Helga Næs

Bio: Helga Næs is an academic researcher from Norwegian Food Research Institute. The author has contributed to research in topics: Lactobacillus paracasei & Fermentation starter. The author has an hindex of 6, co-authored 6 publications receiving 324 citations.

Cloning, sequencing and expression of the gene encoding the cell-envelope-associated proteinase from Lactobacillus paracasei subsp. paracasei NCDO 151.

Abstract: The gene encoding the cell-envelope-associated proteinase of Lactobacillus paracasei subsp. paracasei NCDO 151 (formerly Lactobacillus casei NCDO 151) was cloned and sequenced. The gene was located on the chromosome and encoded a polypeptide of 1902 amino acids. The proteinase is N-terminally cleaved upon maturation. It shows extensive homology to the Lactococcus lactis subsp. cremoris Wg2 proteinase. Similar to the situation in Lactococcus, a maturation gene was found upstream of the proteinase gene. The cloned proteinase gene was expressed in Lactobacillus plantarum. However, no expression was observed when the gene was cloned in Lactococcus lactis.

Accelerated ripening of dry fermented sausage by addition of a Lactobacillus proteinase

Abstract: Accelerated ripening of dry sausage was investigated by adding two different concentrations of proteinase isolated from Lactobacillus paracasei ssp. paracasei NCDO151 to sausage mixtures. Sausages with proteinase showed a greater pH decrease and a greater increase in lactic acid formation, water loss, protein degradation and peptide formation than control, no enzyme, sausages. Changes were most pronounced in the sausages containing 12Ug -1 proteinase. Addition of proteinase caused a specific increase in glutamate, serine and lysine content. Sensory evaluation after 14 days of ripening showed a significant increase in flavour intensity, maturity flavour, acidity, bitter taste and hardness in the proteinase-containing sausages. Addition of proteinase induced changes earlier in the fermentation and ripening period than in the control, thereby indicating an acceleration of maturation.

Bacterial Proteinase Reduces Maturation Time of Dry Fermented Sausages

Abstract: The effect of proteinases, from Lactobacillus paracasei subsp. paracasei NCDO151 and from Bacillus licheniformis (Alcalase, NOVO Nordisk), on the ripening of dry sausages was compared. Increased levels of starter bacteria, d-lactic acid, a sharper pH-drop and changes in chromatographic profiles (by gas chromatography/mass spectrometry) indicated that the enzyme from Lactobacillus paracasei accelerated the dry sausage ripening. This effect was not detected in sausages with the Alcalase enzyme. Higher sensory scores on maturity flavor, color, hardness and others, confirmed that sausages containing proteinase from L. paracasei showed the same maturity after 14 days as those without enzymes or with the Alcalase enzyme after 28 days.

Purification and N-terminal amino acid sequence determination of the cell-wall-bound proteinase from Lactobacillus paracasei subsp. paracasei

Abstract: SUMMARY: The cell-wall-bound proteinase from Lactobacillus paracasei subsp. paracasei NCDO 151 was purified to homogeneity by anion-exchange and hydrophobic-interaction chromatography, chromatofocusing and gelfiltration. The purification resulted in a 600-700-fold increase in specific activity of the proteinase and the final yield was approximately 20%. Upon chromatofocusing, two proteolytically active components, termed pro 135 and pro110, were detected. pro135 had an isoelectric point of 4·2. It had an M r of about 300000 as determined by gelfiltration and 135000 as judged by SDS-PAGE, indicating that it may exist as a dimer in its native state, pro110 had an isoelectric point of 4·4, and an M r of about 150000 as determined by gel-filtration and 110000 as judged by SDS-PAGE. pro110 appears to be a degradation product of pro135 as they have the same N-terminal amino acid sequence. The first N-terminal amino acid was ambiguous for both components, whereas the sequence from the second to the ninth amino acid was Ala-Lys-Ala-Asn-Ser-Met-Ala-Asn. This is identical to the corresponding sequence of the lactococcal cell-wall-bound proteinases. Although the Lactobacillus proteinase was a little smaller than the lactococcal proteinase, their purification characteristics were very similar, suggesting that these proteinases are related.

