The community of aerobic anoxygenic phototrophs was investigated in the Baltic Sea using infrared epifluorescence microscopy from September 2004 to October 2005. The majority of these bacteriochlorophyll-containing organisms exhibited a specific sickle-shaped morphology, with rods or other morphotypes observed only occasionally. Aerobic anoxygenic phototrophs were observed mostly from April to September (1 to 12% of total prokaryotes), peaking in May 2005 at a concentration of up to 0.38 × 10 6 cells ml -1. This peak was associated with the later phase of the spring bloom. In the later months, the amount of phototrophic bacteria gradually declined until the beginning of the fall mixing, and remained low from November to March, contributing only 0 to 2% of total prokaryotes. A novel technique combining fluorescent in situ hybridization (FISH) and infrared epifluorescence microscopy indicated that the Baltic aerobic anoxygenic phototrophs were mostly Gammaproteobacteria, with a smaller fraction of Alphaproteobacteria. KEY WORDS: Aerobic photosynthetic bacteria · Bacteriochlorophyll a · Photoheterotrophy · Epifluorescence microscopy Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 45: [247][248][249][250][251][252][253][254] 2006 thermocline structure gradually dissolves due to the decrease in irradiance and intensified wind mixing. The autumn bloom (September-October) is dominated by cyanobacteria along with dinophytes and chlorophytes as other main contributors (Sto? et al. 2002, Wasmund & Uhlig 2003. By the end of the fall season, the water column becomes homogenous down to the halocline, with mean water temperatures of 3 to 4°C.Earlier studies suggested that Baltic primary production is mostly limited by nitrogen availability, but the activity of nitrogen-fixing cyanobacteria in the summer period may cause limitation by phosphorus (Kivi et al. 1993, Nausch et al. 2004. Knowledge of Baltic bacterioplankton dynamics pattern is fragmentary. In the coastal zone offshore of Sweden, bacterial cell numbers display a relatively simple pattern, with a minimum in winter and a maximum in summer (Hagström et al. 1979). In early spring, the bacterial community is predominantly controlled by nitrogen availability and nanoflagellate grazing (Kuupo et al. 1998). In some studies, a stimulation of bacterial growth by phosphorus was observed in late spring, whereas in summer a great stimulation was induced by the combined addition of nitrogen and phosphorus (Kivi et al. 1993).In a previous study, we surveyed the presence of AAPs in the Baltic Sea in late summer (August -September) 2003 by IR kinetic fluorometry; at that time, Bchl a concentration varied between 8 and 50 ng l -1 . Interestingly, during our next survey in April 2004, the activity of AAPs was below the detection limit of the instrument (~2 ng Bchl a l -1 ; M. Koblí=ek unpubl. data). This result suggested that the community of AAPs in the Baltic Sea undergoes seasonal changes. For this reason, we followed ...

We have engineered polymer-based microenvironments that promote vasculogenesis both in vitro and in vivo through synergistic integrin-growth factor receptor signalling. Poly(ethyl acrylate) (PEA) triggers spontaneous organization of fibronectin (FN) into nanonetworks which provide availability of critical binding domains. Importantly, the growth factor binding (FNIII12-14) and integrin binding (FNIII9-10) regions are simultaneously available on FN fibrils assembled on PEA. This material platform promotes synergistic integrin/VEGF signalling which is highly effective for vascularization events in vitro with low concentrations of VEGF. VEGF specifically binds to FN fibrils on PEA compared to control polymers (poly(methyl acrylate), PMA) where FN remains in a globular conformation and integrin/GF binding domains are not simultaneously available. The vasculogenic response of human endothelial cells seeded on these synergistic interfaces (VEGF bound to FN assembled on PEA) was significantly improved compared to soluble administration of VEGF at higher doses. Early onset of VEGF signalling (PLCγ1 phosphorylation) and both integrin and VEGF signalling (ERK1/2 phosphorylation) were increased only when VEGF was bound to FN nanonetworks on PEA, while soluble VEGF did not influence early signalling. Experiments with mutant FN molecules with impaired integrin binding site (FN-RGE) confirmed the role of the integrin binding site of FN on the vasculogenic response via combined integrin/VEGF signalling. In vivo experiments using 3D scaffolds coated with FN and VEGF implanted in the murine fat pad demonstrated pro-vascularization signalling by enhanced formation of new tissue inside scaffold pores. PEA-driven organization of FN promotes efficient presentation of VEGF to promote vascularization in regenerative medicine applications.

Bone marrow and adipose tissue human mesenchymal stem cells were seeded in highly performing 3D gelatin–chitosan hybrid hydrogels of varying chitosan content in the presence of human platelet lysate and evaluated for their proliferation and osteogenic differentiation. Both bone marrow and adipose tissue human mesenchymal stem cells in gelatin–chitosan hybrid hydrogel 1 (chitosan content 8.1%) or gelatin–chitosan hybrid hydrogel 2 (chitosan 14.9%) showed high levels of viability (80%–90%), and their proliferation and osteogenic differentiation was significantly higher with human platelet lysate compared to fetal bovine serum, particularly in gelatin–chitosan hybrid hydrogel 1. Mineralization was detected early, after 21 days of culture, when human platelet lysate was used in the presence of osteogenic stimuli. Proteomic characterization of human platelet lysate highlighted 59 proteins mainly involved in functions related to cell adhesion, cellular repairing mechanisms, and regulation of cell differentiation. In conclusion, the combination of our gelatin–chitosan hybrid hydrogels with hPL represents a promising strategy for bone regenerative medicine using human mesenchymal stem cells.

Cells interact mechanically with their environment, exerting mechanical forces that probe the extracellular matrix (ECM). The mechanical properties of the ECM determine cell behavior and control cell differentiation both in 2D and 3D environments. Gelatin (Gel) is a soft hydrogel into which cells can be embedded. This study shows signifi cant 3D Gel shrinking due to the high traction cellular forces exerted by the cells on the matrix, which prevents cell differentiation. To modulate this process, Gel with hyaluronic acid (HA) has been combined in an injectable crosslinked hydrogel with controlled Gel-HA ratio. HA increases matrix stiffness. The addition of small amounts of HA leads to a signifi cant reduction in hydrogel shrinking after cell encapsulation (C2C12 myoblasts). We show that hydrogel stiffness counterbalanced traction forces of cells and this was decisive in promoting cell differentiation and myotube formation of C2C12 encapsulated in the hybrid hydrogels.