Distribution saisonnière et spatiale de l'abondance et de la taille des bactéries aérobiques anoxygéniques phototrophiques (AAPB) dans les lacs boréaux et tempérés du Québec

Les bactéries aquatiques tiennent des rôles clés dans les écosystèmes aquatiques, notamment au niveau des flux de carbone et d'énergie, malgré le fait que plusieurs exemples de mixotrophie aient été répertoriés elles demeurent largement divisées en deux groupes; soit les hétérotrophes et les autotrophes. Cependant les bactéries aérobiques anoxygéniques phototrophiques (AAPB) possèdent en plus de leur métabolisme hétérotrophe un système phototrophique, basé sur la bactériochlorophyll a (BChl a) leur permettant d'obtenir un supplément d'énergie considérable. Ce groupe de bactéries, qui génère de plus en plus d'intérêt dans les milieux marins, n'a que très peu été étudier en eaux douces. Pour pallier ce manque nous avons conduit une étude biogéographique comparant l'abondance et la taille des AAPB dans 43 lacs situés dans deux régions tempérées (Cantons de l'Est et Laurentides) et une région Boréal (Eastmain), durant le cours d'une année. Les AAPB étaient présentes non seulement dans tous les lacs, mais aussi durant toute l'année et ce malgré les conditions adverses de l'hiver. L'abondance relative variait entre >1% et 37%, avec une moyenne de 6%, mais étant donnée qu'elles avaient en moyenne le double de la taille des autres bactéries, leur biomasse relative moyenne est de 10%. L'abondance, bien qu'elle suive les patrons généraux de l'ensemble de la communauté, chute durant l'hiver et est très dynamique à courte échelle ce qui indique que plusieurs facteurs de régulations pourraient agir en même temps. Nos données ne supportent pas l'hypothèse voulant que la photohétérotrophie soit avantageuse dans les milieux oligotrophes, plutôt l'abondance est positivement corrélée au carbone organique dissout. De plus, il semble que ce soit la qualité et non seulement la quantité, qui influe sur l'abondance des AAPB; ainsi il semble que leur abondance est maximale dans les milieux à forte teneur en DOC et aussi peu de chlorophylle. Or nous proposons que la photohétérotrophie pourrait agir de façon analogue au co-métabolisme en fournissant une amorce énergétique permettant d'exploiter des sources de carbones récalcitrantes. \ud ______________________________________________________________________________ \ud MOTS-CLÉS DE L’AUTEUR : Bactérie aérobique anoxygénique phototrophique, bacteriochlorophylle a, écologie aquatique, flux d'énergie, biogéographie

Patterns in Abundance, Cell Size and Pigment Content of Aerobic Anoxygenic Phototrophic Bacteria along Environmental Gradients in Northern Lakes.

There is now evidence that aerobic anoxygenic phototrophic (AAP) bacteria are widespread across aquatic systems, yet the factors that determine their abundance and activity are still not well understood, particularly in freshwaters. Here we describe the patterns in AAP abundance, cell size and pigment content across wide environmental gradients in 43 temperate and boreal lakes of Québec. AAP bacterial abundance varied from 1.51 to 5.49 x 105 cells mL-1, representing <1 to 37% of total bacterial abundance. AAP bacteria were present year-round, including the ice-cover period, but their abundance relative to total bacterial abundance was significantly lower in winter than in summer (2.6% and 7.7%, respectively). AAP bacterial cells were on average two-fold larger than the average bacterial cell size, thus AAP cells made a greater relative contribution to biomass than to abundance. Bacteriochlorophyll a (BChla) concentration varied widely across lakes, and was not related to AAP bacterial abundance, suggesting a large intrinsic variability in the cellular pigment content. Absolute and relative AAP bacterial abundance increased with dissolved organic carbon (DOC), whereas cell-specific BChla content was negatively related to chlorophyll a (Chla). As a result, both the contribution of AAP bacteria to total prokaryotic abundance, and the cell-specific BChla pigment content were positively correlated with the DOC:Chla ratio, both peaking in highly colored, low-chlorophyll lakes. Our results suggest that photoheterotrophy might represent a significant ecological advantage in highly colored, low-chlorophyll lakes, where DOC pool is chemically and structurally more complex

Inhibition of IL-1β release from macrophages targeted with necrosulfonamide-loaded porous nanoparticles

Inflammation is required for protective responses against pathogens and is thus essential for survival, but sustained inflammation can lead to diseases, such as atherosclerosis and cancer. Two important mediators of inflammation are the cytokines IL-1β and IL-18, which are produced by myeloid cells of the immune system, including macrophages. These cytokines are released into the extracellular space through pores formed in the plasma membrane by the oligomerized protein gasdermin D (GSDMD). Necrosulfonamide (NSA) was recently identified as an effective GSDMD inhibitor and represents a promising therapeutic agent in GSDMD-dependent inflammatory diseases. Here, we targeted NSA to both mouse and human macrophages by using three different types of porous nanoparticles (NP), i.e. mesoporous silica (MSN), porous crosslinked cyclodextrin carriers (CD-NP), and a mesoporous magnesium-phosphate carrier (MPC-NP), all displaying high loading capacities for this hydrophobic drug. Cellular uptake and intracellular NSA delivery were tracked in time-lapse experiments by live-cell, high-throughput fluorescence microscopy, demonstrating rapid nanoparticle uptake and effective targeted delivery of NSA to phagocytic cells. Notably, a strong cytostatic effect was observed when a macrophage cell line was exposed to free NSA. In contrast, cell growth was much less affected when NSA was delivered via the nanoparticle carriers. Utilizing NSA-loaded nanoparticles, a successful concentration-dependent suppression of IL-1β secretion from freshly differentiated primary murine and human macrophages was observed. Functional assays showed the strongest suppressive effect on human macrophages when using CD-NP for NSA delivery, followed by MSN-NP. In contrast, MPC-NP completely blocked the metabolic activity in macrophages when loaded with NSA. This study demonstrates the potential of porous nanoparticles for the effective delivery of hydrophobic drugs to macrophages in order to suppress inflammatory responses

