to explore the physiological nature and specificity of the endosymbiosis. Therefore this research focuses on the identity and diversity of endosymbiotic bacteria within Bryopsis species. To identify the bacterial partner, epiphytes were chemically and enzymatically removed from Bryopsis plants from diverse geographical regions. Incubation of sterilized Bryopsis samples on Marine Agar plates showed no bacterial growth. Moreover, staining of the sterilized thalli with DAPI revealed the absence of nearly all bacterial fluorescence on the surface of the algae. The algal cells themselves were not lysed, suggesting the endophytic bacteria might still be present within the Bryopsis plants after sterilization. Subsequently, the different samples were submitted to a range of molecular techniques such as 16S rDNA PCR, cloning and DNA sequencing. The phylogenetic analysis revealed that only a small fraction of clones carried bacterial sequences, in contrast to the majority of the clones which had the Bryopsis 16S rRNA chloroplast gene inserted. The obtained bacterial sequences covered just four different species: (i) a Bacteroidetes bacterium, (ii) a species belonging to the Rhizobiales, (iii) a bacterium in tight phylogenetic alliance with Labrenzia alba, and (iv) a species closely related to the Rickettsia symbiont of the paua Haliotis iris. All four bacteria are present in several Bryopsis plants from various regions. Not only does this indicate that these endophytic bacteria are preserved within Bryopsis species, it also suggests that they might be actual endosymbionts with a significant function. The occurrence of bacteria belonging to the Bacteroidetes, Rhizobiales and Rickettsiales, with well-known symbiotic features, validates this hypothesis. Attempts are being made to visualize the endosymbionts with electron microscopy and fluorescent probes to confirm their identification and location inside the algal host.  1. Burr, F.A., and West, J.A. (1970). Light and electron microscope observations on the vegetative and reproductive structures of Bryopsis hypnoides. Phycologia, 9(1), 17-37. 

Endosymbiotic bacteria within Bryopsis species (Bryopsidales, Chlorophyta) : naming the actors

Endosymbiotic Bacteria within Bryopsis species (Bryopsidales, Chlorophyta): Naming the Actors  HOLLANTS Joke 1,2, LELIAERT Frederik2, DE CLERCK Olivier2, and WILLEMS Anne1  1 Laboratory of Microbiology, Department of Biochemistry and Microbiology, Ghent University, Ledeganckstraat 35, 9000 Ghent, Belgium. Joke.Hollants@UGent.be  2 Phycology Research Group, Department of Biology, Ghent University, Krijgslaan 281 (S8), 9000 Ghent, Belgium.   Microbial symbionts have been well documented in animals and plants, but they are also commonly found in association with various algal groups. In the marine green alga Bryopsis the endosymbiotic bacteria even seem to be present in every stage of the life cycle, suggesting vertical transmission of the endosymbionts1. This indicates an ancient association among host and symbiont, rather than a recent opportunistic and non-specific relationship. Although this remarkable algal-bacterial partnership was already noticed in the early 1970s, no research has been performed to explore the physiological nature and specificity of the endosymbiosis. Therefore this research focuses on the identity and diversity of endosymbiotic bacteria within Bryopsis species. To identify the bacterial partner, epiphytes were chemically and enzymatically removed from Bryopsis plants from diverse geographical regions. Incubation of sterilized Bryopsis samples on Marine Agar plates showed no bacterial growth. Moreover, staining of the sterilized thalli with DAPI revealed the absence of nearly all bacterial fluorescence on the surface of the algae. The algal cells themselves were not lysed, suggesting the endophytic bacteria might still be present within the Bryopsis plants after sterilization. Subsequently, the different samples were submitted to a range of molecular techniques such as 16S rDNA PCR, cloning, DGGE and DNA sequencing. The phylogenetic analysis revealed that only a small fraction of clones carried bacterial sequences, in contrast to the majority of the clones which had the Bryopsis 16S rRNA chloroplast gene inserted. The obtained bacterial sequences covered just five different species: (i) two diverse species belonging to the Rhizobiales, (ii) a Bacteroidetes bacterium (iii) a bacterium in tight phylogenetic alliance with Labrenzia alba, and (iv) a species closely related to the Rickettsia symbiont of a marine organism. All five bacteria are present in several Bryopsis plants from various regions. Not only does this indicate that these endophytic bacteria are preserved within Bryopsis species, it also suggests that they might be actual endosymbionts with a significant function. The occurrence of bacteria belonging to the Bacteroidetes, Rhizobiales and Rickettsiales, with well-known symbiotic features, validates this hypothesis. Attempts are being made to visualize the endosymbionts with electron microscopy and fluorescent probes to confirm their identification and location inside the algal host.  1. Burr, F.A., and West, J.A. (1970). Light and electron microscope observations on the vegetative and reproductive structures of Bryopsis hypnoides. Phycologia, 9(1), 17-37. 

https://biblio.ugent.be/publication/934735/file/939546.pdf

Endosymbiotic bacteria within Bryopsis species (Bryopsidales, Chlorophyta) : naming the actors

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Ghent University Academic Bibliography

Ghent University Academic Bibliography