Safety evaluation of an alpha-amylase enzyme preparation derived from the archaeal order Thermococcales as expressed in Pseudomonas fluorescens biovar I

Synergistic inhibition of Pseudomonas fluorescens growth and proteases activities via sodium chlorite-based oxyhalogen

Pseudomonas fluorescens is considered among the main spoilage microorganisms due to its ability to produce proteases. Food deterioration caused by spoilage microorganisms has a major impact on food quality and the environment. The inactivation of Pseudomonas fluorescens growth and protease production was intensively investigated with the use of Salmide®, A Sodium Chlorite-Based Oxy-halogen Disinfectant. A unique M9 media was also developed to assure sufficient protease productions with different mutants of Pseudomonas fluorescens as a microbioreactor. Mutations were induced by classical whole-cell mutagenesis using N-methyl-N'- nitro-N-nitrosoguanidine (NTG). A dramatic decrease occurred in protease activity when different Salmide concentrations (5, 10, and 15 ppm) were added to the growth culture followed by a complete inhibition concentration (20, 25, 50, and 100 ppm) of Salmide. However, no significant inhibition occurred once it is secreted out of cells. Some mutants were resistant and remains highly stable with high protease production under stressful conditions of Sodium Chlorite-Based Oxy-halogen. The production of the protease showed a linear correlation with the increase in incubation time using a continuous culture bioreactor system and recorded maximum protease activity after 40 h. Our findings would offer alternative antimicrobial procedures for food and industrial sectors.

Pseudomonas spp. as cell factories (MCFs) for value-added products: from rational design to industrial applications

In recent years, there has been increasing interest in microbial biotechnology for the production of value-added compounds from renewable resources. Pseudomonas species have been proposed as a suitable workhorse for high-value secondary metabolite production because of their unique characteristics for fast growth on sustainable carbon sources, a clear inherited background, versatile intrinsic metabolism with diverse enzymatic capacities, and their robustness in an extreme environment. It has also been demonstrated that metabolically engineered Pseudomonas strains can produce several industrially valuable aromatic chemicals and natural products such as phenazines, polyhydroxyalkanoates, rhamnolipids, and insecticidal proteins from renewable feedstocks with remarkably high yields suitable for commercial application. In this review, we summarize cell factory construction in Pseudomonas for the biosynthesis of native and non-native bioactive compounds in P. putida, P. chlororaphis, P. aeruginosa, as well as pharmaceutical proteins production by P. fluorescens. Additionally, some novel strategies together with metabolic engineering strategies in order to improve the biosynthetic abilities of Pseudomonas as an ideal chassis are discussed. Finally, we proposed emerging opportunities, challenges, and essential strategies to enable the successful development of Pseudomonas as versatile microbial cell factories for the bioproduction of diverse bioactive compounds.

Safety evaluation of the food enzyme α-amylase from the genetically modified Pseudomonas fluorescens strain BD15754

The food enzyme α‐amylase (4‐a‐d‐glucan glucanohydrolase; EC 3.2.1.1) is produced with the genetically modified Pseudomonas fluorescens strain BD15754 by BASF Enzymes LLC1. The food enzyme is free from viable cells of the production organism and recombinant DNA. The α‐amylase is intended to be used in distilled alcohol production and starch processing for the production of glucose syrups. Residual amounts of total organic solids (TOS) are removed by distillation and by the purification steps applied during the production of glucose syrups, consequently, dietary exposure was not calculated. Genotoxicity tests did not raise a safety concern. The systemic toxicity was assessed by means of a repeated dose 90‐day oral toxicity study in rats. The Panel identified a no observed adverse effect level (NOAEL) at the highest dose of 887 mg TOS/kg body weight (bw) per day. Similarity of the amino acid sequence to those of known allergens was searched and no match was found. The Panel considered that, under the intended conditions of use, the risk of allergic sensitisation and elicitation reactions by dietary exposure cannot be excluded, but the likelihood of such reactions to occur is considered to be low. However, the food enzyme contains residual amounts of a highly important antimicrobial for human medicine, with the consequent risk of promoting the development of resistance. Therefore, the Panel concludes that the food enzyme α‐amylase, produced with the genetically modified P. fluorescens strain BD15754 cannot be considered safe.

