Rhodopseudomonas palustris: A biotechnology chassis

Zero-valent iron as an alternative electron donor for extracellular electron uptake linked to CO2 fixation in Rhodopseudomonas palustris

Anoxygenic phototrophs oxidize both organic and inorganic electron donors for phototrophic fixation of CO2 without O2 generation, playing important roles in global carbon cycles. However, it remains unknown whether and how they can fix CO2 using zero-valent iron (ZVI) as solid-phase electron donor. This study investigated the feasibility of Fe0-driven CO2 fixation by the model bacteria Rhodopseudomonas palustris using nano- (nZVI) and micron-ZVI (mZVI). The results showed that ZVI could empower photoautotrophic and photoheterotrophic growth of R. palustris through iron biocorrosion, with CO2 fixation increased by up to 15%. The ZVI-driven CO2 fixation was attributed to H2-mediated extracellular electron uptake (EEU) and Fe(II) oxidation. The genes encoding EEU-associated pathways were up-regulated in the presence of ZVI, indicating that ZVI promoted CO2 fixation through direct transfer. However, ZVI cannot enable dark CO2 fixation. These findings highlighted the potential of ZVI as a solid electron donor for enhanced microbial CO2 fixation.

Electrochemical enhancement of the accumulation of photosensitive components in anoxygenic phototrophic bacteria extracellular: A new insight into the preparation of degradable microbial photosensitizer for water treatment

Extracellular polymeric substances (EPS) are promising biomaterials for environmental remediation, but their application is hindered by low production efficiency and limited pollutant degradation capacity. In this study, photosynthetic electron extraction enabled Rhodopseudomonas palustris (R. palustris) to efficiently produce EPS enriched with functionalized components. The enhanced EPS (0.2V-EPS), produced from electrically domesticated R. palustris, achieved an 82 % degradation rate of sulfamethoxazole (SMX) within 10 hours, an 18 % improvement compared to EPS produced under open-circuit conditions (OP-EPS). Mechanistic analysis revealed that photosynthetic electron extraction enriched EPS with photosensitive molecules, including tryptophan, humic acid, fulvic acid, which significantly promoted the generation of reactive species. The primary reactive species identified were triplet-excited EPS (³EPS*), ¹O₂, and •OH, with ¹O₂ as the dominant contributor to SMX degradation. The steady-state concentration of ³EPS*, ¹O₂, and •OH increased by 73 %, 34 % and 16 %, respectively, compared to the control. Structural modifications of 0.2V-EPS, including increased hydrophilicity, electronegativity, and aromaticity, enhance its physicochemical properties, thereby facilitating interactions with pollutants. Furthermore, an 88 % reduction in biofilm polysaccharides diminished free radical scavenging activity, promoting the generation of reactive species. This study provides a sustainable strategy for enhancing EPS functionality and offers insights into the metabolic regulation of microorganisms for pollutant degradation.

A Rhodopseudomonas strain with a substantially smaller genome retains the core metabolic versatility of its genus

Rhodopseudomonas are a group of phototrophic microbes with a marked metabolic versatility and flexibility that underpins their potential use in the production of value-added products, bioremediation, and plant growth promotion. Members of this group have an average genome size of about 5.5 Mb, but two closely related strains have genome sizes of about 4.0 Mb. To identify the types of genes missing in a reduced genome strain, we compared strain DSM127 with other Rhodopseudomonas isolates at the genomic and phenotypic levels. We found that DSM127 can grow as well as other members of the Rhodopseudomonas genus and retains most of their metabolic versatility, but it has many fewer genes associated with high-affinity transport of nutrients, iron uptake, nitrogen metabolism, and biodegradation of aromatic compounds. This analysis indicates genes that can be deleted in genome reduction campaigns and suggests that DSM127 could be a favorable choice for biotechnology applications using Rhodopseudomonas or as a strain that can be engineered further to reside in a specialized natural environment.IMPORTANCERhodopseudomonas are a cohort of phototrophic bacteria with broad metabolic versatility. Members of this group are present in diverse soil and water environments, and some strains are found associated with plants and have plant growth-promoting activity. Motivated by the idea that it may be possible to design bacteria with reduced genomes that can survive well only in a specific environment or that may be more metabolically efficient, we compared Rhodopseudomonas strains with typical genome sizes of about 5.5 Mb to a strain with a reduced genome size of 4.0 Mb. From this, we concluded that metabolic versatility is part of the identity of the Rhodopseudomonas group, but high-affinity transport genes and genes of apparent redundant function can be dispensed with.

Photoheterotrophic extracellular reduction of ferrihydrite activates diverse intracellular metabolic pathways in Rhodopseudomonas palustris for enhanced antibiotic degradation

Anoxygenic photosynthetic bacteria (APB) have been frequently detected as a photoautotrophic Fe-carbon cycling drivers in photic and anoxic environment. However, the potential capacity of these bacteria for photoheterotrophic extracellular reduction of iron-containing minerals and their impact on the transformation of organic pollutants remain currently unknown. This study investigated the capacity of R. palustris, a purple non-sulfur anoxygenic photosynthetic bacterium, to reduce ferrihydrite (Fh) and its correlation with sulfamethazine (SDZ) degradation were firstly investigated. The results revealed that R. palustris could undergo photoheterotrophic extracellular reduction of Fh to form goethite through direct contact, facilitating the formation of conductive bands and enter the interior of cells with a maximum Fe(II)/Fe(T) ratio of up to 39 % within 8 days which led to 13 % increase in assimilation rate of acetate carbon and 53.2 % increase in SDZ degradation rates, as compared with those by R. palustris alone. Moreover, the intermediates generated during the degradation of SDZ by R. palustris-Fh exhibited relatively lower developmental toxicity compared with the original SDZ molecule. The extracellular reduction of Fh significantly up-regulated the expression of genes related to photosynthetic metabolic enzymes, extracellular electron transporters, and extracellular degrading enzymes in R. palustris. This enhancement promoted the photoheterotrophic metabolism and extracellular secretion of photosensitive active compounds in R. palustris, thereby enhancing both the biodegradation and photosensitive degradation of SDZ.

