Phototrophic utilization of taurine by the purple nonsulfur bacteria Rhodopseudomonas palustris and Rhodobacter sphaeroides

Functional microorganisms in hydrogen production: Mechanisms and applications

The rapid growth of global energy demand accelerates the development of sustainable, clean, and renewable energy sources. Biohydrogen production, driven by functional microorganisms, offers a promising solution. Multiple species of bacteria, fungi, microalgae, and archaea were able to produce hydrogen. This study reviewed the typical strains, together with their hydrogen-production mechanisms, e.g., bio-photolysis, photo fermentation, and dark fermentation. Bacteria (e.g., purple non-sulfur bacteria) and microalgae (e.g., cyanobacteria) have been widely investigated, with respect to the limited fungi and archaea. It showed that temperature, pH, and substrate availability could all substantially influence the efficiency of biohydrogen production. Meanwhile, photo and dark fermentations are favored for future possible industrial applications. Furthermore, this review summarized practical applications of biohydrogen production, such as applications of bioreactors, waste treatments, and integrated systems for hydrogen production, highlighting the importance of functional microorganisms in advancing biohydrogen technology under global energy crisis.

Characteristics and Application of Rhodopseudomonas palustris as a Microbial Cell Factory

Rhodopseudomonas palustris, a purple nonsulfur bacterium, is a bacterium with the properties of extraordinary metabolic versatility, carbon source diversity and metabolite diversity. Due to its biodetoxification and biodegradation properties, R. palustris has been traditionally applied in wastewater treatment and bioremediation. R. palustris is rich in various metabolites, contributing to its application in agriculture, aquaculture and livestock breeding as additives. In recent years, R. palustris has been engineered as a microbial cell factory to produce valuable chemicals, especially photofermentation of hydrogen. The outstanding property of R. palustris as a microbial cell factory is its ability to use a diversity of carbon sources. R. palustris is capable of CO₂ fixation, contributing to photoautotrophic conversion of CO₂ into valuable chemicals. R. palustris can assimilate short-chain organic acids and crude glycerol from industrial and agricultural wastewater. Lignocellulosic biomass hydrolysates can also be degraded by R. palustris. Utilization of these feedstocks can reduce the industry cost and is beneficial for environment. Applications of R. palustris for biopolymers and their building blocks production, and biofuels production are discussed. Afterward, some novel applications in microbial fuel cells, microbial electrosynthesis and photocatalytic synthesis are summarized. The challenges of the application of R. palustris are analyzed, and possible solutions are suggested.

The adherence-associated Fdp fasciclin I domain protein of the biohydrogen producer Rhodobacter sphaeroides is regulated by the global Prr pathway

Expression of fdp, encoding a fasciclin I domain protein important for adherence in the hydrogen-producing bacterium Rhodobacter sphaeroides, was investigated under a range of conditions to gain insights into optimization of adherence for immobilization strategies suitable for H₂ production. The fdp promoter was linked to a lacZ reporter and expressed in wild type and in PRRB and PRRA mutant strains of the Prr regulatory pathway. Expression was significantly negatively regulated by Prr under all conditions of aerobiosis tested including anaerobic conditions (required for H₂ production), and aerobically regardless of growth phase, growth medium complexity or composition, carbon source, heat and cold shock and dark/light conditions. Negative fdp regulation by Prr was reflected in cellular levels of translated Fdp protein. Since Prr is required directly for nitrogenase expression, we propose optimization of Fdp-based adherence in R. sphaeroides for immobilized biohydrogen production by inactivation of the PrrA binding site(s) upstream of fdp.

Photosynthetic bacteria-based technology is a potential alternative to meet sustainable wastewater treatment requirement?

A paradigm shift is underway in wastewater treatment from pollution removal to resource or energy recovery. However, conventional activated sludge (CAS) as the core technology of wastewater treatment is confronted with severe challenges on high energy consumption, sludge disposal and inevitable greenhouse gas emission, which are posing a serious impact on the current wastewater industry. It is urgent to find new alternative methods to remedy these defects. Photosynthetic bacteria (PSB) have flexible metabolic modes and high tolerance, which enhance the removal of nutrients, heavy metals and organic contaminants efficiency in different wastewater. The unique phototrophic growth of PSB breaks the restriction of nutrient metabolism in the CAS system. Recent studies have shown that PSB-based technologies can not only achieve the recovery of nutrient and energy, but also improve the degradation efficiency of refractory substances. If the application parameters can be determined, there will be great prospects and economic effects. This review summarizes the research breakthroughs and application promotion of PSB-based wastewater treatment technology in recent years. Comparing discussed the superiority and inferiority from the perspective of application range, performance differences and recovery possibility. Pathways involved in the nutrient substance and the corresponding influencing parameters are also described in detail. The mode of PSB biodegradation processes presented a promising alternative for new wastewater treatment scheme. In the future, more mechanical and model studies, deterministic operating parameters, revolutionary process design is need for large-scale industrial promotion of PSB-based wastewater treatment.

