Monitoring transfer of recombinant and nonrecombinant plasmids between Lactococcus lactis strains and members of the human gastrointestinal microbiota in vivo--impact of donor cell number and diet

AIMS

The generation of data of real relevance to the purported risks of DNA transfer from food-borne genetically modified microorganisms (GMMOs) using the human biota associated (HBA) rat model. Plasmid transfer between Lactococcus lactis strains and between donor strains and human gut bacteria was monitored.

METHODS AND RESULTS

Transfer of the recombinant plasmid pCK1 and/or the promiscuous nonrecombinant plasmid pAMbeta1 between L. lactis strains was monitored in vivo in HBA rats. No transfer of pCK1 was observed. Transfer of pAMbeta1 was observed to Enterococcus spp. present in the HBA rats. Transconjugants persisted for 30 d and were distributed throughout the gastrointestinal tract. Both HBA rat diet and donor cell numbers impacted on transconjugant numbers. Fewer transconjugants were observed in animals fed a high-fat human type diet, while high levels of plasmid transfer were only observed at doses of donor L. lactis greater than 109 cfu.

CONCLUSIONS

The utility of models of the human gut in monitoring DNA transfer events within the gut microbiota was demonstrated.

SIGNIFICANCE AND IMPACT OF THE STUDY

Such findings give some confidence for the use of GMMOs with recombinant DNA borne on nonconjugative elements in fermented foods. HBA rats are a suitable model for monitoring the fate of food-borne GMMOs.

Carton sterilization by u.v.-C excimer laser light: recovery of Bacillus subtilis spores on vegetable extracts and food simulation matrices

AIMS

To determine the recovery of Bacillus subtilis spores loaded onto preformed cartons and irradiated with u.v.-excimer laser (248 nm) light.

METHODS AND RESULTS

Bacillus subtilis spores irradiated with u.v.-excimer laser light retained phase brightness, but were blocked at various stages of germination. In the presence of germinant, the majority of spores began to lose phase brightness but only after an extended lag period (ca 90 min). After 6 h ca 9% of the spores had elongated but failed to form new cells, approx. 12% had undergone partial phase darkening (grey spores), 15% remained phase bright whilst the remainder had turned fully phase dark but failed to elongate. No enhanced recovery of u.v.-treated spores (with intact or permeabilized coats) occurred in media containing hen egg white lysozyme or vegetable extracts (celery, carrot, swede or turnip). However, recovery did occur when irradiated spores were incubated for 26 d, semiaerobically, within cartons containing nutrient broth or milk.

CONCLUSIONS

The germination ability of B. subtilis spores is altered following u.v.-excimer laser treatment. Recovery of treated spores was found in liquid systems but not on agar plates supplemented with vegetable extracts or lysozyme.

SIGNIFICANCE AND IMPACT OF THE STUDY

The potential recovery of u.v.-excimer laser-treated spores in a range of carton-packed food systems requires further investigation.

Inactivation of Bacillus subtilis spores on aluminum and polyethylene preformed cartons by UV-excimer laser irradiation

The efficacy of UV KrF-excimer laser light (at 248 nm) to inactivate Bacillus subtilis spores loaded onto preformed cartons was found to be dependent on the interior carton coating and scheme by which the irradiation was applied. When the carton was held static during UV laser treatment, the majority of the dose was delivered to the base of the carton and to a lesser extent to the upper part of the pack. In this arrangement no irradiation of the interior sides of the carton was observed. A more even distribution of dose was achieved, however, by moving the carton within the laser beam during irradiation treatment. The distribution of UV was also found to be dependent on the type of carton interior coating. With aluminum cartons the dose measured was found to be significantly greater (P < 0.01) and more evenly distributed across the interior compared to when polyethylene packs were tested. Under optimized conditions no spore survivors were detected on aluminum cartons preloaded with 9.5 x l0 B. subtilis spores by applying a UV laser output dose of 160 J. In comparison, the same conditions only achieved a significantly lower (P < 0.01) reduction in spore numbers (log count reduction 4.2) when polyethylene cartons were used. This difference in lethality and UV distribution of laser light was associated with the higher internal reflection of photons with aluminum cartons. The suitability of UV-excimer lasers for sterilizing preformed cartons over traditional germicidal lamp-based methods is discussed.

