RESUMO
AIMS: The present work aimed to define a minimal chemically-defined medium which could sustain the growth of most (if not all) strains of Streptococcus thermophilus. METHODS AND RESULTS: A minimal medium containing 20 components, including one carbohydrate source, six amino acids, two metallic ions, six vitamins and urea allowed for growth of 13 out of 15 Strep. thermophilus strains. Growth of the two last strains required the presence of additional amino acids, the number of which depended on the strain. Growth rates of the strains in the minimal medium ranged from 0.38 to 0.64 h(-1), and final populations were about 10(8) cfu ml(-1). CONCLUSIONS: Streptococcus thermophilus appears much less demanding than other lactic acid bacteria. SIGNIFICANCE AND IMPACT OF THE STUDY: The definition of such a growth medium will be very useful for metabolic flux studies as well as peptide transport studies.
Assuntos
Meios de Cultura/química , Streptococcus/crescimento & desenvolvimento , Técnicas Bacteriológicas , Streptococcus/classificaçãoRESUMO
Lactic acid bacteria are nutritionally demanding bacteria which need, among other things, amino acids for optimal growth. We identified the branched-chain amino acid (BCAA) biosynthesis pathway as an essential pathway for optimal growth of Streptococcus thermophilus in milk. Through random insertional mutagenesis, we isolated and characterized two mutants for which growth in milk is affected as a consequence of ilvB and ilvC gene interruptions. This situation demonstrates that the BCAA biosynthesis pathway is active in S. thermophilus. BCAA biosynthesis is necessary but not sufficient for optimal growth of S. thermophilus and is subject to retro-inhibition processes. The specificity of the BCAA biosynthesis pathway in S. thermophilus lies in the independent transcription of the ilvC gene encoding a keto acid reductoisomerase acting on acetolactate at the junction of the BCAA and acetoin biosynthesis pathways. The possible advantages for S. thermophilus of keeping this biosynthesis pathway active could be linked either to adaptation of the organism to milk, which is different than that of other dairy bacteria, or to the role of the pathway in maintaining the internal pH.
Assuntos
Aminoácidos de Cadeia Ramificada/biossíntese , Leite/microbiologia , Streptococcus/crescimento & desenvolvimento , Streptococcus/metabolismo , Animais , Sequência de Bases , Primers do DNA/genética , DNA Bacteriano/genética , Evolução Molecular , Genes Bacterianos , Concentração de Íons de Hidrogênio , Lactococcus lactis/genética , Lactococcus lactis/crescimento & desenvolvimento , Lactococcus lactis/metabolismo , Dados de Sequência Molecular , Mutagênese Insercional , Streptococcus/genéticaRESUMO
Myoglobin is released into the blood after burn injury. We measured it and other analytes in blood collected from 22 burn patients two to seven times during their recovery. There was a significant correlation between myoglobinemia and creatine kinase (CK) activity in serum (r = 0.764; p less than 0.001). In a group of 14 thermal-burn subjects a correlation was found between burn depth (clinically expressed as Unit Burn Surface) and both myoglobinemia (r = 0.825; p less than 0.01) and CK activity (r = 0.686; p less than 0.01). In eight thermal-burn patients who were recovering satisfactorily, myoglobin and CK activity measured on days 2, 4, 7, 10, and 13 after injury were significantly increased (p less than 0.05) on days 2, 4, and 7. Evidently myoglobinemia and CK activity are good biological markers of burn depth, and reflect muscle damage equally well.