University College Cork

About: University College Cork is a education organization based out in Cork, Ireland. It is known for research contribution in the topics: Population & Context (language use). The organization has 12056 authors who have published 28452 publications receiving 958414 citations. The organization is also known as: Coláiste na hOllscoile Corcaigh & National University of Ireland, Cork.

Biological control of Pythium ultimum by Stenotrophomonas maltophilia W81 is mediated by an extracellular proteolytic activity

Abstract: Stenotrophomonas maltophilia strain W81, isolated from the rhizosphere of field-grown sugar beet, produced the extracellular enzymes chitinase and protease and inhibited the growth of the phytopathogenic fungus Pythium ultimum in vitro. The role of these lytic enzymes in the interaction between W81 and P. ultimum was investigated using Tn5 insertion mutants of W81 incapable of producing extracellular protease (W81M1), extracellular chitinase (W81M2) or the two enzymes (W81A1). Lytic enzyme activity was restored in W81A1 following introduction of a 15 kb cosmid-borne fragment of W81 genomic DNA. Incubation of P. ultimum in the presence of commercial purified protease or cell-free supernatants from cultures of wild-type W81, the chitinase-negative mutant W81M2 or the complemented derivative W81A1 (pCU800) resulted in hyphal lysis and loss of subsequent fungal growth ability once re-inoculated onto fresh plates. In contrast, commercial purified chitinase or cell-free supernatants from cultures of the protease-negative mutant WS1M1 or the chitinase- and protease-negative mutant W81A1 had no effect on integrity of the essentially chitin-free Pythium mycelium, and did not prevent subsequent growth of the fungus. In soil microcosms containing soil naturally infested by Pythium spp., strains W81, W81M2 and W81A1(pCU800) reduced the ability of Pythium spp. to colonize the seeds of sugar beet and improved plant emergence compared with the untreated control, whereas W81A1 and W21M1 failed to protect sugar beet from damping-off. Wild-type W81 and its mutant derivatives colonized the rhizosphere of sugar beet to similar extents, it was concluded that the ability of S. maltophilia W81 to protect sugar beet from Pythium -mediated damping-off was due to the production of an extracellular protease.

Proteolysis in Cheese during Ripening

Abstract: This chapter discusses proteolysis process in cheese during ripening. Proteolysis contributes to: (1) The development of cheese texture: via hydrolysis of the protein matrix of cheese; via a decrease in aw through changes to water binding by the new carboxylic acid and amino groups liberated on hydrolysis of peptide bonds. These groups are ionized at the pH of cheese and thus bind water; indirectly via an increase in pH caused by the liberation of ammonia from amino acids produced by proteolysis. (2) Flavor and perhaps the off-flavor of cheese, directly by the production of short peptides and amino acids, some of which have flavors; indirectly by the liberation of amino acids, which act as substrates for a range of catabolic reactions, which generate important volatile flavor compounds; by facilitating the release of sapid compounds from the cheese matrix during mastication. Proteolysis in cheese during ripening is catalyzed by proteinases and peptidases from six sources: (1) the coagulant—the enzymes involved depend on the type of coagulant used. (2) the milk—a number of indigenous proteinases are present in milk, the most important of which is plasmin, which is produced from an inactive precursor, plasminogen. (3) starter lactic acid bacteria (LAB) contain a cell envelope-associated proteinase, which contributes to ripening principally by hydrolyzing intermediate-sized and short peptides produced from the caseins by the action of chymosin or plasmin. The other three sources are nonstarter lactic acid bacteria (NSEAB), secondary starter ( Propionibacterium freudenreichii subsp, shermanii in Swiss-type cheese), and exogenous proteinases and peptidases.

New Evidence for Black Hole Event Horizons from Chandra

Abstract: Previously we claimed that Black Hole X-ray Novae (BHXN) in quiescence are much less luminous than equivalent Neutron Star X-ray Novae (NSXN). This claim was based on the quiescent detection of a single short period BHXN (A0620-00, P(orb)=7.8 hrs) and two longer period BHXN (GRO J1655-40, P(orb)=62.9 hrs; V404 Cyg, P(orb)=155.3 hrs), along with sensitive upper limits. We announce the detection of two more short period BHXN (GRO J0422+32, P(orb)=5.1 hrs; GS 2000+25, P(orb)=8.3 hrs), an upper limit for a third which is improved by two orders of magnitude (4U 1543-47, P(orb)=27.0 hrs) and a new, much lower quiescent measurement of GRO J1655-40. Taken together, these new Chandra measurements confirm that the quiescent X-ray luminosities of BHXN are significantly lower than those of NSXN. We argue that this provides strong evidence for the existence of event horizons in BHXN.