Structural and Biochemical Characterization of the Flavin-Dependent Siderophore-Interacting Protein from Acinetobacter baumannii

Probiotics and biofilm interaction in aquaculture for sustainable food security: A review and bibliometric analysis

Aquaculture is one of the most significant food sources from the prehistoric period. As aquaculture intensifies globally, the prevalence and outbreaks of various pathogenic microorganisms cause fish disease and heavy mortality, leading to a drastic reduction in yield and substantial economic loss. With the modernization of the aquaculture system, a new challenge regarding biofilms or bacterial microenvironments arises worldwide, which facilitates pathogenic microorganisms to survive under unfavorable environmental conditions and withstand various treatments, especially antibiotics and other chemical disinfectants. However, we focus on the mechanistic association between those microbes which mainly form biofilm and probiotics in one of the major food production systems, aquaculture. In recent years, probiotics and their derivatives have attracted much attention in the fisheries sector to combat the survival strategy of pathogenic bacteria. Apart from this, Bibliometric analysis provides a comprehensive overview of the published literature, highlighting key research themes, emerging topics, and areas that require further investigation. This information is valuable for researchers, policymakers, and stakeholders in determining research priorities and allocating resources effectively.

A natural fusion of flavodiiron, rubredoxin, and rubredoxin oxidoreductase domains is a self-sufficient water-forming oxidase of Trichomonas vaginalis

Microaerophilic pathogens such as Giardia lamblia, Entamoeba histolytica, and Trichomonas vaginalis have robust oxygen consumption systems to detoxify oxygen and maintain intracellular redox balance. This oxygen consumption results from H2O-forming NADH oxidase (NOX) activity of two distinct flavin-containing systems: H2O-forming NOXes and multicomponent flavodiiron proteins (FDPs). Neither system is membrane bound, and both recycle NADH into oxidized NAD+ while simultaneously removing O2 from the local environment. However, little is known about the specific contributions of these systems in T. vaginalis. In this study, we use bioinformatics and biochemical analyses to show that T. vaginalis lacks a NOX-like enzyme and instead harbors three paralogous genes (FDPF1-3), each encoding a natural fusion product between the N-terminal FDP, central rubredoxin (Rb), and C-terminal NADH:Rb oxidoreductase domains. Unlike a "stand-alone" FDP that lacks Rb and oxidoreductase domains, this natural fusion protein with fully populated flavin redox centers directly accepts reducing equivalents of NADH to catalyze the four-electron reduction of oxygen to water within a single polypeptide with an extremely high turnover. Furthermore, using single-particle cryo-EM, we present structural insights into the spatial organization of the FDP core within this multidomain fusion protein. Together, these results contribute to our understanding of systems that allow protozoan parasites to maintain optimal redox balance and survive transient exposure to oxic conditions.

Distinctive Roles of Two Acinetobactin Isomers in Challenging Host Nutritional Immunity

The human pathogen Acinetobacter baumannii produces and utilizes acinetobactin for iron assimilation. Although two isomeric structures of acinetobactin, one featuring an oxazoline (Oxa) and the other with an isoxazolidinone (Isox) at the core, have been identified, their differential roles as virulence factors for successful infection have yet to be established. This study provides direct evidence that Oxa supplies iron more efficiently than Isox, primarily owing to its specific recognition by the cognate outer membrane receptor, BauA. The other components in the acinetobactin uptake machinery appear not to discriminate these isomers. Interestingly, Oxa was found to form a stable iron complex that is resistant to release of the chelated iron upon competition by Isox, despite their comparable apparent affinities to Fe(III). In addition, both Oxa and Isox were found to be competent iron chelators successfully scavenging iron from host metal sequestering proteins responsible for nutritional immunity. These observations collectively led us to propose a new model for acinetobactin-based iron assimilation at infection sites. Namely, Oxa is the principal siderophore mediating the core Fe(III) supply chain for A. baumannii, whereas Isox plays a minor role in the iron delivery and, alternatively, functions as an auxiliary iron collector that channels the iron pool toward Oxa. The unique siderophore utilization mechanism proposed here represents an intriguing strategy for pathogen adaptation under the various nutritional stresses encountered at infection sites.