Single cell approach to unravel bacterial diversity changes
The project BASICS set out to devise a system of single-cell analysis applied to pelagic microbes (micro-organisms that inhabit the open water not near the coast or the sea-floor). These are highly important organisms as they play a key role in the recycling of carbon compounds (the carbon biogeochemistry) in the marine ecosystem. Dissolved organic carbon (DOC) concentrations were studied over a period of 18 months in the Bay of Villefranche in the Mediterranean. The values of DOC concentration, as expected, were lowest in winter and highest after the spring bloom when phytoplankton populations increase rapidly. However, other results did not follow these seasonal expectations. Autotrophic microorganisms (those that produces complex organic compounds from simple inorganic molecules, like carbon dioxide) were more abundant in the first half of the year. In contrast, heterotrophic organisms (those that break down complex molecules for their energy source) were more common in the second half of the year. Other parameters measured were bacterial respiration and production and these varied between two consecutive blooms. Associated factors appeared to be the deposition of carbon, nitrate and phosphate from forest fires into the open water column. In a similar vein, the deposition of dust from the Sahara caused bacterial respiration to increase from 60% to 90%. Results of the single-cell study have shown that some of the bacterial diversity and associated trophic activity is attritibutable to recognisable seasonal changes in the marine ecosystem. However, shifts in biogeochemical activity due to external phenomena such as upwelling from the sea floor, forest fires, rainfall and Sahara dust events have proven to be due to a range of complex factors which only further research can unravel.