This apparent specificity is supported by the observation that Bryopsis harbors rather stable endophytic bacterial communities, which showed little time variability after one year cultivation of the algal samples (Figure 1). However, examination of individual DGGE bands did reveal some similarities between intra- and extracellular bacteria. While Bacteroidetes, Flavobacteriaceae and Xanthomonadaceae species seemed exclusively endobiotic, sequence cluster analysis GSK690693 ic50 confirmed that Arcobacter, Labrenzia, Mycoplasma and Phyllobacteriaceae endophytes

were also present in the epiphytic, washing water and/or cultivation water extracts. This latter observation is consistent with the outcome of a study conducted by Maki et al. [22] which revealed similar intracellular and extracellular bacterial populations in and on the harmful Tozasertib marine microalga Heterocapsa circularisquama in culture. Although

the Bryopsis cultures used in this study have been check details kept in the laboratory for almost three years due to experimental restrictions [3], our data allow us to put forward some hypotheses regarding the nature of the endophytic communities within natural Bryopsis populations. Whereas we cannot rule out selection by artificial laboratory growth conditions, Arcobacter, Labrenzia, Mycoplasma and Phyllobacteriaceae endophytes can at least survive without the Bryopsis host, Farnesyltransferase suggesting they might be facultative endogenous bacteria which are acquired from the local environment. This is consistent with the general perception that most plant endophytes originate from the surrounding environment and the outer plant surface [23, 24]. Bacteroidetes, Flavobacteriaceae and Xanthomonadaceae endophytes, on the other hand, appear well adapted to an endobiotic lifestyle as they persist within the Bryopsis interior after prolonged

cultivation. Especially Flavobacteriaceae endophytes, which are present in all five MX samples collected hundreds of kilometres apart, might be obligate endophytes which are strictly dependent on the Bryopsis host for their growth and survival. This co-occurrence of multiple facultative and obligate bacterial endophytes is also well documented in many land plant and insect hosts [23, 25]. Furthermore, the Bryopsis endophytic communities seem also rather specific as the EP, WW and CW extracts contained numerous Alphaproteobacterial, Gammaproteobacterial and Acanthopleuribacterales species which are not present in the EN samples. This apparent specificity is confirmed by our observations that EP, WW, CW (data not shown) and EN (see Figure 1) extracts made at different time points revealed largely consistent banding patterns even after the algal specimens were repeatedly wounded and transferred to fresh, sterile cultivation medium (see material and methods section).