Minicells from Highly Genome Reduced Escherichia coli: Cytoplasmic and Surface Expression of Recombinant Proteins and Incorporation in the Minicells

Manipulating subcellular protein localization to enhance target protein accumulation in minicells

BACKGROUND

Minicells are chromosome-free derivatives of bacteria formed through irregular cell division. Unlike simplified structures, minicells retain all cellular components of the parent cell except for the chromosome. This feature reduces immunogenic responses, making them advantageous for various biotechnological applications, including chemical production and drug delivery. To effectively utilize minicells, it is essential to ensure the accumulation of target proteins within them, enhancing their efficiency as delivery vehicles.

RESULTS

In this study, we engineered Escherichia coli by deleting the minCD genes, generating minicell-producing strains, and investigated strategies to enhance protein accumulation within the minicells. Comparative proteomic analysis revealed that minicells retain most parent-cell proteins but exhibit an asymmetric proteome distribution, leading to selective protein enrichment. We demonstrated that heterologous proteins, such as GFP and RFP, accumulate more abundantly in minicells than in parent cells, regardless of expression levels. To further enhance this accumulation, we manipulated protein localization by fusing target proteins to polar localization signals. While proteins fused with PtsI and Tsr exhibited 2.6-fold and 2.8-fold increases in accumulation, respectively, fusion with the heterologous PopZ protein resulted in a remarkable 15-fold increase in protein concentration under low induction conditions.

CONCLUSIONS

These findings highlight the critical role of spatial protein organization in enhancing the cargo-loading capabilities of minicells. By leveraging polar localization signals, this work provides a robust framework for optimizing minicells as efficient carriers for diverse applications, from therapeutic delivery to industrial biomanufacturing.

Sinorhizobium meliloti FcrX coordinates cell cycle and division during free-living growth and symbiosis by a ClpXP-dependent mechanism

Sinorhizobium meliloti is a soil bacterium that establishes a nitrogen-fixing symbiosis within root nodules of legumes. In this symbiosis, S. meliloti undergoes a drastic cellular change leading to a terminally differentiated form, called bacteroid, characterized by genome endoreduplication, increased cell size, and high membrane permeability. Bacterial cell cycle (mis)regulation is at the heart of this differentiation process. In free-living cells, the master regulator CtrA ensures the progression of cell cycle by activating cell division (controlled by FtsZ) and inhibiting DNA replication, while on the other hand the so far poorly unknown downregulation of CtrA and FtsZ is essential for bacteroid differentiation. Here, we combine cell biology, biochemistry, and bacterial genetics to understand the functions of FcrX, a factor that controls both CtrA and FtsZ in free-living growth and in symbiosis. Depletion of the essential gene fcrX led to abnormally high levels of FtsZ and CtrA and minicell formation. Using multiple complementary techniques, we showed that FcrX may interact with FtsZ and CtrA. Moreover, fcrX transcription is directly controlled by CtrA itself and the FcrX protein displays a cell cycle-dependent pattern. We showed further that FcrX also binds the degradosome complex ClpXP and its adaptors CpdR1 and RcdA, and that CtrA degradation efficiency depends on FcrX. We further showed that, despite weak homology with FliJ-like proteins, only FcrX proteins from closely related species are able to complement S. meliloti fcrX function. Finally, deregulation of FcrX showed abnormal symbiotic behaviors in plants suggesting a putative role of this factor during bacteroid differentiation.

