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

Both 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 3x5 factorial design of experimental media, consisting of five levels of non-haem iron (0, 0.0672, 0.336, 8.40 and 210 mu g ml(-1)) and three levels of cytochrome c (0, 50.0 and 500 mu g 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 mu g ml(-1) iron and 0 mu g ml(-1) cytochrome c, the population growth (2530 +/- 220 nematodes ml(-1)) was very poor. At 0 mu g ml(-1) cytochrome c, as iron level increased to 8.40 mu g ml(-1), the nematode population increased to 5980 +/- 530 nematodes ml(-1). At 0 mu g ml(-1) iron, as cytochrome c level increased from 0 to 500 mu g 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 mu g ml(-1) iron and 500 mu g 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 mu g 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 mu g ml(-1) cytochrome c, the percentage iron absorption decreased from 7.39 to 0.118% with the increase of iron concentration (0-210 mu g ml(-1)) in the media. This observation was in accordance with the 'mucosal block' theory. At 50.0 and 500 mu g 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 mu g ml(-1) iron and 50.0 mu g ml(-1) cytochrome c, indicating an optimal percentage iron absorption in C. elegans.