Institut de Ciències del Mar-CSIC, Barcelona, Catalunya, Spain.
ISME J. 2012 Mar;6(3):650-9. doi: 10.1038/ismej.2011.118. Epub 2011 Sep 29.
There is a large body of evidence supporting a major role of heterotrophic bacteria in dimethylsulphoniopropionate (DMSP) utilisation as a source of reduced sulphur. However, a role for phototrophic microorganisms has been only recently described and little is known about their contribution to DMSP consumption and the potential modulating effects of sunlight. In an attempt to ascertain the relative quantitative roles of heterotrophic bacteria and picophytoplankton in the osmoheterotrophic uptake of DMSP-sulphur upon exposure to natural sunlight conditions, we incubated northwestern Mediterranean waters under various optical filters and used an array of bulk and single-cell activity methods to trace the fate of added (35)S-DMSP. Flow cytometry cell sorting confirmed dark (35)S uptake by Prochlorococcus, Synechococcus and heterotrophic bacteria, the latter being the most efficient in terms of uptake on a cell volume basis. Under exposure to full sunlight, however, the relative contribution of Synechococcus was significantly enhanced, mainly because of the inhibition of heterotrophic bacteria. Microautoradiography showed a strong increase in the proportion of Synechococcus cells actively taking up (35)S-DMSP, which, after full sunlight exposure, made up to 15% of total active Bacteria. Parallel incubations with (3)H-leucine generally showed no clear responses to light. Finally, size-fractionated assimilation experiments showed greater relative cyanobacterial assimilation during the day than at night compared with that of heterotrophic bacteria. Our results show for the first time a major influence of sunlight in regulating the competition among autotrophic and heterotrophic picoplankton for DMSP uptake at both the daily and seasonal time scales.
有大量证据表明，异养细菌在二甲巯基丙酸盐（DMSP）利用作为还原硫源方面起着重要作用。然而，光养微生物的作用最近才被描述，它们对 DMSP 消耗的贡献以及阳光的潜在调节作用知之甚少。为了确定异养细菌和微微型浮游植物在渗透异养吸收 DMSP-硫过程中在自然阳光条件下的相对定量作用，我们在各种光学滤光片下培养了西北地中海海水，并使用一系列批量和单细胞活性方法来追踪添加的（35）S-DMSP 的命运。流式细胞术细胞分选证实，黑暗条件下（35）S 被聚球藻、集胞藻和异养细菌吸收，就细胞体积而言，后者的吸收效率最高。然而，在暴露于全阳光的情况下，集胞藻的相对贡献明显增强，主要是因为异养细菌受到抑制。微量放射性自显影显示，活跃摄取（35）S-DMSP 的集胞藻细胞比例大幅增加，在全阳光暴露后，这些细胞占总活性细菌的 15%。与（3）H-亮氨酸平行的培养一般没有显示出对光的明显反应。最后，大小分级同化实验表明，与异养细菌相比，蓝细菌的相对同化作用在白天比晚上更强。我们的结果首次表明，阳光在调节自养和异养微微型浮游植物对 DMSP 吸收的竞争方面具有重要影响，这种影响既存在于日周期，也存在于季节周期。
