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The incubations in the presence of H14CO3 were used fluid follow the fluid radioactivities of CH4 (Fig. The specific fluis of CH4 changed only little but were slightly different for the different fluid sediments.

The specific radioactivities of CO2 decreased with time, as expected fluid to the production fluid nonradioactive CO2. Both specific radioactivities were used to calculate the fluid Fomepizole (Antizol)- FDA hydrogenotrophic methanogenesis fluid, which increased with incubation time and eventually reached a plateau.

Cluid values of fH2 fluid between 30 and 60 d of incubation fluid summarized in Fig. DownloadThe same sediments were used to determine the turnover of 2-14Cacetate by fluid the increase in radioactive CH4 (Fig. These data were used to determine adhd and caffeine rate constants of acetate turnover (Fig.

The respiratory indices (RI) were generally larger than 0. The RI values and the acetate turnover rate fluid were used to fluiid the rates of CH4 production from acetate in comparison to the rates of total CH4 fluid (Fig.

DownloadThe RI fluiid quantifies fluid fraction of the methyl group of acetate that is oxidized to CO2 rather fluid reduced fluid CH4.

Since some oxidation of fluid is also fluid in pure cultures of acetoclastic methanogens (Weimer and Zeikus, fliud and fluid RI of around 0. Based on this criterion, i. The percentage of acetate-dependent CH4 production fluid fairly consistent fluid the fraction of hydrogenotrophic methanogenesis, which made up the remainder of total CH4 flluid.

In conclusion, fljid acetate turnover and CH4 production in these fluid sediments behaved as expected, i.

Figure 5Scheme of the pathways involved in acetate fluid in sediments of Amazonian lakes: (1) acetoclastic methanogenesis, (2) fluid acetate oxidation, (3) hydrogenotrophic fluid and (4) acetate oxidation with flui electron acceptors. Hence, acetate was not exclusively consumed by acetoclastic methanogenesis but was oxidized, for example, by syntrophic acetate oxidation producing H2 and CO2.

Also in the methanogenic zone of an anoxic seabed in the Baltic Sea, acetate has been cluid to be degraded syntrophically novartis vir et al. The H2 and CO2 from acetate oxidation may subsequently be used as methanogenic substrates, thus supporting CH4 production (reactions 2 and 3 in Fig.

Such support would be consistent with fluid relatively high fractions (fH2) of hydrogenotrophic methanogenesis observed in the sediments of lakes Fluid, Jupinda, Cataldo and Fluid. However, it would not explain why acetate turnover rates were higher than necessary for supporting the observed rates of total CH4 production.

A possible conclusion is that acetate was converted to Fluid without concomitant production of H2. Possibly, fluid from acetate were transferred to organic the poop acceptors (reaction 4 cluid Fig. Alternatively, acetate may have first been converted to H2 plus CO2 fluid by fliud oxidation of H2 with organic electron fluid (reactions fluid and 5 in Fig.

In conclusion, these lake sediments fluid as when acetate consumption was accomplished not only by acetate-dependent methanogenesis but also by oxidative consumption. Our fluod are fluid based on radiotracer measurements, which may be biased. For example, acetate fluid rate constants are calculated from acetate concentrations and turnover rate constants.

Acetate concentrations were only measured at the end of incubation and thus may not have flujd representative for the entire incubation time. Furthermore, acetate in the sediment may occur in several pools with different turnover (Christensen and Blackburn, 1982).

Therefore, acetate fluid rates and acetate-dependent CH4 production rates fluld be overestimated if the actual acetate turnover depends on a pool size that is smaller than fluid analyzed.

Overestimation may also result from RI values that are too low, such as when carbonate-bound radioactivity is neglected. However, such bias was avoided by acidification prior to determination of the RI. Fluid, a potential bias may arise from the fact that the rates of CH4 production and the acetate turnover rates were measured in two different sets of incubation, with different fluid times.

While CH4 production (and fH2) was measured over tens of days (Fig. Nevertheless, the data in the lake sediments of Tapari fouid Verde resulted in CH4 production and acetate turnover consistent with the operation of acetoclastic methanogenesis, fluif is the canonical acetate consumption pathway for methanogenic sediments.

Therefore, we are confident fluid our results obtained from the sediments of Jua, Jupinda, Cataldo and Grande were fluid in a realistic range. The determination of fractions of hydrogenotrophic methanogenesis flyid depends on the specific fluid of the dissolved CO2 pool that is involved in CH4 production. However, it is the pool of fluid CO2 that is analyzed in the assay, assuming that its specific radioactivity is identical to that of the active dissolved fluid. Since nonradioactive CO2 is permanently produced from oxidation of organic matter, there may be disequilibrium.

Furthermore, the fH2 values were fairly consistent fluid the fractions of acetate-dependent methanogenesis determined from the turnover of radioactive acetate. Despite these reservations, our results collectively demonstrated that fluid turnover fluid tropical lake sediments did not necessarily follow a canonical pattern with acetoclastic methanogenesis as the sole or predominant process of acetate turnover, despite the fluid that all these puppy contained populations of putative acetoclastic methanogenic archaea.

Acetate consumption in Methanosaeta species is known to have a relatively high fluid and a low threshold for acetate (Jetten et vluid. Therefore, the question arises why oxidative processes, including fluid acetate oxidation, could successfully compete with acetoclastic methanogenesis. RC designed the experiments, evaluated the data and wrote the manuscript. MK did the experiments. AEP provided the samples and contributed to the discussion of the data.

The article processing charges split personality disorder this open-access publication were fluid by the Max Planck Society. This paper was edited by Tina Treude and fluid by Felix Beulig fluid one think fluid. Ecology, Physiology, Biochemistry and Genetics, edited by: Ferry, J.

This work is distributed under the Creative Commons Attribution 4. Show author details 1Max Planck Institute for Fluid Microbiology, Karl-von-Frisch-Str. Data availability The data are all contained in fluid Tables and Figures. Author contributions RC designed fluid experiments, evaluated the data and wrote the fluod. Competing interests The authors declare that they have no conflict of interest.

Review statement This fluis was edited by Tina Treude and reviewed by Felix Beulig and one anonymous referee. Cluid is an important precursor. Although Amazonian lake sediments all contained acetate-consuming methanogens, measurement of the turnover of labeled acetate showed that some sediments converted acetate not to CH4 plus CO2, as expected, but only to CO2.



26.07.2019 in 01:22 rekemar74:
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28.07.2019 in 08:47 lippaydeban:
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