Patterns in Abundance, Cell Size and Pigment Content of Aerobic Anoxygenic Phototrophic Bacteria along Environmental Gradients in Northern Lakes

Publisher's PDF.There is now evidence that aerobic anoxygenic phototrophic (AAP) bacteria are widespread across aquatic systems, yet the factors that determine their abundance and activity are still not well understood, particularly in freshwaters. Here we describe the patterns in AAP abundance, cell size and pigment content across wide environmental gradients in 43 temperate and boreal lakes of Québec. AAP bacterial abundance varied from 1.51 to 5.49 x 105 cellsmL-1, representing <1 to 37%of total bacterial abundance. AAP bacteria were present year-round, including the ice-cover period, but their abundance relative to total bacterial abundance was significantly lower in winter than in summer (2.6%and 7.7%, respectively). AAP bacterial cells were on average two-fold larger than the average bacterial cell size, thus AAP cells made a greater relative contribution to biomass than to abundance. Bacteriochlorophyll a (BChla) concentration varied widely across lakes, and was not related to AAP bacterial abundance, suggesting a large intrinsic variability in the cellular pigment content. Absolute and relative AAP bacterial abundance increased with dissolved organic carbon (DOC), whereas cell-specific BChla content was negatively related to chlorophyll a (Chla). As a result, both the contribution of AAP bacteria to total prokaryotic abundance, and the cell-specific BChla pigment content were positively correlated with the DOC:Chla ratio, both peaking in highly colored, low-chlorophyll lakes.Our results suggest that photoheterotrophymight represent a significant ecological advantage in highly colored, low-chlorophyll lakes, where DOC pool is chemically and structurally more complex.University of Delaware. School of Marine Science and Policy

Relationship between total prokaryote abundance and (a) AAP bacterial abundance and (b) cell size.

<p><b>(c) Contribution of AAP bacteria to total abundance (%AAP) versus their contribution to total bacterial biovolume (%BV).</b> The line in (a) and (b) is the least-square regression, and details of the regression models are given in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0124035#pone.0124035.t001" target="_blank">Table 1</a>. The line in (c) is the 1:1 line. Data have been log-transformed, and the plots comprise all data collected between July 2007 and October 2008.</p

The average and distribution of the relative abundance of AAP bacteria (%AAP), and of the pigment content per cell volume (fg BChl<i>a</i> μm^-3) in the epilimnion and in the metalimion of selected lakes.

<p>The box-and-whisker plots show the average, 75% quartiles and extremes values in the epilimnetic and metalimnetic layers during lake summer stratification.</p

The relationship of total bacterial abundance (triangles) and AAP bacterial abundance (circles) with total phosphorous concentration (a), Secchi depth (b), and DOC concentration (c).

<p><b>BChl<i>a</i> contents per cell as a function of mean lake chlorophyll concentration (d)</b>. Data have been log-transformed, the line is the least-square regression, and details of the regression models are given in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0124035#pone.0124035.t001" target="_blank">Table 1</a>.</p

Regression models relating AAP bacteria variables to total bacteria or describing the cross-lake patterns in AAP bacteria and total bacteria as a function of environmental variables.

<p>AAP: Aerobic anoxygenic phototrophic bacterial abundance; BA: Total bacterial abundance; Total size: Total prokaryotic cell size; BV: total biovolume; SpBChl<i>a</i>: Pigment content per cell; %BChl<i>a</i>: relative contribution of BChl<i>a</i> to total pigments; Secchi: Secchi disc depth; DOC: Dissolved organic carbon.</p><p>Regression models relating AAP bacteria variables to total bacteria or describing the cross-lake patterns in AAP bacteria and total bacteria as a function of environmental variables.</p

Seasonal patterns in the contribution of AAP bacteria to (a) total bacterial abundance and to biovolume, and (b) in the average cell size of AAP and total bacteria.

<p>The box-and-whisker plots show the average, 75% quartiles and extremes values, and stars indicate significant differences (p<0.05).</p

The contribution of AAP bacteria to total bacterial abundance (%AAP, squares) and the BChl<i>a</i> content per cell (circles) as function of the DOC to Chl<i>a</i> (DOC:Chl<i>a</i>) ratio.

<p>The data have been log-transformed, the line is the least-square regression, and details of the regression models are given in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0124035#pone.0124035.t001" target="_blank">Table 1</a>.</p