A Survey of Heterotrophic Micro-Organisms from Soil for Ability to Form Nitrite and Nitrate

Abstract

SUMMARY: A total of 978 cultures of heterotrophic organisms were isolated from twelve actively nitrifying soils ; each isolate was tested for ability to form nitrite or nitrate in glucose peptone broth. None of the isolates yielded substantial amounts of nitrite ; concentrations found did not exceed 2 pg. nitrite-N/ml. Almost 7 yo of the isolates formed nitrite-N in excess of 0.2 pg./ml., while slightly over 2 yo yielded more than 0.5pg./ml. Fungus isolates were the most numerous and most active nitrite producers ; fifteen of the fungi formed nitrate in addition to nitrite. Concentrations of 5-45 pg. nitrate-N/ml. were recorded for the active fungi. Further isolations of fungi from ten soils of diverse properties resulted in 353 cultures but only three of these formed nitrate. One of these cultures yielded 9Opg. nitrate-N/ml. after 14 days growth in the test medium.Most of the fungi which produced nitrate (16 of the 18 active cultures) were identified as Aspergillus jlavus. A Penicillium sp., and a Cephalosporium sp. also formed low concentrations of nitrate. Each isolate of A . flavus obtained from soil proved capable of nitrate formation. Strains of A . flavus were encountered which did not yield nitrate, but these had been obtained from culture collections, and had been carried on artificial media for many years. Some stock cultures of A . jlavus, several cultures of A . jlavus and one of A . glaucus, freshly isolated from wheat seed, also were active nitrate producers. Ammonium sulphate and urea media supported growth of soil fungus isolates but not nitrate formation. Other organic nitrogen substrates in order of increasing effectiveness in nitrate production were : yeast extract, peptone, Protone and casein.

Heterotrophic nitrification by a thermophilicBacillusspecies as influenced by different culture conditions

“…First, the relatively low substrate supply used in these experiments (1 g·L -1 ) must not be toxic for MS30 nitrification activity. Secondly, it has been reported that complex organic matter favored nitrite production by heterotrophic bacteria (Eylar and Schmidt 1959). However, it has also been shown that several organic nitrogen compounds can inhibit heterotrophic nitrification (Doxtader and Alexander 1965).…”

“…First, numerous organic and inorganic substances can be used as N-sources for heterotrophic nitrification (Focht and Verstraete 1977), and an organic carbon source is necessary not only for growth of the organisms, but also for nitrification of at least inorganic N-sources (Hylin and Matsumoto 1960;Verstraete and Alexander 1972b). Concerning the products of heterotrophic nitrification, hydroxylamine is often the intermediate product, and hydroxamates can be the main product (Verstraete 1974); but the final product of heterotrophic nitrification generally is nitrite (Obaton et al 1968;Verstraete andAlexander 1972a, 1972b;Castignetti and Hollocher 1984), although sometimes some nitrate formation was observed in bacterial cultures (Gunner 1963;Verstraete and Alexander 1972a;Castignetti and Gunner 1981;Papen et al 1989), and most fungi mainly excrete nitrate (Eylar and Schmidt 1959;Marshall and Alexander 1962). In addition, contrary to autotrophic nitrifiers, some heterotrophic microorganisms can carry out dual activity.…”

Functional role of DNRA and nitrite reduction in a pristine south Chilean Nothofagus forest

“…Heterotrophic nitrification is predominantly carried out by fungi (Landi et al 1993) which gain energy from compounds that belong to more recalcitrant organic N pools in soil (Paul 2007). Therefore, NO 3 -production via organic N oxidation is often carried out by acid tolerant fungi in forest soils (Eylar and Schmidt 1959;Stroo et al 1986). …”

Nitrification in coniferous forest soils

“…The first large-scale screening of soil fungi for the ability to nitrify in pure culture was by Eylar and Schmidt (1959) who screened 751 soil fungi. Of these, only three produced significant levels of nitrate from amino-nitrogen.…”