Deep-sea clams adjust bacterial partnerships to cope with dwindling chemical energy

A research team led by professor Qian Peiyuan from The Hong Kong University of Science and Technology has made significant progress in understanding how deep-sea chemosynthetic symbioses, such as those found in deep-sea cold seeps, adapt to fluctuations in chemical energy sources. The study reveals that metabolic flexibility in symbionts, combined with the host's regulation of bacterial populations, enables these systems to maintain energy stability despite environmental changes.

The findings highlight a tiered adaptation strategy, with symbiont metabolism, host regulation, and resource transport playing crucial roles. The research focuses on the deep-sea clam Archivesica marissinica and its sulfur-oxidizing bacterial symbionts. By conducting in situ transplant experiments, the team observed that reduced hydrogen sulfide availability initially triggered metabolic reprogramming in the bacterial symbionts, with pathways involved in sulfide oxidation being suppressed and the soxXYZ gene cluster associated with thiosulfate oxidation being upregulated.

This suggests that symbionts can adjust their sulfur-oxidation strategies when hydrogen sulfide becomes limiting, maintaining energy metabolism and carbon fixation. The study also demonstrates that host regulation of symbionts changes with the severity of hydrogen sulfide limitation. Under moderate limitation, symbiont abundance remains stable, while under severe limitation, symbiont abundance decreases significantly, and the host may enhance symbiont turnover to access limited nutrients.

The gill tissue of Archivesica marissinica also shows a strong capacity for sulfur metabolism and high expression of key enzymes like thiosulfate sulfurtransferase (TST), which converts toxic hydrogen sulfide into thiosulfate, serving as an alternative energy substrate for the symbionts. This metabolic synergy between host detoxification and symbiont utilization provides new insights into the mechanisms by which hosts and symbionts achieve metabolic complementarity under resource-limited conditions.