Characterization and mutagenesis of sulfur-regulated genes in a cyanobacterium: evidence for function in sulfate transport

Abstract

A sulfur-regulated gene (cysA) that encodes the membrane-associated ATP-binding protein of the sulfate transport system of the cyanobacterium Synechococcus sp. strain PCC 7942 was recently isolated and sequenced. Adjacent to cysA and transcribed in the opposite direction is a gene encoding the sulfate-binding protein (sbpA Cyanobacteria are obligate photoautotrophs that undergo a complex set of distinct morphological and physiological changes when deprived of macronutrients such as sulfur and nitrogen. A visually dramatic response to nutrient deprivation is the degradation of the light-harvesting complex, the phycobilisome, and the concomitant decline in the levels of phycocyanin and allophycocyanin. Additionally, there is a decrease in chlorophyll levels and attenuation of the photosynthetic membranes (44, 60). Other changes that accompany nutrient deprivation include cell wall thickening (25) and the accumulation of electron-opaque inclusion bodies in the cytoplasm of the cell (31, 60).In addition to the general responses described above, cyanobacteria exhibit specific responses when deprived of a given nutrient. During growth in sulfur-deficient medium, the unicellular cyanobacterium Anacystis nidulans and the closely related Synechococcus sp. strain PCC 7942 display an increased rate of sulfate transport (15,24 In the enteric bacteria Salmonella typhimurium and Escherichia coli, sulfate transport is accomplished by a single active uptake system. This permease complex is composed of three cytoplasmic membrane components and a substratespecific binding protein located in the periplasmic space (3, 28). The sulfate-binding protein of S. typhimurium has been isolated and sequenced and its crystal structure has been resolved (23,36,40). It is present in the periplasmic space at very high levels and binds one sulfate molecule per molecule of protein. Two of the cytoplasmic membrane proteins appear to span the lipid bilayer and may form a channel for the passage of the substrate. A third membrane protein hydrolyzes ATP to provide the energy required for concentrating the substrate inside the cell (4).Much of the information on sulfate uptake in enteric bacteria has accrued from studies of cysteine auxotrophs. Mutations that block sulfate transport map to the cysA locus; all three cistrons in this locus are required for normal uptake (34,35 In this communication, we present a characterization of the region of DNA adjacent to cysA and conclude that it encodes the remaining components of the sulfate permease. These conclusions are based on homology to analogous polypeptides from both the sulfate permease system of S. typhimurium and E. coli and the phenotype of mutant strains

α-Tocopherol Plays a Role in Photosynthesis and Macronutrient Homeostasis of the Cyanobacterium Synechocystis sp. PCC 6803 That Is Independent of Its Antioxidant Function

“…The nblA and sbpA transcripts have previously been shown to accumulate in response to nitrogen and sulfate limitation, respectively, in Synechocystis sp. PCC 6803 (Laudenbach and Grossman, 1991;Collier and Grossman, 1994;Richaud et al, 2001). Under photoautotrophic growth conditions, the slr1736 mutant accumulated slightly higher levels of these transcripts in comparison to the wild type (Fig.…”

“…The nblA operon, which comprises the nblA1 and nblA2 genes, encodes proteins essential for the regulation of PBP degradation (Baier et al, 2004), whereas the sbpA transcript encodes an inducible high-affinity, periplasmic sulfate-binding protein (Laudenbach and Grossman, 1991). The nblA and sbpA transcripts have previously been shown to accumulate in response to nitrogen and sulfate limitation, respectively, in Synechocystis sp.…”

The Bacillus subtilis cysP gene encodes a novel sulphate permease related to the inorganic phosphate transporter (Pit) family

“…The products of cysT and cysW span the membrane and form a channel for the passage of sulphate and related ions, cysA encodes a hydrophilic membrane-associated ATP-binding protein, and sbp and cysP encode the sulphate and thiosulphate periplasmic binding proteins, respectively (Hryniewicz et al, 1990 ;Sirko et al, 1990). Molecular analysis of sulphate transport in Synechococcus sp., a cyanobacterium, established a four-component membrane sulphate transport system, essentially similar to that of E. coli (Laudenbach & Grossman, 1991).…”

The Cyanobacterial Thioredoxin Gene Is Required for Both Photoautotrophic and Heterotrophic Growth

“…It has been reported previously that thioredoxin is essential for photosynthetic growth in the photoautotrophic cyanobacterium A. nidulans (Muller and Buchanan, 1989) and is also involved in sulfate reduction (Schmidt, 1988;Russell et al, 1990), because the Synechococcus 7942 mutants of sulfate transport were able to grow like the wild-type strain by supplementing the culture medium with sodium thiophosphate (Laudenbach and Grossman, 1991). Since Synechocystis 6803 is capable of growing without an operational PSII (photoheterotrophic and heterotrophic growth conditions), it was thought that inactivation of the trxA gene in all of the chromosome copies could be made possible by growing this cyanobacterium under the aforementioned conditions and in the presence of sodium thiophosphate in the culture medium.…”