Biodegradation of Arsenosugars from Red Alga <i>Pyropia haitanensis</i>

Arsenic accumulates in eukaryotic algae mostly in the form of arsenosugars and arsenosugar phospholipids, and those organoarsenicals are eventually released and biodegraded to maintain the dynamic balance of arsenic species in the environment. However, the specific bacteria involved in the biodegradation of arsenosugars released from the marine algae remains unknown. Our current work aims to identify bacteria linked to organoarsenical degradation under both anaerobic and aerobic conditions. In this study, red alga <i>Pyropia haitanensis</i> was degraded under anaerobic and aerobic conditions for 28 days after being incubated in seawater with or without 1 μM arsenite under aerobic conditions for 5 days. The compositions of the bacterial community, total arsenic, and arsenic species were analyzed. Both total arsenic and arsenolipids were released from the algae more rapidly under anaerobic conditions than under aerobic conditions. After 28 days of aerobic incubation, the predominant arsenic species inside the algae were phosphate arsenosugars (89.1%), while dimethylarsonic acid (83.8%) was the major species under anaerobic conditions. Moreover, the analysis of the bacterial community structure revealed that different bacteria were enriched under anaerobic (<i>Pseudoalteromonas</i>) and aerobic conditions (<i>Pir4_lineage</i>). <i>Pseudoalteromonas</i> sp. C71 isolated from seawater was used to degrade arsenosugars. The results showed that <i>Pseudoalteromonas</i> sp. C71 efficiently transformed phosphate arsenosugar to glycerol arsenosugar extracellularly and intracellularly. This study offers new insights into the interaction between bacteria and organoarsenical degradation, contributing to our understanding of arsenic biogeochemical cycles in marine systems.