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A Mutant Allele of rpoD Results in Increased Conversion of Aminoimidazole Ribotide to Hydroxymethyl Pyrimidine in Salmonella enterica. Michael J. Dougherty, 2004.An allele of rpoD (rpoD1181) that results in increased synthesis of the pyrimidine moiety of thiamine in Salmonella enterica was identified . The S508Y substitution caused by rpoD1181 is analogous to the S506F derivative of the Escherichia coli protein . The properties of this E . coli mutant protein have been well characterized in vitro . Identification of a metabolic phenotype caused by the rpoD1181 allele of S . enterica allows past in vitro results to be incorporated in continuing efforts to understand cellular processes that are integrated with the thiamine biosynthetic pathway . YfiK from Escherichia coli Promotes Export of O-Acetylserine and Cysteine. Isabel Franke, 2003.yfiK was discovered as a gene augmenting cysteine production when it was overexpressed in an industrial Escherichia coli production strain . The gene product is an integral membrane protein with about six predicted transmembrane helices; it belongs to the RhtB family of export proteins . YfiK overproduction from a plasmid leads to drastic and parallel secretion of O-acetylserine and cysteine into the medium but only when the organism possesses a serine transacetylase that is feedback insensitive to cysteine . Externally provided O-acetylserine obviated this requirement for cysteine secretion both in the yfiK-carrying transformant and in the wild type . A  yfiK mutant did not show any phenotype, and it exported O-acetylserine and cysteine when transformed with a plasmid carrying ydeD, a previously characterized, alternate O-acetylserine/cysteine exporter . Since a ydeD-yfiK double mutant showed the same pattern, it appears that YfiK and YdeD act independently . The necessity for the cell to regulate the size of the internal pool of O-acetylserine via synthesis of exporter proteins could be connected to the fact that this compound (when supplied externally) inhibits growth . Overexpression of either ydeD or yfiK leads to alleviation of this inhibition paralled by increased resistance to azaserine, which is an analog of O-acetylserine .
Evaluation of F+ RNA and DNA Coliphages as Source-Specific Indicators of Fecal Contamination in Surface Waters. Dana Cole, 2003.Male-specific (F+) coliphages have been investigated as viral indicators of fecal contamination that may provide source-specific information for impacted environmental waters . This study examined the presence and proportions of the different subgroups of F+ coliphages in a variety of fecal wastes and surface waters with well-defined potential waste impacts . Municipal wastewater samples had high proportions of F+ DNA and group II and III F+ RNA coliphages . Bovine wastewaters also contained a high proportion of F+ DNA coliphages, but group I and IV F+ RNA coliphages predominated . Swine wastewaters contained approximately equal proportions of F+ DNA and RNA coliphages, and group I and III F+ RNA coliphages were most common . Waterfowl (gull and goose) feces contained almost exclusively F+ RNA coliphages of groups I and IV . No F+ coliphages were isolated from the feces of the other species examined . F+ coliphage recovery from surface waters was influenced by precipitation events and animal or human land use . There were no significant differences in coliphage density among land use categories . Significant seasonal variation was observed in the proportions of F+ DNA and RNA coliphages . Group I F+ RNA coliphages were the vast majority (90%) of those recovered from surface waters . The percentage of group I F+ RNA coliphages detected was greatest at background sites, and the percentage of group II F+ RNA coliphages was highest at human-impacted sites . Monitoring of F+ coliphage groups can indicate the presence and major sources of microbial inputs to surface waters, but environmental effects on the relative occurrence of different groups need to be considered .
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