Title

Whole genome transcription profiling of Thermotoga maritima in response to growth on glucose, lactose and maltose

Date of Completion

January 2004

Keywords

Biology, Microbiology

Degree

Ph.D.

Abstract

Thermotoga spp. are hyperthermophilic, anaerobic bacteria that can grow on a wide variety of mono- to polysaccharides by fermentation. This ability is reflected in the large number of genes encoding proteins involved in carbohydrate utilization and transport in the genome of Thermotoga maritima. Due to their phylogenetic position as the deepest branch of bacterial heterotrophs, knowledge of the physiology of Thermotoga offers an evolutionary perspective on systems in other organisms. ^ The major objective of this thesis was to use DNA microarrays to obtain a global view of gene expression of T. maritima grown on glucose, lactose and maltose, and to have a better understanding of the metabolism and transports of these disaccharides in this bacterium. Expression in glucose-grown cells was used as the reference. The expression data from microarray analyses were confirmed by Northern and DNA dot blot hybridizations and real-time PCR. ^ Out of 1,865 ORFs, 106 were differentially expressed in lactose- and only 24 were in maltose-grown cells. In lactose-grown cells, increases in expression of the β-galactosidase genes as well as genes encoding xylanase, xylosidase and glucuronidase suggested that a β-galactoside might be recognized by T. maritima as potential presence of more complex polysaccharides. Differential expression of genes encoding ABC oligopeptide transporters was also seen and is consistent with previous observations of oligopeptide-like binding proteins that actually bind oligosaccharides. Differential expression in genes encoding NADH dehydrogenases and NADH oxidase suggested a connection between redox balance and disaccharide catabolism. A potential role for dihydrolipoamidellipoamide in galactoside transport was proposed to explain the observed differential expression of a dihydrolipoamide dehydrogenase gene. Differential expression of the iron-sulfur cluster assembly SufBCDS, ferrous ion transporters and several iron-sulfur proteins in glucose- and lactose-grown cells may point to a complex interaction of sugar, iron and sulfur metabolisms. ^ The data gathered from this work provide new information on how T. maritima responds to a β-galactoside and an α-glucoside as the sole carbon source. The proposed hypotheses offer new directions for future investigations into sugar transport and metabolism in this organism. ^