Zinc deficiency impacts CO2 assimilation and disrupts copper homeostasis in Chlamydomonas reinhardtii.

Zinc is an essential nutrient because of its role in catalysis and in protein stabilization, but excess zinc is deleterious. We distinguished four nutritional zinc states in the alga Chlamydomonas reinhardtii: toxic, replete, deficient, and limited. Growth is inhibited in zinc-limited and zinc-toxic cells relative to zinc-replete cells, whereas zinc deficiency is visually asymptomatic but distinguished by the accumulation of transcripts encoding ZIP family transporters. To identify targets of zinc deficiency and mechanisms of zinc acclimation, we used RNA-seq to probe zinc nutrition-responsive changes in gene expression. We identified genes encoding zinc-handling components, including ZIP family transporters and candidate chaperones. Additionally, we noted an impact on two other regulatory pathways, the carbon-concentrating mechanism (CCM) and the nutritional copper regulon. Targets of transcription factor Ccm1 and various CAH genes are up-regulated in zinc deficiency, probably due to reduced carbonic anhydrase activity, validated by quantitative proteomics and immunoblot analysis of Cah1, Cah3, and Cah4. Chlamydomonas is therefore not able to grow photoautotrophically in zinc-limiting conditions, but supplementation with 1% CO2 restores growth to wild-type rates, suggesting that the inability to maintain CCM is a major consequence of zinc limitation. The Crr1 regulon responds to copper limitation and is turned on in zinc deficiency, and Crr1 is required for growth in zinc-limiting conditions. Zinc-deficient cells are functionally copper-deficient, although they hyperaccumulate copper up to 50-fold over normal levels. We suggest that zinc-deficient cells sequester copper in a biounavailable form, perhaps to prevent mismetallation of critical zinc sites.

Manganous ion supplementation accelerates wild type development, enhances stress resistance, and rescues the life span of a short-lived Caenorhabditis elegans mutant.

Relative to iron and copper we know very little about the cellular roles of manganese. Some studies claim that manganese acts as a radical scavenger in unicellular organisms, while there have been other reports that manganese causes Parkinson's disease-like syndrome, DNA fragmentation, and interferes with cellular energy production. The goal of this study was to uncover if manganese has any free radical scavenging properties in the complex multicellular organism, Caenorhabditis elegans. We measured internal manganese in supplemented worms using inductively coupled plasma mass spectrometry (ICP-MS) and the data obtained suggest that manganese supplemented to the growth medium is taken up by the worms. We found that manganese did not appear to be toxic as supplementation did not negatively effect development or fertility. In fact, supplementation at higher levels accelerated development and increased total fertility of wild type worms by 16%. Manganese-supplemented wild type worms were found to be thermotolerant and, under certain conditions, long-lived. In addition, the oxidatively challenged C. elegans strain mev-1's short life span was significantly increased after manganese supplementation. Although manganese appears to be beneficial to C. elegans, the mode of action remains unclear. Manganese may work directly as a free radical scavenger, as it has been postulated to do so in unicellular organisms, or may work indirectly by up regulating several protective factors.