Mining Genomes of Marine Cyanobacteria for Elements of Zinc Homeostasis

Abstract

Zinc is a recognized essential element for the majority of organisms, and is indispensable for the correct function of hundreds of enzymes and thousands of regulatory proteins. In aquatic photoautotrophs including cyanobacteria, zinc is thought to be required for carbonic anhydrase and alkaline phosphatase, although there is evidence that at least some carbonic anhydrases can be cambialistic, i.e., are able to acquire in vivo and function with different metal cofactors such as Co2+ and Cd2+. Given the global importance of marine phytoplankton, zinc availability in the oceans is likely to have an impact on both carbon and phosphorus cycles. Zinc concentrations in seawater vary over several orders of magnitude, and in the open oceans adopt a nutrient-like profile. Most studies on zinc handling by cyanobacteria have focused on freshwater strains and zinc toxicity; much less information is available on marine strains and zinc limitation. Several systems for zinc homeostasis have been characterized in the freshwater species Synechococcus sp. PCC 7942 and Synechocystis sp. PCC 6803, but little is known about zinc requirements or zinc handling by marine species. Comparative metallo-genomics has begun to explore not only the putative zinc proteome, but also specific protein families predicted to have an involvement in zinc homeostasis, including sensors for excess and limitation (SmtB and its homologs as well as Zur), uptake systems (ZnuABC), putative intracellular zinc chaperones (COG0523) and metallothioneins (BmtA), and efflux pumps (ZiaA and its homologs).

Ferric Uptake Regulator (FUR) protein: properties and implications in cyanobacteria

“…FurB expression increases drastically under the influence of ROS and protects DNA against the damage caused by ROS, by binding to unspecific sequences. As observed in several other cyanobacteria (Barnett et al 2012) and heterotrophic bacteria (Patzer 2000;Lindsay and Foster 2001;Fuangthong and Helmann 2003;Maciag et al 2007), FurB (or Zur) controls zinc homeostasis by binding to upstream promoter regions of target genes, such as those encoding putative metallochaperones (All4722, All1751), zinc metalloproteins (All4725/HemE, All4723/ThrS), components of plasma membrane ABC transport systems (ZnuABC) and several outer membrane proteins (Alr3242, Alr4028) in a zinc-dependent manner in the cyanobacterium Anabaena sp. PCC 7120 (Napolitano et al 2012).…”

Heavy Metals Pollution Influence the Community Structure of Cyanobacteria in Nutrient Rich Tropical Estuary

“…Mesocosm studies using Synechococcus PCC 7942 demonstrated the synthesis of a 56 aminoacid cysteine rich metal binding protein, SmtA, which binds and sequesters metal ions within the cells and thereby maintains the homeostasis between the metal concentration and cyanobacterial viability [61]. Beyond tolerable limits, the Zn may out compete less competitive metal ions such as Fe and Mn for their protein binding sites [18]. In a mesocosm study, it was reported that Zeaxanthin level in the water collected from Godavari River decreased with increasing Zn concentration from 1 × 10 -7 to 2.5 × 10 -7 M [62].…”

“…Interestingly, microorganisms acquired several mechanisms to maintain the homeostasis between the available metal concentration and microbial physiology [12,16,17]. In oligotrophic marine environments, cyanobacteria secrete ligands that bind with biologically important metals like copper, iron, cobalt and zinc [18]. The laboratory scale experiments showed that trace metals above optimum levels can influence the general growth, pigment composition, photosynthesis and enzyme expression of cyanobacteria [19].…”

Environmental Bioinorganic Chemistry of Aquatic Microbial Organisms

“…A research topic exploring current research themes in environmental aquatic bioinorganic chemistry should thus incorporate articles on a diverse range of subjects. We have been honored to include both reviews and original research articles that taken together, reflect the interdisciplinary nature of the subject area and the diversity of geomes and biomes in which inorganic elements, particularly metals, play a fundamental role.We have thus been able to include articles on metals, their speciation, and interactions with phytoplankton (Cuss and Gueguen, 2012;Hassler et al, 2012; Shaked and Lis, 2012; Sunda, 2012), on metal acquisition and use by microbes (Barnett et al, 2012;Desai et al, 2012;Glass and Orphan, 2012;Morrissey and Bowler, 2012;Nuester et al, 2012;Scheidegger et al, 2012) and on the effect of inorganic ions in the environment on organism interactions and community structure (Boyd et al, 2012;Gledhill et al, 2012). Barnett, J. P., Millard, A., Ksibe, A., Scanlan, D. J., Schmid, R., and Blindauer, C. A.…”

“…We have thus been able to include articles on metals, their speciation, and interactions with phytoplankton (Cuss and Gueguen, 2012;Hassler et al, 2012;Shaked and Lis, 2012;Sunda, 2012), on metal acquisition and use by microbes (Barnett et al, 2012;Desai et al, 2012;Glass and Orphan, 2012;Morrissey and Bowler, 2012;Nuester et al, 2012;Scheidegger et al, 2012) and on the effect of inorganic ions in the environment on organism interactions and community structure (Boyd et al, 2012;Gledhill et al, 2012).…”