Endogenous peptidoglycan (PG)-hydrolyzing enzymes, the autolysins, are needed to relax the rigid PG sacculus to allow bacterial cell growth and separation. PGs of pathogens and commensal bacteria may also be degraded by hydrolases of animal origin (lysozymes), which act as antimicrobials. The genetic mechanisms regulating PG resistance to hydrolytic degradation were dissected in the Gram-positive bacterium Lactococcus lactis. We found that the ability of L. lactis to counteract PG hydrolysis depends on the degree of acetylation. Overexpression of PG O-acetylase (encoded by oatA) led to bacterial growth arrest, indicating the potential lethality of oatA and a need for its tight regulation. A novel regulatory factor, SpxB (previously denoted as YneH), exerted a positive effect on oatA expression. Our results indicate that SpxB binding to RNA polymerase constitutes a previously missing link in the multistep response to cell envelope stress, provoked by PG hydrolysis with lysozyme. We suggest that the two-component system CesSR responds to this stress by inducing SpxB, thus favoring its interactions with RNA polymerase. Induction of PG O-acetylation by this cascade renders it resistant to hydrolysis. Peptidoglycan (PG)7 is the major and essential component of the bacterial cell envelope, the main function of which is to preserve cell integrity by withstanding internal osmotic pressure (1, 2). It is also responsible for cell shape, participates in cell division, and serves as support for attachment of other cell wall molecules such as teichoic acids, proteins, and exopolysaccharides (3). The bacterial PG is a giant multilayer polymer that envelops the cell as a rigid sacculus. It is composed of N-acetylglucosamine-N-acetylmuramic acid disaccharide pentapeptide blocks that are synthesized intracellularly and transported through the cytoplasmic membrane as lipid-disaccharide pentapeptides. These blocks are covalently linked to the pre-existing PG polymers by high molecular weight penicillin-binding proteins (4).To allow cell division and surface expansion, the rigid PG sacculus has to be relaxed. This is achieved by PG ruptures, which could be introduced in several ways. First, not all possible covalent bonds are formed during PG synthesis; for example, only 36% of possible PG cross-links between stem peptides are formed in Lactococcus lactis (5). Bacteria also possess a number of endogenous bacterial enzymes (collectively called autolysins) that disrupt PG and can result in cell lysis. According to their hydrolytic bond specificity and products, autolysins are classified as muramidases, lytic transglycosylases, glucosaminidases, amidases, and peptidases (6). Bacteria often possess several autolysins, e.g. L. lactis encodes a main autolysin (N-acetylglucosaminidase AcmA) (7, 8) and four minor PG hydrolases (9, 10) as well as prophage-encoded bacteriolytic enzymes (11).In the human or animal host, antimicrobial PG lytic enzymes such as lysozyme constitute a first line of defense against infection. Bactericidal propertie...
Introducción. La morera (Morus alba), planta originaria de China, se utiliza como forraje en algunas granjas. Su alto contenido de proteína estimula la producción de leche en el ganado; sin embargo, se desconoce si sus flavonoides pueden ser incorporados en la leche caprina. Objetivo. Evaluar el efecto de una dieta enriquecida con morera, sobre la concentración de flavonoides y parámetros bromatológicos de leche de cabras alpinas estabuladas. Materiales y métodos. El experimento se realizó en el año 2019, con cabras de una granja particular ubicada en Veracruz, México. Se formaron dos grupos (A con el tratamiento y B control) con cinco cabras de raza alpina cada uno, de características similares (alimentación estabulada, tres partos, sin mastitis, ordeño manual matutino y vespertino). El grupo A recibió forraje sin morera antes y después del tratamiento (días 1-10 y 21-31, respectivamente), y una dieta de forraje modificada con morera (días 11-20, tratamiento); el grupo B se alimentó con forraje sin morera los 31 días de experimentación. Además, se analizó el contenido de flavonoides en la morera y cada tres días en muestras de leche, además de los bromatológicos de contenido de proteína, grasa, lactosa, sólidos no grasos y densidad. Resultados. Durante la dieta modificada con morera, la concentración de flavonoides alcanzó un máximo de 53,45 mg mL-1 EQ en el grupo A al día 20, descendió de forma paulatina durante el periodo posterior al tratamiento; además, mantuvo un 20 % más de flavonoides que el grupo control. Se observó también un incremento significativo del contenido de proteína en el grupo A, sin diferencia significativa en los demás parámetros bromatológicos de la leche entre los dos grupos. Conclusión. Las dietas modificadas con morera favorecieron la incorporación de flavonoides y el incremento de proteína en la leche de cabra, sin modificar los demás parámetros bromatológicos.
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