In 11 species of rumen ciliates belonging to nine genera of the family Ophryoscolecidae (order Entodiniomorphida) an ectosymbiosis with methanogenic bacteria was found. The bacteria could be identified as methanogens on the basis of the presence of specific fluorescent coenzymes (F:3!-ro and F420). This somatic interaction may reflect a metabolic interaction in which efficient interspecies hydrogen transfer benefits both partners.

We have screened more than 110 representatives of the different taxa of terrsrial arthropods for methane production in order to obtain additional information about the origins of biogenic methane. Methanogenic bacteria occur in the hindguts of nearly all tropical representatives of millipedes (Diplopoda), cockroaches (Blattaria), termites (Isoptera), and scarab beetles (Scarabaeidae), while such methanogens are absent from 66 other arthropod species investigated. Three types of symbiosis were found: in the first type, the arthropod's hindgut is colonized by free methanogenic bacteria; in the second type, methanogens are closely associated with chitinous structures formed by the host's hindgut; the third type is mediated by intestinal anaerobic protists with intracellular methanogens. Such symbiotic associations are likely to be a characteristic property of the particular taxon. Since these taxa represent many families with thousands of species, the world populations of methane-producing arthropods constitute an enormous biomass. We show that arthropod symbionts can contribute substantially to atmospheric methane.Biopolymer degradation by anaerobic biota is responsible for most atmospheric methane, but there is still a considerable lack of knowledge about its sources and sinks (1, 2). A long-standing dispute concerns the potential contributions to atmospheric methane by methanogenic bacteria in the hindguts of insects (3-9). We (Table 1). They were subjected to measurements of gas emissions within 24-48 hr. For this period, the animals were fed their particular diet.Screening Procedure. The living arthropods were placed into serum vials (50 or 250 ml) and sealed with butyl rubber stoppers. For 2-12 hr the arthropods (0.5-50 g fresh weight, depending on size and availability of specimens) were incubated at room temperature (210C). The detection limit for methane was in the nmol range, guaranteeing that any significant methane emission could be detected by gas chromatography of gas samples taken at the end ofthe incubation period. Under these conditions, all methane-emitting species produced >100 nmol of methane during the incubation period. All nonproducers failed to produce methane concentrations higher than the background level (maximum, 10-20 nmol), even if the incubation time was prolonged and higher numbers of arthropods were incubated. Specimens of representative species of nonproducers were subjected to microscopic inspection (cf. Table 1); in all cases, the absence of methanogenic bacteria was confirmed. Small insects mining in wood were incubated in situ in heavily populated blocks of wood in 1-literjars for prolonged periods (up to 1 week, with daily gas measurements).Quantitative Gas Chromatographic Determinations. Determinations of methane were performed by using ethane as an internal standard (5). Continuous monitoring of the methane emission of the different cockroach species and millipedes with the aid of an experimental photoacoustic CO laser setup confirmed that the intestinal methane w...

1. The frequency of association between methanogenic bacteria and ovine rumen ciliates was studied in the rumen fluid of a fistulated sheep. 2.A period of fasting and flushing of the rumen content with nitrogen resulted in a relatively high association, whereas the intake of food and flushing with hydrogen caused a detachment of the methanogenic bacteria from the ciliates.3. The changes in the frequency of association can be correlated with the relative attribution to the H, production by hydrogenogenic bacteria and rumen ciliates.In the anaerobic environment of the rumen various nutritional interrelationships exist between bacteria and ciliates (Wolin, 1979;Prins & Clarke, 1980). One of these interactions consists of the production of hydrogen by bacteria (Joyner et al. 1977) and ciliates (Abou Akkada & Howard, 1960;Hungate, 1966; Prins & Prast, 1973;Williams & Harfoot, 1976) and the utilization of H, as substrates for the production of methane by methanogenic bacteria (Hungate, 1967;Hungate et al. 1970). Recently Vogels et al. (1980) described a somatic association between methanogenic bacteria and several species of entodiniomorph ciliates from rumens of slaughtered cows. We now report the results of a study concerning methanogen-ciliate association in the rumen of a fistulated sheep under various circumstances of fasting and feeding. MATERIALS A N D METHODSA Texel ram (body-weight 98 kg) was provided with a rumen fistula. Rumen fluid was taken anaerobically by means of a water suction pump. The experiments were performed during the summer season and the sheep was kept on a pasture. Part of the samples were taken after the animal had been fasted for 14 h (during the night). Measurement of methane productionAmounts of 3 ml rumen fluid were injected anaerobically into 50 ml bottles with 30 ml liquid medium according to Clarke (1963) and a gas phase of nitrogen-carbon dioxide (80 : 20, v/v) containing a small amount of ethane as the reference gas. The bottles were incubated in a New Brunswick G24 shaker at 190 rev./min and 39". Every hour during a period of 4 h a gas sample was taken and the methane content was measured in a Pye Unicam GCV gas-liquid chromatograph. The methane production was calculated by the zero-time rate method (Hungate, 1966). The results were expressed as 1 CH, produced/ 1 rumen fluid per 24 h. Interaction of methanogenic bacteria with ciliatesThe methanogen-ciliate association was checked by means of Leitz epifluorescence microscopy as described earlier (Vogels et al. 1980) and is defined positive if at least twenty bacteria were attached to a ciliate cell. At least 100 ciliates were randomly checked in each rumen sample immediately after collection. Because Eudiplodinium maggii and Diplodinium dentatum were most numerous among the entodiniomorphs the values reported refer only to these two species. 4-2at https://www.cambridge.org/core/terms. https://doi

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Yeast strains (157) belonging to at least 9 genera were isolated from natural habitats and screened for killer-sensitive relationships. Killer and sensitive characteristics were exhibited by 17 and 11% of the isolates, respectively. The strains belong to either one of two mutually exclusive killer-sensitive groups.