Application of R. Palustris in simulated wastewater purification and the degradation mechanism of crystal violet

Azo dyes and triphenylmethane dyes poses a large threat to human health, There are many ways to degrade dyes while biodegraded are considered simpler, environmentally friendly, and economical. This study have researched the ability of Rhodopseudomonas palustris (R. palustris) to degrade multiple dyes. In this study, the ability of R. palustris to degrade multiple dyes was investigated. Specifically, the degradation efficiency of R. palustris for crystal violet (CV), malachite green (MG), congo red (CR), as well as COD, inorganic phosphorus, nitro, and nitroso compounds in simulated wastewater was evaluated using colorimetric methods. CV was selected for further analysis, and its intermediate metabolites were characterized using UV-vis spectroscopy, GC-MS, and HPLC-MS. Additionally, the gene expression levels of key enzymes involved in CV degradation were analyzed by RT-PCR, and a potential degradation pathway for CV was proposed. The results demonstrated that the degradation rates of CV, MG, and CR in simulated wastewater reached 97%, 92%, and 58%, respectively. Meanwhile, the degradation rates of COD, inorganic phosphorus, nitro, and nitroso compounds were up to 89.51%, 92.83%, 86.49%, and 85.91%, respectively. The intermediate metabolites of CV degradation by R. palustris included leucocrystal violet, triphenylmethane, and phenol. Notably, the gene expression levels of NADH-QO, NADH-FO, P450, Mett, and Nir were upregulated in the presence of CV. Based on these findings, a potential degradation pathway for CV by R. palustris was proposed: CV undergoes deamination via nitroreductase, followed by triphenylmethane cleavage into benzene and methylbenzene through oxidoreductases. Methylbenzene is then converted to phenol by methyltransferase. Although a potential degradation pathway for CV by R. palustris has been proposed, it remains a hypothesis. It still need to comprehensively investigate the genes associated with dye degradation in R. palustris through transcriptomics and to further validate the crystal violet degradation pathway proposed in this study.

Propionic acid enhances H2 production in purple phototrophic bacteria: Insights into carbon and reducing equivalent allocation

Biohydrogen is gaining popularity as a clean and cost-effective energy source. Among the various production methods, photo fermentation (PF) with purple phototrophic bacteria (PPB) has shown great opportunity due to its high hydrogen yield. In practice, this yield is influenced by several factors, with the carbon source, particularly simple organic acid, being a key element that has attracted considerable research interest. Short-chain volatile fatty acids (VFAs), such as acetate, propionate, and butyrate, are widely found in waste streams and dark fermentation (DF) effluent. However, most studies on these VFAs focus mainly on performance evaluation, with few exploring the underlying mechanisms, which limits their applicability in real-world scenarios. To uncover the metabolic mechanisms, this study uses metagenomics to clarify the processes of reducing power production and distribution during substrate assimilation. Meanwhile, this study presents the impact of short-chain VFAs on biohydrogen, polyhydroxyalkanoates (PHA) and glycogen production by PPB. The results show that: (1) over long-term cultivation at similar COD consumption rates of 0.06 g COD/d, PPB possessed the highest hydrogen yield when fed with propionate (0.620 L H2·g COD-1) compared with butyrate (0.434) and acetate (0.361); (2) with propionate as the substrate, PPB accumulated less PHA (7 % of dry biomass) but more glycogen content (11 %), compared to butyrate (15 % PHA and 8 % glycogen) and acetate (21 % PHA and 5 % glycogen); (3) metagenomic analysis revealed that propionate resulted in the highest amounts of reducing equivalents, followed by butyrate and acetate; hydrogen production was the most efficient pathway for utilizing the reducing power with propionate, as the CO2 fixation and PHA or glycogen synthesis were ineffective for electron dissipation. This study offers insights into metabolic mechanism that could guide waste stream selection and pretreatment processes to provide favorable VFAs for the PF process, thereby enhancing PPB biohydrogen production performance in practical applications.

Engineering a Photoautotrophic Microbial Coculture toward Enhanced Biohydrogen Production

The application of synthetic phototrophic microbial consortia holds promise for sustainable bioenergy production. Nevertheless, strategies for the efficient construction and regulation of such consortia remain challenging. Applying tools of genetic engineering, this study successfully constructed a synthetic community of phototrophs using Rhodopseudomonas palustris (R. palustris) and an engineered strain of Synechocystis sp PCC6803 for acetate production (Synechocystis_acs), enabling the production of biohydrogen and fatty acids during nitrogen and carbon dioxide fixation. Elemental balance confirmed carbon capture and nitrogen fixation into the consortium. The strategy of circadian illumination effectively limited oxygen levels in the system, ensuring the activity of the nitrogenase in R. palustris, despite oxygenic photosynthesis happening in Synechocystis. When infrared light was introduced into the circadian illumination, the production of H2 (9.70 μmol mg-1) and fatty acids (especially C16 and C18) was significantly enhanced. Proteomic analysis indicated acetate exchange and light-dependent regulation of metabolic activities. Infrared illumination significantly stimulated the expression of proteins coding for nitrogen fixation, carbohydrate metabolism, and transporters in R. palustris, while constant white light led to the most upregulation of photosynthesis-related proteins in Synechocystis_acs. This study demonstrated the successful construction and light regulation of a phototrophic community, enabling H2 and fatty acid production through carbon and nitrogen fixation.

