Bio-denitrification is widely used for remediation of nitrate contaminated site or removal of nitrate from wastewater, but its efficiency is not always satisfied and high nitrite accumulation and nitrous oxide emission occur frequently. Iron plays an important role in achieving efficient biological denitrification. Nevertheless, its concentration in cells is usually inadequate, and additional supply of iron to denitrification system has been adopted in the literature. In this study, a novel approach to increase the intracellular iron concentration of denitrifying microbes by using graphene to accelerate iron transport, which significantly enhanced bio-denitrification and decreased intermediates accumulations, was reported, and the underlying mechanisms were explored. The presence of 50 mg/L of graphene was observed to not only significantly promote nitrate removal efficiency by 67.3%, but also decrease nitrite and nitrous oxide generation by 49.0% and 63.9%, respectively. It was found that graphene promoted the generation, transfer and consumption of electrons, increased the activities or gene expressions of Fe-containing enzymes (such as complex I, complex III, various cytochromes , and most denitrification reductases), and enhanced the growth of denitrifiers due to iron acquisition by denitrifying bacteria being remarkably facilitated, leading to a significant increment of intracellular iron concentration. Meanwhile, the intracellular proton-motive force and ATP levels were promoted as well. This study provided a new approach to enhancing bio-denitrification and revealed a novel insight into biological iron acquisition.
Klebsiella pneumoniae is a major cause of endogenous endophthalmitis, a rapidly progressing intraocular infection associated with severe inflammation and vision loss. The vitreous body presents a hypoxic and iron-restricted environment, yet the bacterial metabolic adaptations that enable persistence in this niche remain largely unknown. Here, we show that K. pneumoniae undergoes metabolic reprogramming to facilitate intraocular survival, characterized by enhanced glycolysis and siderophore-mediated iron acquisition. Proteomic profiling under vitreous-mimicking conditions revealed significant upregulation of PfkA, PykF, and EntB. Targeted deletion of these genes impaired bacterial growth under hypoxia and iron limitation, and significantly reduced intraocular colonization, proinflammatory cytokine production, and visual impairment in a murine model. Double mutants lacking both glycolytic and iron acquisition pathways were nearly avirulent. Correspondingly, infected eyes exhibited lower levels of lactate and iron, reflecting reduced bacterial metabolic activity. These findings establish glycolysis and iron acquisition as critical determinants of K. pneumoniae virulence in the eye and provide insight into the metabolic strategies underpinning bacterial persistence in nutrient-limited host environments.
With the increasing concerns regarding bacterial adaption to nanomaterials , it is critical to explore the main mechanism behind the adaptive morphogenesis of microorganisms . In this work, the biofilms formed from activated sludge exposed to 5 and 50 mg/L nTiO 2 in the dark had increased biomass and selectively enriched pathogens . To further elaborate adaptive mechanism of biofilm formation induced by nTiO 2 , the protein response and protein phosphorylation modification of Escherichia coli K12 were determined using integrative systems biology analyses of proteomics and phosphoproteomics. Results identified that E. coli cultivated with nTiO 2 considerably upregulated iron acquisition, and regulated protein phosphorylation states associated with of transcription and translation and biofilm formation relative to unexposed controls. Accordingly, bacteria increased siderophores and exopolysaccharide content (increased by about 57% and 231%, respectively), and enhanced resistance to transcriptional inhibitory antibiotics. Moreover, a dose of an iron chelator, i.e., deferoxamine mesylate salt, effectively retarded the biofilm development of bacteria exposed to 50 mg/L nTiO 2 . Overall, this work will provide a new insight for biofouling control, and contribute to an improved understanding of microbial adaption to nanomaterials.
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