Requirements of non-haem iron and haem iron in the nematode Caenorhabditis elegans

Abstract

AbstractBoth non-haem iron (iron salt) and haem iron (cytochrome c) are components of the Caenorhabditis elegans Maintenance Medium (CeMM). However, the quantitative requirements of non-haem iron and its relationship with haem iron were unknown. A basal medium was prepared with both non-haem iron and haem iron eliminated from the CeMM. After being pre-cultured in this basal medium, C. elegans were inoculated into a 3 × 5 factorial design of experimental media, consisting of five levels of non-haem iron (0, 0.0672, 0.336, 8.40 and 210 μg ml–1) and three levels of cytochrome c (0, 50.0 and 500 μg ml–1). The population growth of C. elegans in various experimental media was counted at day 28, and the iron uptake (ng (1000 nematodes)–1) and percentage iron absorption (total iron in nematode tissue/total iron in original media) of the nematodes were analysed by atomic absorption spectrophotometry (AAS). At 0 μg ml–1 iron and 0 μg ml–1 cytochrome c, the population growth (2530±220 nematodes ml–1) was very poor. At 0 μg ml –1 cytochrome c, as iron level increased to 8.40 μg ml–1, the nematode population increased to 5980±530 nematodes ml–1. At 0 μg ml–1 iron, as cytochrome c level increased from 0 to 500 μg ml–1, the population growth was greatly increased from 2530±220 nematodes ml–1 to 45 900±3600 nematodes ml–1. Under the experimental conditions, the highest population growth (258 000±9000 nematodes ml–1) was achieved at 8.40 μg ml–1 iron and 500 μg ml–1 cytochrome c, suggesting an additive requirement of non-haem and haem iron. As the concentration of iron further increased from 8.40 to 210 μg ml–1, significant declines in nematode population were observed, indicating iron toxicity. Based on the Atomic Absorption analysis, the iron uptake by C. elegans increased when either non-haem or haem iron concentration increased in the media. At 0 μg ml–1 cytochrome c, the percentage iron absorption decreased from 7.39 to 0.118% with the increase of iron concentration (0-210 μg ml–1) in the media. This observation was in accordance with the 'mucosal block' theory. At 50.0 and 500 μg ml–1 cytochrome c, the percentage iron absorption greatly increased, and percentage iron absorption reached a maximum of 85.9% when media contained 0.336 μg ml–1 iron and 50.0 μg ml–1 cytochrome c, indicating an optimal percentage iron absorption in C. elegans.