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Oxidative stress and starvation in Dinoroseobacter shibae: the role of extrachromosomal elements.

Soora M, Tomasch J, Wang H, Michael V, Petersen J, Engelen B, Wagner-Döbler I, Cypionka H - Front Microbiol (2015)

Bottom Line: However, light exposure results in the production of cytotoxic reactive oxygen species in AAPs.The observed decrease of gene expression was not due to plasmid loss, as all five ECRs were maintained in the cells.Interestingly, the genes on the 72-kb chromid were the least downregulated, and one region with genes of the oxygen stress response and a light-dependent protochlorophyllide reductase of cyanobacterial origin was strongly activated under the light/dark cycle.

View Article: PubMed Central - PubMed

Affiliation: Institute for Chemistry and Biology of the Marine Environment (ICBM), Carl-von-Ossietzky University of Oldenburg Oldenburg, Germany.

ABSTRACT
Aerobic anoxygenic phototrophic bacteria (AAP) are abundant in the photic zone of the marine environment. Dinoroseobacter shibae, a representative of the Roseobacter group, converts light into additional energy that enhances its survival especially under starvation. However, light exposure results in the production of cytotoxic reactive oxygen species in AAPs. Here we investigated the response of D. shibae to starvation and oxidative stress, focusing on the role of extrachromosomal elements (ECRs). D. shibae possessing five ECRs (three plasmids and two chromids) was starved for 4 weeks either in the dark or under light/dark cycles and the survival was monitored. Transcriptomics showed that on the chromosome genes with a role in oxidative stress response and photosynthesis were differentially expressed during the light period. Most extrachromosomal genes in contrast showed a general loss of transcriptional activity, especially in dark-starved cells. The observed decrease of gene expression was not due to plasmid loss, as all five ECRs were maintained in the cells. Interestingly, the genes on the 72-kb chromid were the least downregulated, and one region with genes of the oxygen stress response and a light-dependent protochlorophyllide reductase of cyanobacterial origin was strongly activated under the light/dark cycle. A Δ72-kb curing mutant lost the ability to survive under starvation in a light/dark cycle demonstrating the essential role of this chromid for adaptation to starvation and oxidative stress. Our data moreover suggest that the other four ECRs of D. shibae have no vital function under the investigated conditions and therefore were transcriptionally silenced.

No MeSH data available.


Related in: MedlinePlus

Light-dependent chlorophyllide reductase (LPOR) in marine Roseobacter and Erythrobacter strains. (A) Maximum likelihood tree of the LPOR protein sequences of marine Cyanobacteria, Roseobacter and Erythrobacter strains. The latter ones are highlighted in red. 1000 bootstrap replicates were performed. The percentage of trees in which the associated taxa clustered together is shown next to the branches. The tree is drawn to scale, with branch lengths measured in the number of substitutions per site. (B) Genomic neighborhood of the LPOR gene in Roseobacter strains and Erythrobacter litoralis. Genes discussed in the manuscript are highlighted.
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Figure 7: Light-dependent chlorophyllide reductase (LPOR) in marine Roseobacter and Erythrobacter strains. (A) Maximum likelihood tree of the LPOR protein sequences of marine Cyanobacteria, Roseobacter and Erythrobacter strains. The latter ones are highlighted in red. 1000 bootstrap replicates were performed. The percentage of trees in which the associated taxa clustered together is shown next to the branches. The tree is drawn to scale, with branch lengths measured in the number of substitutions per site. (B) Genomic neighborhood of the LPOR gene in Roseobacter strains and Erythrobacter litoralis. Genes discussed in the manuscript are highlighted.

Mentions: The expression pattern of the 72-kb chromid was remarkably different from all other ECRs. Under light/dark condition, the bias toward downregulation was the lowest of all ECRs. Furthermore, the expression of the replication genes did not drop at day eight of starvation in the dark. These findings indicate a starvation-specific role for this chromid. The region ranging from Dshi_4160 to Dshi_4171 was even higher expressed in starved cells under light/dark cycles when compared with the positive control. The upregulated genes have previously been identified to play a role in the singlet oxygen (1O2) stress response in D. shibae (Tomasch et al., 2011). One particular gene from this region (Dshi_4160) encodes a light-dependent protochlorophyllide reductase (LPOR, EC 1.3.1.33) of cyanobacterial origin that has recently been proven to be involved in the biosynthesis of Bchl a (Kaschner et al., 2014). Among the Proteobacteria, homologous genes are only present in two other roseobacters, i.e., Sulfitobacter guttiformis KCTC 32187 (WP_025063112) and Loktanella vestfoldensis DSM 16212 (WP_026352701), as well as the Spingomonadales strain Erythrobacter litoralis DSM 8509 (KEO90002) that has been isolated from a cyanobacterial mat. All four LPOR sequences cluster together apart from the cyanobacterial homologs indicating that they share the same origin (Figure 7A). In Sulfitobacter the gene is located next to a region coding for a bacteriorhodopsin, carotenoid-synthesis and a blue light sensor. In Loktanella vestfoldensis this gene is located in proximity to another enzyme of the Bchl-a synthesis pathway, the divinylchlorophyllide 8-vinylreductase (EC 1.3.1.75). In Erythrobacter strain, the LPOR gene is integrated into a locus with genes coding for transporters (Figure 7B). Kaschner and colleagues speculate that this enzyme complements the dark-operative protochlorophyllide reductase (DPOR) encoded in the PGC on the chromosome and thus contributes to adaptation and fine-tuning of Bchl a synthesis in fluctuating environments. Their findings support the current results about the specific role of the 72-kb chromid for the adaptation to light/dark cycles.


