Loss of Dihydroxyacid Dehydratase Induces Auxotrophy in Bacillus anthracis

Natural polysaccharide hydrogel with bioadhesion characters to synergistically enhance berberine's antibacterial effect by regulating the PTS system of Staphylococcus aureus

The global spread of Staphylococcus aureus (S. aureus) not only causes significant economic losses but also poses a serious threat to public health. Consequently, there is an urgent need for multidimensional strategies to develop antimicrobial dressings to combat bacterial infections. In response, we have developed a plant polysaccharide antibacterial hydrogel formed through the self-assembly of edible Kudzu powder (KP) and the natural star molecule berberine (BBR). Rheological tests show that natural polysaccharide KP-BBR hydrogel (BBR@KP) exhibits excellent injectability and adhesion. And the degradation of the hydrogel exceeded 90 % within 3 days. The synergistic effect of these two ingredients enhances the antibacterial activity of BBR and can increase the MIC of BBR to 0.05 mM. Specifically, KP promotes the affinity of the Phosphoenolpyruvate Phosphotransferase System (PTS) of S. aureus, enabling KP, with its bioadhesive properties, to adhere to the bacterial surface and continuously release BBR. Subsequently, BBR effectively exerts its antibacterial effect by inhibiting the synthesis of histidine and isoleucine. Furthermore, the BBR@KP hydrogel exhibits negligible cytotoxicity and hemolytic toxicity, underscoring its favorable biosafety profile. This synergistic natural antibacterial hydrogel, formulated through a green and straightforward methodology, not only holds promise for broad clinical applications but also provides novel perspectives for the utilization and development of plant polysaccharides in the biomedical field.

Biodegradation of nitrate and p-bromophenol using hydrogen-based membrane biofilm reactors in parallel

ABSTRACTP-bromophenol (4-BP) is a toxic halogenated phenolic organic compound. The conventional treatment processes for 4-BP elimination are costly and inefficient, with complete mineralization remaining a challenge for water treatment. To overcome these limitations, we investigated the treatment of 4-BP in a membrane biofilm reactor (MBfR) using hydrogen as an electron donor. The pathway of 4-BP degradation within the H2-MBfR was investigated through long-term operational experiments by considering the effect of nitrate and 4-BP concentrations, hydrogen partial pressure, static experiments, and microbial community diversity, which was studied using 16S rRNA. The results showed that H2-MBfR could quickly remove approximately 100% of 4-BP (up to 20 mg/L), with minimal intermediate product accumulation and 10 mg/L of nitrate continuously reduced. The microbial community structure showed that the presence of H2 created an anaerobic environment, and Thauera was the dominant functional genus involved in the degradation of 4-BP. The genes encoding related enzymes were further enhanced. This study provides an economically viable and environmentally friendly bioremediation technique for water bodies that contain 4-BP and nitrates.

BrnQ-Type Branched-Chain Amino Acid Transporters Influence Bacillus anthracis Growth and Virulence

Bacillus anthracis, the anthrax agent, exhibits robust proliferation in diverse niches of mammalian hosts. The metabolic attributes of B. anthracis that permit rapid growth in multiple mammalian tissues have not been established. We posit that branched-chain amino acid (BCAA) (isoleucine, leucine, and valine) metabolism is key to B. anthracis pathogenesis. Increasing evidence indicates the relationships between B. anthracis virulence and the expression of BCAA-related genes. The expression of some BCAA-related genes is altered during culture in bovine blood in vitro, and the bacterium exhibits valine auxotrophy in a blood serum mimic medium. Transcriptome analyses have revealed that the virulence regulator AtxA, which positively affects the expression of the anthrax toxin and capsule genes, negatively regulates genes predicted to be associated with BCAA biosynthesis and transport. Here, we show that B. anthracis growth in defined medium is severely restricted in the absence of exogenous BCAAs, indicating that BCAA transport is required for optimal growth in vitro. We demonstrate functional redundancy among multiple BrnQ-type BCAA transporters. Three transporters are associated with isoleucine and valine transport, and the deletion of one, BrnQ3, attenuates virulence in a murine model for anthrax. Interestingly, an ilvD-null mutant lacking dihydroxy acid dehydratase, an enzyme essential for BCAA synthesis, exhibits unperturbed growth when cultured in medium containing BCAAs but is highly attenuated in the murine model. Finally, our data show that BCAAs enhance AtxA activity in a dose-dependent manner, suggesting a model in which BCAAs serve as a signal for virulence gene expression. IMPORTANCE Infection with B. anthracis can result in systemic disease with large numbers of the bacterium in multiple tissues. We found that branched-chain amino acid (BCAA) synthesis is insufficient for the robust growth of B. anthracis; access to BCAAs is necessary for the proliferation of the pathogen during culture and during infection in a murine model for anthrax. B. anthracis produces an unusually large repertoire of BCAA-related transporters. We identified three isoleucine/valine transporters with partial functional redundancy during culture. The deletion of one of these transporters, BrnQ3, resulted in attenuated virulence. Interestingly, a BCAA biosynthesis mutant grew well in medium containing BCAAs but, like BrnQ3, was attenuated for virulence. These results suggest that BCAAs are limiting in multiple niches during infection and further our understanding of the nutritional requirements of this important pathogen.