Oxygen-driven metabolic coupling in the extensive catabolism of leucomalachite green by Sphingobium naphthae: Deciphering the biochemical pathways

Abstract

Leucomalachite green (LMG) poses significant risks to aquatic food safety as a recalcitrant and toxic metabolite of malachite green. This study reports the first isolation of Sphingobium naphthae FC210-1 from white shrimp (Penaeus vannamei), demonstrating its robust capacity for extensive catabolism and deep biodegradation of LMG. The isolate exhibited broad physiological adaptability, including halotolerance and heavy metal resistance, achieving a 97.54% removal efficiency under oxygen-supplied conditions. Integrated metabolomic analyses proposed a novel oxygen-dependent metabolic bifurcation governing LMG transformation: oxygen-supplied degradation was characterized by efficient oxidative metabolism and elevated citric acid levels, suggesting that putative TCA cycle involvement provides critical energetic support for this extensive catabolism. Conversely, oxygen limitation triggered a metabolic bottleneck, reducing efficiency to similar to 65% and leading to the partial reoxidation of LMG to malachite green, alongside the enrichment of stress-associated metabolites such as deoxyinosine. A critical finding was the non-linear response to bioaugmentation frequency, where a 28-day dosing interval significantly outperformed frequent 7-day additions (61.56% vs. 48.87%), suggesting that excessive biomass triggers counterproductive intraspecific competition. Furthermore, the short-term safety and biocompatibility of the isolate were demonstrated in Nile tilapia (Oreochromis niloticus), as growth parameters showed no adverse deviations across all treatments (p > 0.05). Collectively, these findings identify oxygen availability as the primary determinant of redox routing and provide a proposed metabolic framework detailing the biological fate of LMG.