Utilizing Microbial Electrochemical Methods to Enhance Lycopene Production in Rhodopseudomonas palustris

Utilizing Rhodopseudomonas palustris (R. pal), this study constructed a dual-chamber microbial electrosynthesis system, based on microbial electrolysis cells, that was capable of producing lycopene. Cultivation within the electrosynthesis chamber yielded a lycopene concentration of 282.3722 mg/L when the optical density (OD) reached 0.6, which was four times greater than that produced by original strains. The mutant strain showed significantly higher levels of extracted riboflavin compared to the wild-type strain, and the riboflavin content of the mutant strain was 61.081 mg/L, which was more than 10 times that of the original strain. Furthermore, sequencing and analyses were performed on the mutant strains observed during the experiment. The results indicated differences in antibiotic resistance genes, carbohydrate metabolism-related genes, and the frequencies of functional genes between the mutant and original strains. The mutant strain displayed potential advantages in specific antibiotic resistance and carbohydrate degradation capabilities, likely attributable to its adaptation to electrogenic growth conditions. Moreover, the mutant strain demonstrated an enrichment of gene frequencies associated with transcriptional regulation, signal transduction, and amino acid metabolism, suggesting a complex genetic adaptation to electrogenic environments. This study presents a novel approach for the efficient and energy-conserving production of lycopene while also providing deeper insights into the genetic basis of electro-resistance genes.

Biodegradation of organosulfur with extra carbon source: Insights into biofilm formation and bacterial metabolic processes

Organosulfur compounds are prevalent in wastewater, presenting challenges for biodegradation, particularly in low-carbon environments. Supplementing additional carbon sources not only provides essential nutrients for microbial growth but also serves as regulators, influencing adaptive changes in biofilm and enhancing the survival of microorganisms in organosulfur-induced stress bioreactors. This study aims to elucidate the biodegradation of organosulfur under varying carbon source levels, placing specific emphasis on functional bacteria and metabolic processes. It has been observed that higher levels of carbon supplementation led to significantly improved total sulfur (TS) removal efficiencies, exceeding 83 %, and achieve a high organosulfur CH3SH removal efficiency of ~100 %. However, in the reactor with no external carbon source added, the oxidation end-product SO42- accumulated significantly, surpassing 120 mEq/m2-day. Furthermore, the TB-EPS concentration consistently increasedwith the ascending glucose concentration. The analysis of bacterial community reveals the enrichment of functional bacteria involved in sulfur metabolism and biofilm formation (e.g. Ferruginibacter, Rhodopeudomonas, Gordonia, and Thiobacillus). Correspondingly, the gene expressions related to the pathway of organosulfur to SO42- were notably enhanced (e.g. MTO increased by 27.7 %). In contrast, extra carbon source facilitated the transfer of organosulfur into amino acids in sulfur metabolism and promoted assimilation. These metabolic insights, coupled with kinetic transformation results, further validate distinct sulfur pathways under different carbon source conditions. The intricate interplay between bacteria growth regulation, pollutant biodegradation, and microbial metabolites underscores a complex network relationship that significantly contributes to efficient operation of bioreactors.

Enhancing the biodegradation of hydrophobic volatile organic compounds: A study on microbial consortia adaptation and the role of surfactants

The emission of hydrophobic Volatile Organic Compounds (VOCs) is a serious environmental issue. Typically, biofilters (BFs) are employed for their treatment, with the potential enhancement of mass transfer through the addition of surfactants. However, disparate results in previous studies have been observed, attributed to uncontrolled conditions during the introduction of surfactants to BFs. Additionally, there has been limited exploration of microbial consortium adaptation to surfactants. To address these gaps, this study followed two approaches. First, the long-term (247 days) removal of cyclohexane was studied in a stirred tank bioreactor (STBR) inoculated with Rhodococcus erythropolys E1 and using Tween 80 at three times the critical micelle concentration (CMC). Second, the short-term (9 days) impact of two (bio)surfactants [Tween 80 (1 × CMC) and Quillaja Saponin (QS, 1 × CMC)] on the removal of cyclohexane, hexane and toluene was investigated in batch tests using three types of inocula: a pure culture of Rhodococcus erythropolys E1 (X0), a microbial consortium adapted to cyclohexane (X1), and a microbial consortium adapted to cyclohexane with Tween 80 (X2). For long-term operation, the addition of Tween 80 at 3 × CMC improved cyclohexane removal efficiency (RE) to 87 ± 1% (elimination capacity, EC = 145 ± 25 mg m-3 h-1, gas residence time, GRT = 20 min, inlet concentration, Cin = 14.9 ± 2.5 ppmv), compared to a RE of 32 ± 9% (EC = 44 ± 8 mg m-3 h-1, GRT = 20 min, Cin = 15.1 ± 0.7 ppmv) under similar conditions without surfactants. For short-term operation, the addition of QS at 1 × CMC significantly increased biomass growth, resulting in lower maximum specific consumption rates for X1 and X2 compared to scenarios without surfactants or 1 × CMC Tween 80. The most abundant genera in X1 and X2 were Paludisphaera (26-23%), 67-14 genus (17-23%), and Rhodococcus (9-18%), respectively.

