Endophytic microbe Acinetobacter lwoffii MA1 alters the cadmium content in Spinacia oleracea through membrane proteins-mediated adsorption

Abstract

Vegetables such as spinach, celery, water spinach, and edible mushrooms are more prone to heavy metal accumulation. While the mechanism of heavy metal accumulation in vegetables and whether it is related to endophytic microorganisms remain unclear. In this study, we isolated an endophytic microorganism, A. lwoffii MA1, from spinach seeds that is tolerant to cadmium. Pot experiments demonstrated that enriching seeds with A. lwoffii MA1 increased the Cd content in spinach from 0.82 to 0.94 mg/kg, while microbial sequencing counts rose from 139.77 to 247.82, indicating that the addition of A. lwoffii MA1 affects Cd levels in spinach. Inoculation with A. lwoffii MA1 enhanced the microbial diversity of the spinach rhizosphere soil compared to the non‑inoculated control, suggesting that the introduction of this endophytic strain positively modulates the indigenous soil microbial community. Subsequent analyses of the adsorption mechanism using SEM, ATR-FTIR, affinity chromatography, and mass spectrometry revealed that A. lwoffii MA1 captures positively charged Cd2+ through negatively charged cell surface groups such as amino and carboxyl groups. Additionally, three membrane proteins in the cell membrane may also play important roles in the adsorption process, including the TonB-dependent receptor, the RND transporter AdeIJK, and the outer membrane protein assembly factor BamD.These results provide novel insights into the influence of endophytic microorganisms on cadmium accumulation, offering a promising approach for mitigating cadmium content in spinach and other vegetables.