chee370_as1 - CHEE370HomeworkAssignment#1 #1

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CHEE-370 Homework Assi gnment #1                  #1                  Of the genus  Lactococcus , a very high dairy significance bears the species  Lactococcus lactis . This is a non-sporulating,  non-motile, non-fimbriated, Gram-positive bacteria, which can usually be found in plants and dairy products.  It generally  has a circular, sometimes oval shape, and typically appears in pairs or chains.  L. lactis is of antigen group N and is therefore not considered pathogenic. As a lactic acid (L+) producing bacteria, it  grows aerobically, and is of strong importance to humans due to its wide application in buttermilk and cheese production.  Additional properties of L. lactis: not sensitive to oxygen, can grow in its presence (aerotolerant aerobes). Also considered  homofermentative – produces only lactic acid. Obtains energy by substrate-level phosphorylation.                            Figure 1. Lactococcus lactis. Macro view.       Figure 2. Paired groups and chains of L.  lactis.        #2                  Sergei Winogradsky proposed the concepts of  chemolithotrophy  and  chemoautotrophy , he also formulated the concept  of bacterial  nitrogen fixation From   his   studies   of   the   sulfur-oxidizing   bacteria,   the   chemolitotrophy   concept   was   developed   -   it   links   energy  conservation to the oxidation of inorganic compounds. Chemoautotrophy was proposed when Winogradsky observed the  nitrifying bacteria oxidize ammonia to nitrate and concluded that they obtain carbon from carbon dioxide. Lastly, when he  isolated the nigrogen-fixing bacterium  Clostridium pasteurianum , there came to life the concept of nitrogen fixation – a  process allowing the cell to extract nitrogen from nitrogen gas. #3
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This note was uploaded on 12/01/2009 for the course CHEM ENG CHEE 370 taught by Professor Tufenkji,jones during the Fall '09 term at McGill.

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chee370_as1 - CHEE370HomeworkAssignment#1 #1

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