High-Level Production of Bacteriotoxic Phospholipase A1 in Bacterial Host Pseudomonas fluorescens Via ABC Transporter-Mediated Secretion and Inducible Expression

Bacterial phospholipase A1 (PLA1) is used in various industrial fields because it can catalyze the hydrolysis, esterification, and transesterification of phospholipids to their functional derivatives. It also has a role in the degumming process of crude plant oils. However, bacterial expression of the foreign PLA1-encoding gene was generally hampered because intracellularly expressed PLA1 is inherently toxic and damages the phospholipid membrane. In this study, we report that secretion-based production of recombinant PlaA, a bacterial PLA1 gene, or co-expression of PlaS, an accessory gene, minimizes this harmful effect. We were able to achieve high-level PlaA production via secretion-based protein production. Here, TliD/TliE/TliF, an ABC transporter complex of Pseudomonas fluorescens SIK-W1, was used to secrete recombinant proteins to the extracellular medium. In order to control the protein expression with induction, a new strain of P. fluorescens, which had the lac operon repressor gene lacI, was constructed and named ZYAI strain. The bacteriotoxic PlaA protein was successfully produced in a bacterial host, with help from ABC transporter-mediated secretion, induction-controlled protein expression, and fermentation. The final protein product is capable of degumming oil efficiently, signifying its application potential.

Statement complementing the EFSA Scientific Opinion on application (EFSA‐GMO‐UK‐2006‐34) for authorisation of food and feed containing, consisting of and produced from genetically modified maize 3272

Following a request from the European Commission, the GMO Panel assessed additional information related to the application for authorisation of food and feed containing, consisting of and produced from genetically modified (GM) maize 3272 (EFSA‐GMO‐UK‐2006‐34). The applicant conducted new agronomic, phenotypic and compositional analysis studies on maize 3272 and assessed the allergenic potential of AMY797E protein, addressing elements that remained inconclusive from previous EFSA opinion issued in 2013. The GMO Panel is of the opinion that the agronomic and phenotypic characteristics as well as forage and grain composition of maize 3272 do not give rise to food and feed safety, and nutritional concerns when compared to non‐GM maize. Considering the scope of this application and the characteristics of the trait introduced in this GM maize, the effect of processing and potential safety implications of specific food or feed products remain to be further investigated. Regarding the allergenic potential of AMY797E protein and considering all possible food and feed uses of maize 3272, the Panel concludes that the information provided does not fully address the concerns previously raised by the Panel in 2013. Owing to the nature and the knowledge available on this protein family, it is still unclear whether under specific circumstances the alpha‐amylase AMY797E has the capacity to sensitise certain individuals and to cause adverse effects. To further support the safety of specific products of maize 3272, the applicant provided thorough information relevant for the allergenicity assessment of dried distiller grains with solubles (DDGS), which is the main product of interest for importation into the EU. Having considered the information provided on this product, the Panel is of the opinion that under the specific conditions of use described by the applicant, DDGS produced from maize 3272 does not raise concerns when compared to DDGS from non‐GM maize.

Biotechnological production of the angiotensin-converting enzyme inhibitory dipeptide isoleucine-tryptophan

Peptides with angiotensin-converting enzyme (ACE)-inhibitory and antihypertensive effects are suggested as innovative food additives to prevent or treat hypertension. Currently, these substances are isolated from food proteins following nonselective hydrolysis as a mixture of ACE-inhibitory peptides and other protein fragments. This study presents an innovative biotechnological method, based on recombinant DNA technology that was established to specifically produce the ACE-inhibitory dipeptide isoleucine-tryptophan. In a first step, a repetitive isoleucine-tryptophan construct fused to the maltose-binding protein was generated and expressed in Escherichia coli BL21 cells. The chromatographically purified recombinant fusion protein was enzymatically hydrolyzed using α-chymotrypsin to liberate the dipeptide isoleucine-tryptophan. The identity of the liberated isoleucine-tryptophan was confirmed by MS and derivatization of its N-terminus. The ACE-inhibitory effect of the recombinant dipeptide on soluble and membrane bound ACE was found to be indistinguishable from the inhibitory potential of the chemically produced commercially available dipeptide. The established experimental strategy represents a promising approach to the biotechnical production of sufficient amounts of recombinant peptide-based ACE-inhibitory and antihypertensive substances that are applicable as functional food additives to delay or even prevent hypertension.

