Differential Regulation of Soluble and Membrane-Bound Inorganic Pyrophosphatases in the Photosynthetic Bacterium Rhodospirillum rubrum Provides Insights into Pyrophosphate-Based Stress Bioenergetics

Abstract

Soluble and membrane-bound inorganic pyrophosphatases (sPPase and H؉ -PPase, respectively) of the purple nonsulfur bacterium Rhodospirillum rubrum are differentially regulated by environmental growth conditions. Both proteins and their transcripts were found in cells of anaerobic phototrophic batch cultures along all growth phases, although they displayed different time patterns. However, in aerobic cells that grow in the dark, which exhibited the highest growth rates, Northern and Western blot analyses as well as activity assays demonstrated high sPPase levels but no H ؉ -PPase. It is noteworthy that H ؉ -PPase is highly expressed in aerobic cells under acute salt stress (1 M NaCl). H ؉ -PPase was also present in anaerobic cells growing at reduced rates in the dark under either fermentative or anaerobic respiratory conditions. Since H ؉ -PPase was detected not only under all anaerobic growth conditions but also under salt stress in aerobiosis, the corresponding gene is not invariably repressed by oxygen. Primer extension analyses showed that, under all anaerobic conditions tested, the R. rubrum H ؉ -PPase gene utilizes two activator-dependent tandem promoters, one with an FNR-like sequence motif and the other with a RegA motif, whereas in aerobiosis under salt stress, the H ؉ -PPase gene is transcribed from two further tandem promoters involving other transcription factors. These results demonstrate a tight transcriptional regulation of the H ؉ -PPase gene, which appears to be induced in response to a variety of environmental conditions, all of which constrain cell energetics.

The H+-pyrophosphatase of Rhodospirillum rubrum Is Predominantly Located in Polyphosphate-rich Acidocalcisomes

“…The results presented in this work are also in agreement with a recent report (47) that showed a higher expression of the H ϩ -PPase in cells grown anaerobically in the light than in cells grown in the dark in aerobic cultures not subjected to intense agitation.…”

Evolutionarily divergent, Na+-regulated H+-transporting membrane-bound pyrophosphatases

“…Other probable mechanisms include downregulation of PPase activity by bound cellular proteins [46] and mobilization of the PP i pool within acidocalcisome-like structures [47]. Differential regulation of soluble and membrane PPases at the level of gene expression was also documented [48].…”

H+‐PPases: yesterday, today and tomorrow

“…2). The bacterial H þ -PPase appears therefore to be transcriptionally induced in response to a variety of conditions that constrain cell bioenergetics (54). On the other hand, algal and plant H þ -PPases are induced under anoxia, chilling and salt stresses (55,56), and overexpression of the vacuolar H þ -PPase isoform AVP1 in the model plant Arabidopsis has been claimed to confer increased saline and drought tolerance (57).…”

“…The hpp gene, the operon of biosynthetic genes for photosynthetic pigments and the reaction center (puc genes), and the operon of genes encoding ATP-synthase F o -subunits are located in different regions of the R. rubrum genome. The same transcriptional regulatory factor RegA (or another member of the CheY superfamily) should bind, after it has been phosphorylated under anaerobic conditions, to the promoter regions of hpp and the photosynthetic genes operon (upstream dashed lines), thus functioning as a transcriptional activator of all these genes (54). This concurrent transcriptional activation reveals associated physiological roles and possible ancestral relationships (cf.…”