Global Proteomic Analysis Reveals High Light Intensity Adaptation Strategies and Polyhydroxyalkanoate Production in Rhodospirillum rubrum Cultivated With Acetate as Carbon Source

Abstract

Purple non-sulfur bacteria (PNSBs) are well known for their metabolic versatility. Among them, Rhodospirillum rubrum can assimilate a broad range of carbon sources, including volatile fatty acids (VFAs), such as acetate, propionate or butyrate. These carbon sources are gaining increasing interest in bioindustrial processes since they allow reduction of the production costs. Recently, our lab discovered that, after long term cultivation with acetate as unique carbon source, Rs. rubrum got acclimated to this carbon source which resulted in a drastic reduction of the lag phase. This acclimation was characterized by the amplification of the genomic region containing, among others, genes belonging to the ethylmalonyl-CoA (EMC) pathway, which has been demonstrated to be required for acetate assimilation in Rs. rubrum. In this paper, we combined bacterial growth analysis with proteomic (SWATH-Sequential Windowed Acquisition of All Theoretical Fragment Ion Mass Spectra-processing) investigation to better understand the bacterial response to a sudden increase of the light intensity. We compared the impact of suddenly increasing light intensity on the WT strain to that on the newly described acetate-competent strain in the presence of acetate. Contrary to what was observed with the WT strain, we observed that the acetate-competent strain was tolerant to the light stress. Proteomic analysis revealed that increasing light intensity had a significant impact on the photosynthetic apparatus, especially in the wild-type strain cultivated in the presence of acetate and low concentration of HCO 3 −. This phenomenon was accompanied by a relatively higher abundance of certain stress related proteins. Our results suggested that the production of PHA, but also potentially of branched chain amino acids synthesis, could be part of the mechanism used by Rs. rubrum to adapt to the light stress and the redox imbalance it triggered.

New perspectives on butyrate assimilation in Rhodospirillum rubrum S1H under photoheterotrophic conditions

“…2) and could thus serve as an electron balancing function. ILV biosynthesis pathway was also recently observed as upregulated in response to light stress under acetate condition in our lab [11] and a role in redox balancing was also suggested.…”

“…rubrum growing in succinate or butyrate conditions using targeted mass spectrometry analysis (MRM). As a role in redox balancing is more likely to be observed at the beginning of the growth curve [10,11], we analyzed samples harvested during the early exponential growth phase (OD 680nm ± 0.7). If no difference was observed between succinate and butyrate condition regarding valine content, we observed a large increase in isoleucine relative abundance under butyrate condition (Fig.…”

“…The detection was performed by refractometry at 210 nm. The amounts of succinate, butyrate and acetate were determined by integrating their specific peaks (9,11,16 min RT, respectively) and compared to standard curves.…”

Photoheterotrophic Assimilation of Valerate and Associated Polyhydroxyalkanoate Production by Rhodospirillum rubrum

“…Our whole-metabolism analyses reveal that a fully functional methylmalonyl-CoA pathway is mandatory for the photoheterotrophic assimilation of valerate and that the ethylmalonyl-CoA pathway is not necessary for the assimilation of acetyl-CoA issued from valerate cleavage. We suggest that other pathways, such as those for pyruvate ferredoxin oxidoreductase (PFOR) or isoleucine biosynthesis, may take part in this assimilation process as has already been suggested by our previous studies (11,12,14,15). We also investigated PHA production by R. rubrum, highlighting the production of copolymers with an outstanding HV monomer percentage, even in conditions of full nutrient availability.…”

“…The role of this pathway was first characterized by Alber and coworkers (9,10). In addition to the EMC pathway, the use of additional metabolic routes, such as the isoleucine biosynthesis and degradation pathways (MBC pathway) or the pyruvate ferredoxin oxydoreductase (PFOR) pathway, remains obscure, and further studies are still needed to attest to their involvement in acetate assimilation (11,12,14,15).…”