Surface Proteins of Gram-Positive Bacteria and Mechanisms of Their Targeting to the Cell Wall Envelope

Abstract: The cell wall envelope of gram-positive bacteria is a macromolecular, exoskeletal organelle that is assembled and turned over at designated sites. The cell wall also functions as a surface organelle that allows gram-positive pathogens to interact with their environment, in particular the tissues of the infected host. All of these functions require that surface proteins and enzymes be properly targeted to the cell wall envelope. Two basic mechanisms, cell wall sorting and targeting, have been identified. Cell well sorting is the covalent attachment of surface proteins to the peptidoglycan via a C-terminal sorting signal that contains a consensus LPXTG sequence. More than 100 proteins that possess cell wall-sorting signals, including the M proteins of Streptococcus pyogenes, protein A of Staphylococcus aureus, and several internalins of Listeria monocytogenes, have been identified. Cell wall targeting involves the noncovalent attachment of proteins to the cell surface via specialized binding domains. Several of these wall-binding domains appear to interact with secondary wall polymers that are associated with the peptidoglycan, for example teichoic acids and polysaccharides. Proteins that are targeted to the cell surface include muralytic enzymes such as autolysins, lysostaphin, and phage lytic enzymes. Other examples for targeted proteins are the surface S-layer proteins of bacilli and clostridia, as well as virulence factors required for the pathogenesis of L. monocytogenes (internalin B) and Streptococcus pneumoniae (PspA) infections. In this review we describe the mechanisms for both sorting and targeting of proteins to the envelope of gram-positive bacteria and review the functions of known surface proteins.

Lactic acid bacteria: classification and physiology.

Abstract: Lactic acid bacteria (LAB) constitute a group of gram-positive bacteria united by a constellation of morphological, metabolic, and physiological characteristics The general description of the bacteria included in the group is gram-positive, nonsporing, nonrespiring cocci or rods, which produce lactic acid as the major end product during the fermentation of carbohydrates The LAB term is intimately associated with bacteria involved in food and feed fermentation, including related bacteria normally associated with the (healthy) mucosal surfaces of humans and animals The boundaries of the group have been subject to some controversy, but historically the genera Lactobacillus, Leuconostoc, Pediococcus, and Streptococcus form the core of the group Taxonomic revisions of these genera and the description of new genera mean that LAB could, in their broad physiological definition, comprise around 20 genera However, from a practical, food-technology point of view, the following genera are considered the principal LAB: Aerococcus, Carnobacterium, Enterococcus, Lactobacillus, Lactococcus, Leuconostoc, Oenococcus, Pediococcus, Streptococcus, Tetragenococcus, Vagococcus, and Weissella The genus Bifidobacterium, often considered in the same context as the genuine lactic acid bacteria and sharing some of their typical features, is phylogenetically unrelated and has a unique mode of sugar fermentation The classification of lactic acid bacteria into different genera is largely based on morphology, mode of glucose fermentation, growth at different temperatures, configuration of the lactic acid produced, ability to grow at high salt concentrations, and acid or alkaline tolerance Chemotaxonomic markers such as fatty acid composition and constituents of the cell wall are also used in classification In addition, the present taxonomy relies partly on true phylogenetic relationships,

The proteolytic systems of lactic acid bacteria

Abstract: Proteolysis in dairy lactic acid bacteria has been studied in great detail by genetic, biochemical and ultrastructural methods. From these studies the picture emerges that the proteolytic systems of lactococci and lactobacilli are remarkably similar in their components and mode of action. The proteolytic system consists of an extracellularly located serine-proteinase, transport systems specific for di-tripeptides and oligopeptides (> 3 residues), and a multitude of intracellular peptidases. This review describes the properties and regulation of individual components as well as studies that have led to identification of their cellular localization. Targeted mutational techniques developed in recent years have made it possible to investigate the role of individual and combinations of enzymes in vivo. Based on these results as well as in vitro studies of the enzymes and transporters, a model for the proteolytic pathway is proposed. The main features are: (i) proteinases have a broad specificity and are capable of releasing a large number of different oligopeptides, of which a large fraction falls in the range of 4 to 8 amino acid residues; (ii) oligopeptide transport is the main route for nitrogen entry into the cell; (iii) all peptidases are located intracellularly and concerted action of peptidases is required for complete degradation of accumulated peptides.

Proteolytic systems of lactic acid bacteria

Abstract: Lactic acid bacteria (LAB) have a very long history of use in the manufacturing processes of fermented foods and a great deal of effort was made to investigate and manipulate the role of LAB in these processes. Today, the diverse group of LAB includes species that are among the best-studied microorganisms and proteolysis is one of the particular physiological traits of LAB of which detailed knowledge was obtained. The proteolytic system involved in casein utilization provides cells with essential amino acids during growth in milk and is also of industrial importance due to its contribution to the development of the organoleptic properties of fermented milk products. For the most extensively studied LAB, Lactococcus lactis, a model for casein proteolysis, transport, peptidolysis, and regulation thereof is now established. In addition to nutrient processing, cellular proteolysis plays a critical role in polypeptide quality control and in many regulatory circuits by keeping basal levels of regulatory proteins low and removing them when they are no longer needed. As part of the industrial processes, LAB are challenged by various stress conditions that are likely to affect metabolic activities, including proteolysis. While environmental stress responses of LAB have received increasing interest in recent years, our current knowledge on stress-related proteolysis in LAB is almost exclusively based on studies on L. lactis. This review provides the current status in the research of proteolytic systems of LAB with industrial relevance.