Dynamic of bacterial communities attached to lightened phytodetritus
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The effects of singlet oxygen (1O2) transfer to bacteria attached on phytodetritus were investigated under laboratory-controlled conditions. For this purpose, a nonaxenic culture of Emiliania huxleyi in late stationary phase was studied for bacterial viability. Our results indicated that only 9 ± 3 % of attached bacteria were alive compared to 46 ± 23 % for free bacteria in the E. huxleyi culture. Apparently, under conditions of low irradiance (36 W m−2), during the culture, the cumulative dose received (22,000 kJ m−2) was sufficiently important to induce an efficient 1O2 transfer to attached bacteria during the senescence of E. huxleyi cells. At this stage, attached bacteria appeared to be dominated by pigmented bacteria (Maribacter, Roseobacter, Roseovarius), which should resist to 1O2 stress probably due to their high contents of carotenoids. After subsequent irradiation of the culture until fully photodegradation of chlorophyll, DGGE analyses showed that the diversity of bacteria attached to E. huxleyi cells is modified by light. Photooxidative alterations of bacteria were confirmed by the increasing amounts of cis-vaccenic photoproducts (bacterial marker) per bacteria observed during irradiation time. Interestingly, preliminary chemotaxis experiments showed that Shewanella oneidensis considered here as a model of motile bacteria was attracted by phytodetritus producing or not 1O2. This lack of repulsive effects could explain the high mortality rate of bacteria measured on E. huxleyi cells.
KeywordsSinglet oxygen Attached bacteria Photodegradation Phytodetritus Furan AAnP
This work was performed in the framework of the transverse axis DEBAT of the MIO and funded by research grants from the PHOTOMED (MERMEX/MISTRALS WP4) and TRANSPHYTOBAC (EC2CO-Microbien) research projects. The PhD scholarship for MP was provided by Aix Marseille University (EDSV 251) and the Ministry of Research and Technology. Thanks are due to two anonymous reviewers for their useful and constructive comments.
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