3D reconstruction and flexibility of the hybrid engine Acetobacterium woodii F-ATP synthase.

The Na+-translocating F1FO ATP synthase from Acetobacterium woodii (AwF-ATP synthase) with a subunit stoichiometry of α3:ß3:γ:δ:ε:a:b2:(c2/3)9:c1 represents an evolutionary path between ATP-synthases and vacuolar ATPases, by containing a heteromeric rotor c-ring, composed of subunits c1, c2 and c3, and an extra loop (γ195-211) within the rotary γ subunit. Here, the recombinant AwF-ATP synthase was subjected to negative stain electron microscopy and single particle analysis. The reference free 2D class averages revealed high flexibility of the enzyme, wherein the F1 and FO domains distinctively bended to adopt multiple conformations. Moreover, both the F1 and FO domains tilted relative to each other to a maximum extent of 28° and 30°, respectively. The first 3D reconstruction of the AwF-ATP synthase was determined which accommodates well the modelled structure of the AwF-ATP synthase as well as the γ195-211-loop. Molecular simulations of the enzyme underlined the bending features and flexibility observed in the electron micrographs, and enabled assessment of the dynamics of the extra γ195-211-loop.

Nonacetogenic growth of the acetogen Acetobacterium woodii on 1,2-propanediol.

Acetogenic bacteria can grow by the oxidation of various substrates coupled to the reduction of CO2 in the Wood-Ljungdahl pathway. Here, we show that growth of the acetogen Acetobacterium woodii on 1,2-propanediol (1,2-PD) as the sole carbon and energy source is independent of acetogenesis. Enzymatic measurements and metabolite analysis revealed that 1,2-PD is dehydrated to propionaldehyde, which is further oxidized to propionyl coenzyme A (propionyl-CoA) with concomitant reduction of NAD. NADH is reoxidized by reducing propionaldehyde to propanol. The potential gene cluster coding for the responsible enzymes includes genes coding for shell proteins of bacterial microcompartments. Electron microscopy revealed the presence of microcompartments as well as storage granules in cells grown on 1,2-PD. Gene clusters coding for the 1,2-PD pathway can be found in other acetogens as well, but the distribution shows no relation to the phylogeny of the organisms.

Cold-active acetogenic bacteria from surficial sediments of perennially ice-covered Lake Fryxell, Antarctica.

Cold-active acetogenic bacteria in the permanently cold sediments of Lake Fryxell, Antarctica were investigated using culture-based methods. Two psychrophilic, acetogenic strains were isolated and found to be physiologically and phylogenetically related to Acetobacterium bakii and Acetobacterium tundrae. However, the Antarctic isolates showed a lower growth temperature range than other species of Acetobacterium, with growth occurring from -2.5 to 25 degrees C and optimally at 19-21 degrees C. Cultures incubated at +5 and +1 degrees C grew with generation times of 7 and 9 days, respectively. The rapid growth of these strains at low temperatures suggests that acetogenesis may be an important anaerobic process in the sediments of Lake Fryxell.

Anaerobic biodegradation of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) by Acetobacterium malicum strain HAAP-1 isolated from a methanogenic mixed culture.

In previous work, we studied the anaerobic biodegradation of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) by a methanogenic mixed culture that biodegrades RDX by using H2 as the sole electron donor. Strain HAAP-1 was isolated after enriching for the homoacetogens in a mineral medium containing RDX and an H2-CO2 (80:20) headspace. Strain HAAP-1 degraded 29.0 microM RDX in <14 days and formed 13.0 mM acetate when grown in a mineral medium with an H2-CO2 headspace. Methylenedinitramine was observed as a transient intermediate, indicating ring cleavage had occurred. In live cultures containing an N2-CO2 headspace, RDX was not degraded, and no acetate was formed. The 16S rRNA gene sequence for strain HAAP-1, consisting of 1485 base pairs, had a 99.2% and 99.1% sequence similarity to Acetobacterium malicum and A. wieringae, respectively. This is the first report of RDX degradation by a homoacetogen growing autotrophically and extends the number of genera known to carry out this transformation.