Limits...
Effect of nitrogen starvation on desiccation tolerance of Arctic Microcoleus strains (cyanobacteria).

Tashyreva D, Elster J - Front Microbiol (2015)

Bottom Line: Although desiccation tolerance of Microcoleus species is a well-known phenomenon, there is very little information about their limits of desiccation tolerance in terms of cellular water content, the survival rate of their cells, and the environmental factors inducing their resistance to drying.However, these treatments were critical for the survival of incomplete desiccation: cultures grown under optimal conditions failed to survive even incomplete desiccation; a low temperature enabled only 0-15% of cells to survive, while 39.8-65.9% of cells remained alive and intact after nitrogen starvation.Instead, it seems that the survival strategy of Microcoleus in periodically dry habitats involves avoidance of complete desiccation, but tolerance to milder desiccation stress, which is induced by suboptimal conditions (e.g., nitrogen starvation).

View Article: PubMed Central - PubMed

Affiliation: Centre for Polar Ecology, Faculty of Science, University of South Bohemia České Budějovice, Czech Republic ; Department of Botany, Faculty of Science, University of South Bohemia České Budějovice, Czech Republic.

ABSTRACT
Although desiccation tolerance of Microcoleus species is a well-known phenomenon, there is very little information about their limits of desiccation tolerance in terms of cellular water content, the survival rate of their cells, and the environmental factors inducing their resistance to drying. We have discovered that three Microcoleus strains, isolated from terrestrial habitats of the High Arctic, survived extensive dehydration (to 0.23 g water g(-1) dry mass), but did not tolerate complete desiccation (to 0.03 g water g(-1) dry mass) regardless of pre-desiccation treatments. However, these treatments were critical for the survival of incomplete desiccation: cultures grown under optimal conditions failed to survive even incomplete desiccation; a low temperature enabled only 0-15% of cells to survive, while 39.8-65.9% of cells remained alive and intact after nitrogen starvation. Unlike Nostoc, which co-exists with Microcoleus in Arctic terrestrial habitats, Microcoleus strains are not truly anhydrobiotic and do not possess constitutive desiccation tolerance. Instead, it seems that the survival strategy of Microcoleus in periodically dry habitats involves avoidance of complete desiccation, but tolerance to milder desiccation stress, which is induced by suboptimal conditions (e.g., nitrogen starvation).

No MeSH data available.


Related in: MedlinePlus

Microcoleus vaginatus 858 CCALA after rehydration from incomplete desiccation (85% RH). (A) Culture grown under optimal conditions containing cells with a few large CTC-formazan crystals (arrows), which are visible under transmitted light as dark-red deposits. (B,C) Culture, kept at low temperature, viewed by light (B), and fluorescence (C) microscopy; cells contain CTC-formazan crystals, which range from a few big ones (asterisks) to numerous small ones (arrows). (D–F) Nitrogen-starved culture, viewed by light microscopy (D), and stained with SYTOX Green (E), and CTC (F); live cells are SYTOX Green-negative and CTC-positive; dead cells are SYTOX Green-positive and CTC-negative. Scale bars are 20 μm.
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Figure 5: Microcoleus vaginatus 858 CCALA after rehydration from incomplete desiccation (85% RH). (A) Culture grown under optimal conditions containing cells with a few large CTC-formazan crystals (arrows), which are visible under transmitted light as dark-red deposits. (B,C) Culture, kept at low temperature, viewed by light (B), and fluorescence (C) microscopy; cells contain CTC-formazan crystals, which range from a few big ones (asterisks) to numerous small ones (arrows). (D–F) Nitrogen-starved culture, viewed by light microscopy (D), and stained with SYTOX Green (E), and CTC (F); live cells are SYTOX Green-negative and CTC-positive; dead cells are SYTOX Green-positive and CTC-negative. Scale bars are 20 μm.

Mentions: The samples contained 0.23 ± 0.01 g water g-1 dry mass (mean ± SD) after being stored over KCl solution for 2 weeks. In cultures grown under optimal conditions, only a few viable cells (5–20) per whole sample (i.e., millions of cells) were detected in some of the replicates, whereas others lacked any viable cells (Figure 3C). The absence of viable cells also proves that the drying treatment itself did not induce development of desiccation tolerance. Those solitary cells were scattered uniformly across the sample. They were SYTOX Green-negative and accumulated CTC-formazan deposits (data not shown). However, the deposits were only few and appeared much bigger in size (Figure 5A) compared to those in non-desiccated cells grown under optimal conditions (Figures 2A,C). A similar pattern of CTC-formazan deposition was observed in cells treated with sub-lethal concentrations of formaldehyde, possibly indicating cellular damage which cannot be tracked with SYTOX Green staining (Tashyreva et al., 2013). Apparently, such cells did not propagate because there was no evidence of growth, even after 5 weeks of cultivation.