Leveraging Engineered Pseudomonas putida Minicells for Bioconversion of Organic Acids into Short-Chain Methyl Ketones

Methyl ketones, key building blocks widely used in diverse industrial applications, largely depend on oil-derived chemical methods for their production. Here, we investigated biobased production alternatives for short-chain ketones, adapting the solvent-tolerant soil bacterium Pseudomonas putida as a host for ketone biosynthesis either by whole-cell biocatalysis or using engineered minicells, chromosome-free bacterial vesicles. Organic acids (acetate, propanoate and butanoate) were selected as the main carbon substrate to drive the biosynthesis of acetone, butanone and 2-pentanone. Pathway optimization identified efficient enzyme variants from Clostridium acetobutylicum and Escherichia coli, tested with both constitutive and inducible expression of the cognate genes. By implementing these optimized pathways in P. putida minicells, which can be prepared through a simple three-step purification protocol, the feedstock was converted into the target short-chain methyl ketones. These results highlight the value of combining morphology and pathway engineering of noncanonical bacterial hosts to establish alternative bioprocesses for toxic chemicals that are difficult to produce by conventional approaches.

Harnessing and Mimicking Bacterial Features to Combat Cancer: From Living Entities to Artificial Mimicking Systems

Bacterial-derived micro-/nanomedicine has garnered considerable attention in anticancer therapy, owing to the unique natural features of bacteria, including specific targeting ability, immunogenic benefits, physicochemical modifiability, and biotechnological editability. Besides, bacterial components have also been explored as promising drug delivery vehicles. Harnessing these bacterial features, cutting-edge physicochemical and biotechnologies have been applied to attenuated tumor-targeting bacteria with unique properties or functions for potent and effective cancer treatment, including strategies of gene-editing and genetic circuits. Further, the advent of bacteria-inspired micro-/nanorobots and mimicking artificial systems has furnished fresh perspectives for formulating strategies for developing highly efficient drug delivery systems. Focusing on the unique natural features and advantages of bacteria, this review delves into advances in bacteria-derived drug delivery systems for anticancer treatment in recent years, which has experienced a process from living entities to artificial mimicking systems. Meanwhile, a summary of relative clinical trials is provided and primary challenges impeding their clinical application are discussed. Furthermore, future directions are suggested for bacteria-derived systems to combat cancer.

Advancing cancer treatment: in vivo delivery of therapeutic small noncoding RNAs

In recent years, small non-coding RNAs (ncRNAs) have emerged as a new player in the realm of cancer therapeutics. Their unique capacity to directly modulate genetic networks and target oncogenes positions them as valuable complements to existing small-molecule drugs. Concurrently, the advancement of small ncRNA-based therapeutics has rekindled the pursuit of efficacious in vivo delivery strategies. In this review, we provide an overview of the most current clinical and preclinical studies in the field of small ncRNA-based cancer therapeutics. Furthermore, we shed light on the pivotal challenges hindering the successful translation of these promising therapies into clinical practice, with a specific focus on delivery methods, aiming to stimulate innovative approaches to address this foundational aspect of cancer treatment.

Efficient Cytotoxicity of Recombinant Azurin in Escherichia coli Nissle 1917-Derived Minicells against Colon Cancer Cells

Compared to chemical drugs, therapeutic proteins exhibit higher specificity and activity and are generally well-tolerated by the human body. However, the limitations, such as poor stability both in vivo and in vitro as well as difficulties in penetrating cell membranes, hinder their widespread application. To overcome the challenges, a highly efficient protocol was developed and implemented for the recombinant expression of the therapeutic protein azurin and secretion into minicells derived from probiotic Escherichia coli Nissle 1917. The novel coupled production with a delivery system of therapeutic proteins based on minicells was obtained through purification to enhance protein activity, circulation characteristics, and targeting specificity. This protein drug carrier integrates the production of carrier materials and the loading of expression proteins. The drug carrier also protects the encapsulated polypeptide drugs from enzymatic or gastric acid degradation until they are released. Escherichia coli Nissle 1917-derived minicells have natural targeting to colon cancer cells, low toxicity, and can accumulate for a long time after penetrating tumor tissue. This self-produced protein drug delivery system simplified the process of protein preparation, and its inhibitory effect on different types of colon cancer cells was verified by CCK-8 cytotoxicity assay, cancer cell invasion, and migration assay. This work provided a simple method to prepare minicell drug delivery systems for protein drug production and a novel approach for the transport of recombinant protein drugs.