Engineering Microbiology最新文献

The adaptive survival mechanisms of bacterial pathogens under host-induced stress are crucial for understanding pathogenesis. Recently, Uppalapati et al. revealed a unique dual function of the Gifsy-1 prophage terminase in Salmonella enterica: it acts as a transfer ribonuclease (tRNase) under oxidative stress. The Gifsy-1 prophage terminase targets and fragments tRNA^Leu to halt translation and temporarily impairs bacterial growth when exposed to high levels of ROS generated by the host immune cells. This response not only preserves genomic integrity by facilitating DNA repair but also inhibits prophage mobilization, thereby aiding in bacterial survival within vertebrate hosts. This study highlights a novel intersection between phage biology and bacterial adaptive strategies.

A novel cellulolytic bacterial strain, ROBY, was isolated from a bovine rumen sample using the enrichment culture method. This isolate was found to be Acinetobacter pittii, with >99 % similarity according to 16S rRNA gene sequence analysis. The potential use of this strain in combination with doxorubicin (Dox)-integrated cellulose nanoparticles (Dox-CNPs) was evaluated as a proof-of-concept study for the further development of this approach as a novel controlled-release drug delivery strategy. The isolate can utilize CNPs as the sole carbon source for growth and degrade both Dox-CNPs and empty CNPs with high efficiency. Extracellular cellulases isolated from bacteria may also be used to trigger Dox release. The results also demonstrated that the release of Dox into the environment due to nanoparticle degradation in the samples incubated with Dox-CNPs significantly affected bacterial cell viability (∼75 % decrease), proving the release of Dox due to bacterial cellulase activity and suggesting the great potential of this approach for further development.

Tigecycline serves as a critical “final-resort” antibiotic for treating bacterial infections caused by multidrug-resistant bacteria for which treatment options are severely limited. The increasing prevalence of tigecycline resistance, particularly among Gram-negative bacteria, is a major concern. Various mechanisms have been identified as contributors to tigecycline resistance, including upregulation of nonspecific Resistance Nodulation Division (RND) efflux pumps due to mutations in transcriptional regulators, enzymatic modification of tigecycline by monooxygenase enzymes, and mutations affecting tigecycline binding sites. This review aims to consolidate our understanding of tigecycline resistance mechanisms in Gram-negative bacteria and offer insights and perspectives for further drug development.

The consumption of non-renewable fossil fuels has directly contributed to a dramatic rise in global carbon dioxide (CO₂) emissions, posing an ongoing threat to the ecological security of the Earth. Microbial electrosynthesis (MES) is an innovative energy regeneration strategy that offers a gentle and efficient approach to converting CO₂ into high-value products. The cathode chamber is a vital component of an MES system and its internal factors play crucial roles in improving the performance of the MES system. Therefore, this review aimed to provide a detailed analysis of the key factors related to the cathode chamber in the MES system. The topics covered include inward extracellular electron transfer pathways, cathode materials, applied cathode potentials, catholyte pH, and reactor configuration. In addition, this review analyzes and discusses the challenges and promising avenues for improving the conversion of CO₂ into high-value products via MES.

Microbial fuel cells (MFCs) employing Pseudomonas putida B6-2 (ATCC BAA-2545) as an exoelectrogen have been developed to harness energy from various conventional substrates, such as acetate, lactate, glucose, and fructose. Owing to its metabolic versatility, P. putida B6-2 demonstrates adaptable growth rates on diverse, cost-effective carbon sources within MFCs, exhibiting distinct energy production characteristics. Notably, the anode chamber's pH rises with carboxylates' (acetate and lactate) consumption and decreases with carbohydrates' (glucose and fructose) utilization. The MFC utilizing fructose as a substrate achieved the highest power density at 411 mW m⁻². Initial analysis revealed that P. putida B6-2 forms biofilms covered with nanowires, contributing to bioelectricity generation. These microbial nanowires are likely key players in direct extracellular electron transport through physical contact. This study established a robust foundation for producing valuable compounds and bioenergy from common substrates in bioelectrochemical systems (BESs) utilizing P. putida as an exoelectrogen.

Industrial manufacturing of bioproducts, especially bioethanol, can benefit from high-temperature fermentation, which requires the use of thermotolerant yeast strains. Mitochondrial activity in yeast is closely related to its overall metabolism. However, the mitochondrial respiratory changes in response to adaptive thermotolerance are still poorly understood and have been rarely utilized for developing thermotolerant yeast cell factories. Here, adaptive evolution and transcriptional sequencing, as well as whole-genome-level gene knockout, were used to obtain a thermotolerant strain of Saccharomyces cerevisiae. Furthermore, thermotolerance and bioethanol production efficiency of the engineered strain were examined. Physiological evaluation showed the boosted fermentation capacity and suppressed mitochondrial respiratory activity in the thermotolerant strain. The improved fermentation produced an increased supply of adenosine triphosphate required for more active energy-consuming pathways. Transcriptome analysis revealed significant changes in the expression of the genes involved in the mitochondrial respiratory chain. Evaluation of mitochondria-associated gene knockout confirmed that ADK1, DOC1, or MET7 were the key factors for the adaptive evolution of thermotolerance in the engineered yeast strain. Intriguingly, overexpression of DOC1 with TEF1 promoter regulation led to a 10.1% increase in ethanol production at 42 °C. The relationships between thermotolerance, mitochondrial activity, and respiration were explored, and a thermotolerant yeast strain was developed by altering the expression of mitochondrial respiration-related genes. This study provides a better understanding on the physiological mechanism of adaptive evolution of thermotolerance in yeast.