Effect of nitrogen starvation on desiccation tolerance of Arctic Microcoleus strains (cyanobacteria).

Tashyreva D, Elster J - Front Microbiol (2015)

Microcoleus vaginatus 858 CCALA after rehydration from incomplete desiccation (85% RH). (A) Culture grown under optimal conditions containing cells with a few large CTC-formazan crystals (arrows), which are visible under transmitted light as dark-red deposits. (B,C) Culture, kept at low temperature, viewed by light (B), and fluorescence (C) microscopy; cells contain CTC-formazan crystals, which range from a few big ones (asterisks) to numerous small ones (arrows). (D–F) Nitrogen-starved culture, viewed by light microscopy (D), and stained with SYTOX Green (E), and CTC (F); live cells are SYTOX Green-negative and CTC-positive; dead cells are SYTOX Green-positive and CTC-negative. Scale bars are 20 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4389727&req=5

Figure 5: Microcoleus vaginatus 858 CCALA after rehydration from incomplete desiccation (85% RH). (A) Culture grown under optimal conditions containing cells with a few large CTC-formazan crystals (arrows), which are visible under transmitted light as dark-red deposits. (B,C) Culture, kept at low temperature, viewed by light (B), and fluorescence (C) microscopy; cells contain CTC-formazan crystals, which range from a few big ones (asterisks) to numerous small ones (arrows). (D–F) Nitrogen-starved culture, viewed by light microscopy (D), and stained with SYTOX Green (E), and CTC (F); live cells are SYTOX Green-negative and CTC-positive; dead cells are SYTOX Green-positive and CTC-negative. Scale bars are 20 μm.
Mentions: The samples contained 0.23 ± 0.01 g water g-1 dry mass (mean ± SD) after being stored over KCl solution for 2 weeks. In cultures grown under optimal conditions, only a few viable cells (5–20) per whole sample (i.e., millions of cells) were detected in some of the replicates, whereas others lacked any viable cells (Figure 3C). The absence of viable cells also proves that the drying treatment itself did not induce development of desiccation tolerance. Those solitary cells were scattered uniformly across the sample. They were SYTOX Green-negative and accumulated CTC-formazan deposits (data not shown). However, the deposits were only few and appeared much bigger in size (Figure 5A) compared to those in non-desiccated cells grown under optimal conditions (Figures 2A,C). A similar pattern of CTC-formazan deposition was observed in cells treated with sub-lethal concentrations of formaldehyde, possibly indicating cellular damage which cannot be tracked with SYTOX Green staining (Tashyreva et al., 2013). Apparently, such cells did not propagate because there was no evidence of growth, even after 5 weeks of cultivation.

Bottom Line: Although desiccation tolerance of Microcoleus species is a well-known phenomenon, there is very little information about their limits of desiccation tolerance in terms of cellular water content, the survival rate of their cells, and the environmental factors inducing their resistance to drying.However, these treatments were critical for the survival of incomplete desiccation: cultures grown under optimal conditions failed to survive even incomplete desiccation; a low temperature enabled only 0-15% of cells to survive, while 39.8-65.9% of cells remained alive and intact after nitrogen starvation.Instead, it seems that the survival strategy of Microcoleus in periodically dry habitats involves avoidance of complete desiccation, but tolerance to milder desiccation stress, which is induced by suboptimal conditions (e.g., nitrogen starvation).

View Article: PubMed Central - PubMed

Affiliation: Centre for Polar Ecology, Faculty of Science, University of South Bohemia České Budějovice, Czech Republic ; Department of Botany, Faculty of Science, University of South Bohemia České Budějovice, Czech Republic.

ABSTRACT
Although desiccation tolerance of Microcoleus species is a well-known phenomenon, there is very little information about their limits of desiccation tolerance in terms of cellular water content, the survival rate of their cells, and the environmental factors inducing their resistance to drying. We have discovered that three Microcoleus strains, isolated from terrestrial habitats of the High Arctic, survived extensive dehydration (to 0.23 g water g(-1) dry mass), but did not tolerate complete desiccation (to 0.03 g water g(-1) dry mass) regardless of pre-desiccation treatments. However, these treatments were critical for the survival of incomplete desiccation: cultures grown under optimal conditions failed to survive even incomplete desiccation; a low temperature enabled only 0-15% of cells to survive, while 39.8-65.9% of cells remained alive and intact after nitrogen starvation. Unlike Nostoc, which co-exists with Microcoleus in Arctic terrestrial habitats, Microcoleus strains are not truly anhydrobiotic and do not possess constitutive desiccation tolerance. Instead, it seems that the survival strategy of Microcoleus in periodically dry habitats involves avoidance of complete desiccation, but tolerance to milder desiccation stress, which is induced by suboptimal conditions (e.g., nitrogen starvation).

No MeSH data available.


Related in: MedlinePlus