Sterols and hopanoids are chemically and structurally related lipids mostly found in eukaryotic and bacterial cell membranes. Few bacterial species have been reported to produce sterols and this anomaly had originally been ascribed to lateral gene transfer (LGT) from eukaryotes. In addition, the functions of sterols in these bacteria are unknown and the functional overlap between sterols and hopanoids is still unclear.
Gemmata obscuriglobus
is a bacterium from the
Planctomycetes
phylum that synthesizes sterols, in contrast to its hopanoid-producing relatives. Here we show that sterols are essential for growth of
G. obscuriglobus
, and that sterol depletion leads to aberrant membrane structures and defects in budding cell division. This report of sterol essentiality in a prokaryotic species advances our understanding of sterol distribution and function, and provides a foundation to pursue fundamental questions in evolutionary cell biology.
The dogma of coupled transcription and translation in bacteria has been challenged by recent reports of spatial segregation of these processes within the relatively simple cellular organization of the model organisms Escherichia coli and Bacillus subtilis. The bacterial species Gemmata obscuriglobus possesses an extensive endomembrane system. The membranes generate a very convoluted intracellular architecture in which some of the cell's ribosomes appear to have less direct access to the cell's nucleoid(s) than others. This observation prompted us to test the hypothesis that a substantial proportion of G. obscuriglobus translation may be spatially segregated from transcription. Using immunofluorescence and immunoelectron microscopy, we showed that translating ribosomes are localized throughout the cell, with a quantitatively greater proportion found in regions distal to nucleoid(s). Our results extend information about the phylogenetic and morphological diversity of bacteria in which the spatial organization of transcription and translation has been studied. These findings also suggest that endomembranes may provide an obstacle to colocated transcription and translation, a role for endomembranes that has not been reported previously for a prokaryotic organism. Our studies of G. obscuriglobus may provide a useful background for consideration of the evolutionary development of eukaryotic cellular complexity and how it led to decoupled processes of gene expression in eukaryotes.
The discovery of complete aerobic and anaerobic ammonia-oxidizing bacteria (Comammox and Anammox) significantly altered our understanding of the global nitrogen cycle. A high affinity for ammonia (Km(app),NH3 ≈ 63nM) and oxygen place the first described isolate, Comammox Nitrospira inopinata in the same trophic category as organisms such as some ammonia-oxidizing archaea. However, N. inopinata has a relatively low affinity for nitrite (Km,NO2 ≈ 449.2μM) suggesting it would be less competitive for nitrite than other nitrite-consuming aerobes and anaerobes. We examined the ecological relevance of the disparate substrate affinities by coupling it with Anammox (Nitrospira inopinata and Brocadia anammoxidans, respectively). Synthetic communities were established in hydrogel granules in which Comammox grew in the aerobic outer layer to provide Anammox with nitrite in the inner anoxic core to form dinitrogen gas. This spatial organization was confirmed with FISH imaging, supporting a mutualistic or commensal relationship. Successful co-habitation of Comammox N. inopinata and Anammox in synthetic granules broadens our limited understanding of the interplay between these two species and offers potential biotechnological applications to study any type of bacterial pairings in a systematic and reproducible manner.
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