Inactivation of Bacillus subtilis spores on packaging surfaces by u. v. excimer laser irradiation

Ultraviolet (u.v.) laser irradiation has been used to inactivate Bacillus subtilis spores deposited on to planar aluminium- and polyethylene-coated packaging surfaces. Kill kinetics were found to be diphasic, with an initial rapid inactivation phase followed by tailing. Although no definitive evidence was obtained, it is thought that spores located within packaging crevices/pores were primarily responsible for the observed tailing. Surviving spores were also found on the unexposed underside of cards and, to a lesser extent, within clumps. The log count reduction in B. subtilis was dependent on spore loading and total u.v. dose. In comparison, packaging surface composition, fluence (2-18 Jm-2) and frequency (40-150 Hz) had only a negligible effect. By irradiating boards carrying 106 spores, with a dose of 11.5 J cm-2, a log count reduction >5 was obtained. The mode of spore inactivation was primarily through DNA disruption. This was confirmed by the high sensitivity of spores lacking protective, small, acid-soluble proteins, in addition to the high frequency of auxotrophic and asporogenous mutations found amongst survivors.

Association of c-fos mRNA expression and excitotoxicity in primary cultures of mouse neocortical and cerebellar neurons

The effect of excitatory amino acids (EAAs) on c-fos mRNA expression was studied in primary cultures of mouse cerebellar granule cells and in neocortical neurons after 2 and 7 days in vitro (div). In cultured granule cells at 2 and 7 div, and in cortical neurons at 2 div, exposure to low levels (< or = 10 microM) of a variety of EAAs (viz. glutamate [Glu], S-sulpho-L-cysteine [SC], N-methyl-D-aspartate [NMDA], alpha-amino-3-hydroxy-5-methyl-4-isoxazole [AMPA], and kainate [KA]) resulted in a transient increase in the level of c-fos mRNA which peaked at 30 min but returned to a basal level by 120 min. However, exposure of granule cells (7 div) to high levels (250 microM) of Glu, NMDA, KA, SC and of cortical neurons (7 div) to high levels (250 microM) of Glu, NMDA, KA, SC, or AMPA and to low levels (< or = 10 microM) of Glu and AMPA resulted in a delay in c-fos mRNA induction but a subsequent, progressive increase that was sustained for at least 240 min. Furthermore, this effect was accompanied by a dose-related increase in the release of the cytosolic enzyme, lactate dehydrogenase, used as an indicator of excitotoxicity. A ratio (Q240/30) for the steady-state levels of c-fos mRNA after 30 min and 240 min of exposure to EAAs was determined which showed that Q240/30 >2 correlated reproducibly with excitotoxic cell death, whereas a ratio of < or = 1 correlated with a nonexcitotoxic event. In both cell types at 7 div, coadministration of the selective NMDA receptor antagonist, DL(+/-)-2-amino-5-phosphonopentanoic acid (APV) with cytotoxic levels of Glu 1) protected against EAA-induced neurotoxicity and 2) exhibited a transient c-fos mRNA expression (Q240/30 values approximately 1). In contrast, the AMPA/KA receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), provided no protection against excitotoxicity and had no significant effect on the Glu-induced delay in c-fos mRNA expression. These results suggest that the Q240/30 c-fos mRNA ratio may 1) be used as a predictive index for excitotoxic neuronal death, 2) provide information on the identity of the receptor subtype mediating excitotoxicity in different brain cell types, and 3) aid in establishing the role of excitotoxicity during the development of neurons in vitro.

Structural gene coding for multifunctional protein carrying orotate phosphoribosyltransferase and OMP decarboxylase activity is located on long arm of human chromosome 3

In humans, deficiency in the last two enzymes of UMP biosynthesis, orotate phosphoribosyltransferase (OPRT) and OMP decarboxylase results in the inborn error of metabolism hereditary orotic aciduria, type 1. In this manuscript, we present immunologic, molecular, biochemical, and genetic evidence that the gene coding for this set of enzymatic activities is located on the long arm of human chromosome 3. The evidence presented here is consistent with both these activities being carried on the same multifunctional protein in mammalian cells. These studies allow further genetic analysis of human chromosome 3, confirming that human markers ACY-1, previously assigned to 3p21, and beta-gal, previously assigned by others to the region 3(p21-q21), must be in the region 3 (cen-p21) and confirming the regional assignment of a human DNA segment, D3S1, to 3q12. The significance of these studies to genetic analysis of genes on human chromosome 3, some of which appear to play a role in some forms of malignancy, is discussed.