Highly flexible metabolism of the marine euglenozoan protist Diplonema papillatum.

BACKGROUND: The phylum Euglenozoa is a group of flagellated protists comprising the diplonemids, euglenids, symbiontids, and kinetoplastids. The diplonemids are highly abundant and speciose, and recent tools have rendered the best studied representative, Diplonema papillatum, genetically tractable. However, despite the high diversity of diplonemids, their lifestyles, ecological functions, and even primary energy source are mostly unknown. RESULTS: We designed a metabolic map of D. papillatum cellular bioenergetic pathways based on the alterations of transcriptomic, proteomic, and metabolomic profiles obtained from cells grown under different conditions. Comparative analysis in the nutrient-rich and nutrient-poor media, as well as the absence and presence of oxygen, revealed its capacity for extensive metabolic reprogramming that occurs predominantly on the proteomic rather than the transcriptomic level. D. papillatum is equipped with fundamental metabolic routes such as glycolysis, gluconeogenesis, TCA cycle, pentose phosphate pathway, respiratory complexes, ß-oxidation, and synthesis of fatty acids. Gluconeogenesis is uniquely dominant over glycolysis under all surveyed conditions, while the TCA cycle represents an eclectic combination of standard and unusual enzymes. CONCLUSIONS: The identification of conventional anaerobic enzymes reflects the ability of this protist to survive in low-oxygen environments. Furthermore, its metabolism quickly reacts to restricted carbon availability, suggesting a high metabolic flexibility of diplonemids, which is further reflected in cell morphology and motility, correlating well with their extreme ecological valence.

Antibacterial Activity of Different Blossom Honeys: New Findings.

Antibacterial activity is the most investigated biological property of honey. The goal of this study was to evaluate the antibacterial activity of 57 Slovak blossom honeys against Staphylococcus aureus and Pseudomonas aeruginosa and investigate the role of several bioactive substances in antibacterial action of honeys. Inhibitory and bactericidal activities of honeys were studied to determine the minimum inhibitory and bactericidal concentrations. The contents of glucose oxidase (GOX) enzyme, hydrogen peroxide (H2O2), and total polyphenols (TP) were determined in honeys. We found that honey samples showed different antibacterial efficacy against the tested bacteria as follows: wildflower honeys > acacia honeys > rapeseed honeys. Overall antibacterial activity of the honeys was statistically-significantly correlated with the contents of H2O2 and TP in honeys. A strong correlation was found between the H2O2 and TP content. On the other hand, no correlation was found between the content of GOX and level of H2O2. Antibacterial activity of 12 selected honeys was markedly reduced by treatment with catalase, but it remained relatively stable after inactivation of GOX with proteinase-K digestion. Obtained results suggest that the antibacterial activity of blossom honeys is mainly mediated by H2O2 levels present in honeys which are affected mainly by polyphenolic substances and not directly by GOX content.

Trophic flexibility of marine diplonemids - switching from osmotrophy to bacterivory.

Diplonemids are one of the most abundant groups of heterotrophic planktonic microeukaryotes in the world ocean and, thus, are likely to play an essential role in marine ecosystems. So far, only few species have been introduced into a culture, allowing basic studies of diplonemid genetics, morphology, ultrastructure, metabolism, as well as endosymbionts. However, it remains unclear whether these heterotrophic flagellates are parasitic or free-living and what are their predominant dietary patterns and preferred food items. Here we show that cultured diplonemids, maintained in an organic-rich medium as osmotrophs, can gradually switch to bacterivory as a sole food resource, supporting positive growth of their population, even when fed with a low biovolume of bacteria. We further observed remarkable differences in species-specific feeding patterns, size-selective grazing preferences, and distinct feeding strategies. Diplonemids can discriminate between low-quality food items and inedible particles, such as latex beads, even after their ingestion, by discharging them in the form of large waste vacuoles. We also detected digestion-related endogenous autofluorescence emitted by lysosomes and the activity of a melanin-like material. We present the first evidence that these omnipresent protists possess an opportunistic lifestyle that provides a considerable advantage in the generally food resource-limited marine environments.

Microwave processing of honey negatively affects honey antibacterial activity by inactivation of bee-derived glucose oxidase and defensin-1.

Microwave (MW) thermal heating has been proposed as an efficient method for honey liquefaction, while maintaining honey quality criteria. However, little is known about the effects of MW thermal heating on honey antibacterial activity. In this study, we aimed to determine the effects of MW heating on the antibacterial activity of raw rapeseed honeys against Pseudomonas aeruginosa and Staphylococcus aureus, with a particular focus on two major bee-derived antibacterial components, defensin-1 and hydrogen peroxide (H2O2). Our results demonstrated that MW thermal heating completely abolished honey antibacterial activity whereas conventional thermal treatment at 45 and 55°C did not affect the antibacterial activity of honey samples. A significant decrease in both glucose oxidase activity and H2O2 production as well as defensin-1 amount was observed in MW-treated samples. Given that defensin-1 and H2O2 are regular antibacterial components of all honeys, MW heating may have similar negative effects on every type of crystallized/liquid honey.

Effect of thermal liquefying of crystallised honeys on their antibacterial activities.

Thermal liquefying of crystallised honey is the most convenient option for beekeepers to fully liquefy honey. A controlled mild thermal treatment is widely used for effective and safe liquefying of crystallised honey. In this study, we demonstrated that thermal liquefying at different temperatures of 45, 55 and 65 °C does not affect the overall honey antibacterial activity against Pseudomonas aeruginosa and Staphylococcus aureus, and, in some cases, it may even increase the antibacterial potential of honey. A mild thermal treatment of crystallised honey was able to significantly increase its glucose oxidase (GOX) enzyme activity. On the other hand, the increased GOX activity in treated honey samples did not affect levels of accumulated H2O2, suggesting that some phytochemicals may contribute to or modulate antibacterial activity. Taken together, a mild thermal liquefaction of crystallised honey may increase the potential bioactivity of this matrix, which is also affected by the botanical origin.