Fig. 2: Degradation and digestion of host chromosomes and nucleus by the parasite Amoebophrya unveiled by 3D electron microscopy and nanoSIMS.

A 3D reconstruction of the nucleolus and individual chromosomes of non-infected hosts (about 113–119 per host cell of about 0.33 ± 0.10 µm³ each; n = 346). B Host nucleus, infected by two trophont parasites, displayed smaller chromosomes and nucleolus compared to non-infected hosts. C–E At later infection stages, the mature trophont parasite developed multiple phagotrophic vacuoles to engulf and ingest host chromosomes. D Electron microscopy micrograph showing the engulfment of an electron-dense host chromosome (C) into the vacuole (V) of a mature trophont parasite within the host nucleus (N). F, G Volumes of the heterochromatin and nucleolus (in µm³) of non-infected and infected host cells assessed after FIB-SEM-based 3D reconstruction. H–J NanoSIMS (Nanoscale Secondary Ion Mass Spectrometry) mapping of the elements Phosphorous (H, ³¹P¹⁶O₂/¹²C₂), Sulfur (I, ³⁴S/¹²C₂) and Nitrogen (J, ¹²C¹⁴N/¹²C₂), showing that host chromosomes (C) are highly concentrated in these nutrients compared to the nuclear parasite. (Scale bar: 2 µm). K Phosphorous (P) content calculated as ³¹P¹⁶O₂/¹²C₂ from nanoSIMS ion count map in the host chromosomes and parasite cell (including nucleus and cytoplasm). P content of the host chromosomes (n = 131) were estimated to be about 10 times more important than in the parasite cell (n = 22) (See also Table S3). Brown: parasite; light blue: nucleolus; dark blue: heterochromatin. See also Table S1 for morphometrics data.