To analyze the transcriptional response ofYersinia enterocoliticacells to prolonged growth at low temperature, a collection ofluxCDABEtransposon mutants was cultivated in parallel at optimal (30°C) and suboptimal (10°C) temperatures and screened for enhanced promoter activities during growth until entering stationary phase. Among 5,700Y. enterocoliticamutants, 42 transcriptional units were identified with strongly enhanced or reduced promoter activity at 10°C compared to 30°C, and changes in their transcriptional levels over time were measured. Green fluorescent protein fusions to 10 promoter regions confirmed the data. The temporal order of induction of the temperature-responsive genes ofY. enterocoliticawas deduced, starting with the expression of cold shock genescspAandcspBand the elevated transcription of a glutamate-aspartate symporter. Subsequently, cold-adapted cells drastically up-regulated genes encoding environmental sensors and regulators, such as UhpABC, ArcA, and methyl-accepting chemotaxis protein I (MCPI). Among the most prominent cold-responsive elements that were transcriptionally induced during growth in early and middle exponential phase are the insecticidal toxin genestcaAandtcaB, as well as genes involved in flagellar synthesis and chemotaxis. The expression pattern of the late-exponential- to early-stationary-growth phase is dominated by factors involved in biodegradative metabolism, namely, a histidine ammonia lyase, three enzymes responsible for uptake and utilization of glycogen, the urease complex, and a subtilisin-like protease. Double-knockout mutants and complementation studies demonstrate inhibitory effects of MCPI and UhpC on the expression of a putative hemolysin transporter. The data partially delineate the spectrum of gene expression ofY. enterocoliticaat environmental temperatures, providing evidence that an as-yet-unknown insect phase is part of the life cycle of this human pathogen.

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