Effect of ocean acidification on production and decomposition of exudates - first results from a joint batch experiment

The effects of increasing CO2 concentrations (180, 380, and 780 ppm, representing past, present-day, and future atmospheric pCO2, respectively) on marine production, bacterial growth and activity as well as degradation of organic matter was studied during a joint bipartite laboratory experiment (Part I: Production, Part II: Degradation) of BIOACID subprojects 1.2.1, 1.2.2, 1.23 and 1.2.4 in April/May 2010. Here we report on the effect of pCO2 on the turn-over of dissolved organic matter (DOM) and transparent exopolymer particles (TEP) as well as activity rates of extracellular enzymes. The latter play an important role in the turn-over of DOM as they process organic matter degradation as well as nutrient regeneration. Ocean acidification (OA) is expected to affect the enzymatic hydrolysis, resulting in changes of the microbial decomposition of exopolymers. During Part I, growth and total TEP production of Nodularia was significantly enhanced at 780 ppm. TEP production normalized to chlorophyll a was highest at 180 ppm, suggesting that cell growth was more stimulated by CO2 than TEP production. During Part II, degradation of TEP was low in all treatments with highest decline at 780 ppm. Throughout the Part I, aminopeptidase activity increased over time in all CO2 treatments, whereas alpha- and beta-glucosidase activity remained very low. Inorganic phosphate was rapidly depleted in all treatments. Activity rates of extracellular phosphatase were highest at 780ppm, which is confirmed by strongest decline of dissolved organic phosphorus (DOP) in these treatments. No phosphatase activity was measured after removing Nodularia cells in Part II. These results suggest that ocean acidification may increase the rates of organic phosphorus recycling and therewith indirectly support algal growth

Response of Nodularia spumigena to pCO2 – Part 3: Turnover of phosphorus compounds

Diazotrophic cyanobacteria often form extensive summer blooms in the Baltic Sea driving their environment into phosphate limitation. One of the main species is the heterocystous cyanobacterium Nodularia spumigena. N. spumigena exhibits accelerated uptake of phosphate through the release of the exoenzyme alkaline phosphatase that also serves as an indicator of the hydrolysis of dissolved organic phosphorus (DOP). The present study investigated the utilization of DOP and its compounds (e.g. ATP) by N. spumigena during growth under varying CO2 concentrations, in order to estimate potential consequences of ocean acidification on the cell's supply with phosphorus. Cell growth, phosphorus pool fractions, and four DOP-compounds (ATP, DNA, RNA, and phospholipids) were determined in three set-ups with different CO2 concentrations (341, 399, and 508 μatm) during a 15-day batch experiment. The results showed rapid depletion of dissolved inorganic phosphorus (DIP) in all pCO2 treatments while DOP utilization increased with elevated pCO2, in parallel with the growth stimulation of N. spumigena. During the growth phase, DOP uptake was enhanced by a factor of 1.32 at 399 μatm and of 2.25 at 508 μatm compared to the lowest pCO2 concentration. Among the measured DOP compounds, none was found to accumulate preferentially during the incubation or in response to a specific pCO2 treatment. However, at the beginning 61.9 ± 4.3% of the DOP were not characterized but comprised the most highly utilized fraction. This is demonstrated by the decrement of this fraction to 27.4 ± 9.9% of total DOP during the growth phase, especially in response to the medium and high pCO2 treatment. Our results indicate a stimulated growth of diazotrophic cyanobacteria at increasing CO2 concentrations that is accompanied by increasing utilization of DOP as an alternative P source

Measuring bacterial activity and community composition at high hydrostatic pressure using a novel experimental approach: a pilot study

In this pilot study, we describe a high-pressure incubation system allowing multiple subsampling of a pressurized culture without decompression. The system was tested using one piezophilic (Photobacterium profundum), one piezotolerant (Colwellia maris) bacterial strain and a decompressed sample from the Mediterranean deep sea (3044 m) determining bacterial community composition, protein production (BPP) and cell multiplication rates (BCM) up to 27 MPa. The results showed elevation of BPP at high pressure was by a factor of 1.5 ± 1.4 and 3.9 ± 2.3 for P. profundum and C. maris, respectively, compared to ambient-pressure treatments and by a factor of 6.9 ± 3.8 fold in the field samples. In P. profundum and C. maris, BCM at high pressure was elevated (3.1 ± 1.5 and 2.9 ± 1.7 fold, respectively) compared to the ambient-pressure treatments. After 3 days of incubation at 27 MPa, the natural bacterial deep-sea community was dominated by one phylum of the genus Exiguobacterium, indicating the rapid selection of piezotolerant bacteria. In future studies, our novel incubation system could be part of an isopiestic pressure chain, allowing more accurate measurement of bacterial activity rates which is important both for modeling and for predicting the efficiency of the oceanic carbon pump