Release of the recombinant proteins, human serum albumin, beta-glucuronidase, glycoprotein B from human cytomegalovirus, and green fluorescent protein, in root exudates from transgenic tobacco and their effects on microbes and enzymatic activities in soil

Biomedicine in the environment: sorption of the cyclotide kalata B2 to montmorillonite, goethite, and humic acid

Cyclotides are bioactive, stable mini-proteins produced in high amounts in Violaceae and Rubiaceae with promising pharmaceutical and agrochemical applications. Environmental issues must be addressed before large-scale plant cultivation of cyclotides for pharmaceutical or pesticidal purposes can commence. The objective of the present study was to investigate sorption of the cyclotide kalata B2 (kB2), because knowledge of cyclotide biogeochemistry will aid our understanding of environmental fate. The octanol-water partitioning coefficient was determined to be 2.8 ± 0.6 (log K(OW)  = 0.4 ± 0.1). Sorption of kB2 by montmorillonite, goethite, and humic acid was investigated at different concentrations and under varying acidity and reached equilibrium within minutes. The kB2 sorption at a solution concentration of 0.2 mg/L to montmorillonite was high (120 mg/g) compared to humic acid (0.60 mg/g) and goethite (0.03 mg/g). Kalata B2 intercalated the interlayer space of montmorillonite. The sorption isotherm for humic acid was linear up to a solution concentration of 0.8 mg/L and concave for montmorillonite and goethite up to an equilibrium solution concentration of 1.5 mg/L. Sorption to goethite was unaffected by pH, but sorption to montmorillonite and humic acid at pH near the isoelectric point (pI) was threefold the sorption when pH > the isoelectric point, suggesting that electrostatic interaction/repulsion between kB2 and sorbents play an important role. The strong sorption to montmorillonite reduces exposure to below toxic threshold values. In addition, the transport risk of soluble cyclotides is reduced, but particle-bound cyclotides may be transported to recipient aquatic sediments with the associated risk of adversely affecting sediment-dwelling organisms.

Biomedicine in the environment: cyclotides constitute potent natural toxins in plants and soil bacteria

Bioactive compounds produced by plants are easily transferred to soil and water and may cause adverse ecosystem effects. Cyclotides are gene-encoded, circular, cystine-rich mini-proteins produced in Violaceae and Rubiaceae in high amounts. Based on their biological activity and stability, cyclotides have promising pharmaceutical and agricultural applications. We report the toxicity of the cyclotides: kalata B1, kalata B2, and cycloviolacin O2 extracted from plants to green algae (Pseudokirchneriella subcapitata), duckweed (Lemna minor L.), lettuce (Lactuca sativa L.), and bacteria extracted from soil measured as [³H]leucine incorporation. Quantification by liquid chromatography-mass spectrometry demonstrated up to 98% loss of cyclotides from aqueous solutions because of sorption to test vials. Sorption was prevented by adding bovine serum albumin (BSA) to the aqueous media. Cyclotides were toxic to all test organisms with EC50 values of 12 through 140 µM (algae), 9 through 40 µM (duckweed), 4 through 54 µM (lettuce), and 7 through 26 µM (bacteria). Cycloviolacin O2 was the most potent cyclotide in all assays examined. This report is the first to document toxic effects of cyclotides in plants and soil bacteria and to demonstrate that cyclotides are as toxic as commonly used herbicides and biocides. Hence, cyclotides may adversely affect soil and aquatic environments, which needs to be taken into account in future risk assessment of cropping systems for production of these highly bioactive compounds.

Investigating recombinant protein exudation from roots of transgenic tobacco

It is widely acknowledged that plant-made pharmaceuticals (PMPs) offer numerous benefits, including inexpensive production, biological safety and the facility for production at agricultural scale. At the same time, it is important to minimize any potential risk associated with this new technology, including the potential release of bioactive proteins into the environment. To address this issue, we studied transgenic Nicotiana benthamiana and Nicotiana tabacum plants expressing two recombinant single-chain variable fragment (scFv) antibodies, respectively scFvB9 and scFvH10. ScFvB9 was raised against glycoprotein G1 of Tomato spotted wilt virus (TSWV), and scFvH10 was raised against human tumor-associated antigen tenascin-C. Both antibodies were targeted to the secretory pathway using the N-terminal signal peptide from Phaseolus vulgaris polygalacturonase-inhibiting protein (PGIP), and scFvH10 carried in addition a C-terminal KDEL tetrapeptide for retention in the endoplasmic reticulum (ER). Sterile hydroponic cultures were established, allowing us to investigate whether scFvB9 and scFvH10 were present in root exudates. Intercellular fluids extracted from different plant tissues were analyzed by western blotting revealing the presence of scFvB9. Successful secretion of scFvB9 in hydroponic medium was also demonstrated, whereas no scFvH10 could be detected in the leaf, stem or root apoplast, nor secreted into the hydroponic medium. Our results show that scFvH10 release or diffusion from the roots of transgenic plants was not occurring, suggesting that the KDEL signal might contribute to the environmental biosafety of crops producing PMPs.

Do transgenic plants affect rhizobacteria populations?

Plant genetic manipulation has led to the development of genetically modified plants (GMPs) expressing various traits. Since their first commercial use in 1996, GMPs have been increasingly used, reaching a global cultivating production area of 114.3 million hectares in 2007. The rapid development of agricultural biotechnology and release of GMPs have provided many agronomic and economic benefits, but has also raised concerns over the potential impact these plants might have on the environment. Among these environmental concerns, the unintentional impact that GMPs might have on soil‐associated microbes, especially rhizosphere‐inhabiting bacteria or rhizobacteria, represents one of the least studied and understood areas. As rhizobacteria are responsible for numerous key functions including nutrient cycling and decomposition, they have been defined as good indicator organisms to assess the general impact that GMPs might have on the soil environment. This minireview summarizes the results of various experiments that have been conducted to date on the impact of GMPs on rhizobacteria. Both biological and technical parameters are discussed and an attempt is made to determine if specific rhizobacterial responses exist for the different categories of GMPs developed to date.

Microbial populations and enzyme activities in soil in situ under transgenic corn expressing cry proteins from Bacillus thuringiensis

Transgenic Bt crops produce insecticidal Cry proteins that are released to soil in plant residues, root exudates, and pollen and that may affect soil microorganisms. As a continuation of studies in the laboratory and a plant-growth room, a field study was conducted at the Rosemount Experiment Station of the University of Minnesota. Three Bt corn varieties that express the Cry1Ab protein, which is toxic to the European corn borer (Ostrinia nubilalis Hübner), and one Bt corn variety that expresses the Cry3Bb1 protein, which is toxic to the corn rootworm complex (Diabrotica spp.), and their near-isogenic non-Bt varieties were evaluated for their effects on microbial diversity by classical dilution plating and molecular (polymerase chain reaction-denaturing gradient gel electrophoresis) techniques and for the activities of some enzymes (arylsulfatases, acid and alkaline phosphatases, dehydrogenases, and proteases) involved in the degradation of plant biomass. After 4 consecutive years of corn cultivation (2003-2006), there were, in general, no consistent statistically significant differences in the numbers of different groups of microorganisms, the activities of the enzymes, and the pH between soils planted with Bt and non-Bt corn. Numbers and types of microorganisms and enzyme activities differed with season and with the varieties of corn, but these differences were not related to the presence of the Cry proteins in soil. The Cry1Ab protein of Bt corn (events Bt11 and MON810) was detected in most soils during the 4 yr, whereas the Cry3Bb1 protein was not detected in soils of Bt corn (event MON863) expressing the cry3Bb1 gene.