Anaerobic experiments

It is reasonable to assume that there may be a loss of a volatile fraction of OM because of the bubbling of the water in the aerobic experiment. But this loss was considered negligible since all forms of N and P at all periods of the experiment were balanced. The organic acids in the anaerobic experiments were determined by a variant of potentiometric titration suggested by E.S. Bikbulatov. The results of these investigations are summarised in Table VI. 

In the anaerobic experiment (at 20° C) the initial and final contents of total organic mass in dry weight, organic C, N and P, carbohydrates, protein, lipids in the particulate matter were respectively 720 and 252, 380 and 129,... 

The relative content of organic components in the particulate matter in the successive periods of the anaerobic experiment (in %)... 

In both experiments, during the first 6—10 days, when the labile organic compounds were mostly subject to degradation, the process was described by a first-order reaction equation, the rate constants of which were less than 0.1 day". The rate constants according to organic carbon were 0.041 day" at the fourth day and 0.039 day" at the seventh in the aerobic experiment, and 0.024 day" at the fifth and 0.022 day" at the twelfth in the anaerobic experiment. The decrease in their value in later periods is attributed to the increasing influence from the decomposition of more stable organic constituents. 

A bacterium isolated from a soil culture can utilize ribose as a sole source of carbon when grovm anaerobically. Experiments show that in the anaerobic pathways leading to ATP production, three molecules of ribose are converted to five molecules of CO2 and five molecules of ethanol. These organisms also use ribose for the production of NADPH. The assimilation of ribose begins with its conversion to ribose 5-phosphate, with ATP serving as a phosphoryl donor. 

The ability of nitrous acid to react with common constituents of soil organic matter has also been demonstrated by Stevenson et al. (1970) in anaerobic experiments conducted in solutions buffered at pH 6-7 (see Chapter 13). These studies emphasize the kinds and amounts of gases produced rather than the amount of the nitrite that reacted with the organic compounds and was fixed by them doubtless fixation considerably exceeded volatilization. 

A second procedure was used when samples were unstable in air or when a higher concentration of components was desired. In this case, the a- and -polypeptides were dissolved in 0.5 mL of 4.5% OG in 0.05 M phosphate buffer, pH 7.5, and 2.0 mL phosphate buffer (no OG) added. For anaerobic experiments, all the following steps were conducted under nitrogen. BChl a or an analog was added from an acetone or a pyridine solution and then additional buffer added until the B820 spectra were optimal (usually between 0.65 and 0.75% OG). For B873 formation, the sample was handled as in the first procedure. 

CJ -carotene was the only product formed from radiolabelled 15-cis phytoene. When such a dissected system was investigated more closely, it was found that it worked independently of usual cofactors, FAD and NADP, so that the nature of the electron acceptor became a matter of interest. Decisive evidence in this respect came from strictly anaerobic experiments, made in the presence of helium (Fig. 1). For as long as 0 was absent, no formation of [ C] -carotene was observed, and the substrate 15-cis[ C]phy-toene was not metabolized. On the addition of 0, the reaction accelerated to normal values. 

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