[Soluble and particulate aldehyde dehydrogenases of Pseudomonas aeruginosa]

Fatty aldehyde dehydrogenases in Acinetobacter sp. strain HO1-N: role in hexadecanol metabolism

The role of fatty aldehyde dehydrogenases (FALDHs) in hexadecane and hexadecanol metabolism was studied in Acinetobacter sp. strain HO1-N. Two distinct FALDHs were demonstrated in Acinetobacter sp. strain HO1-N: a membrane-bound, NADP-dependent FALDH activity induced 5-, 15-, and 9-fold by growth on hexadecanol, dodecyl aldehyde, and hexadecane, respectively, and a constitutive, NAD-dependent, membrane-localized FALDH. The NADP-dependent FALDH exhibited apparent Km and Vmax values for decyl aldehyde of 5.0, 13.0, 18.0, and 18.3 microM and 537.0, 500.0, 25.0, and 38.0 nmol/min in hexadecane-, hexadecanol-, ethanol-, palmitate-grown cells, respectively. FALDH isozymes ald-a, ald-b, and ald-c were demonstrated by gel electrophoresis in extracts of hexadecane- and hexadecanol-grown cells. ald-a, ald-b, and ald-d were present in dodecyl aldehyde-grown cells, while palmitate-grown control cells contained ald-b and ald-d. Dodecyl aldehyde-negative mutants were isolated and grouped into two phenotypic classes based on growth: class 1 mutants were hexadecane and hexadecanol negative and class 2 mutants were hexadecane and hexadecanol positive. Specific activity of NADP-dependent FALDH in Ald21 (class 1 mutant) was 85% lower than that of wild-type FALDH, while the specific activity of Ald24 (class 2 mutant) was 55% greater than that of wild-type FALDH. Ald21R, a dodecyl aldehyde-positive revertant able to grow on hexadecane, hexadecanol, and dodecyl aldehyde, exhibited a 100% increase in the specific activity of the NADP-dependent FALDH. The oxidation of [3H]hexadecane byAld21 yielded the accumulation of 61% more fatty aldehyde than the wild type, while Ald24 accumulated 27% more fatty aldehyde, 95% more fatty alcohol, and 65% more wax ester than the wild type. This study provides genetic and physiological evidence for the role of fatty aldehyde as an essential metabolic intermediate and NADP-dependent FALDH as a key enzyme in the dissimilation of hexadecane, hexadecanol, and dodecyl aldehyde in Acinetobactor sp. strain HO1-N.

Purification and characterization of two aldehyde dehydrogenases from Pseudomonas aeruginosa

Two soluble aldehyde dehydrogenases isoenzymes have been purified and separated from extracts of a paraffin-assimilating bacterium, Pseudomonas aeruginosa. The first one, obtained at an estimated purity of 20% (spec. act. with butanal 0.33 kat/kg) was NAD-dependent. It was rapidly inactivated at pH 8.6 but was efficiently protected by NAD. It had a molecular weight of 225000 and presented a high affinity for aldehydes of short and middle chain lengths. The second enzyme, obtained in a nearly homogenous state (spec. act. with pentanal 0.62 kat/kg) was NADP-dependent. It was activated by ions, in particular potassium ions, and had a good affinity for aldehydes of higher chain lengths. Both enzymes were stabilized by thiols and glycerol and were inactivated by reagents of sulfhydryl groups. These enzymes are 'constitutive' and their physiological function is uncertain. When the bacteria were grown on n-paraffin a new membrane-bound NAD-dependent aldehyde dehydrogenase activity was produced.

[Hydrocarbon metabolism in a marine bacterium]

The marine bacterium L.16.1 (Alcaligenes sp.) grows preferentially on alkanes (C10 to C18) with a very high growth yield (98 per cent); optimal growth depends strictly on the presence of a well-defined NaCl concentration (100 mM). Our strain is constitutive for the enzymatic systems responsible for the oxidation of alkanes to fatty acids, i.e. NADH-dependent hydroxylase, alcohol and aldehyde dehydrogenases, the latter of which located at the cytoplasmic membrane level. The aerobic oxidation of primary alcohols by particulate extracts prepared in the presence of 400 mM NaCl is NAD+-dependent (Km = 0.082 mM, Vmax = 238 with decanol). With extracts prepared in the absence of NaCl, Vmax undergoes a very strong decrease. On the contrary , the NAD+ (P)+-dependent oxidation of aldehydes is carried out anaerobically by the same extracts irrespective of the presence or the absence of added Na+ in the solutions used for the preparation of these extracts. A possible explanation for our results could be that Na+ acts on the enzymatic systems for which the maintenance of the membrane integrity is essential. This interpretation is consistent with the slowing down of the growth speed accompanying the decrease of NaCl concentration in the growth medium. With regard to alcohol and aldehyde-dehydrogenases, it is noteworthy that these enzymes behave like similar enzymatic activities induced by alkanes in other microorganisms.