Synthesis and Biological Screening of New Lawson Derivatives as Selective Substrate-Based Inhibitors of Cytochrome bo3 Ubiquinol Oxidase from Escherichia coli

Effects of Isaria cicadae on growth, gut microbiota, and metabolome of Larimichthys crocea

The large yellow croaker (Larimichthys crocea) is the most productive mariculture fish in China, and its aquaculture scale is expanding along the southeastern coast of China, but that development is causing environmental damage by increasing the use of antibiotics and other chemicals. How to improve fish immunity through non-antibiotic substances is still a problem facing aquaculture industry. At present, the experiments have shown that Isaria cicadae spent substrate (IC) can improve the growth performance and immunity of Oreochromis niloticus. Therefore, I. cicadae may be a natural alternative to antibiotic for aquaculture. In order to study the effects of IC on growth performance, serum biochemical indices, intestinal microbiota, and intestinal metabolism of large yellow croakers, the fish were divided into three groups with three replicates in each group. Basal diet, basal diet with 2% and 6% IC supplementation (IC2 and IC6 groups), respectively. The results showed that weight gain rate (WG) and specific growth rate (SGR) of large yellow croaker significantly increased (P < 0.05) in IC6 group. The content of triglyceride (TG), low density lipoprotein cholesterol (LDL-C), total protein (TP) and albumin (ALB) increased significantly (P < 0.05), and total cholesterol (T-CHO) decreased significantly (P < 0.05) in IC2 group. Compared to IC0 group, the activity of malondialdehyde (MDA) , superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) increased significantly (P < 0.05) in IC2 group, the activity of total antioxidant capacity (T-AOC) and GSH-Px increased significantly (P < 0.05) in IC6 group, and the activity of lysozyme (LZM) increased significantly in IC2 and IC6 groups. The addition of IC in the diets significantly increased the diversity of the microbial community in the intestine of large yellow croaker (P < 0.05), significantly improved the relative abundance of Acidobacteriota (P < 0.05) at the phylum level, and reduced the relative abundance of Bacteroidota, Desulfobacterota, and Synergistota (P < 0.05). At the genus level, the relative abundance of Bacteroides, Cetobacterium and Mycoplasma, which are dominant bacteria in fish gut, significantly increased (P < 0.05). The relative abundance of Ruminofilibacter, Desulfomicrobium, DMER64, Syntrophomonas, Hydrogenophaga, and Aminobacterium reduced significantly (P < 0.05). Among them, Ruminofilibacter, DMER64, Syntrophomonas and Hydrogenophaga are bacteria that can participate in the hydrolysis and acidification of organic matter, while DMER64 is the hydrogen carrier. The intestinal metabolome analysis showed that IC could improve metabolic composition and function, which was related to host immunity and metabolism. In conclusion, I. cicadae can improve the growth performance, regulate the lipid metabolism and immune and antioxidant capacity of large yellow croakers by regulating intestinal microbiota and intestinal metabolism. This study provides a reference for the application of IC in aquaculture.

Dynamic changes in the microbial community in the surface seawater of Jiaozhou Bay after crude oil spills: An in situ microcosm study

The changes in the composition and structure of microbial communities in Jiaozhou Bay are strongly affected by marine oil pollution, but the outcomes of the microbial responses and effects of dispersant application remain unclear. Herein, we performed an in situ microcosm study to investigate the response of the indigenous microbial community under crude oil alone and combined oil and dispersant treatment in the surface seawater of a semi-enclosed marine area of Jiaozhou Bay. The dynamics of the bacterial classification based on 16s rDNA sequencing were used to assess the changes with the crude oil concentration, dispersant use, and time. The crude oil resulted in a high abundance of the genera Pseudohongiella, Cycloclasticus, Marivita, and C1-B045 from the Gammaproteobacteria and Alphaproteobacteria classes, suggesting for hydrocarbon degradation. However, the dispersant treatment was more advantageous for Pacificibacter, Marivita, and Loktanella. Besides accelerating the rate of bacterial community succession, the dispersants had significantly stronger effects on the structure of the bacterial community and the degradation functions than the oil. A higher dose of oil exposure corresponded to fewer dominant species with a high relative abundance. Our study provides information for screening potential degradation bacteria and assessing the risks that oil spills pose to marine ecosystems.

