Hongbo Hu

Collagenases can specifically degrade collagen, showing a wide application prospect in food, leather, waste utilization, biotechnology, and other industries. Currently, Hathewaya histolytica is commonly used in industry to produce collagenases, but its application is greatly limited by its pathogenicity. This study first identified five potential Pseudomonas-derived collagenases by sequence alignment. Bioinformatics tools were used to analyze their structures and functions. Heterologous expression of two P. chlororaphis-derived collagenases was achieved in E. coli, and their enzymatic properties were characterized. Bioinformatics analysis shows that the Pseudomonas-derived collagenases had low molecular weights (22.1~50.5 kDa) and good thermal stability (aliphatic index 73.73~88.81). Deletion of P. chlororaphis GP72ANO strain colP1 and colP2 genes had no significant effect on cell growth. The yields of collagenase ColP1 and ColP2 obtained from E. coli BL21(DE3) cultivation broth were 148 mg/L and 322 mg/L, respectively. The optimum temperature of each collagenase was 28 °C, and the soluble collagen activities of ColP1 and ColP2 were up to 42.64 U/mg and 21.21 U/mg, respectively. Collagenase ColP1 had the highest enzyme activity at pH 8, while collagenase ColP2 had the highest enzyme activity at pH 4. Metal ions such as Na⁺, K⁺, Mg²⁺, Ca²⁺, Ni²⁺, and Mn²⁺ inhibited the activity of collagenases to different degrees. This study successfully achieved recombinant expression and preliminary purification of Pseudomonas-derived collagenases in E. coli and explored their function and physicochemical properties.

Phenazines are bioactive secondary metabolites with antifungal, anticancer, and insecticidal properties, while hydroxylated derivatives often exhibit enhanced bioactivity. 2‐hydroxyphenazine (2‐OH‐PHZ), which is synthesised by the flavin‐dependent monooxygenase PhzO from phenazine‐1‐carboxylic acid (PCA), shows better bioactivity against the pathogenic fungus Gaeumannomyces graminis vars. tritici . However, the low catalytic efficiency (10%–20% conversion) of PhzO limited 2‐OH‐PHZ production. To boost PhzO activity, engineering flavin reductase (Fre)‐mediated FADH ₂ regeneration was applied to Pseudomonas chlororaphis LX24AE. Remarkably, this approach improved catalytic efficiency from 25% to 40% and increased the production of a novel dihydroxylated derivative. Then, it was first characterised by UPLC‐MS and NMR, and identified as 3,4‐dihydroxyphenazine‐1‐carboxylic acid (3,4‐OH‐PCA). Next, the Fre‐PhzO module through heterologous co‐expression in P. putida KT2440 demonstrated a 4.5‐fold enhancement in hydroxylation efficiency relative to the PhzO mono‐component system, which also confirmed that PhzO and flavin reductase are essential for 3,4‐OH‐PCA biosynthesis. Moreover, in vitro assays further verified that PhzO exhibits FAD‐dependent catalytic promiscuity, simultaneously generating 2‐OH‐PCA and 3,4‐OH‐PCA. Furthermore, in vitro and in vivo assay s demonstrated that substrate concentration affected the distribution of products. Finally, cytotoxicity evaluation of the isolated 3,4‐OH‐PCA was performed, and it showed substantial inhibition against oesophageal cancer TE‐1 cells and human cervical cancer HeLa cells with an IC ₅₀ value of 8.55 μM and 17.69 μM, respectively. This work redefines PhzO as a promiscuous biocatalyst capable of dual hydroxylation, offering a modular platform for engineering bioactive phenazine derivatives.

Phenazine compounds are widely used in agricultural control and the medicine industry due to their high inhibitory activity against pathogens and antitumor activity. The green and sustainable method of synthesizing phenazine compounds through microbial fermentation often requires a complex culture medium containing tryptone and yeast extract, and its cost is relatively high, which greatly limits the large-scale industrial production of phenazine compounds by fermentation. The aim of this study was to develop a cost-effective minimal medium for the efficient synthesis of phenazine compounds by Pseudomonas chlororaphis. Through testing the minimum medium commonly used by Pseudomonas, an ME medium for P. chlororaphis with a high production of phenazine compounds was obtained. Then, the components of the ME medium and the other medium were compared and replaced to verify the beneficial promoting effect of Fe²⁺ and NH₄⁺ on phenazine compounds. A cost-effective general defined medium (GDM) using glycerol as the sole carbon source was obtained by optimizing the composition of the ME medium. Using the GDM, the production of phenazine compounds by P. chlororaphis reached 1073.5 mg/L, which was 1.3 times that achieved using a complex medium, while the cost of the GDM was only 10% that of a complex medium (e.g., the KB medium). Finally, by engineering the glycerol metabolic pathway, the titer of phenazine-1-carboxylic acid reached the highest level achieved using a minimum medium so far. This work demonstrates how we systematically analyzed and optimized the composition of the medium and integrated a metabolic engineering method to obtain the most cost-effective fermentation strategy.