Overexpression of RuBisCO form I and II genes in Rhodopseudomonas palustris TIE-1 augments polyhydroxyalkanoate production heterotrophically and autotrophically

With the rising demand for sustainable renewable resources, microorganisms capable of producing bioproducts such as bioplastics are attractive. While many bioproduction systems are well-studied in model organisms, investigating non-model organisms is essential to expand the field and utilize metabolically versatile strains. This investigation centers on Rhodopseudomonas palustris TIE-1, a purple non-sulfur bacterium capable of producing bioplastics. To increase bioplastic production, genes encoding the putative regulatory protein PhaR and the depolymerase PhaZ of the polyhydroxyalkanoate (PHA) biosynthesis pathway were deleted. Genes associated with pathways that might compete with PHA production, specifically those linked to glycogen production and nitrogen fixation, were deleted. Additionally, RuBisCO form I and II genes were integrated into TIE-1's genome by a phage integration system, developed in this study. Our results show that deletion of phaR increases PHA production when TIE-1 is grown photoheterotrophically with butyrate and ammonium chloride (NH4Cl). Mutants unable to produce glycogen or fix nitrogen show increased PHA production under photoautotrophic growth with hydrogen and NH4Cl. The most significant increase in PHA production was observed when RuBisCO form I and form I & II genes were overexpressed, five times under photoheterotrophy with butyrate, two times with hydrogen and NH4Cl, and two times under photoelectrotrophic growth with N2 . In summary, inserting copies of RuBisCO genes into the TIE-1 genome is a more effective strategy than deleting competing pathways to increase PHA production in TIE-1. The successful use of the phage integration system opens numerous opportunities for synthetic biology in TIE-1.IMPORTANCEOur planet has been burdened by pollution resulting from the extensive use of petroleum-derived plastics for the last few decades. Since the discovery of biodegradable plastic alternatives, concerted efforts have been made to enhance their bioproduction. The versatile microorganism Rhodopseudomonas palustris TIE-1 (TIE-1) stands out as a promising candidate for bioplastic synthesis, owing to its ability to use multiple electron sources, fix the greenhouse gas CO2, and use light as an energy source. Two categories of strains were meticulously designed from the TIE-1 wild-type to augment the production of polyhydroxyalkanoate (PHA), one such bioplastic produced. The first group includes mutants carrying a deletion of the phaR or phaZ genes in the PHA pathway, and those lacking potential competitive carbon and energy sinks to the PHA pathway (namely, glycogen biosynthesis and nitrogen fixation). The second group comprises TIE-1 strains that overexpress RuBisCO form I or form I & II genes inserted via a phage integration system. By studying numerous metabolic mutants and overexpression strains, we conclude that genetic modifications in the environmental microbe TIE-1 can improve PHA production. When combined with other approaches (such as reactor design, use of microbial consortia, and different feedstocks), genetic and metabolic manipulations of purple nonsulfur bacteria like TIE-1 are essential for replacing petroleum-derived plastics with biodegradable plastics like PHA.

Deciphering the differentiated performance on electricity generation and COD degradation by Rhodopseudomonas-dominated bioanode in light or dark

Anoxygenic phototrophic bacteria is a promising catalyst for constructing bioanode, but the mixed culture with non-photosynthetic bacteria is inevitable in an open environment application. In this study, a Rhodopseudomonas-dominated mixed culture with other electrogenic bacteria was investigated for deciphering the differentiated performance on electricity generation in light or dark conditions. The kinetic study showed that reaction rate of OM degradation was 9 times higher than that under dark condition, demonstrating that OM degradation was enhanced by photosynthesis. However, CE under light condition was lower. It indicated that part of OM was used to provide hydrogen donors for the fixation of CO2 or hydrogen production in photosynthesis, decreasing the OM used for electron transfer. In addition, higher COD concentration was not conducive to electricity generation. EIS analysis demonstrated that higher OM concentration would increase Rct to hinder the transfer of electrons from bacteria to the electrode. Indirect and direct electron transfer were revealed by CV analysis for light and dark biofilm, respectively, and nanowires were also observed by SEM graphs, further revealing the differentiate performance. Microbial community analysis demonstrated Rhodopseudomonas was dominated in light and decreased in dark, but Geobacter increased apparently from light to dark, resulting in different power generation performance. The findings revealed the differentiated performance on electricity generation and pollutant removal by mixed culture of phototrophic bacteria in light or dark, which will improve the power generation from photo-microbial fuel cells.

Interactions of Brominated Flame Retardants with Membrane Models of Dehalogenating Bacteria: Langmuir Monolayer and Grazing Incidence X-ray Diffraction Studies

Brominated flame retardants (BFRs) are small organic molecules containing several bromine substituents added to plastics to limit their flammability. BFRs can constitute up to 30% of the weight of some plastics, which is why they are produced in large quantities. Along with plastic waste and microplastic particles, BFRs end up in the soil and can easily leach causing contamination. As polyhalogenated molecules, multiple BFRs were classified as persistent organic pollutants (POPs), meaning that their biodegradation in the soils is especially challenging. However, some anaerobic bacteria as Dehaloccocoides can dehalogenate BFRs, which is important in the bioremediation of contaminated soils. BFRs are hydrophobic, can accumulate in plasma membranes, and disturb their function. On the other hand, limited membrane accumulation is necessary for BFR dehalogenation. To study the BFR-membrane interaction, we created membrane models of soil dehalogenating bacteria and tested their interactions with seven legacy and novel BFRs most common in soils. Phospholipid Langmuir monolayers with appropriate composition were used as membrane models. These membranes were doped in the selected BFRs, and the incorporation of BFR molecules into the phospholipid matrix and also the effects of BFR presence on membrane physical properties and morphology were studied. It turned out that the seven BFRs differed significantly in their membrane affinity. For some, the incorporation was very limited, and others incorporated effectively and could affect membrane properties, while one of the tested molecules induced the formation of bilayer domains in the membranes. Thus, Langmuir monolayers can be effectively used for pretesting BFR membrane activity.

