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Growth on urea can trigger death and peroxidation of the cyanobacterium Synechococcus sp. strain PCC 7002.

ABSTRACT: Laboratory conditions have been identified that cause the rapid death of cultures of cyanobacteria producing urease. Once the death phase had initiated in the stationary growth phase, cells were rapidly bleached of all pigmentation. Null mutations in the ureC gene, encoding the alpha subunit of urease, were constructed, and these mutants were no longer sensitive to growth in the presence of urea. High levels of peroxides, including lipid peroxides, were detected in the bleaching cells. Exogenously added polyunsaturated fatty acids triggered a similar death response. Vitamin E suppressed the formation of peroxides and delayed the onset of cell bleaching. The results suggest that these cyanobacterial cells undergo a metabolic imbalance that ultimately leads to oxidative stress and lipid peroxide formation. These observations may provide insights into the mechanism of sudden cyanobacterial bloom disappearance in nature.

SUBMITTER: Sakamoto T

PROVIDER: S-EPMC106396 | biostudies-literature | 1998 Jul

REPOSITORIES: biostudies-literature

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Growth on urea can trigger death and peroxidation of the cyanobacterium Synechococcus sp. strain PCC 7002.

Sakamoto T T Delgaizo V B VB Bryant D A DA

Applied and environmental microbiology 19980701 7

Laboratory conditions have been identified that cause the rapid death of cultures of cyanobacteria producing urease. Once the death phase had initiated in the stationary growth phase, cells were rapidly bleached of all pigmentation. Null mutations in the ureC gene, encoding the alpha subunit of urease, were constructed, and these mutants were no longer sensitive to growth in the presence of urea. High levels of peroxides, including lipid peroxides, were detected in the bleaching cells. Exogenous ...[more]

PMID: 9647800

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Project description:RNA degradation is an important process that influences the ultimate concentration of individual proteins inside cells. While the main enzymes that facilitate this process have been identified, global maps of RNA turnover are available for only a few species. Even in these cases, there are few sequence elements that are known to enhance or destabilize a native transcript; even fewer confer the same effect when added to a heterologous transcript. To address this knowledge gap, we assayed genome-wide RNA degradation in the cyanobacterium Synechococcus sp. strain PCC 7002 by collecting total RNA samples after stopping nascent transcription with rifampin. We quantified the abundance of each position in the transcriptome as a function of time using RNA-sequencing data and later analyzed the global mRNA decay map using machine learning principles. Half-lives, calculated on a per-ORF (open reading frame) basis, were extremely short, with a median half-life of only 0.97 min. Despite extremely rapid turnover of most mRNA, transcripts encoding proteins involved in photosynthesis were both highly expressed and highly stable. Upon inspection of these stable transcripts, we identified an enriched motif in the 3' untranslated region (UTR) that had similarity to Rho-independent terminators. We built statistical models for half-life prediction and used them to systematically identify sequence motifs in both 5' and 3' UTRs that correlate with stabilized transcripts. We found that transcripts linked to a terminator containing a poly(U) tract had a longer half-life than both those without a poly(U) tract and those without a terminator.IMPORTANCE RNA degradation is an important process that affects the final concentration of individual mRNAs, affecting protein expression and cellular physiology. Studies of how RNA is degraded increase our knowledge of this fundamental process as well as enable the creation of genetic tools to manipulate RNA stability. By studying global transcript turnover, we searched for sequence elements that correlated with transcript (in)stability and used these sequences to guide tool design. This study probes global RNA turnover in a cyanobacterium, Synechococcus sp. strain PCC 7002, that both has a unique array of RNases that facilitate RNA degradation and is an industrially relevant strain that could be used to convert CO2 and sunlight into useful products.

Project description:UnlabelledThe cyanobacterium Synechococcus sp. strain PCC 7002 is a cobalamin auxotroph and utilizes this coenzyme solely for the synthesis of l-methionine by methionine synthase (MetH). Synechococcus sp. strain PCC 7002 is unable to synthesize cobalamin de novo, and because of the large size of this tetrapyrrole, an active-transport system must exist for cobalamin uptake. Surprisingly, no cobalamin transport system was identified in the initial annotation of the genome of this organism. With more sophisticated in silico prediction tools, a btuB-cpdA-btuC-btuF operon encoding components putatively required for a B12 uptake (btu) system was identified. The expression of these genes was predicted to be controlled by a cobalamin riboswitch. Global transcriptional profiling by high-throughput RNA sequencing of a cobalamin-independent form of Synechococcus sp. strain PCC 7002 grown in the absence or presence of cobalamin confirmed regulation of the btu operon by cobalamin. Pérez et al. (A. A. Pérez, Z. Liu, D. A. Rodionov, Z. Li, and D. A. Bryant, J Bacteriol 198:2743-2752, 2016, http://dx.doi.org/10.1128/JB.00475-16) developed a cobalamin-dependent yellow fluorescent protein reporter system in a Synechococcus sp. strain PCC 7002 variant that had been genetically modified to allow cobalamin-independent growth. This reporter system was exploited to validate components of the btu uptake system by assessing the ability of targeted mutants to transport cobalamin. The btuB promoter and a variant counterpart mutated in an essential element of the predicted cobalamin riboswitch were fused to a yfp reporter. The combined data indicate that the btuB-cpdA-btuF-btuC operon in this cyanobacterium is transcriptionally regulated by a cobalamin riboswitch.ImportanceWith a cobalamin-regulated reporter system for expression of yellow fluorescent protein, genes previously misidentified as encoding subunits of a siderophore transporter were shown to encode components of cobalamin uptake in the cyanobacterium Synechococcus sp. strain PCC 7002. This study demonstrates the importance of experimental validation of in silico predictions and provides a general scheme for in vivo verification of similar cobalamin transport systems. A putative cobalamin riboswitch was identified in Synechococcus sp. strain PCC 7002. This riboswitch acts as a potential transcriptional attenuator of the btu operon that encodes the components of the cobalamin active-transport system.

Dataset Information

Growth on urea can trigger death and peroxidation of the cyanobacterium Synechococcus sp. strain PCC 7002.

Publications

Growth on urea can trigger death and peroxidation of the cyanobacterium Synechococcus sp. strain PCC 7002.

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