Oxidative stress and starvation in Dinoroseobacter shibae: the role of extrachromosomal elements.

Soora M, Tomasch J, Wang H, Michael V, Petersen J, Engelen B, Wagner-Döbler I, Cypionka H - Front Microbiol (2015)

Light-dependent chlorophyllide reductase (LPOR) in marine Roseobacter and Erythrobacter strains. (A) Maximum likelihood tree of the LPOR protein sequences of marine Cyanobacteria, Roseobacter and Erythrobacter strains. The latter ones are highlighted in red. 1000 bootstrap replicates were performed. The percentage of trees in which the associated taxa clustered together is shown next to the branches. The tree is drawn to scale, with branch lengths measured in the number of substitutions per site. (B) Genomic neighborhood of the LPOR gene in Roseobacter strains and Erythrobacter litoralis. Genes discussed in the manuscript are highlighted.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4373377&req=5

Figure 7: Light-dependent chlorophyllide reductase (LPOR) in marine Roseobacter and Erythrobacter strains. (A) Maximum likelihood tree of the LPOR protein sequences of marine Cyanobacteria, Roseobacter and Erythrobacter strains. The latter ones are highlighted in red. 1000 bootstrap replicates were performed. The percentage of trees in which the associated taxa clustered together is shown next to the branches. The tree is drawn to scale, with branch lengths measured in the number of substitutions per site. (B) Genomic neighborhood of the LPOR gene in Roseobacter strains and Erythrobacter litoralis. Genes discussed in the manuscript are highlighted.
Mentions: The expression pattern of the 72-kb chromid was remarkably different from all other ECRs. Under light/dark condition, the bias toward downregulation was the lowest of all ECRs. Furthermore, the expression of the replication genes did not drop at day eight of starvation in the dark. These findings indicate a starvation-specific role for this chromid. The region ranging from Dshi_4160 to Dshi_4171 was even higher expressed in starved cells under light/dark cycles when compared with the positive control. The upregulated genes have previously been identified to play a role in the singlet oxygen (1O2) stress response in D. shibae (Tomasch et al., 2011). One particular gene from this region (Dshi_4160) encodes a light-dependent protochlorophyllide reductase (LPOR, EC 1.3.1.33) of cyanobacterial origin that has recently been proven to be involved in the biosynthesis of Bchl a (Kaschner et al., 2014). Among the Proteobacteria, homologous genes are only present in two other roseobacters, i.e., Sulfitobacter guttiformis KCTC 32187 (WP_025063112) and Loktanella vestfoldensis DSM 16212 (WP_026352701), as well as the Spingomonadales strain Erythrobacter litoralis DSM 8509 (KEO90002) that has been isolated from a cyanobacterial mat. All four LPOR sequences cluster together apart from the cyanobacterial homologs indicating that they share the same origin (Figure 7A). In Sulfitobacter the gene is located next to a region coding for a bacteriorhodopsin, carotenoid-synthesis and a blue light sensor. In Loktanella vestfoldensis this gene is located in proximity to another enzyme of the Bchl-a synthesis pathway, the divinylchlorophyllide 8-vinylreductase (EC 1.3.1.75). In Erythrobacter strain, the LPOR gene is integrated into a locus with genes coding for transporters (Figure 7B). Kaschner and colleagues speculate that this enzyme complements the dark-operative protochlorophyllide reductase (DPOR) encoded in the PGC on the chromosome and thus contributes to adaptation and fine-tuning of Bchl a synthesis in fluctuating environments. Their findings support the current results about the specific role of the 72-kb chromid for the adaptation to light/dark cycles.

Bottom Line: However, light exposure results in the production of cytotoxic reactive oxygen species in AAPs.The observed decrease of gene expression was not due to plasmid loss, as all five ECRs were maintained in the cells.Interestingly, the genes on the 72-kb chromid were the least downregulated, and one region with genes of the oxygen stress response and a light-dependent protochlorophyllide reductase of cyanobacterial origin was strongly activated under the light/dark cycle.

View Article: PubMed Central - PubMed

Affiliation: Institute for Chemistry and Biology of the Marine Environment (ICBM), Carl-von-Ossietzky University of Oldenburg Oldenburg, Germany.

ABSTRACT
Aerobic anoxygenic phototrophic bacteria (AAP) are abundant in the photic zone of the marine environment. Dinoroseobacter shibae, a representative of the Roseobacter group, converts light into additional energy that enhances its survival especially under starvation. However, light exposure results in the production of cytotoxic reactive oxygen species in AAPs. Here we investigated the response of D. shibae to starvation and oxidative stress, focusing on the role of extrachromosomal elements (ECRs). D. shibae possessing five ECRs (three plasmids and two chromids) was starved for 4 weeks either in the dark or under light/dark cycles and the survival was monitored. Transcriptomics showed that on the chromosome genes with a role in oxidative stress response and photosynthesis were differentially expressed during the light period. Most extrachromosomal genes in contrast showed a general loss of transcriptional activity, especially in dark-starved cells. The observed decrease of gene expression was not due to plasmid loss, as all five ECRs were maintained in the cells. Interestingly, the genes on the 72-kb chromid were the least downregulated, and one region with genes of the oxygen stress response and a light-dependent protochlorophyllide reductase of cyanobacterial origin was strongly activated under the light/dark cycle. A Δ72-kb curing mutant lost the ability to survive under starvation in a light/dark cycle demonstrating the essential role of this chromid for adaptation to starvation and oxidative stress. Our data moreover suggest that the other four ECRs of D. shibae have no vital function under the investigated conditions and therefore were transcriptionally silenced.

No MeSH data available.


Related in: MedlinePlus