Carbazomycins (1–8) are a subgroup of carbazole derivatives that contain oxygen at the C3 and C4 positions and an unusual asymmetric substitution pattern. Several of these compounds exhibit antifungal and antioxidant activities. To date, no systematic biosynthetic studies have been conducted on carbazomycins. In this study, carbazomycins A and B (1 and 2) were isolated from Streptomyces luteosporeus NRRL 2401 using a one-strain-many-compound (OSMAC)-guided natural product mining screen. A biosynthetic gene cluster (BGC) was identified, and possible biosynthetic pathways for 1 and 2 were proposed. The in vivo genetic manipulation of the O-methyltransferase-encoding gene cbzMT proved indispensable for 1 and 2 biosynthesis. Size exclusion chromatography indicated that CbzMT was active as a dimer. In vitro biochemical assays confirmed that CbzMT could repeatedly act on the hydroxyl groups at C3 and C4, producing monomethylated 2 and dimethylated 1. Monomethylated carbazomycin B (2) is not easily methylated; however, CbzMT seemingly prefers the dimethylation of the dihydroxyl substrate (12) to 1, even with a low conversion efficiency. These findings not only improve the understanding of carbazomycin biosynthesis but also expand the inventory of OMT-catalyzing iterative methylations on different acceptor sites, paving the way for engineering biocatalysts to synthesize new active carbazomycin derivatives.

The human intestinal microbiota that comprise over 1,000 species thrive in dark and anaerobic environments. They are recognized for the production of diverse low-molecular-weight metabolites crucial to human health and diseases. Carotenoids, low-molecular-weight pigments known for their antioxidative activity, are delivered to humans through oral intake. However, it remains unclear whether human intestinal bacteria biosynthesize carotenoids as part of the in-situ microbiota. In this study, we investigated carotenoid synthesis genes in various human gut and probiotic bacteria. As a result, novel candidates, the crtM and crtN genes, were identified in the carbon monoxide-utilizing gut anaerobe Eubacterium limosum and the lactic acid bacterium Leuconostoc mesenteroides subsp. mesenteroides. These gene candidates were isolated, introduced into Escherichia coli, which synthesized a carotenoid substrate, and cultured aerobically. Structural analysis of the resulting carotenoids revealed that the crtM and crtN gene candidates of E. limosum and L. mesenteroides mediate the production of 4,4′-diaponeurosporene through 15-cis-4,4′-diapophytoene. Evaluation of the crtE-homologous genes in these bacteria indicated their non-functionality for C₄₀-carotenoid production. E. limosum and L. mesenteroides, along with the known carotenogenic lactic acid bacterium Lactiplantibacillus plantarum, were observed to produce no carotenoids under strictly anaerobic conditions. The two lactic acid bacteria synthesized detectable levels of 4,4′-diaponeurosporene under semi-aerobic conditions. The findings highlight that the obligate anaerobe E. limosum retains aerobically functional C₃₀-carotenoid biosynthesis genes, potentially with no immediate self-utility, suggesting an evolutionary direction in carotenoid biosynthesis. (229 words)

Lignocellulosic biomass is an abundant and renewable bioresource for the production of biofuels and biochemical products. The classical biorefinery process for lignocellulosic degradation and conversion comprises three stages, i.e., pretreatment, enzymatic saccharification, and fermentation. However, the complicated pretreatment process, high cost of cellulase production, and insufficient production performance of fermentation strains have restricted the industrialization of biorefinery. Consolidated bioprocessing (CBP) technology combines the process of enzyme production, enzymatic saccharification, and fermentation in a single bioreactor using a specific microorganism or a consortium of microbes and represents another approach worth exploring for the production of chemicals from lignocellulosic biomass. The present review summarizes the progress made in research of CBP technology for lignocellulosic biomass conversion. In this review, different CBP strategies in lignocellulose biorefinery are reviewed, including CBP with natural lignocellulose-degrading microorganisms as the chassis, CBP with biosynthetic microorganisms as the chassis, and CBP with microbial co-culturing systems. This review provides new perspectives and insights on the utilization of low-cost feedstock lignocellulosic biomass for production of biochemicals.

The association between cigarette smoking and the gut microbiota remains unclear, and there is no agreement on how smoking affects the composition of gut microorganisms. In this study, the relationship between smoking status and gut microbial composition was investigated by performing 16S rRNA gene amplicon sequencing analysis of stool samples from 80 healthy Chinese adults. The results showed that smoking did not cause significant changes to the composition and microbial functional pathways of the gut microbiota. However, smoking altered the relative abundance of several specific taxa, where Phascolarctobacterium and Fusobacterium increased and Dialister decreased. Notably, our analysis revealed that smoking introduced more microbial interactions to the interaction network and decreased its modularity. Overall, this study provides new insights into the association between smoking status and the gut microbiota.