Simultaneous treatment and single cell protein production from agri-industrial wastewaters using purple phototrophic bacteria or microalgae - A comparison

Resource recovery, preferably as high value products, is becoming an integral part of modern wastewater treatment, with conversion to heterotrophic or phototrophic/photosynthetic microbes a key option to minimise dissipation, and maximise recovery. This study compares the treatment capacities of purple phototrophic bacteria (PPB) and microalgae of five agri-industrial wastewaters (pork, poultry, red meat, dairy and sugar) to recover carbon, nitrogen, and phosphorous as a microbial product. The mediators have different advantages, with PPB offering moderate removals (up to 74% COD, 80% NH₄-N, 55% PO₄-P) but higher yields (>0.75 gCOD_removed gCOD_added^-1) and a more consistent, PPB dominated (>50%) product, with a higher crude protein product (>0.6 gCP gVSS^-1). The microalgae tests achieved a better removal outcome (up to 91%COD, 91% NH₄-N, 73%PO₄-P), but with poorer quality product, and <30% abundance as algae.

Growth performance and immunological and antioxidant status of Chinese shrimp, Fennerpenaeus chinensis reared in bio-floc culture system using probiotics

Chinese shrimp Fennerpenaeus chinensis (mean length 1.86 ± 0.15 cm, and weight 137.4 ± 12.7 mg) were reared in the different concentrations of bio-floc (control, 60, 80, 100, 120, and 140%) for 90 days. The growth rate was significantly increased over 100% bio-floc concentrations. In the immunological parameters, the gene expression of proPO and lysozyme was considerably increased over 120% bio-floc concentrations. The gene expression of SP was notably elevated at 140% bio-floc concentration. In the antioxidant enzymes, the activity of SOD was considerably decreased over 80% bio-floc concentrations. A notable decline in the activity of CAT was observed over 120% bio-floc concentrations. The results indicate that rearing of Chinese shrimp in bio-floc system can induce the increase of growth performance, enhancement of immune responses, and reduction of oxidative stress.

Characterization of Rhodopseudomonas palustris strain 2C as a potential probiotic

Photosynthetic bacteria (PSB) are prokaryotes that first appeared on the earth 2 billion years ago. Being rich in nutrients and having unique biological transformational function, PSB have been used as medicinal ingredients and healthcare products. However, there is insufficient information about the probiotic properties of PSB. The aim of this study was to characterize the potential probiotic properties of Rhodopseudomonas palustris strain 2C. The tolerance of strain 2C to low pH, high bile salt and simulated gastrointestinal conditions was determined. The susceptibility of strain 2C to 11 antibiotics was screened. The in vitro antioxidative activity and acute toxicity of strain 2C were performed. The survival duration of strain 2C after it had been repeatedly ingested by Wistar rats was determined. Strain 2C was tolerant to low pH, high bile salt concentration, and simulated gastrointestinal conditions. Strain 2C was only resistant to two of the 11 tested antibiotics (penicillin and ampicillin), and it showed antioxidative activity in vitro. When ingested by rats, strain 2C did not cause any bacteria translocation or tissue damage. The survival duration of strain 2C depending on doses ingested by the rats, 3 days after the termination of intake, it could no longer be enriched from the feces. Taken together, these findings indicate that strain 2C may be a potential probiotic strain.

iRsp1095: a genome-scale reconstruction of the Rhodobacter sphaeroides metabolic network

BACKGROUND

Rhodobacter sphaeroides is one of the best studied purple non-sulfur photosynthetic bacteria and serves as an excellent model for the study of photosynthesis and the metabolic capabilities of this and related facultative organisms. The ability of R. sphaeroides to produce hydrogen (H₂), polyhydroxybutyrate (PHB) or other hydrocarbons, as well as its ability to utilize atmospheric carbon dioxide (CO₂) as a carbon source under defined conditions, make it an excellent candidate for use in a wide variety of biotechnological applications. A genome-level understanding of its metabolic capabilities should help realize this biotechnological potential.

RESULTS

Here we present a genome-scale metabolic network model for R. sphaeroides strain 2.4.1, designated iRsp1095, consisting of 1,095 genes, 796 metabolites and 1158 reactions, including R. sphaeroides-specific biomass reactions developed in this study. Constraint-based analysis showed that iRsp1095 agreed well with experimental observations when modeling growth under respiratory and phototrophic conditions. Genes essential for phototrophic growth were predicted by single gene deletion analysis. During pathway-level analyses of R. sphaeroides metabolism, an alternative route for CO₂ assimilation was identified. Evaluation of photoheterotrophic H2 production using iRsp1095 indicated that maximal yield would be obtained from growing cells, with this predicted maximum ~50% higher than that observed experimentally from wild type cells. Competing pathways that might prevent the achievement of this theoretical maximum were identified to guide future genetic studies.