In green chemistry, filamentous fungi are regarded as a kind of robust microorganism for the biotransformation of natural products. Nonetheless, the screening of microorganisms is crucial for the effective biotransformation of natural products, such as phenazine compounds. The precursor metabolite of most phenazine derivatives in Pseudomonas spp. is phenazine-1-carboxylic acid (PCA), the key constituent of shenqinmycin, widely used to control rice sheath blight in southern China. In this study, a new fungus strain Aspergillus sclerotiorum was isolated, which can efficiently convert PCA into 3-hydroxy-phenazine 1-carboxylic acid (3-OH-PCA). Moreover, an effective whole cells biotransformation system was designed by screening optimal reaction conditions and carbon sources. Hence, Aspergillus sclerotiorum exhibited desirable adaptation by the consumption of different carbon sources and maximum whole-cell biomass (10.6 g/L DCW) was obtained as a biocatalyst from glucose. Optimal conditions for whole-cell biocatalysis of PCA were evaluated, including a PCA concentration of 1120 mg/L, a pH of 7.0, a temperature of 25 °C, a rotation rate of 200 rpm, and dry cell weight of 15 g/L for 60 h; thus, 1060 mg/L of 3-OH-PCA was obtained and the conversion efficiency of PCA was 94%. Hence, the results of the repeated batch mood revealed that the biotransformation efficiency of fungus pellets reduced with each subsequent cycle, but remained stable in all five cycles with the provision of a glucose supplement. These findings present the prospect of using filamentous fungi for the whole-cell biocatalysis of phenazine in enormous amounts and the efficient production of 3-OH-PCA. Moreover, these results laid the foundation for further research to disclose the genetic-based mechanism of the strain responsible for PCA biotransformation.

Summary: Pseudomonas chlororaphis is a non‐pathogenic, plant growth‐promoting rhizobacterium that secretes phenazine compounds with broad‐spectrum antibiotic activity. Currently available genome‐editing methods for P. chlororaphis are based on homologous recombination (HR)‐dependent allelic exchange, which requires both exogenous DNA repair proteins (e.g. λ‐Red–like systems) and endogenous functions (e.g. RecA) for HR and/or providing donor DNA templates. In general, these procedures are time‐consuming, laborious and inefficient. Here, we established a CRISPR‐assisted base‐editing (CBE) system based on the fusion of a rat cytidine deaminase (rAPOBEC1), enhanced‐specificity Cas9 nickase (eSpCas9pp ^D10A ) and uracil DNA glycosylase inhibitor (UGI). This CBE system converts C:G into T:A without DNA strands breaks or any donor DNA template. By engineering a premature STOP codon in target spacers, the hmgA and phzO genes of P . chlororaphis were successfully interrupted at high efficiency. The phzO ‐inactivated strain obtained by base editing exhibited identical phenotypic features as compared with a mutant obtained by HR‐based allelic exchange. The use of this CBE system was extended to other P. chlororaphis strains (subspecies LX24 and HT66) and also to P. fluorescens 10586, with an equally high editing efficiency. The wide applicability of this CBE method will accelerate bacterial physiology research and metabolic engineering of non‐traditional bacterial hosts.

Phenazine-1-carboxamide (PCN) is effective to control many plant pathogens, and improving PCN production would be of great significance in promoting its development as a biopesticide. This study was conducted to improve the PCN production of Pseudomonas chlororaphis H5△fleQ△relA through fermentation optimization in both shake flask and bioreactor. The PCN production of H5△fleQ△relA was improved from 2.75 ± 0.23 g/L to 5.51 ± 0.17 g/L by medium optimization in shake flask using Plackett-Burman design, the path of steepest ascent experiment and central composite design. Then, PCN production reached 8.58 ± 0.25 g/L through optimizing pH in 1 L bioreactor. After pH optimization, the transcriptional levels of ccoO_2 and ccoQ_2 genes related to microbial aerobic respiration were significantly upregulated, and the relative abundance of 3-oxo-C14-HSL was significantly enhanced 15-fold, and these changes were vital for cell activity and metabolites production. Furthermore, the PCN production reached 9.58 ± 0.57 g/L after optimization of the fed-batch fermentation strategy in 1 L bioreactor. Finally, the fermentation scale-up of the optimal medium and optimal feeding strategy were conducted in 30 L bioreactor at the optimal pH, and their PCN production reached 9.17 g/L and 9.62 g/L respectively, which were comparable to that in 1 L bioreactor. In this study, the high PCN production was achieved from the shake-flask fermentation to 30 L bioreactor, and the optimal feeding strategy improved PCN production in bioreactor without increasing total glycerol compared with in shake flask. It provides promising pathways for the optimization of processes for the production of other phenazines.