Rodney A. Asher

Microbial nitrogen transformations in sediments and inorganic nitrogen fluxes across the sediment/water interface on the South Island West Coast, New Zealand

Abstract In January 1982, sediment microbial N transformations and inorganic N fluxes across the sediment/water interface were studied at nine sites off the South Island West Coast, New Zealand. The sediments showed a great variety in physical, chemical and biological properties. The sediment organic matter had a molar C N ratio of 5.9–10.9, and the total N P ratio was 1.2–4.0. The denitrification capacity in the top 7.5 cm of sediment was 0.1–77.2 mmol N m −2 day −1 and generally declined with increasing sediment depth. The in situ denitrification rate was 0.02–1.84 mmol N m −2 day −1 and highest activities were generally found in surface sediments and at 6–7.5 cm depth. Denitrification accounted for 82–100% of total nitrate reduction. Net N mineralization was indirectly estimated at 0.6–2.4 mmol N m −2 day −1 , and the experimental determination of this N transformation gave 0.6–3.2 mmol N m −2 day −1 . Denitrification accounted for 3–75% of net N mineralization. The diffusive flux of ammonium and nitrate across the sediment/water interface was 0.1–0.7 and 0.1–0.6 mmol N m −2 day −1 , respectively.

Eubacterium callanderi sp. nov. That Demethoxylates O-Methoxylated Aromatic Acids to Volatile Fatty Acids

We describe a bacterium which demethoxylates O-methoxylated aromatic acids to give mixed volatile fatty acids. The cell wall composition and deoxyribonucleic acid-deoxyribonucleic acid homology data allow the organism to be included within the genus Eubacterium. Although the guanine-plus-cytosine content (47 mol%) is the same as that for Eubacterium limosum and the morphologies of the two organisms are similar, the new isolate differs in that it cannot utilize H2-CO2, methanol, or other one-carbon compounds or the amino acid isoleucine as growth substrates and in defined media requires acetate as a growth factor. The new species is named Eubacterium callanderi; the type strain is strain FD (= DSM 3662).

Isolation from a methanogenic ferulate degrading consortium of an anaerobe that converts methoxyl groups of aromatic acids to volatile fatty acids

An anaerobic, non-motile, rod shaped bacterium is described which cleaves the phenylether bonds of methoxylated aromatic substrates to give the corresponding hydroxy aromatic derivatives and mixed volatile fatty acids, chain length, C1, C2 and C4. The bacterium was isolated from an anaerobic digestor fed with contents from a wood fiber to alcohol fermentation plant, using anaerobic rolltube medium with ferulate as the carbon and energy source. Moles fatty acid produced per 100 mole of methoxyl group of aromatic substrate fermented were approximately: acetate, 14; butyrate, 18; and formate, 15. For the fermentation of equimolar amounts of methoxylated aromatic compounds, growth yields were proportional to the number of methoxylated groups per molecule, and the amount of cells per methoxyl group did not alter when phenylacrylate derivatives were used as substrates. The organism was unable to reduce the side-chain double bond of phenylacrylate derivatives. Coculture of the bacterium on ferulate with Methanospirillum hungatei, or Desulfovibrio in the presence of SO4=resulted in no nett production of formate, and small quantities of methane and sulfide were produced respectively. The isolate utilized glucose, fructose, and lactate, but not methanol or H2−CO2 as growth substrates. Lactate, butyrate, acetate, formate and small quantities of H2 were produced from glucose fermentation. No reduction of SO4=or NO3-occurred during fermentation of glucose or methoxylated aromatics and no growth occurred in the presence of oxygen.

Inhibition of the methylcoenzyme M methylreductase system by NAD+ and NADP+ in cell-extracts of Methanosarcinabarkeri

In cell extracts of Methanosarcina barkeri, the methylcoenzyme M methylreductase system with H2 as the electron donor was inhibited by NAD+ and NADP+, but NADH and NADPH had no effect on enzyme activity. NAD+ (4 and 8 mM) shifted the saturation curve for methylcoenzyme M from hyperbolic (Hill coefficient [nH] = 1.0; concentration of substrate giving half maximal velocity [Km] = 0.21 mM) to sigmoidal (nH = 1.5 and 2.0), increased Km (Km = 0.25 and 0.34 mM), and slightly decreased Vmax. Similarly NADP+ at 4m and 8 mM increased nH to 1.6 and 1.85 respectively, but the Km values (0.3 and 0.56 mM) indicated that NADP+ was a more efficient inhibitor than NAD+.