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UBC Theses and Dissertations

The development of membrane associated functions in Micrococcaceae Groot Obbink, Derk Jan


Members of the Micrococcaceae were shown to have broad differences in the base composition of their DNA and to exhibit a strong correlation between aerobiosis and a high %GC. An analysis of the genome sizes of the DNA revealed a four-fold difference in the range. In general the organisms with a large genome had a high %GC. P. aerogenes, which had the smallest genome, was an anaerobe and had a genome comparable in size to that reported for mycoplasma. Hybridization studies between some organisms with small genomes showed that they were a genetically heterogeneous group. An examination of the amino acid requirements of the organisms showed that aerobic organisms with large genomes and high %GC were nutritionally independent while anaerobic organisms with small genomes and a low %GC had broad nutritional requirements. P. aerogenes would grow only in complex medium. In an effort to ob serve any developmental changes, amino acid transport, as one type of membrane associated function, was studied in a series of micrococci selected for their differences in genetic complexity. With the exception of P. aerogenes, which would grow only in complex medium, and with which no proline transport could be demonstrated, the transport of proline was a well developed process. It was shown to be energy dependent, specific for proline, to display saturation kinetics and to be derepressed in organisms auxotrophic for, and starved for this amino acid. Transport for isoleucine and methionine were also shown to be well developed in M. varians, M.sp.250 and SL aureus and it was concluded that the development of active transport was an early function in bacteria which may have given them a selective advantage. A study of membrane bound oxidative and phosphorylative enzymes showed that there was a strong correlation between the number of membrane bound oxidative and phosphorylative enzymes and aerobiosis. Treatment of the membranes with a dilute buffer containing EDTA, which affected the hydrophilic interactions in the membrane, had variable effects on the solubilization and activity of membrane bound enzymes. Triton-X which affected hydrophobic interactions had less variable results. The effect on the level of activity and the pattern of solubilization of a particular enzyme was similar in the different membrane systems studied. Therefore, hydrophobic interactions may be stable characteristics that are conserved. A study of the protein structure of the membrane revealed an increase in number of protein subunits and a general increase in the molecular weight of the subunits with increasing genetic complexity. Although increasing genome size seemed to confer nutritional independence and increased number and size of membrane subunits, functional aspects of the membrane were well developed in organisms with a small genome size.

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