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The sensitivity of coastal marine bacterioplankton to natural photosynthetically active radiation ( PAR, 400-700 nm) and ultraviolet radiation ( UVR, 280-400 nm) was evaluated in five experiments over a seasonal cycle in the Blanes Bay, NW Mediterranean Sea. Exposure to natural solar radiation generally inhibited bulk bacterial activities or damaged membrane integrity when irradiances were high (i.e. spring and summer experiments) and, in general, UVB (280-320 nm) accounted for most of the inhibition. When assessing activity (3H-leucine uptake) at the single-cell level by microautoradiography and rRNA gene probing, seasonally varying responses and sensitivities were found among bacterial groups. While autumn and winter irradiances seemed too low to cause changes in activity, variable effects were found in spring and summer. SAR11 was consistently inhibited by UVR and PAR exposure, whereas G ammaproteobacteria and B acteroidetes showed higher resistance. R oseobacter, S ynechococcus and the NOR5 clade were occasionally photostimulated in their activity, mainly because of PAR. Our results indicate that a component of seasonality exists in the bacterial responses to solar radiation, which vary not only depending on the irradiance and the spectral characteristics, but also on the previous light history and the taxonomic composition of the community. [ABSTRACT FROM AUTHOR]

Two diel cycle studies were conducted to determine the effect of day-night light changes on winter bacterial activity in the coastal Mediterranean (Blanes Bay Microbial Observatory). Bacterial abundances, bacterial heterotrophic activity, and flagellate grazing counts were determined at 4-h intervals during two 3-d periods separated by 2 d. Twice a day, the single-cell activity of major bacterial groups was further analyzed by applying microautoradiography combined with catalyzed reporter deposition-fluorescence in situ hybridization. During the first cycle, all the measured parameters (including the number of active cells in most groups) varied synchronously, with higher values at night and lower during the day. An episode of strong winds between the two studied periods disrupted this periodicity at the onset of the second cycle. The bulk incorporation of ³H-leucine recovered the diel pattern after 2 d, mostly driven by the activity of Gammaproteobacteria. Among the possibilities considered, the observed nighttime increases in the grazing activity of heterotrophic nanoflagellates appeared to partially drive the activity of all bacterial taxa through potential periodic release of dissolved organic matter. [ABSTRACT FROM AUTHOR]

Catalysed reporter deposition-fluorescence in situ hybridization (CARD-FISH) is a powerful approach to quantify bacterial taxa. In this study, we compare the performance of the widely used Bacteroidetes CF319a probe with the new CF968 probe. In silico analyses and tests with isolates demonstrate that CF319a hybridizes with non-Bacteroidetes sequences from the Rhodobacteraceae and Alteromonadaceae families. We test the probes' accuracy in 37 globally distributed marine samples and over two consecutive years at the Blanes Bay Microbial Observatory (NW Mediterranean). We also compared the CARD-FISH data with the Bacteroidetes 16S rRNA gene sequences retrieved from 27 marine metagenomes from the TARA Oceans expedition. We find no significant differences in abundances between both approaches, although CF319a targeted some unspecific sequences and both probes displayed different abundances of specific Bacteroidetes phylotypes. Our results demonstrate that quantitative estimations by using both probes are significantly different in certain oceanographic regions (Mediterranean Sea, Red Sea and Arabian Sea) and that CF968 shows seasonality within marine Bacteroidetes, notably large differences between summer and winter that is overlooked by CF319a. We propose CF968 as an alternative to CF319a for targeting the whole Bacteroidetes phylum since it has better coverage, greater specificity and overall better quantifies marine Bacteroidetes., (© 2014 Society for Applied Microbiology and John Wiley & Sons Ltd.)