l -Methionine, a Precursor of Trace Methane in Some Proteolytic Clostridia

Abstract

Sainit-Etienntie dii Rou'ray, Section d'Etiudes et d'Analvse Isotopique et Nuclelaire, Cenitre dcEtidcles Nucl&iires de Saclay, 91191 Gij'sir-Yivette C&dex, a(1ld

Non-microbial methane formation in oxic soils

“…Methane emissions under UV radiation were found to be in the range of 0.25 to 7.28 µg m −2 h −1 for various soils in the UV-B intensity range of 1 to 4 W m −2 . Again, these emission rates are considerably lower than emissions observed from natural wetlands (Morrissey and Livingston, 1992;Roulet et al, 1992;Cao et al, 1998). Further studies on samples collected from different vegetation zones, including subtropical and tropical regions, would be required to better estimate the global implications of our findings.…”

“…Assuming that the first five centimetres of the soil horizon account for most of the CH 4 production, the emission rates from dry and wet soil at 30 to 40 • C (Table 1) would correspond to emission rates of 0 to 18 µg m −2 h −1 , assuming a dry bulk density of 1.5 g cm −3 for soil and 0.1 g cm −3 for peat (Minkinnen and Laine, 1998). These emissions increase up to an order of magnitude when the soil surface temperature reaches 50 to 70 • C. Although these temperatures are often only observed at soil surfaces in tropical and savannah regions, when compared to field measurements from wetlands with observed CH 4 emissions up to 11.9 mg m −2 h −1 (286.5 mg m −2 d −1 ) and calculated average emission rates of 2.1 mg m 2 h −1 (51 mg m −2 d −1 ) (Morrissey and Livingston, 1992;Roulet et al, 1992;Cao et al, 1998), these are relatively minor emissions. The CH 4 emissions under UV light are consistent with findings by Vigano et al (2008) and McLeod et al (2008), who showed that UV irradiation drives CH 4 production from dried plant matter.…”

“…to methanogenesis. Methane production by oxic eubacteria (Rimbault et al, 1988) and anaerobic microsites, a refuge for methanogens (Peters and Conrad, 1995), were offered as possible explanations even though CH 4 production from eubacteria could only be detected in trace quantities. In experiments by Kammann et al (2009), soil cores emitted up to 4.58 µg kg −1 d −1 CH 4 per core even after homogenization, which may be expected to lead to the destruction of anoxic microsites.…”

Separating methane production and consumption with a field‐based isotope pool dilution technique

“…Microbial activity within anoxic microsites has been hypothesized to occur, based on the presence of anaerobic organisms in oxic soils [Peters and Conrad, 1995] and on the propensity for oxic soils to produce methane rapidly when placed under anoxic conditions [Yavitt et al, 1995] and from oxygen microprobes [Sexstone et al, 1985]. However, Rimbault et al [1988] have measured extremely low rates of methane production resulting as a metabolic byproduct in the eubacteria, Clostridia. On the basis of the potential for nonmethanogenic organisms to produce trace quantities of methane, it seems premature to assume that methanogens, alone, are responsible for production of methane in oxic soils.…”

Gas chromatographic detection of sulphur compounds as methyl esters after growth of anaerobic bacteria in broth media

“…They proposed that certain anaerobic bacteria are able to form 4-(methylthi0)-butanoic acid through deamination of methionine and/or 3-(methy1thio)-propanoic acid by deamination and decarboxylation reactions. It is known that several Clostridium species as well as gram-negative anaerobic rods can degrade methionine resulting in the production of volatile sulphur compounds (Rimbault et al 1988;Claesson et ul. 1990).…”