Diel and Seasonal Variations in Abundance, Activity, and Community Structure of Particle-Attached and Free-Living Bacteria in NW Mediterranean Sea

Abstract

Diel and seasonal variations in abundance, activity, and structure of particle-attached vs free-living bacterial communities were investigated in offshore NW Mediterranean Sea (0-1000 m). Attached bacteria were always less abundant and less diverse but generally more active than free-living bacteria. The most important finding of this study was that the activity of attached bacteria showed pronounced diel variations in the upper mixed water column with higher activities at night. Under mesotrophic conditions, the contribution of attached bacteria to total bacterial activity increased from less than 10% at day time to 83% at night time. At high chlorophyll a concentration, the highest cell-specific activities and contribution to total bacterial activity were due to free-living bacteria at day and to attached bacteria at night. Under summer oligotrophic conditions, free-living bacteria dominated and contributed to the most important part of the bacterial activity at both day and night, whereas attached bacteria were much less abundant but presented the highest cell-specific activities. These diel and seasonal variations in activities were concomitant to changes in bacterial community structure, mainly in the upper layer. The number of attached ribotypes was fairly constant suggesting that particles are colonized by a relatively limited number of ubiquitous ribotypes. Most of these ribotypes were also free-living ribotypes suggesting that attached bacteria probably originate from colonization of newly formed particles by free-living bacteria in the upper layer. These results reinforce the biogeochemical role of attached bacteria in the cycling of particulate organic carbon in the NW Mediterranean Sea and the importance of diel variability in these processes.

Short-scale temporal variability of physical, biological and biogeochemical processes in the NW Mediterranean Sea: an introduction

“…Bacterial production, in carbon units averaged about 29 mg C m −2 d −1 over the top 150 m of the water column , equivalent to 0.2 mg C m −3 , suggesting that bacterial production was very low relative to both total bacterial biomass and phytoplankton production. In contrast, periodically, a large portion (up to about 50%) of bacterial activity was associated with particleattached bacteria, as previously observed at the same sampling site under spring conditions (Ghiglione et al, 2007).…”

“…Below we will first very briefly review the cruise plan then highlight some of the findings described in detail in the individual papers of this special section. In the framework of the PECHE project, two additional shortcruises were conducted at the DYFAMED site in March and June 2003 (Garcia et al, 2006;Ghiglione et al, 2007;Bourguet et al, 2009) whose results are used as spring and early summer reference in several individual papers of this special issue.…”

Short-term changes in particulate fluxes measured by drifting sediment traps during end summer oligotrophic regime in the NW Mediterranean Sea

“…With the decline in chlorophyll concentration as the season advanced towards autumn, phospholipids, triacylglycerols and wax esters dominated the lipid material in the traps. Change in POM and DOM lipid composition from a glycolipidsdominated lipid pool, to a neutral (wax esters, triacylglycerols) and phospholipids-dominated lipid pool, has already been observed in ecosystems changing from micro-and or pico-phytoplankton to heterotrophs-dominated regimes (Smith et al, 1997;Goutx et al, 2000;Ghiglione et al, 2007;Bourguet et al, 2008). During DYNAPROC 2, a similar shift occurred in the suspended particles and dissolved matter .…”

Organic-Aggregate-Attached Bacteria in Aquatic Ecosystems: Abundance, Diversity, Community Dynamics and Function

“…Abundant researches carried out in marine and deep lakes showed that attached bacteria were always less abundant and less diverse but generally more active than free-living bacteria (Ghiglione et al 2007, Grossart et al 2003b, Simon et al 2002. Using 16S ribosomal desoxynucleic acid (rDNA) based clone library analysis, however, we found that in shallow productive eutrophic Lake Taihu, OA harbors diverse bacterial clusters (Tang et al 2010).…”