3 research outputs found
Anoxic Iron Cycling Bacteria from an Iron Sulfide- and Nitrate-Rich Freshwater Environment
In this study, both culture-dependent and culture-independent methods were used to determine whether the iron sulfide mineral- and nitrate-rich freshwater nature reserve Het Zwart Water accommodates anoxic microbial iron cycling. Molecular analyses (16S rRNA gene clone library and fluorescence in situ hybridization, FISH) showed that sulfur-oxidizing denitrifiers dominated the microbial population. In addition, bacteria resembling the iron-oxidizing, nitrate-reducing Acidovorax strain BrG1 accounted for a major part of the microbial community in the groundwater of this ecosystem. Despite the apparent abundance of strain BrG1-like bacteria, iron-oxidizing nitrate reducers could not be isolated, likely due to the strictly autotrophic cultivation conditions adopted in our study. In contrast an iron-reducing Geobacter sp. was isolated from this environment while FISH and 16S rRNA gene clone library analyses did not reveal any Geobacter sp.-related sequences in the groundwater. Our findings indicate that iron-oxidizing nitrate reducers may be of importance to the redox cycling of iron in the groundwater of our study site and illustrate the necessity of employing both culture-dependent and independent methods in studies on microbial processes
Subunits of Mitochondrial Complex I Exist as Part of Matrix- and Membrane-associated Subcomplexes in Living Cells*S⃞
Mitochondrial complex I (CI) is a large assembly of 45 different subunits,
and defects in its biogenesis are the most frequent cause of mitochondrial
disorders. In vitro evidence suggests a stepwise assembly process
involving pre-assembled modules. However, whether these modules also exist
in vivo is as yet unresolved. To answer this question, we here
applied submitochondrial fluorescence recovery after photobleaching to HEK293
cells expressing 6 GFP-tagged subunits selected on the basis of current CI
assembly models. We established that each subunit was partially present in a
virtually immobile fraction, possibly representing the holo-enzyme. Four
subunits (NDUFV1, NDUFV2, NDUFA2, and NDUFA12) were also present as highly
mobile matrix-soluble monomers, whereas, in sharp contrast, the other two
subunits (NDUFB6 and NDUFS3) were additionally present in a slowly mobile
fraction. In the case of the integral membrane protein NDUFB6, this fraction
most likely represented one or more membrane-bound subassemblies, whereas
biochemical evidence suggested that for the NDUFS3 protein this fraction most
probably corresponded to a matrix-soluble subassembly. Our results provide
first time evidence for the existence of CI subassemblies in mitochondria of
living cells