A vector system for ABC transporter-mediated secretion and purification of recombinant proteins in Pseudomonas species

Pseudomonas fluorescens is an efficient platform for recombinant protein production. P. fluorescens has an ABC transporter secreting endogenous thermostable lipase (TliA) and protease, which can be exploited to transport recombinant proteins across the cell membrane. In this study, the expression vector pDART was constructed by inserting tliDEF, genes encoding the ABC transporter, along with the construct of the lipase ABC transporter recognition domain (LARD), into pDSK519, a widely used shuttle vector. When the gene for the target protein was inserted into the vector, the C-terminally fused LARD allowed it to be secreted through the ABC transporter into the extracellular medium. After secretion of the fused target protein, the LARD containing a hydrophobic C terminus enabled its purification through hydrophobic interaction chromatography (HIC) using a methyl-Sepharose column. Alkaline phosphatase (AP) and green fluorescent protein (GFP) were used to validate the expression, export, and purification of target proteins by the pDART system. Both proteins were secreted into the extracellular medium in P. fluorescens. In particular, AP was secreted in several Pseudomonas species with its enzymatic activity in extracellular media. Furthermore, purification of the target protein using HIC yielded some degree of AP and GFP purification, where AP was purified to almost a single product. The pDART system will provide greater convenience for the secretory production and purification of recombinant proteins in Gram-negative bacteria, such as Pseudomonas species.

Lipase and protease double-deletion mutant of Pseudomonas fluorescens suitable for extracellular protein production

Pseudomonas fluorescens, a widespread Gram-negative bacterium, is an ideal protein manufacturing factory (PMF) because of its safety, robust growth, and high protein production. P. fluorescens possesses a type I secretion system (T1SS), which mediates secretion of a thermostable lipase (TliA) and a protease (PrtA) through its ATP-binding cassette (ABC) transporter. Recombinant proteins in P. fluorescens are attached to the C-terminal signal region of TliA for transport as fusion proteins to the extracellular medium. However, intrinsic TliA from the P. fluorescens genome interferes with detection of the recombinant protein and the secreted recombinant protein is hydrolyzed, due to intrinsic PrtA, resulting in decreased efficiency of the PMF. In this research, the lipase and protease genes of P. fluorescens SIK W1 were deleted using the targeted gene knockout method. Deletion mutant P. fluorescens ΔtliA ΔprtA secreted fusion proteins without TliA or protein degradation. Using wild-type P. fluorescens as an expression host, degradation of the recombinant protein varied depending on the type of culture media and aeration; however, degradation did not occur with the P. fluorescens ΔtliA ΔprtA double mutant irrespective of growth conditions. By homologous expression of tliA and the ABC transporter in a plasmid, TliA secreted from P. fluorescens ΔprtA and P. fluorescens ΔtliA ΔprtA cells was found to be intact, whereas that secreted from the wild-type P. fluorescens and P. fluorescens ΔtliA cells was found to be hydrolyzed. Our results demonstrate that the P. fluorescens ΔtliA ΔprtA deletion mutant is a promising T1SS-mediated PMF that enhances production and detection of recombinant proteins in extracellular media.