The production, recovery, and valorization of polyhydroxybutyrate (PHB) based on circular bioeconomy

As an energy-storage substance of microorganisms, polyhydroxybutyrate (PHB) is a promising alternative to petrochemical polymers. Under appropriate fermentation conditions, PHB-producing strains with metabolic diversity can efficiently synthesize PHB using various carbon sources. Carbon-rich wastes may serve as alternatives to pure sugar substrates to reduce the cost of PHB production. Genetic engineering strategies can further improve the efficiency of substrate assimilation and PHB synthesis. In the downstream link, PHB recycling strategies based on green chemistry concepts can replace PHB extraction using chlorinated solvents to enhance the economics of PHB production and reduce the potential risks of environmental pollution and health damage. To avoid carbon loss caused by biodegradation in the traditional sense, various strategies have been developed to degrade PHB waste into monomers. These monomers can serve as platform chemicals to synthesize other functional compounds or as substrates for PHB reproduction. The sustainable potential and cycling value of PHB are thus reflected. This review summarized the recent progress of strains, substrates, and fermentation approaches for microbial PHB production. Analyses of available strategies for sustainable PHB recycling were also included. Furthermore, it discussed feasible pathways for PHB waste valorization. These contents may provide insights for constructing PHB-based comprehensive biorefinery systems.

A novel alginate-embedded magnetic biochar-anoxygenic photosynthetic bacteria composite microspheres for multipollutant removal: Mechanisms of photo-bioelectrochemical enhancement and excellent reusability performance

Existing wastewater treatment technologies face the key challenge of simultaneously removing emerging contaminants and nutrients from wastewater efficiently, with a simplified technological process and minimized operational costs. In this study, a novel alginate-embedded magnetic biochar-anoxygenic photosynthetic bacteria composite microspheres (CA-MBC-PSB microspheres) was prepared for efficient, cost-effective and one-step removal of antibiotics and NH4+-N from wastewater. Our results demonstrated that the CA-MBC-PSB microspheres removed 97.23% of sulfadiazine (SDZ) within 7 h and 91% of NH4+-N within 12 h, which were 21.23% and 38% higher than those achieved by pure calcium alginate-Rhodopseudomonas palustris microspheres (53% and 45.7%), respectively. The enhanced SDZ and NH4+-N removal were attributed to the enhanced photoheterotrophic metabolism and excretion of extracellular photosensitive active substances from R. Palustris through the photo-bioelectrochemical interaction between R. Palustris and magnetic biochar. The long-term pollutants removal performance of the CA-MBC-PSB microspheres was not deteriorated but continuously improved with increasing ruse cycles with a simultaneous removal efficiency of 99% for SDZ and 92% for NH4+-N after three cycles. The excellent stability and reusability were due to the fact that calcium alginate acts as an encapsulating agent preventing the loss and contamination of R. palustris biomass. The CA-MBC-PSB microspheres also exhibited excellent performance for simultaneous removal of SDZ (89% in 7 h) and NH4+-N (90.7% in 12 h) from the secondary effluent of wastewater treatment plant, indicating the stable and efficient performance of CA-MBC-PSB microspheres in practical wastewater treatment.

Biosurfactant potential and antiviral activity of multistrain probiotics

The COVID-19 caused by the SARS-CoV-2 has become a great threat to humans. However, there is no recommendation for an effective and safe drug to treat the disease. The strategy developed in this study is to utilize biosurfactant potential activity of Lactobacillus spp. and Rhodopseudomonas palustris probiotics to prevent the virus from entering human body. The outer membrane of the virus is comprising of phospholipid compounds. Biosurfactants, are known to have detergent-like properties (able to dissolve lipids) that are safe for in vivo use. Thus, the biosurfactant potential activity of the multistrain probiotics extract is expected to be able to disrupt the phospholipid membrane, resulting in the inactivity of the virus to infect human body. The biosurfactant potential activity of the probiotics extract was evaluated using oil spreading, drop collapse, and emulsification methods. The virus infectivity was evaluated on the SARS-CoV-2 of delta variant as a virus model. The results indicated that the probiotics extract has biosurfactant potential activity, able to inhibit virus growth up to 99.9 % within 48 h in the prevention platform, and up to 99.6 % within 48 h in the treatment platform. Therefore, the multistrain probiotics extract was identified to have potential as a promising antiviral agent.

Purification mechanism of microbial metabolism in kitchen-oil wastewater enhanced by cationic vacancies on γ-Al2O3

The use of catalyst materials to mediate the enhancement of microbial degradation in wastewater is a new economic and energy saving breakthrough in water treatment technology. In this study, γ-Al2O3, which is commonly used as catalyst/carrier, is used as biological filler to treat kitchen-oil wastewater with low biodegradability, and the COD removal rate is about 50 %. It is found that the complexation of cationic vacancies on Al2O3 surface with extracellular polymeric substance (EPS) secreted by microorganisms in wastewater lead to the polarization of electron distribution on biofilm. The efficient degrading bacteria are enriched on reaction interface and obtain electrons to maintain electron dynamic balance by enhancing the transmembrane metabolism of pollutants. The aluminum vacancies on Al2O3 surface accelerate the microbial degradation of pollutants. The cationic vacancies in the structure of catalyst accelerate the acquisition of exogenous electrons by microorganisms without the addition of external energy, which provides a new idea for catalytic fillers to enhance wastewater degradation.

