The Reduction of Formaldehyde by Bacterial Cells

Abstract

In the course of an investigation of the metabolic activities of art atypical, creatinine-decomposing strain of Pseudomonas aeruginosa, it was shown by Xopper and Robin (1950) that this organism decomposed sarcosine by oxidative demethylation to formaldehyde and glycine. The presence of formaldehyde, however, could be detected only when autolyzed bacteria were allowed to act on the substrate. Resting bacterial cells produced glycine, but no formaIdehyde from sarcosine. On the basis of further observations in connection with a study of the enzyme responsible for the breakdown of sarcosine it was suggested by Kopper (1950) that living cells might be capable of disposing of formaldehyde through reduction, a process made possible by the reducing potential of the cell. The purpose of this report is to present experimental evidence in support of this hypothesis. EXPERr~WF~NTAL Preparation of the Bacterial Cell SuspensionThe organisms were grown on meat extract agar at room temperature for 40 hours. They were then washed off with distilled water and centrifuged. Following one more washing and centrifugation, the bacteria were suspended in distilled water. An aliquot of this suspension was adjusted turbidimetrieally to give a reading of 53 on the scale of the Leitz photoelectric colorimeter (C filter). By means of nutrient agar plate surface counts, this optical density was found to correspond to approximately 3 X 109 viable cells per ml. Unless indicated otherwise, 3 × 10 x° cells in 0.1 ml. of distilled water were used throughout the course of the experiments. Materials and MethodsCommercial formalin (40 per cent formaldehyde, u.s.1,.) was diluted to the desired concentration with distilled water. The quantitative determination of I-ICHO was carried out with chromotropic acid reagent, as previously described (Kopper, 1950).Two methods were employed for measuring small amounts of methyl alcohol Reaction mixtures from which all HCHO had disappeared were treated with K1VInOt in accordance with the procedure outlined by Boos (1948). The chromotropic acid 573

Studies on Bacterial Reducing Activity in Relation to Age of Culture

“…A long lag period was encountered with low bacterial concentrations (2 X 109 or less). This has also been observed in studies on the reduction of formaldehyde (Kopper, 1951b) and sodium nitrate and methylene blue (Kopper, 1951c).…”

“…In the course of the present study it was observed that young cells of E. coli, while far more vigorous than old cells in reducing sodium nitrate, methylene blue, and tetrazolium salt, all ionizable compounds, were unable to take up formaldehyde. Since the reduction of HCHO by old cells of E. coli had been established previously (Kopper, 1951b), it would seem logical to conclude that HCHO was somehow prevented from diffusing into that region of the young cell where it could be reduced. The same mechanism may be operative in causing the rapid decline in the reduction of 2,3 ,5-triphenyltetrazolium chloride at alkaline pH when the salt in increasingly larger amounts is converted into undissociated base.…”