Safety evaluation of a lipase enzyme (BD29241 Palmitase) preparation, expressed in Pseudomonas fluorescens, intended for removing palmitic acid from triacylglycerol

The lipase enzyme, BD29241 Palmitase, can be used as a processing aid for removing palmitic acid from triacylglycerol in the production of refined oil. This enzyme was produced from a Pseudomonas fluorescens (P. fluorescens) production strain and was tested in acute, inhalation, and subchronic toxicity studies. In addition, this enzyme was also tested for its potential to induce genotoxicity. Dosages of the test article preparation ranged from 5000μg/plate for in vitro toxicity studies to 2000mg/kg/day for in vivo toxicity studies. The highest oral dose tested in vivo (NOAEL of 2000mg/kg/day) resulted in a safety margin of 2.442×10(3) based on a conservative estimate of the total human consumption of BD29241 Palmitase of 0.819mg/kg/day. There was no toxicity reported for any of these studies including additional safety studies. A review of the literature indicates that P. fluorescens fulfills recognized safety criteria pertinent to microbial production strains used in the manufacture of food enzyme preparations. The results of the toxicity studies presented herein attest to the safety of BD29241 Palmitase for its above-stated intended use.

Impact of food processing on the safety assessment for proteins introduced into biotechnology-derived soybean and corn crops

The food safety assessment of new agricultural crop varieties developed through biotechnology includes evaluation of the proteins introduced to impart desired traits. Safety assessments can include dietary risk assessments similar to those performed for chemicals intentionally, or inadvertently added to foods. For chemicals, it is assumed they are not degraded during processing of the crop into food fractions. For introduced proteins, the situation can be different. Proteins are highly dependent on physical forces in their environment to maintain appropriate three-dimensional structure that supports functional activity. Food crops such as corn and soy are not consumed raw but are extensively processed into various food fractions. During processing, proteins in corn and soy are subjected to harsh environmental conditions that drastically change the physical forces leading to denaturation and loss of protein function. These conditions include thermal processing, changes in pH, reducing agents, mechanical shearing etc. Studies have shown that processing of introduced proteins such as enzymes that impart herbicide tolerance or proteins that control insect pests leads to a complete loss of functional activity. Thus, dietary exposure to functionally active proteins in processed food products can be negligible and below levels of any safety concerns.

The Acinetobacter sp. chnB promoter together with its cognate positive regulator ChnR is an attractive new candidate for metabolic engineering applications in bacteria

Over the last 10 years there has been an extremely fast development in the global characterization of bacteria at the genome, transcriptome, proteome and metabolome levels. To further explore and apply these complex data sets there is now a need for new biological tools that can be used to test or verify hypotheses generated on the basis of all the new information. Here, we report the integration of an expression cassette based on the Acinetobacter sp. chnB promoter and its cognate positive regulator chnR gene into a replicon derived from the broad-host-range plasmid RK2. Cyclohexanone was found to be the most efficient inducer of this system in Escherichia coli, using firefly luciferase as a reporter. To explore the potential of the system in another species, we show that the system can be used in combination with another similar expression cassette (Pm/xylS) to control the monomer composition of the industrially widely used exopolysaccharide alginate, produced by Pseudomonas fluorescens.

Studies on the non-pathogenicity of Chryseobacterium proteolyticum and on the safety of the enzyme: protein-glutaminase

Protein-glutaminase (PG) is a protein-deamidating enzyme produced from the microorganism Chryseobacterium proteolyticum strain 9670. Food safety studies were conducted on both the enzyme and the production organism. The strain was evaluated for pathogenicity and toxigenicity by intravenous and oral inoculation studies in Slc:ICR male SPF mice. The results demonstrate that the tested C. proteolyticum strain is of very low pathogenicity comparable to known food source bacterial strains and is very unlikely to demonstrate any pathogenicity in animals or humans. The level of endotoxin is very low and typical of the endotoxin levels in drinking water and teas. A 90-day study of PG, conducted in Sprague-Dawley rats, showed no adverse effects due to the enzyme up to dose levels of 2500 mg/kg-bw/day (NOAEL). Details of the study are presented, including, organ and body weights, histological findings, and blood and urine chemistry. Additionally, bacterial reverse mutation test (Ames test) and chromosomal aberration test using mammalian established cell line were conducted, resulting in the absence of mutagenicity in PG.