Microbial degradation and transformation of PPCPs in aquatic environment: A review

The Pharmaceuticals and Personal Care Products (PPCPs) presence at harmful levels has been identified in aquatic ecosystems all over the world. Currently, PPCPs are more common in aquatic regions and have been discovered to be extremely harmful to aquatic creatures. Waste-water treatment facilities are the primary cause of PPCPs pollution in aquatic systems due to their limited treatment as well as the following the release of PPCPs. The degree of PPCPs elimination is primarily determined by the method applied for the remediation. It must be addressed in an eco-friendly manner in order to significantly improve the environmental quality or, at the very least, to prevent the spread as well as effects of toxic pollutants. However, when compared to other methods, environmentally friendly strategies (biological methods) are less expensive and require less energy. Most biological methods under aerobic conditions have been shown to degrade PPCPs effectively. Furthermore, the scientific literature indicates that with the exception of a few extremely hydrophobic substances, biological degradation by microbes is the primary process for the majority of PPCPs compounds. Hence, this review discusses about the optimistic role of microbe concerned in the degradation or transformation of PPCPs into non/less toxic form in the polluted environment. Accordingly, more number of microbial strains has been implicated in the biodegradation/transformation of harmful PPCPs through a process termed as bioremediation and their limitations.

The genome-scale metabolic model for the purple non-sulfur bacterium Rhodopseudomonas palustris Bis A53 accurately predicts phenotypes under chemoheterotrophic, chemoautotrophic, photoheterotrophic, and photoautotrophic growth conditions

The purple non-sulfur bacterium Rhodopseudomonas palustris is recognized as a critical microorganism in the nitrogen and carbon cycle and one of the most common members in wastewater treatment communities. This bacterium is metabolically extremely versatile. It is capable of heterotrophic growth under aerobic and anaerobic conditions, but also able to grow photoautotrophically as well as mixotrophically. Therefore R. palustris can adapt to multiple environments and establish commensal relationships with other organisms, expressing various enzymes supporting degradation of amino acids, carbohydrates, nucleotides, and complex polymers. Moreover, R. palustris can degrade a wide range of pollutants under anaerobic conditions, e.g., aromatic compounds such as benzoate and caffeate, enabling it to thrive in chemically contaminated environments. However, many metabolic mechanisms employed by R. palustris to breakdown and assimilate different carbon and nitrogen sources under chemoheterotrophic or photoheterotrophic conditions remain unknown. Systems biology approaches, such as metabolic modeling, have been employed extensively to unravel complex mechanisms of metabolism. Previously, metabolic models have been reconstructed to study selected capabilities of R. palustris under limited experimental conditions. Here, we developed a comprehensive metabolic model (M-model) for R. palustris Bis A53 (iDT1294) consisting of 2,721 reactions, 2,123 metabolites, and comprising 1,294 genes. We validated the model using high-throughput phenotypic, physiological, and kinetic data, testing over 350 growth conditions. iDT1294 achieved a prediction accuracy of 90% for growth with various carbon and nitrogen sources and close to 80% for assimilation of aromatic compounds. Moreover, the M-model accurately predicts dynamic changes of growth and substrate consumption rates over time under nine chemoheterotrophic conditions and demonstrated high precision in predicting metabolic changes between photoheterotrophic and photoautotrophic conditions. This comprehensive M-model will help to elucidate metabolic processes associated with the assimilation of multiple carbon and nitrogen sources, anoxygenic photosynthesis, aromatic compound degradation, as well as production of molecular hydrogen and polyhydroxybutyrate.

Protein Interactions in Rhodopseudomonas palustris TIE-1 Reveal the Molecular Basis for Resilient Photoferrotrophic Iron Oxidation

Rhodopseudomonas palustris is an alphaproteobacterium with impressive metabolic versatility, capable of oxidizing ferrous iron to fix carbon dioxide using light energy. Photoferrotrophic iron oxidation is one of the most ancient metabolisms, sustained by the pio operon coding for three proteins: PioB and PioA, which form an outer-membrane porin-cytochrome complex that oxidizes iron outside of the cell and transfers the electrons to the periplasmic high potential iron-sulfur protein (HIPIP) PioC, which delivers them to the light-harvesting reaction center (LH-RC). Previous studies have shown that PioA deletion is the most detrimental for iron oxidation, while, the deletion of PioC resulted in only a partial loss. The expression of another periplasmic HiPIP, designated Rpal_4085, is strongly upregulated in photoferrotrophic conditions, making it a strong candidate for a PioC substitute. However, it is unable to reduce the LH-RC. In this work we used NMR spectroscopy to map the interactions between PioC, PioA, and the LH-RC, identifying the key amino acid residues involved. We also observed that PioA directly reduces the LH-RC, and this is the most likely substitute upon PioC deletion. By contrast, Rpal_4085 demontrated significant electronic and structural differences from PioC. These differences likely explain its inability to reduce the LH-RC and highlight its distinct functional role. Overall, this work reveals the functional resilience of the pio operon pathway and further highlights the use of paramagnetic NMR for understanding key biological processes.

