Abstract
The photooxidation of cellular monounsaturated fatty acids was investigated in senescent phytoplanktonic cells (Emiliania huxleyi) and in their attached bacteria under laboratory controlled conditions. Our results indicated that UV-visible irradiation of phytodetritus induced the photooxidation of oleic (produced by phytoplankton and bacteria) and cis-vaccenic (specifically produced by bacteria) acids. These experiments confirmed the involvement of a substantial singlet oxygen transfer from senescent phytoplanktonic cells to attached bacteria, and revealed a significant correlation between the concentration of chlorophyll, a photosensitizer, in the phytodetritus and the photodegradation state of bacteria. Hydroperoxyacids (fatty acid photoproducts) appeared to be quickly degraded to ketoacids and hydroxyacids in bacteria and in phytoplanktonic cells. This degradation involves homolytic cleavage (most likely induced by UV and/or transition metal ions) and peroxygenase activity (yielding epoxy acids).
Highlights
It is generally accepted that the majority of the marine particulate organic matter (POM) produced by phytoplankton, in the oceanic euphotic layer, is recycled within the food web and microbial loop in surface water [1], and that only a small fraction of POM is exported by particles, sinking towards the deep ocean and seafloor [2]
Specific attention was devoted to the transfer of singlet oxygen from the phytodetritus to the attached bacteria
The first experiment confirmed some previous results concerning the transfer of singlet oxygen from senescent phytoplanktonic cells to attached bacteria [12,21,51] and revealed a significant correlation between the concentration of degraded chlorophyll a in the phytodetritus, and the photodegradation state of the attached bacteria
Summary
It is generally accepted that the majority of the marine particulate organic matter (POM) produced by phytoplankton (phytodetritus), in the oceanic euphotic layer, is recycled within the food web and microbial loop in surface water [1], and that only a small fraction of POM is exported by particles, sinking towards the deep ocean and seafloor [2]. We intend to (i) confirm the role played by 1O2 in altering the bacteria attached to phytodetritus, (ii) correlate the photodegradation state of the bacteria with the evolution of the concentration of chlorophyll (sensitizer) in the phytodetritus, and (iii) compare the behavior of photochemically-produced hydroperoxides in bacteria and phytoplankton cells under PAR + UV irradiations. For this purpose, the photooxidation of oleic (produced by phytoplankton and bacteria) and cis-vaccenic ( produced by bacteria) acids in a non-axenic senescent culture of Emiliania huxleyi was investigated under laboratory controlled conditions
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