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The fatty acid biosynthesis pathway (FAS) was a fundamental procedure to generate a diversity of lipid components for cellular metabolism in bacteria, while the mechanism of substrate recognition remains unclear. The β-hydroxyacyl-acyl carrier protein dehydratase hexamer (FabZ) is an essential module in the elongation cycle of type-II FAS, catalyzing the dehydration of β-hydroxyacyl-lipid substrate carried by the holo form acyl carrier protein (holo-ACP). We previously elucidated an alternating seesaw-like ACP loading manner within a FabZ dimer subunits, mediated by a front-door residue Tyrosine (Tyr100). Here, we demonstrated that a back-door residue Phenylalanine (Phe83) of FabZ regulates the stepwise hexameric loading of ACP. Our finding represents clues as to the dynamic ACP recognition and catalysis mechanism of dehydratase in fatty acid biosynthesis, and provides critical information for developing antimicrobials targeting the dehydratase module in fatty acid biosynthesis pathway.

The phosphopantetheinyl transferases (PPTases) catalyze the post-translational modification of carrier proteins (CPs) from fatty acid synthases (FASs) in primary metabolism and from polyketide synthases (PKSs) and non-ribosomal polypeptide synthases (NRPSs) in secondary metabolism. Based on the conserved sequence motifs and substrate specificities, two types (AcpS-type and Sfp-type) of PPTases have been identified in prokaryotes. We present here that Porphyromonas gingivalis, the keystone pathogen in chronic periodontitis, harbors merely one PPTase, namely PptP. Complementation and gene deletion experiments clearly show that PptP can replace the function of Escherichia coli AcpS and is essential for the growth of P. gingivalis. Purified PptP transfers the 4-phosphopantetheine moiety of CoA to inactive apo-acyl carrier protein (ACP) to form holo-ACP, which functions as an active carrier of the acyl intermediates of fatty acid synthesis. Moreover, PptP exhibits broad substrate specificity, modifying all ACP substrates tested and catalyzing the transfer of coenzyme A (CoA) derivatives. The lack of sequence alignment with known PPTases together with phylogenetic analyses revealed PptP as a new class of PPTases. Identification of the new PPTase gene pptP exclusive in Porphyromonas species reveals a potential target for treating P. gingivalis infections.

Marine-derived fungi can usually produce structurally novel and biologically potent metabolites. In this study, a new diketopiperazine alkaloid (1) and two new polyketides (10 and 11), along with 8 known diketopiperazine alkaloids (2-9) were isolated from marine-derived fungus Penicillium sp. TW58-16. Their structures were fully elucidated by analyzing UV, IR, HR-ESI-MS, 1D, and 2D NMR spectroscopic data. The absolute configurations of the new compounds 1, 10 and 11 were ascertained by X-ray diffraction (Cu Kα radiation) and comparing their CD data with those reported. In addition, the antibacterial activities of these compounds against Helicobacter pylori in vitro were assessed. Results showed that compounds 3, 6, 8 and 9 displayed moderate antibacterial activity against standard strains and drug-resistant clinical isolates of H. pylori in vitro. This result demonstrates that diketopiperazine alkaloids could be lead compounds to be explored for the treatment of H. pylori infection.

Chemical investigation of the extracts of Aspergillus sp. CSYZ-1 resulted in the identification of compound 1, aspergillactone, a new 3,5-dimethylorsellinic acid-based meroterpenoid, together with four known metabolites (2–5). The structure and relative configuration of 1 were unambiguously determined by nuclear magnetic resonance (NMR), mass spectrometry. The absolute configuration of 1 was defined by quantum chemical TDDFT calculated and the experimental ECD spectra. The possible biosynthetic pathway of compound 1 was also proposed. The new compound exhibited potent antimicrobial activity against Helicobacter pylori and Staphylococcus aureus with MIC values of around 1–4 and 2–16 μg/mL, respectively.

Omadacycline and eravacycline are newly approved tetracycline analogues with excellent activity against a broad spectrum of Gram-positive and Gram-negative microorganisms; however, no data are available regarding Helicobacter pylori. The susceptibility of 201 clinical isolates of H. pylori collected in China to omadacycline, eravacycline, and the comparator tetracycline was determined by an agar dilution method. They showed greater activity than tetracycline. The MIC50/90 values of omadacycline, eravacycline, and tetracycline were 0.125/0.25 μg/mL, 0.063/0.125 μg/mL, and 0.25/1 μg/mL, respectively. Omadacycline and eravacycline were potent in vitro against all the isolates tested, including tetracycline-resistant strains, and warrant further investigation as potential antibiotics for H. pylori treatment.

Algae cells were the main sources of dissolved organic nitrogen (DON) in raw water with plenty of algae, and ultrasonic pretreatment was one of the algae-controlling methods through the damage of algae cells. However, the variation of DON concentration during the ultrasonic treatment process was not confirmed. Variation of DON concentration during the processes of low frequency ultrasound treatment of Microcystis aeruginosa was investigated. In addition, the effect of sonication on the metabolite concentration, algae cellar activity and the subsequent coagulation performance were discussed. The results showed that after a long duration of ultrasonic (60 s), nearly 90% of the algal cells were damaged and the maximum concentration of DON attained more than 3 mg/L. In order to control the leakage extent of DON, the sonication time should be less than 30 s with power intensity of more than 1.0 W/cm(3). In the mean time, ultrasonic treatment could inhibit the reactivation and the proliferation of algal, keep the algae cell wall integrity and enhance coagulation effectively under the same condition. However, ultrasound frequency had little effect on DON at the frequency range used in this study (20-150 kHz).

SummaryIn the classical anaerobic pathway of unsaturated fatty acid biosynthesis, that of Escherichia coli, the double bond is introduced into the growing acyl chain by the FabA dehydratase/isomerase. Another dehydratase, FabZ, functions in the chain elongation cycle. In contrast, Aerococcus viridans has only a single FabA/FabZ homolog we designate FabQ. FabQ can not only replace the function of E. coli FabZ in vivo, but it also catalyzes the isomerization required for unsaturated fatty acid biosynthesis. Most strikingly, FabQ in combination with E. coli FabB imparts the surprising ability to bypass reduction of the trans-2-acyl-ACP intermediates of classical fatty acid synthesis. FabQ allows elongation by progressive isomerization reactions to form the polyunsaturated fatty acid, 3-hydroxy-cis-5, 7-hexadecadienoic acid, both in vitro and in vivo. FabQ therefore provides a potential pathway for bacterial synthesis of polyunsaturated fatty acids.