Improving bioplastic production by Rhodopseudomonas palustris TIE-1 using synthetic biology and metabolic engineering

With the increasing demand for sustainably produced renewable resources, it is important to look towards microorganisms capable of producing bioproducts such as biofuels and bioplastics. Though many systems for bioproduct production are well documented and tested in model organisms, it is essential to look beyond to non-model organisms to expand the field and take advantage of metabolically versatile strains. This investigation centers on Rhodopseudomonas palustris TIE-1, a purple, non-sulfur autotrophic, and anaerobic bacterium capable of producing bioproducts that are comparable to their petroleum-based counterparts. To induce bioplastic overproduction, genes that might have a potential role in the PHB biosynthesis such as the regulator, phaR, and phaZ known for its ability to degrade PHB granules were deleted using markerless deletion. Mutants in pathways that might compete with polyhydroxybutyrate (PHB) production such as glycogen and nitrogen fixation previously created to increase n -butanol production by TIE-1 were also tested. In addition, a phage integration system was developed to insert RuBisCO (RuBisCO form I and II genes) driven by a constitutive promoter P _aphII into TIE- 1 genome. Our results show that deletion of the phaR gene of the PHB pathway increases PHB productivity when TIE-1 was grown photoheterotrophically with butyrate and ammonium chloride (NH ₄ Cl). Mutants unable to make glycogen or fix dinitrogen gas show an increase in PHB productivity under photoautotrophic growth conditions with hydrogen. In addition, the engineered TIE-1 overexpressing RuBisCO form I and form II produces significantly more polyhydroxybutyrate than the wild type under photoheterotrophy with butyrate and photoautotrophy with hydrogen. Inserting RuBisCO genes into TIE-1 genome is a more effective strategy than deleting competitive pathways to increase PHB production in TIE-1. The phage integration system developed for TIE-1 thus creates numerous opportunities for synthetic biology in TIE-1.

Performance of production of polyhydroxyalkanoates from food waste fermentation with Rhodopseudomonas palustris

The use of waste as a carbon source can significantly reduce the cost of production of Polyhydroxyalkanoates (PHAs). In this study, an acidified hydrolysate solution derived from food waste (FW) was used as a carbon source for the synthesis of PHAs by Rhodopseudomonas palustris (R. palustris) and optimized the process parameters. The results showed that the PHAs yield reached 48.62% under optimal conditions (an incubation time of 30 days, volatile fatty acids (VFAs) in substrate concentration of 2202.21 mg⋅L^-1, an initial pH of 8.0, and inoculum concentration of 15%). The fraction of VFAs affects the composition of PHAs, R. palustris first uses VFAs with an even number of carbons to synthesize poly(3-hydroxybutyrate)(3HB), and later uses VFAs with an odd number of carbons to synthesize poly-3-hydroxyvalerate (3HV). Pathways for the synthesis of PHAs by R. palustris were inferred. R. palustris is a strain with the potential to synthesize PHAs.

Light-dependent biohydrogen production: Progress and perspectives

The fourth industrial revolution anticipates energy to be sustainable, renewable and green. Hydrogen (H₂) is one of the green forms of energy and is deemed a possible solution to climate change. Light-dependent H₂ production is a promising method derived from nature's most copious resources: solar energy, water and biomass. Reduced environmental impacts, absorption of carbon dioxide, relative efficiency, and cost economics made it an eye-catching approach. However, low light conversion efficiency, limited ability to utilize complex carbohydrates, and the O₂ sensitivity of enzymes result in low yield. Isolation of efficient H₂ producers, development of microbial consortia having a synergistic impact, genetically improved strains, regulating bidirectional hydrogenase activity, physiological parameters, immobilization, novel photobioreactors, and additive strategies are summarized for their possibilities to augment the processes of bio-photolysis and photo-fermentation. The challenges and future perspectives have been addressed to explore a sustainable way forward in a bio-refinery approach.

Lumichrome from the photolytic riboflavin acts as an electron shuttle in microbial photoelectrochemical systems

Riboflavin has been proposed to serve as an electron shuttle in photoelectrochemical systems. However, riboflavin was also observed for abiotic photolysis under illumination. Such conflicting reports raise the necessity for further investigation. In this study, riboflavin secreted by Rhodopseudomonas palustris was studied to clarify its stability and electron shuttle function under illumination. The data of high-performance liquid chromatography-mass spectrometry showed that the riboflavin was photolyzed to lumichrome in microbial photoelectrochemical systems. In addition, the anodic current increased by 75% after adding lumichrome compared with that of the control; it further demonstrated that lumichrome, not riboflavin, as an electron shuttle could facilitate microbial electron transfer. This study clarifies the mechanism of the interface process in microbial photoelectrochemical systems.

Effects of Mineral on Taxonomic and Functional Structures of Microbial Community in Tengchong Hot Springs via in-situ cultivation

Diverse mineralogical compositions occur in hot spring sediments, but the impact of minerals on the diversity and structure of microbial communities remains poorly elucidated. In this study, different mineral particles with various chemistries (i.e., hematite, biotite, K-feldspar, quartz, muscovite, aragonite, serpentine, olivine, barite, apatite, and pyrite) were incubated for ten days in two Tengchong hot springs, one alkaline (pH ~ 8.34) with a high temperature (~ 82.8 °C) (Gumingquan, short as GMQ) and one acidic (pH ~ 3.63) with a relatively low temperature (~ 43.3 °C) (Wenguangting, short as WGT), to determine the impacts of minerals on the microbial communities taxonomic and functional diversities. Results showed that the mineral-associated bacterial taxa differed from those of the bulk sediment samples in the two hot springs. The relative abundance of Proteobacteria, Euryarchaeota, and Acidobacteria increased in all minerals, indicating that these microorganisms are apt to colonize on solid surfaces. The α-diversity indices of the microbial communities on the mineral surfaces in the WGT were higher than those from the bulk sediment samples (p < 0.05), which may be caused by the stochastically adhering process on the mineral surface during 10-day incubation, different from the microbial community in sediment which has experienced long-term environmental and ecological screening. Chemoheterotrophy increased with minerals incubation, which was high in most cultured minerals (the relative contents were 5.8 - 21.4%). Most notably, the sulfate respiration bacteria (mainly related to Desulfobulbaceae and Syntrophaceae) associated with aragonite in the acidic hot spring significantly differed from other minerals, possibly due to the pH buffering effect of aragonite providing more favorable conditions for their survival and proliferation. By comparison, aragonite cultured in the alkaline hot spring highly enriched denitrifying bacteria and may have promoted the nitrogen cycle within the system. Collectively, we speculated that diverse microbes stochastically adhered on the surface of minerals in the water flows, and the physicochemical properties of minerals drove the enrichment of certain microbial communities and functional groups during the short-term incubation. Taken together, these findings thereby provide novel insights into mechanisms of community assembly and element cycling in the terrestrial hydrothermal system associated with hot springs.

