Tep production under oxidative stress of the picocyanobacterium Synechococcus

Transparent exopolymer particles (TEP) are mainly acidic polysaccharides directly or indirectly formed by phytoplankton and bacteria. These particles are often colonized by picoplankton and considered a hot spot for microbial activity. Recent studies suggested an important role of Synechococcus in TEP production found in lakes and prompted us to further investigate this issue using monoclonal xenic cultures of Synechococcus. We tested TEP production under oxidative stress in two treatments, one with hydrogen peroxide and another treated with ultraviolet radiation (UVR) and high photosynthetic active radiation (PAR), compared with an unstressed control. Our results showed a cell-normalized TEP production, ranging from 12 to 238 ng C cell among strains, not only under stress but also in the control with non-limiting nutrients. Our data prove that freshwater communities of Synechococcus and their associated het-erotrophic microflora, are capable of producing TEP even during growth phase. The oxidative stress induced extra production of TEP up to 400 ng C cell in one of our phycocyanin-type (PC) strain. The phycoerythrin-type (PE) strains increased TEP production, particularly under UV-PAR stress, whereas the PC strains did it under HO stress. This study provides new perspectives on the potential role of freshwater Synechococcus in TEP production. se only.