High Levels of CO2 Induce Spoilage by Leuconostoc mesenteroides by Upregulating Dextran Synthesis Genes

During nonventilated storage of carrots, CO2 gradually accumulates to high levels and causes modifications in the carrot's microbiome toward dominance of Lactobacillales and Enterobacteriales The lactic acid bacterium Leuconostoc mesenteroides secretes a slimy exudate over the surface of the carrots. The objective of this study was to characterize the slime components and the potential cause for its secretion under high CO2 levels. A proteomic analysis of the exudate revealed bacterial glucosyltransferases as the main proteins, specifically, dextransucrase. A chemical analysis of the exudate revealed high levels of dextran and several simple sugars. The exudate volume and dextran amount were significantly higher when L. mesenteroides was incubated under high CO2 levels than when incubated in an aerated environment. The treatment of carrot medium plates with commercial dextransucrase or exudate protein extract resulted in similar sugar profiles and dextran production. Transcriptome analysis demonstrated that dextran production is related to the upregulation of the L. mesenteroides dextransucrase-encoding genes dsrD and dsrT during the first 4 to 8 h of exposure to high CO2 levels compared to aerated conditions. A phylogenetic analysis of L. mesenteroides YL48 dsrD revealed a high similarity to other dsr genes harbored by different Leuconostoc species. The ecological benefit of dextran production under elevated CO2 requires further investigation. However, this study implies an overlooked role of CO2 in the physiology and fitness of L. mesenteroides in stored carrots, and perhaps in other food items, during storage under nonventilated conditions.IMPORTANCE The bacterium Leuconostoc mesenteroides is known to cause spoilage of different types of foods by secreting a slimy fluid that damages the quality and appearance of the produce. Here, we identified a potential mechanism by which high levels of CO2 affect the spoilage caused by this bacterium by upregulating dextran synthesis genes. These results have broader implications for the study of the physiology, degradation ability, and potential biotechnological applications of Leuconostoc.

Differential response to heat stress in outer and inner onion bulb scales

The formation of brown protective skin in onion bulbs can be induced by rapid post-harvest heat treatment. Onions that are peeled to different depths and are exposed to heat stress show that only the outer scales form the dry brown skin, whereas the inner scales maintain high water content and do not change color. Our study demonstrates that browning of the outer scale during heat treatment is due to an enzymatic process that is associated with high levels of oxidation components, such as peroxidase and quercetin glucoside. De novo transcriptome analysis revealed differential molecular responses of the outer and inner scales to heat stress. Genes involved in lipid metabolism, oxidation pathways, and cell-wall modification were highly expressed in the outer scale during heating. Defense response-related genes such as those encoding heat-shock proteins, antioxidative stress defense, or production of osmoprotectant metabolites were mostly induced in the inner scale in response to heat exposure. These transcriptomic data led to a conceptual model that suggests sequential processes for the development of browning and desiccation of the outer scale versus processes associated with defense response and heat tolerance in the inner scales.

Emergence of Leuconostoc mesenteroides as a causative agent of oozing in carrots stored under non-ventilated conditions

Long-term storage and transport of post-harvest carrots (Daucus carota L.) require a low-temperature, high-relative-humidity environment, usually with low ventilation. Following long-term storage, a slimy exudate (oozing) often appears on the carrots, leading to severe spoilage. We characterized the environmental conditions leading to these symptoms and identified the causative agent. Simulation of non-ventilated storage conditions revealed accumulation of CO2 (to 80%) and ethanol (to 1000 ppm); then, a transparent exudate appeared on the carrot surface which, upon ventilation, developed into tissue browning and soft rot. Peels from oozing carrots contained over 10-fold the total bacterial counts of healthy carrots. The total peel microbiome was determined by 16S rDNA sequencing. During oozing stage, the surface of carrots incubated in a CO2 -rich (98%) environment harboured a bacterial population dominated by Lactobacillales and Enterobacteriales, differing markedly from those incubated in air. Three prevalent bacterial isolates from the oozing carrots were identified as Pantoea agglomerans, Rahnella aquatilis and Leuconostoc mesenteroides. Inoculation of carrot discs with L. mesenteroides, but not the others, induced oozing under high CO2 , suggesting that this bacterium is responsible for oozing of stored carrots. These findings should enable development of approaches to preventing carrot spoilage during long-term storage.

Cellular and Molecular Changes Associated with Onion Skin Formation Suggest Involvement of Programmed Cell Death

Skin formation of onion (Allium cepa L.) bulb involves scale desiccation accompanied by scale senescence, resulting in cell death and tissue browning. Understanding the mechanism of skin formation is essential to improving onion skin and bulb qualities. Although onion skin plays a crucial role in postharvest onion storage and shelf life, its formation is poorly understood. We investigated the mode of cell death in the outermost scales that are destined to form the onion skin. Surprisingly, fluorescein diacetate staining and scanning electron microscopy indicated that the outer scale desiccates from the inside out. This striking observation suggests that cell death in the outer scales, during skin formation, is an internal and organized process that does not derive only from air desiccation. DNA fragmentation, a known hallmark of programmed cell death (PCD), was revealed in the outer scales and gradually decreased toward the inner scales of the bulb. Transmission electron microscopy further revealed PCD-related structural alterations in the outer scales which were absent from the inner scales. De novo transcriptome assembly for three different scales: 1st (outer), 5th (intermediate) and 8th (inner) fleshy scales identified 2,542 differentially expressed genes among them. GO enrichment for cluster analysis revealed increasing metabolic processes in the outer senescent scale related to defense response, PCD processes, carbohydrate metabolism and flavonoid biosynthesis, whereas increased metabolism and developmental growth processes were identified in the inner scales. High expression levels of PCD-related genes were identified in the outer scale compared to the inner ones, highlighting the involvement of PCD in outer-skin development. These findings suggest that a program to form the dry protective skin exists and functions only in the outer scales of onion.

