160 Chapter 5 harbor AsrC (Yu et al., 2018). Another study recently described Group III Dsr-LP sulfite reductases in high quality “Ca. Methanoperedens” MAGs resolved from freshwater meromictic Lake Cadagno sediment (Echeveste Medrano et al., 2024c, Chapter 7). In those ecosystems, the role of Group III Dsr-LP sulfite reductases for sulfite detoxification seems more probable over nitrite removal, given the low availability of nitrate/nitrite and particularly the high availability of sulfate (Echeveste Medrano et al., 2024c, Chapter 7). Furthermore, the described Lake Cadagno “Ca. Methanoperedens” MAGs harbor neither a nitrate reductase nor DNRA potential through nrfAH, suggesting that nitrate reduction to nitrite, N2 or ammonia is not relevant in this ecosystem. To disentangle the nitrite/sulfite preferences of “Ca. Methanoperedens” Group III Dsr-LP, further protein purification and enzymatic assays to determine the preferences for either sulfite or nitrite are needed. PHA and (de)granulation upon long-term sulfide exposure To investigate whether “Ca. Methanoperedens” would shift aggregation levels or use its storage compounds to counteract sulfide stress, we determined the amount of PHA per biomass and the amount of planktonic cells. We observed a reduction in the PHAs especially after long term exposure to sulfide (Figure 4). The expression of genes encoding proteins responsible for the degradation of PHA did not change significantly (Supplementary Table 6).
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