Abstract
AbstractMarine bacterial diversity is vast, but seasonal variation in diversity is poorly understood. Here we present the longest bacterial diversity time series consisting of monthly (72) samples from the western English Channel over a 6 year period (2003-2008) using 747,494 16SrDNA-V6 amplicon-pyrosequences. Although there were characteristic cycles for each phylum, the overall community cycle was remarkably stable year after year. The majority of taxa were not abundant, although on occasion these rare bacteria could dominate the assemblage. Bacterial diversity peaked at the winter solstice and showed remarkable synchronicity with day-length, which had the best explanatory power compared to a combination of other variables (including temperature and nutrient concentrations). Day-length has not previously been recognised as a major force in structuring microbial communities.
Highlights
Environmental factors driving the structure and function of microbial community are still poorly understood
We examined the role of a broad range of biotic and abiotic parameters, including the concentrations of ammonia, nitrate + nitrite, phosphate, silicate, total organic carbon and total organic nitrogen, salinity, chlorophyll, and temperature in determining bacterial diversity
Upon investigation of notable outlying data points in the Nonparametric ordination by multidimensional scaling (NMDS) plot (Fig 2) we discovered that the distant relationship of these samples was due to blooms of otherwise extremely rare taxa
Summary
This study demonstrates a strong statistical relationship between the availability of sunlight and the diversity of microbial communities. The observed bacterial taxa present on any particular day are the result of the combined responses of many taxa to events over the preceding days or weeks (fast division rates) and are integrating the environmental ‘climate’, the net effect of many variables changing seasonally, rather than the environmental ‘weather’, the effects of individual variables operating on the exact day of measurement. This is the first reported evidence that it is day-length that has the most significant impact on microbial diversity in a well-studied marine habitat. While there is some year on year variation, which is occasionally driven by blooms of rare taxa, it is the seasonal cycle that dominates; so that for all their astonishing variability bacteria seem to show an extraordinarily consistent seasonal cycle
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