The polyhydroxyalkanoate biosynthesis genes are differentially regulated in planktonic- and biofilm-grown Pseudomonas aeruginosa

Use Intein Cleavable Polyhydroxyalkanoate Synthase Fusions to Improve Protein Solubility

Recombinant E. coli producing intein-cleavable polyhydroxyalkanoate synthase fusions mediates the intracellular formation of polyhydroxyalkanoate (PHA) particles densely coated with intein-cleavable target protein fusion. These PHA particles can be efficiently purified from lysed cells. The self-cleaving intein performs as a bio-linker between the PHA synthase and the target protein. The tagless target protein can be released as pure soluble protein from the PHA particles by a simple pH reduction to 6.0. Here we describe that PHA particles serve as bioseparation resin for purification of soluble target proteins with pharmaceutical grade purity, similar to commercial affinity separation technologies. This cost-effective technique does not involve multiple complicated protein purification procedures, and we have exploited this approach to purify six target proteins: green fluorescent protein (GFP) from A. victoria, antigen Rv1626 from M. tuberculosis, the immunoglobulin G (IgG) binding ZZ domain of protein A derived from Staphylococcus aureus, human tumor necrosis factor alpha (TNFα), human granulocyte colony-stimulating factor (G-CSF), and human interferon alpha 2b (IFNα2b).

Bacterial biopolymers: from pathogenesis to advanced materials

Bacteria are prime cell factories that can efficiently convert carbon and nitrogen sources into a large diversity of intracellular and extracellular biopolymers, such as polysaccharides, polyamides, polyesters, polyphosphates, extracellular DNA and proteinaceous components. Bacterial polymers have important roles in pathogenicity, and their varied chemical and material properties make them suitable for medical and industrial applications. The same biopolymers when produced by pathogenic bacteria function as major virulence factors, whereas when they are produced by non-pathogenic bacteria, they become food ingredients or biomaterials. Interdisciplinary research has shed light on the molecular mechanisms of bacterial polymer synthesis, identified new targets for antibacterial drugs and informed synthetic biology approaches to design and manufacture innovative materials. This Review summarizes the role of bacterial polymers in pathogenesis, their synthesis and their material properties as well as approaches to design cell factories for production of tailor-made bio-based materials suitable for high-value applications.

Bioengineered Polyhydroxyalkanoates as Immobilized Enzyme Scaffolds for Industrial Applications

Enzymes function as biocatalysts and are extensively exploited in industrial applications. Immobilization of enzymes using support materials has been shown to improve enzyme properties, including stability and functionality in extreme conditions and recyclability in biocatalytic processing. This review focuses on the recent advances utilizing the design space of in vivo self-assembled polyhydroxyalkanoate (PHA) particles as biocatalyst immobilization scaffolds. Self-assembly of biologically active enzyme-coated PHA particles is a one-step in vivo production process, which avoids the costly and laborious in vitro chemical cross-linking of purified enzymes to separately produced support materials. The homogeneous orientation of enzymes densely coating PHA particles enhances the accessibility of catalytic sites, improving enzyme function. The PHA particle technology has been developed into a remarkable scaffolding platform for the design of cost-effective designer biocatalysts amenable toward robust industrial bioprocessing. In this review, the PHA particle technology will be compared to other biological supramolecular assembly-based technologies suitable for in vivo enzyme immobilization. Recent progress in the fabrication of biological particulate scaffolds using enzymes of industrial interest will be summarized. Additionally, we outline innovative approaches to overcome limitations of in vivo assembled PHA particles to enable fine-tuned immobilization of multiple enzymes to enhance performance in multi-step cascade reactions, such as those used in continuous flow bioprocessing.

Innovative antigen carrier system for the development of tuberculosis vaccines

A major obstacle to tuberculosis (TB)-subunit-vaccine development has been the induction of inadequate levels of protective immunity due to the limited breadth of antigen in vaccine preparations. In this study, immunogenic mycobacterial fusion peptides Ag85B-TB10.4 and Ag85B-TB10.4-Rv2660c were covalently displayed on the surface of self-assembled polyester particles. This study investigated whether polyester particles displaying mycobacterial antigens could provide augmented immunogenicity (i.e., offer an innovative vaccine formulation) when compared with free soluble antigens. Herein, polyester particle-based particulate vaccines were produced in an endotoxin-free Escherichia coli strain and emulsified with the adjuvant dimethyl dioctadecyl ammonium bromide. C57BL/6 mice were used to study the immunogenicity of formulated particulate vaccines. The result of humoral immunity showed the antibodies only interacted with target antigens and not with PhaC and the background proteins of the production host. The analysis of T helper 1 cellular immunity indicated that a relatively strong production of cellular immunity biomarkers, IFN-γ and IL-17A cytokines, was induced by particulate vaccines when compared with the respective soluble controls. This study demonstrated that polyester particles have the potential to perform as a mycobacterial antigen-delivery agent to induce augmented antigen-specific immune responses in contrast to free soluble vaccines.-Chen, S., Sandford, S., Kirman, J. R., Rehm, B. H. A. Innovative antigen carrier system for the development of tuberculosis vaccines.

Mechanisms of Competition in Biofilm Communities

Bacterial biofilms are dense and often mixed-species surface-attached communities in which bacteria coexist and compete for limited space and nutrients. Here we present the different antagonistic interactions described in biofilm environments and their underlying molecular mechanisms, along with ecological and evolutionary insights as to how competitive interactions arise and are maintained within biofilms.