Recent Applications and Strategies to Enhance Performance of Electrochemical Reduction of CO2 Gas into Value-Added Chemicals Catalyzed by Whole-Cell Biocatalysts

Carbon dioxide (CO2) is one of the major greenhouse gases that has been shown to cause global warming. Decreasing CO2 emissions plays an important role to minimize the impact of climate change. The utilization of CO2 gas as a cheap and sustainable source to produce higher value-added chemicals such as formic acid, methanol, methane, and acetic acid has been attracting much attention. The electrochemical reduction of CO2 catalyzed by whole-cell biocatalysts is a promising process for the production of value-added chemicals because it does not require costly enzyme purification steps and the supply of exogenous cofactors such as NADH. This study covered the recent applications of the diversity of microorganisms (pure cultures such as Shewanella oneidensis MR1, Sporomusa species, and Clostridium species and mixed cultures) as whole-cell biocatalysts to produce a wide range of value-added chemicals including methane, carboxylates (e.g., formate, acetate, butyrate, caproate), alcohols (e.g., ethanol, butanol), and bioplastics (e.g., Polyhydroxy butyrate). Remarkably, this study provided insights into the molecular levels of the proteins/enzymes (e.g., formate hydrogenases for CO2 reduction into formate and electron-transporting proteins such as c-type cytochromes) of microorganisms which are involved in the electrochemical reduction of CO2 into value-added chemicals for the suitable application of the microorganism in the chemical reduction of CO2 and enhancing the catalytic efficiency of the microorganisms toward the reaction. Moreover, this study provided some strategies to enhance the performance of the reduction of CO2 to produce value-added chemicals catalyzed by whole-cell biocatalysts.

ATP Is a Major Determinant of Phototrophic Bacterial Longevity in Growth Arrest

How bacteria transition into growth arrest as part of stationary phase has been well-studied, but our knowledge of features that help cells to stay alive in the following days and weeks is incomplete. Most studies have used heterotrophic bacteria that are growth-arrested by depletion of substrates used for both biosynthesis and energy generation, making is difficult to disentangle the effects of the two. In contrast, when grown anaerobically in light, the phototrophic bacterium Rhodopseudomonas palustris generates ATP from light via cyclic photophosphorylation, and builds biomolecules from organic substrates, such as acetate. As such, energy generation and carbon utilization are independent from one another. Here, we compared the physiological and molecular responses of R. palustris to growth arrest caused by carbon source depletion in light (energy-replete) and dark (energy-depleted) conditions. Both sets of cells remained viable for 6 to 10 days, at which point dark-incubated cells lost viability, whereas light-incubated cells remained fully viable for 60 days. Dark-incubated cells were depleted in intracellular ATP prior to losing viability, suggesting that ATP depletion is a cause of cell death. Dark-incubated cells also shut down measurable protein synthesis, whereas light-incubated cells continued to synthesize proteins at low levels. Cells incubated in both conditions continued to transcribe genes. We suggest that R. palustris may completely shut down protein synthesis in dark, energy-depleted, conditions as a strategy to survive the nighttime hours of day/night cycles it experiences in nature, where there is a predictable source of energy in the form of sunlight only during the day. IMPORTANCE The molecular and physiological basis of bacterial longevity in growth arrest is important to investigate for several reasons. Such investigations could improve treatment of chronic infections, advance use of non-growing bacteria as biocatalysts to make high yields of value-added products, and improve estimates of microbial activities in natural habitats, where cells are often growing slowly or not at all. Here, we compared survival of the phototrophic bacterium Rhodopseudomonas palustris under conditions where it generates ATP (incubation in light), and where it does not generate ATP (incubation in dark) to directly assess effects of energy depletion on long-term viability. We found that ATP is important for long-term survival over weeks. However, R. palustris survives 12 h periods of ATP depletion without loss of viability, apparently in anticipation of sunrise and restoration of its ability to generate ATP. Our work suggests that cells respond to ATP depletion by shutting down protein synthesis.

Self-Adaptive Antibacterial Scaffold with Programmed Delivery of Osteogenic Peptide and Lysozyme for Infected Bone Defect Treatment

Bone defects caused by disease or trauma are often accompanied by infection, which severely disrupts the normal function of bone tissue at the defect site. Biomaterials that can simultaneously reduce inflammation and promote osteogenesis are effective tools for addressing this problem. In this study, we set up a programmed delivery platform based on a chitosan scaffold to enhance its osteogenic activity and prevent implant-related infections. In brief, the osteogenic peptide sequence (YGFGG) was modified onto the surface of cowpea chlorotic mottle virus (CCMV) to form CCMV-YGFGG nanoparticles. CCMV-YGFGG exhibited good biocompatibility and osteogenic ability in vitro. Then, CCMV-YGFGG and lysozyme were loaded on the chitosan scaffold, which exhibited a good antibacterial effect and promoted bone regeneration for infected bone defect treatment. As a delivery platform, the scaffold showed staged release of lysozyme and CCMV-YGFGG, which facilitates the regeneration of infected bone defects. Our study provides a novel and promising strategy for the treatment of infected bone defects.