SU-E-I-89: Applying Image Gently and Image Wisely in Nuclear Medicine

PURPOSE

To demonstrate how principles and recommendations of the Image Gently® and Image Wisely™ campaigns can be clinically implemented.

METHODS

Implementation of Image Gently® and Image Wisely™ guidelines was a quality and safety improvement project for our Nuclear Medicine department in 2011. Pediatric administered radiopharmaceutical doses were compared to recommended doses in the North American Consensus Guidelines for AdministeredRadiopharmaceutical Activities in Children and Adolescents and the European Association of Nuclear Medicine Paediatric Dose Card. Adult administered radiopharmaceutical doses were compared to administered doses in NCRP Report No. 160 and IAEA Report No. 40.

RESULTS

Evaluation of site administered radiopharmaceutical doses showed that nearly all doses were comparable to those recommended by national and international advisory bodies. Administered doses for the pediatric renogram and the adult gastric emptying were adjusted to match the recommendations and resultant image quality evaluated.

CONCLUSIONS

Radiation dose from nuclear medicine procedures should not be overlooked in the focus on CT dose reduction. An estimated 19.7 million nuclear medicine procedures are done annually in the U.S., with doses comparable to that from CT scans. Nuclear medicine departments should evaluate their pediatric administeredradiopharmaceutical doses against the North American Consensus Guidelines for Administered Radiopharmaceutical Activities in Children and Adolescents and evaluate their adult doses against national and international standards. Administered doses that are not comparable to the recommended values should be adjusted accordingly. Additional steps to reduce patient radiation dose include decision support to reduce inappropriate ordering, technique optimization for the CT scan portion of SPECT/CT and PET/CT, use of vendor's dose reduction camera and software technology, use of shorter lived radiopharmaceuticals, and 'right sizing' patient doses by weight.

Characterization of extracellular lytic enzymes produced by the yeast biocontrol agent Candida oleophila

The yeast Candida oleophila, the base of the commercial product Aspire, is recommended for the control of postharvest decay of citrus and pome fruit. Competition for nutrients and space is believed to be the major mode of action. Involvement of fungal cell wall-degrading enzymes is also suggested to play a role in the mechanism of action of yeast antagonists. The present study showed that the yeast C. oleophila is capable of producing and secreting various cell wall-degrading enzymes, including exo-beta-1,3-glucanase, chitinase and protease. Exo-beta-1,3-glucanase and chitinase were produced and maximized in the early stages of growth, whereas protease reached a maximum level only after 6-8 days. Production of exo-beta-1,3-glucanase, chitinase and protease was stimulated by the presence of cell wall fragments of Penicillium digitatum in the growth medium, in addition to glucose. This study also provided evidence that C. oleophila is capable of secreting exo-beta-1,3-glucanase into the wounded surface of grapefruit. The role of exo-beta-1,3-glucanase ( CoEXG1) in the biocontrol activity of C. oleophila was tested using CoEXG1-knockouts and double- CoEXG1 over-producing transformants. In vitro bioassays showed that wild-type C. oleophila and exo-beta-1,3-glucanase over-expressing transformants had similar inhibitory effects on spore germination and germ-tube elongation; and both were more inhibitory to the fungus than the knockout transformant. In experiments conducted on fruit to test the biocontrol activity against infection by P. digitatum, no significant difference in inhibition was observed between transformants and untransformed C. oleophila cells at the high concentrations of cells used, whereas at a lower concentration of yeast cells the knockout transformants appeared to be less effective.

Induction of Resistance to Penicillium digitatum in Grapefruit by the Yeast Biocontrol Agent Candida oleophila

ABSTRACT The yeast Candida oleophila, the base of the commercial product Aspire, is recommended for the control of postharvest decay in citrus and pome fruit. Its modes of action include nutrient competition, site exclusion, and direct mycoparasitism. In the present study, we showed that application of Candida oleophila to surface wounds or to intact 'Marsh Seedless' grapefruit elicited systemic resistance against Penicillium digitatum, the main postharvest pathogen of citrus fruit. The induction of pathogen resistance in fruit was already pronounced 24 h after elicitation; it was distance, concentration, and time dependent and restricted to the peel tissue closely surrounding the yeast application site. The induction of pathogen resistance required viable yeast cells at concentrations of 10(8) to 10(9) cells ml(-1). Nonviable autoclaved or boiled yeast cells or lower yeast concentrations were ineffective in enhancing fruit disease resistance. Application of Candida oleophila cell suspensions to grapefruit peel tissue increased ethylene biosynthesis, phenylalanine ammonia lyase activity, and phytoalexin accumulation, and increased chitinase and beta-1,3-endoglucanase protein levels, indicated by western immunoblotting analysis. Scanning electron microscope observations revealed that spore germination and germ tube growth of Penicillium digitatum were markedly inhibited in wounds made near the yeast-treated sites. Overall, this study provides evidence that induced resistance against postharvest decay of citrus fruit should be considered an important component of the multiple modes of action of the yeast Candida oleophila.