VarR controls colonization and virulence in the marine macroalgal pathogen Nautella italica R11

There is increasing evidence to suggest that macroalgae (seaweeds) are susceptible to infectious disease. However, to date, little is known about the mechanisms that facilitate the colonization and virulence of microbial seaweed pathogens. One well-described example of a seaweed disease is the bleaching of the red alga Delisea pulchra, which can be caused by the bacterium Nautella italica R11, a member of the Roseobacter clade. This pathogen contains a unique luxR-type gene, varR, which we hypothesize controls its colonization and virulence. We show here that a varR knock-out strain is deficient in its ability to cause disease in D. pulchra and is defective in biofilm formation and attachment to a common algal polysaccharide. Moreover complementation of the varR gene in trans can restore these functions to the wild type levels. Proteomic analysis of bacterial cells in planktonic and biofilm growth highlight the potential importance of nitrogen scavenging, mobilization of energy reserves, and stress resistance in the biofilm lifestyle of N. italica R11. Moreover, we show that VarR regulates the expression of a specific subset of biofilm-associated proteins. Taken together these data suggest that VarR controls colonization and persistence of N. italica R11 on the surface of a macroalgal host and that it is an important regulator of virulence.

Polyhydroxyalkanoates: Much More than Biodegradable Plastics

Bacterial polyhydroxyalkanoates (PHAs) are isotactic polymers that play a critical role in central metabolism, as they act as dynamic reservoirs of carbon and reducing equivalents. These polymers have a number of technical applications since they exhibit thermoplastic and elastomeric properties, making them attractive as a replacement of oil-derived materials. PHAs are accumulated under conditions of nutritional imbalance (usually an excess of carbon source with respect to a limiting nutrient, such as nitrogen or phosphorus). The cycle of PHA synthesis and degradation has been recognized as an important physiological feature when these biochemical pathways were originally described, yet its role in bacterial processes as diverse as global regulation and cell survival is just starting to be appreciated in full. In the present revision, the complex regulation of PHA synthesis and degradation at the transcriptional, translational, and metabolic levels are explored by analyzing examples in natural producer bacteria, such as Pseudomonas species, as well as in recombinant Escherichia coli strains. The ecological role of PHAs, together with the interrelations with other polymers and extracellular substances, is also discussed, along with their importance in cell survival, resistance to several types of environmental stress, and planktonic-versus-biofilm lifestyle. Finally, bioremediation and plant growth promotion are presented as examples of environmental applications in which PHA accumulation has successfully been exploited.

Accumulation of high-value lipids in single-cell microorganisms: a mechanistic approach and future perspectives

In recent years attention has been focused on the utilization of microorganisms as alternatives for industrial and nutritional applications. Considerable research has been devoted to techniques for growth, extraction, and purification of high-value lipids for their use as biofuels and biosurfactants as well as high-value metabolites for nutrition and health. These successes argue that the elucidation of the mechanisms underlying the microbial biosynthesis of such molecules, which are far from being completely understood, now will yield spectacular opportunities for industrial scale biomolecular production. There are important additional questions to be solved to optimize the processing strategies to take advantage of the assets of microbial lipids. The present review describes the current state of knowledge regarding lipid biosynthesis, accumulation, and transport mechanisms present in single-cell organisms, specifically yeasts, microalgae, bacteria, and archaea. Similarities and differences in biochemical pathways and strategies of different microorganisms provide a diverse toolset to the expansion of biotechnologies for lipid production. This paper is intended to inspire a generation of lipid scientists to insights that will drive the biotechnologies of microbial production as uniquely enabling players of lipid biotherapeutics, biofuels, biomaterials, and other opportunity areas into the 21st century.

Understanding the antimicrobial mechanism of TiO₂-based nanocomposite films in a pathogenic bacterium

Titania (TiO₂)-based nanocomposites subjected to light excitation are remarkably effective in eliciting microbial death. However, the mechanism by which these materials induce microbial death and the effects that they have on microbes are poorly understood. Here, we assess the low dose radical-mediated TiO₂ photocatalytic action of such nanocomposites and evaluate the genome/proteome-wide expression profiles of Pseudomonas aeruginosa PAO1 cells after two minutes of intervention. The results indicate that the impact on the gene-wide flux distribution and metabolism is moderate in the analysed time span. Rather, the photocatalytic action triggers the decreased expression of a large array of genes/proteins specific for regulatory, signalling and growth functions in parallel with subsequent selective effects on ion homeostasis, coenzyme-independent respiration and cell wall structure. The present work provides the first solid foundation for the biocidal action of titania and may have an impact on the design of highly active photobiocidal nanomaterials.

Selection of hyperadherent mutants in Pseudomonas putida biofilms

A number of genetic determinants required for bacterial colonization of solid surfaces and biofilm formation have been identified in different micro-organisms. There are fewer accounts of mutations that favour the transition to a sessile mode of life. Here we report the isolation of random transposon Pseudomonas putida KT2440 mutants showing increased biofilm formation, and the detailed characterization of one of them. This mutant exhibits a complex phenotype, including altered colony morphology, increased production of extracellular polymeric substances and enhanced swarming motility, along with the formation of denser and more complex biofilms than the parental strain. Sequence analysis revealed that the pleiotropic phenotype exhibited by the mutant resulted from the accumulation of two mutations: a transposon insertion, which disrupted a predicted outer membrane lipoprotein, and a point mutation in lapG, a gene involved in the turnover of the large adhesin LapA. The contribution of each alteration to the phenotype and the possibility that prolonged sessile growth results in the selection of hyperadherent mutants are discussed.