CONCLUSIONS

iRsp1095 provides a robust framework for future metabolic engineering efforts to optimize the solar- and nutrient-powered production of biofuels and other valuable products by R. sphaeroides and closely related organisms.

Tripartite ATP-independent periplasmic (TRAP) transporters in bacteria and archaea

The tripartite ATP-independent periplasmic (TRAP) transporters are the best-studied family of substrate-binding protein (SBP)-dependent secondary transporters and are ubiquitous in prokaryotes, but absent from eukaryotes. They are comprised of an SBP of the DctP or TAXI families and two integral membrane proteins of unequal sizes that form the DctQ and DctM protein families, respectively. The SBP component has a structure comprised of two domains connected by a hinge that closes upon substrate binding. In DctP-TRAP transporters, substrate binding is mediated through a conserved and specific arginine/carboxylate interaction in the SBP. While the SBP component has now been relatively well characterized, the membrane components of TRAP transporters are still poorly understood both in terms of their structure and function. We review the expanding repertoire of substrates and physiological roles for experimentally characterized TRAP transporters in bacteria and discuss mechanistic aspects of these transporters using data primarily from the sialic acid-specific TRAP transporter SiaPQM from Haemophilus influenzae, which suggest that TRAP transporters are high-affinity, Na(+)-dependent unidirectional secondary transporters.

The sulfonated osmolyte N-methyltaurine is dissimilated by Alcaligenes faecalis and by Paracoccus versutus with release of methylamine

Selective enrichments yielded bacterial cultures able to utilize the osmolyte N-methyltaurine as sole source of carbon and energy or as sole source of fixed nitrogen for aerobic growth. Strain MT1, which degraded N-methyltaurine as a sole source of carbon concomitantly with growth, was identified as a strain of Alcaligenes faecalis. Stoichiometric amounts of methylamine, whose identity was confirmed by matrix-assisted, laser-desorption ionization time-of-flight mass spectrometry, and of sulfate were released during growth. Inducible N-methyltaurine dehydrogenase, sulfoacetaldehyde acetyltransferase (Xsc) and a sulfite dehydrogenase could be detected. Taurine dehydrogenase was also present and it was hypothesized that taurine dehydrogenase has a substrate range that includes N-methyltaurine. Partial sequences of a tauY-like gene (encoding the putative large component of taurine dehydrogenase) and an xsc gene were obtained by PCR with degenerate primers. Strain N-MT utilized N-methyltaurine as a sole source of fixed nitrogen for growth and could also utilize the compound as sole source of carbon. This bacterium was identified as a strain of Paracoccus versutus. This organism also expressed inducible (N-methyl)taurine dehydrogenase, Xsc and a sulfite dehydrogenase. The presence of a gene cluster with high identity to a larger cluster from Paracoccus pantotrophus NKNCYSA, which is now known to dissimilate N-methyltaurine via Xsc, allowed most of the overall pathway, including transport and excretion, to be defined. N-Methyltaurine is thus another compound whose catabolism is channelled directly through sulfoacetaldehyde.

Sulfoacetaldehyde is excreted quantitatively by Acinetobacter calcoaceticus SW1 during growth with taurine as sole source of nitrogen

Eighteen enrichment cultures with taurine (2-aminoethanesulfonate) as the sole source of combined nitrogen under aerobic conditions were all successful, and 24 pure cultures were obtained. Only three of the cultures yielded an inorganic product, sulfate, from the sulfonate moiety of taurine, and the others were presumed to yield organosulfonates. Sulfoacetate, known from Rhodopseudomonas palustris CGA009 under these conditions, was not detected in any culture, but sulfoacetaldehyde (as a hydrazone derivative) was tentatively detected in the outgrown medium of nine isolates. The compound was stable under these conditions and the identification was confirmed by MALDI-TOF-MS. Most sulfoacetaldehyde-releasing isolates were determined to be strains of Acinetobacter calcoaceticus, and a representative organism, strain SW1, was chosen for further work. A quantitative enzymic determination of sulfoacetaldehyde and its bisulfite addition complex was developed: it involved the NAD-coupled sulfoacetaldehyde dehydrogenase from R. palustris. A. calcoaceticus SW1 utilized taurine quantitatively and concomitantly with growth in, for example, an adipate-salts medium, and the release of sulfoacetaldehyde was stoichiometric. The deamination reaction involved a taurine dehydrogenase. Enrichment cultures to explore the possible release of organophosphonates from the analogous substrate, 2-aminoethanephosphonate, led to 33 isolates, all of which released inorganic phosphate quantitatively.