Bacterial community in the tunic matrix of a colonial ascidian Diplosoma migrans

This paper provides the first information on the morphology of different morphotypes of bacteria in the tunic matrix of the colonial ascidian Diplosoma migrans. Ascidians were collected from waters near Helgoland (German Bight, North Sea). The dominant type is represented by extremely high numbers of long, needle-like rods (length 10-30 mum, width 0.5 mum). The bacteria are motile by means of bipolar monotrichous flagella, generating swift sigmoidal movement. Bacteria are already present during different embryonic stages. It is assumed that they are transferred during sexual propagation from the parental colony to its offspring. As a second morphotype, the tunic harbors screw-like bacteria in low numbers (length 4-10 mum, width 0.5 mum). Besides these conspicuous morphotypes, occasionally motile rods with spore-like globules at one end and additional coccoid forms in large quantities of unknown meaning (possibly spores) were found. The taxonomic status and ecological functions of these differently shaped bacterial groups are unclear.