Mechanistic and structural diversity between cytochrome bd isoforms of Escherichia coli

The treatment of infectious diseases caused by multidrug-resistant pathogens is a major clinical challenge of the 21st century. The membrane-embedded respiratory cytochrome bd-type oxygen reductase is a critical survival factor utilized by pathogenic bacteria during infection, proliferation and the transition from acute to chronic states. Escherichia coli encodes for two cytochrome bd isoforms that are both involved in respiration under oxygen limited conditions. Mechanistic and structural differences between cydABX (Ecbd-I) and appCBX (Ecbd-II) operon encoded cytochrome bd variants have remained elusive in the past. Here, we demonstrate that cytochrome bd-II catalyzes oxidation of benzoquinols while possessing additional specificity for naphthoquinones. Our data show that although menaquinol-1 (MK1) is not able to directly transfer electrons onto cytochrome bd-II from E. coli, it has a stimulatory effect on its oxygen reduction rate in the presence of ubiquinol-1. We further determined cryo-EM structures of cytochrome bd-II to high resolution of 2.1 Å. Our structural insights confirm that the general architecture and substrate accessible pathways are conserved between the two bd oxidase isoforms, but two notable differences are apparent upon inspection: (i) Ecbd-II does not contain a CydH-like subunit, thereby exposing heme b ₅₉₅ to the membrane environment and (ii) the AppB subunit harbors a structural demethylmenaquinone-8 molecule instead of ubiquinone-8 as found in CydB of Ecbd-I Our work completes the structural landscape of terminal respiratory oxygen reductases of E. coli and suggests that structural and functional properties of the respective oxidases are linked to quinol-pool dependent metabolic adaptations in E. coli.

Short-chain aurachin D derivatives are selective inhibitors of E. coli cytochrome bd-I and bd-II oxidases

Cytochrome bd-type oxidases play a crucial role for survival of pathogenic bacteria during infection and proliferation. This role and the fact that there are no homologues in the mitochondrial respiratory chain qualify cytochrome bd as a potential antimicrobial target. However, few bd oxidase selective inhibitors have been described so far. In this report, inhibitory effects of Aurachin C (AurC-type) and new Aurachin D (AurD-type) derivatives on oxygen reductase activity of isolated terminal bd-I, bd-II and bo₃ oxidases from Escherichia coli were potentiometrically measured using a Clark-type electrode. We synthesized long- (C10, decyl or longer) and short-chain (C4, butyl to C8, octyl) AurD-type compounds and tested this set of molecules towards their selectivity and potency. We confirmed strong inhibition of all three terminal oxidases for AurC-type compounds, whereas the 4(1H)-quinolone scaffold of AurD-type compounds mainly inhibits bd-type oxidases. We assessed a direct effect of chain length on inhibition activity with highest potency and selectivity observed for heptyl AurD-type derivatives. While Aurachin C and Aurachin D are widely considered as selective inhibitors for terminal oxidases, their structure–activity relationship is incompletely understood. This work fills this gap and illustrates how structural differences of Aurachin derivatives determine inhibitory potency and selectivity for bd-type oxidases of E. coli.

Synthesis and Biological Screening of New Lawson Derivatives as Selective Substrate-Based Inhibitors of Cytochrome bo3 Ubiquinol Oxidase from Escherichia coli

The respiratory chain of Escherichia coli contains two different types of terminal oxidase that are differentially regulated as a response to changing environmental conditions. These oxidoreductases catalyze the reduction of molecular oxygen to water and contribute to the proton motive force. The cytochrome bo3 oxidase (cyt bo3 ) acts as the primary terminal oxidase under atmospheric oxygen levels, whereas the bd-type oxidase is most abundant under microaerobic conditions. In E. coli, both types of respiratory terminal oxidase (HCO and bd-type) use ubiquinol-8 as electron donor. Here, we assess the inhibitory potential of newly designed and synthesized 3-alkylated Lawson derivatives through L-proline-catalyzed three-component reductive alkylation (TCRA). The inhibitory effects of these Lawson derivatives on the terminal oxidases of E. coli (cyt bo3 and cyt bd-I) were tested potentiometrically. Four compounds were able to reduce the oxidoreductase activity of cyt bo3 by more than 50 % without affecting the cyt bd-I activity. Moreover, two inhibitors for both cyt bo3 and cyt bd-I oxidase could be identified. Based on molecular-docking simulations, we propose binding modes of the new Lawson inhibitors. The molecular fragment benzyl enhances the inhibitory potential and selectivity for cyt bo3 , whereas heterocycles reduce this effect. This work extends the library of 3-alkylated Lawson derivatives as selective inhibitors for respiratory oxidases and provides molecular probes for detailed investigations of the mechanisms of respiratory-chain enzymes of E. coli.