Characterization of the SOS response of Pseudomonas fluorescens strain DC206 using whole-genome transcript analysis

DNA microarray technology was used to survey changes in gene expression in Pseudomonas fluorescens after mitomycin C treatment. As expected, genes associated with the SOS response were upregulated, such as those encoding the recombination protein RecA, DNA repair protein RecN, excinuclease ABC subunit A UvrA, and the LexA repressor protein. Interestingly, expression of 33 clustered bacteriophage-like genes was upregulated, suggesting that mitomycin C (MMC) may induce a prophage resident in the P. fluorescens genome. However, no phage particles were detected in P. fluorescens strain DC206 that had been treated with MMC using transmission electron microscopy. The same preparation failed to produce phage plaques on lawns of any of 10 different Pseudomonas strains tested, indicating that the 33 bacteriophage-like gene cluster represents a defective prophage.

Food-processing enzymes from recombinant microorganisms--a review

Enzymes are commonly used in food processing and in the production of food ingredients. Enzymes traditionally isolated from culturable microorganisms, plants, and mammalian tissues are often not well-adapted to the conditions used in modern food production methods. The use of recombinant DNA technology has made it possible to manufacture novel enzymes suitable for specific food-processing conditions. Such enzymes may be discovered by screening microorganisms sampled from diverse environments or developed by modification of known enzymes using modern methods of protein engineering or molecular evolution. As a result, several important food-processing enzymes such as amylases and lipases with properties tailored to particular food applications have become available. Another important achievement is improvement of microbial production strains. For example, several microbial strains recently developed for enzyme production have been engineered to increase enzyme yield by deleting native genes encoding extracellular proteases. Moreover, certain fungal production strains have been modified to reduce or eliminate their potential for production of toxic secondary metabolites. In this article, we discuss the safety of microorganisms used as hosts for enzyme-encoding genes, the construction of recombinant production strains, and methods of improving enzyme properties. We also briefly describe the manufacture and safety assessment of enzyme preparations and summarize options for submitting information on enzyme preparations to the US Food and Drug Administration.

Overview of bacterial expression systems for heterologous protein production: from molecular and biochemical fundamentals to commercial systems

During the proteomics period, the growth in the use of recombinant proteins has increased greatly in the recent years. Bacterial systems remain most attractive due to low cost, high productivity, and rapid use. However, the rational choice of the adequate promoter system and host for a specific protein of interest remains difficult. This review gives an overview of the most commonly used systems: As hosts, Bacillus brevis, Bacillus megaterium, Bacillus subtilis, Caulobacter crescentus, other strains, and, most importantly, Escherichia coli BL21 and E. coli K12 and their derivatives are presented. On the promoter side, the main features of the l-arabinose inducible araBAD promoter (PBAD), the lac promoter, the l-rhamnose inducible rhaP BAD promoter, the T7 RNA polymerase promoter, the trc and tac promoter, the lambda phage promoter p L , and the anhydrotetracycline-inducible tetA promoter/operator are summarized.

Auxotrophic markers pyrF and proC can replace antibiotic markers on protein production plasmids in high-cell-density Pseudomonas fluorescens fermentation

The use of antibiotic-resistance genes as selectable markers in transgenic organisms is coming under increased scrutiny, for fear that they may spread to human pathogens, thereby reducing the effectiveness of antibiotic therapy. A current Pseudomonas fluorescens protein expression system uses a tetracycline resistance gene (tetR/tetA) to maintain an expression plasmid under control of a repressible promoter and a kanamycin resistance gene (kanR) to maintain a plasmid carrying a repressor gene. We investigated using auxotrophic markers to replace these two antibiotic resistance genes: pyrF (encoding orotidine-5'-phosphate decarboxylase) in place of tetR/tetA and proC (encoding pyrroline-5-carboxylate reductase) in place of kanR, complementing their respective precise chromosomal deletions created by allele exchange using a suicide vector carrying pyrF as a counterselectable marker. The resulting strains, devoid of antibiotic-resistance genes, were shown to achieve high productivity of nitrilase and thermostable alpha-amylase equal to that of the former antibiotic-resistant production host. The production plasmids were stable. The pyrF (uracil-dependent) background of the production host strain also allows us to sequentially alter the genome to incorporate other desired genomic changes, deletions, or insertions using 5'-fluoroorotic acid counterselection, restoring the selectable marker after each step.