[This corrects the article on p. 100 in vol. 41.].

Energy conservation in chemotrophic anaerobic bacteria.

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Purification and Characterization

Biofilms are complex communities of microorganisms attached to surfaces or associated with interfaces. Despite the focus of modern microbiology research on pure culture, planktonic (free-swimming) bacteria, it is now widely recognized that most bacteria found in natural, clinical, and industrial settings persist in association with surfaces. Furthermore, these microbial communities are often composed of multiple species that interact with each other and their environment. The determination of biofilm architecture, particularly the spatial arrangement of microcolonies (clusters of cells) relative to one another, has profound implications for the function of these complex communities. Numerous new experimental approaches and methodologies have been developed in order to explore metabolic interactions, phylogenetic groupings, and competition among members of the biofilm. To complement this broad view of biofilm ecology, individual organisms have been studied using molecular genetics in order to identify the genes required for biofilm development and to dissect the regulatory pathways that control the plankton-to-biofilm transition. These molecular genetic studies have led to the emergence of the concept of biofilm formation as a novel system for the study of bacterial development. The recent explosion in the field of biofilm research has led to exciting progress in the development of new technologies for studying these communities, advanced our understanding of the ecological significance of surface-attached bacteria, and provided new insights into the molecular genetic basis of biofilm development.

Microbial Biofilms: from Ecology to Molecular Genetics

Methanogens: reevaluation of a unique biological group.

Agricultural lands occupy 37% of the earth's land surface. Agriculture accounts for 52 and 84% of global anthropogenic methane and nitrous oxide emissions. Agricultural soils may also act as a sink or source for CO2, but the net flux is small. Many agricultural practices can potentially mitigate greenhouse gas (GHG) emissions, the most prominent of which are improved cropland and grazing land management and restoration of degraded lands and cultivated organic soils. Lower, but still significant mitigation potential is provided by water and rice management, set-aside, land use change and agroforestry, livestock management and manure management. The global technical mitigation potential from agriculture (excluding fossil fuel offsets from biomass) by 2030, considering all gases, is estimated to be approximately 5500–6000 Mt CO2-eq. yr−1, with economic potentials of approximately 1500–1600, 2500–2700 and 4000–4300 Mt CO2-eq. yr−1 at carbon prices of up to 20, up to 50 and up to 100 US$ t CO2-eq.−1, respectively. In addition, GHG emissions could be reduced by substitution of fossil fuels for energy production by agricultural feedstocks (e.g. crop residues, dung and dedicated energy crops). The economic mitigation potential of biomass energy from agriculture is estimated to be 640, 2240 and 16 000 Mt CO2-eq. yr−1 at 0–20, 0–50 and 0–100 US$ t CO2-eq.−1, respectively.

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Greenhouse gas mitigation in agriculture

Formation of Methane by Bacterial Extracts

Two bacterial species were isolated from cultures of Methanobacillus omelianskii grown on media, containing ethanol as oxidizable substrate. One of these, the S organism, is a gram negative, motile, anaerobic rod which ferments ethanol with production of H2 and acetate but is inhibited by inclusion of 0.5 atm of H2 in the gas phase of the medium. The other organism is a gram variable, nonmotile, anaerobic rod which utilizes H2 but not ethanol for growth and methane formation. The results indicate that M. omelianskii maintained in ethanol media is actually a symbiotic association of the two species.

Methanobacillus omelianskii, a Symbiotic Association of Two Species of Bacteria*

Wolin, E. A. (University of Illinois, Urbana), R. S. Wolfe, and M. J. Wolin. Viologen dye inhibition of methane formation by Methanobacillus omelianskii. J. Bacteriol. 87:993–998. 1964.—Low concentrations of methyl or benzyl viologen inhibit the formation of CH4 from ethanol and CO2 by washed cells of Methanobacillus omelianskii. Hydrogen, which is normally formed from ethanol, accumulates in greater quantities when CH4 formation is inhibited by viologens. The viologens do not stimulate H2 formation from ethanol in the absence of CO2. Inhibition of CH4 formation by the viologens is not reversed by H2. A variety of other dyes and possible electron acceptors were tested for inhibition, and none was inhibitory in the same low-concentration range at which the viologens were effective.

E.A. Wolin

Papers

Formation of Methane by Bacterial Extracts

Methanobacillus omelianskii, a Symbiotic Association of Two Species of Bacteria*

Viologen dye inhibition of methane formation by methanobacillus omelianskii

ATP-dependent formation of methane from methylcobalamin by extracts of Methanobacillusomelianskii

The cobalamin product of the conversion of methylcobalamin to CH4 by extracts of Methanobacillusomelianskii