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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

Microscopic and graphical representation of viable D. shibae wild-type and ECR cured cells. (A) Live/Dead staining where green and red color denotes viable and dead cells, respectively. (B) Viability of wild type and plasmid cured mutants (Δ72-kb and Δ86-kb) under LD and DD condition during 3 weeks of starvation.
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Figure 6: Microscopic and graphical representation of viable D. shibae wild-type and ECR cured cells. (A) Live/Dead staining where green and red color denotes viable and dead cells, respectively. (B) Viability of wild type and plasmid cured mutants (Δ72-kb and Δ86-kb) under LD and DD condition during 3 weeks of starvation.

Mentions: Live/dead staining and microscopic observation revealed remarkable differences in the ratio of viable (green) to dead cells (red) for those strains depending on the light regimes (Figures 6A,B). After 3 weeks of starvation the wild type D. shibae showed a three-fold higher viability under LD compared with DD conditions reaching 32 and 7% of viable cells, respectively. The decrease of living Δ72-kb mutant cells was comparable under both conditions to that of the wild type under DD. After 3 weeks of starvation, only 10 and 9% of viable cells were counted for the LD and DD samples, respectively. The viability of the Δ86-kb mutant decreased slower than that of the Δ72-kb mutant but also reached only 10% of viable cells after 3 weeks in continuous darkness. However, under light/dark cycles 19% of the cells were still viable. Microscopy showed that the Δ86-kb plasmid cured mutant tends to aggregate under LD conditions, a phenotype that has not been observed for the wild type and the Δ72-kb mutant.


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)

Microscopic and graphical representation of viable D. shibae wild-type and ECR cured cells. (A) Live/Dead staining where green and red color denotes viable and dead cells, respectively. (B) Viability of wild type and plasmid cured mutants (Δ72-kb and Δ86-kb) under LD and DD condition during 3 weeks of starvation.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 6: Microscopic and graphical representation of viable D. shibae wild-type and ECR cured cells. (A) Live/Dead staining where green and red color denotes viable and dead cells, respectively. (B) Viability of wild type and plasmid cured mutants (Δ72-kb and Δ86-kb) under LD and DD condition during 3 weeks of starvation.
Mentions: Live/dead staining and microscopic observation revealed remarkable differences in the ratio of viable (green) to dead cells (red) for those strains depending on the light regimes (Figures 6A,B). After 3 weeks of starvation the wild type D. shibae showed a three-fold higher viability under LD compared with DD conditions reaching 32 and 7% of viable cells, respectively. The decrease of living Δ72-kb mutant cells was comparable under both conditions to that of the wild type under DD. After 3 weeks of starvation, only 10 and 9% of viable cells were counted for the LD and DD samples, respectively. The viability of the Δ86-kb mutant decreased slower than that of the Δ72-kb mutant but also reached only 10% of viable cells after 3 weeks in continuous darkness. However, under light/dark cycles 19% of the cells were still viable. Microscopy showed that the Δ86-kb plasmid cured mutant tends to aggregate under LD conditions, a phenotype that has not been observed for the wild type and the Δ72-kb mutant.

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