Delivery of cargo proteins via protein secretion systems has been shown as a promising tool in various applications. However, secretion systems are often used by pathogens to cause disease.
A consistent life cycle assessment (LCA) methodology was employed to show how the type of alkali (NaOH or Na2CO3) used for extracting water glass from rice husks, as well as the type of acid (HCl, H2SO4, or HNO3) used for precipitating water glass to nanosilica, affects the environmental emissions of rice husk-derived nanosilica (RH nanosilica). Six nanosilica production scenarios were explicitly compared to determine the most environmentally friendly route. The LCA results show that under the same circumstances, the majority of the environmental emissions of sodium hydroxide (NaOH) are significantly better than those of sodium carbonate (Na2CO3), except for the MAETP and ODP indicators. Similarly, except for the MAETP indicator, the environmental emissions of hydrochloric acid (HCl) are generally superior to those of sulfuric acid (H2SO4) and nitric acid (HNO3). NaOH and HCl were selected as preferable for the extraction of silica from rice husks and the precipitation of water glass, respectively. In addition, the preferred route underwent further in-depth optimization with the aim of achieving optimal environmental emissions for RH nanosilica. The effects of electricity, diesel, fertilizers, and pesticides on the life cycle emission factors of RH nanosilica were examined. The results demonstrate that replacing traditional coal power with cleaner alternatives, such as wind, hydropower, solar power (both photovoltaic and thermal), and biogas electricity, can result in a substantial decrease in the life cycle emission factors of nanosilica, with reductions varying between 20% and 60%. An effective method to reduce emissions associated with diesel, fertilizers, and pesticides is to adopt effective measures to decrease their consumption. These findings provide valuable theoretical foundations and insights for the industrial application of RH nanosilica. These results have great significance for guiding and promoting the industrialization process of nanosilica derived from rice husks and accelerating its commercialization.
Pseudomonas aeruginosa employs its type VI secretion system (T6SS) as a highly effective and tightly regulated weapon to deliver toxic molecules to target cells. T6SS-secreted proteins of P. aeruginosa can be detected in the sputum of cystic fibrosis (CF) patients, who typically present a chronic and polymicrobial lung infection. However, the mechanism of T6SS activation in the CF lung is not fully understood. Here we demonstrate that extracellular DNA (eDNA), abundant within the CF airways, stimulates the dynamics of the H1-T6SS cluster apparatus in Pseudomonas aeruginosa PAO1. Addition of Mg(2+) or DNase with eDNA abolished such activation, while treatment with EDTA mimicked the eDNA effect, suggesting that the eDNA-mediated effect is due to chelation of outer membrane-bound cations. DNA-activated H1-T6SS enables P. aeruginosa to nonselectively attack neighboring species regardless of whether or not it was provoked. Because of the importance of the T6SS in interspecies interactions and the prevalence of eDNA in the environments that P. aeruginosa inhabits, our report reveals an important adaptation strategy that likely contributes to the competitive fitness of P. aeruginosa in polymicrobial communities.
To recognize and manipulate a specific microbe of a crowded community is a highly challenging task in synthetic biology. Here we introduce a highly selective protein delivery platform, termed DUEC, which responds to direct contact of attacking cells by engineering the tit-for-tat/dueling response of H1-T6SS (type VI secretion system) in Pseudomonas aeruginosa. Using a Cre-recombinase-dependent reporter, we screened H1-T6SS-secreted substrates and developed Tse6N as the most effective secretion tag for Cre delivery. DUEC cells can discriminately deliver the Tse6N–Cre cargo into the cytosol of T6SS+ but not T6SS– Vibrio cholerae cells. DUEC could also deliver a nuclease cargo, Tse6N–NucSe1, to selectively kill provoking cells in a mixed community. These data demonstrate that the DUEC cell not only is a prototypical physical-contact sensor and delivery platform but also may be coupled with recombination-based circuits with the potential for complex tasks in mixed microbial communities.
Significance How microbes respond to lethal attacks from competing species is not fully understood. Here, we investigated the response of Escherichia coli to attacks from the type VI secretion system (T6SS), bacteriophage P1 vir , and polymyxin B. We report that generation of reactive oxygen species (ROS) is a general outcome of potentially lethal activities mediated by contact-dependent or contact-independent interactions of aggressive competing bacterial species and phage. An ROS response gene, soxS , is highly induced in response to all sources of attacks tested. This discovery will likely prompt other investigations into why evolution has selected expression of this gene as a “first responder” to potentially lethal interspecies competition.
Abstract To recognize and manipulate a specific microbe of a crowded community is a highly challenging task in synthetic biology. Here, we introduce a highly-selective protein delivery platform, termed DUEC, which responds to direct contact of attacking cells by engineering the tit-for-tat/dueling response of H1-T6SS (type VI secretion system) in Pseudomonas aeruginosa . Using a Cre-recombinase-dependent reporter, we screened H1-T6SS secreted substrates and developed Tse6 N as the most effective secretion tag for Cre delivery. DUEC cells can discriminately deliver the Tse6 N -Cre cargo into the cytosol of T6SS + but not T6SS − Vibrio cholerae cells in a mixed population. These data demonstrate that the DUEC cell is not only a prototypical physical-contact sensor and delivery platform but also may be coupled with recombination-based circuits with the potential for complex tasks in mixed microbial communities.
The type VI secretion system (T6SS) is a lethal microbial weapon that injects a large needle-like structure carrying toxic effectors into recipient cells through physical penetration. How recipients respond to physical force and effectors remains elusive. Here, we use a series of effector mutants of Vibrio cholerae to determine how T6SS elicits response in Pseudomonas aeruginosa and Escherichia coli. We show that TseL, but no other effectors or physical puncture, triggers the tit-for-tat response of P. aeruginosa H1-T6SS. Although E. coli is sensitive to all periplasmically expressed effectors, P. aeruginosa is most sensitive to TseL alone. We identify a number of stress response pathways that confer protection against TseL. Physical puncture of T6SS has a moderate inhibitory effect only on envelope-impaired tolB and rseA mutants. Our data reveal that recipient cells primarily respond to effector toxicity but not to physical contact, and they rely on the stress response for immunity-independent protection.
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