The genome sequence of Flavobacterium psychrophilum strain CSF259-93, isolated from rainbow trout (Oncorhynchus mykiss), consists of a single circular genome of 2,900,735 bp and 2,701 predicted open reading frames (ORFs). Strain CSF259-93 has been used to select a line of rainbow trout with increased genetic resistance against bacterial cold water disease.

Adaptation is key for survival as vector-borne pathogens transmit between the arthropod and vertebrate, and temperature change is an environmental signal inducing alterations in gene expression of tick-borne spirochetes. While plasmids are often associated with adaptation, complex genomes of relapsing fever spirochetes have hindered progress in understanding the mechanisms of vector colonization and transmission. We utilized recent advances in genome sequencing to generate the most complete version of the Borrelia turicatae 150 kb linear megaplasmid (lp150). Additionally, a transcriptional analysis of open reading frames (ORFs) in lp150 was conducted and identified regions that were up-regulated during in vitro cultivation at tick-like growth temperatures (22°C), relative to bacteria grown at 35°C and infected murine blood. Evaluation of the 3’ end of lp150 identified a cluster of ORFs that code for putative surface lipoproteins. With a microbe’s surface proteome serving important roles in pathogenesis, we confirmed the ORFs expression in vitro and in the tick compared to spirochetes infecting murine blood. Transcriptional evaluation of lp150 indicates the plasmid likely has essential roles in vector colonization and/or initiating mammalian infection. These results also provide a much needed transcriptional framework to delineate the molecular mechanisms utilized by relapsing fever spirochetes during their enzootic cycle.

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The risk ofC. aurisinfection is high because it can colonize the body, resist antifungal treatment, and evade the immune system. The genetic mechanisms for these traits are not well-known. We present an analysis of the genetics and gene expression patterns ofC. auriscarbon metabolism, drug resistance, and macrophage interaction. We chose to study twoC. aurisisolates simultaneously, one drug sensitive (B11220 from Clade II) and one drug resistant (B11221 from Clade III). We found that B11220 was missing a 12.8 kb gene cluster encoding proteins related to alternative sugar utilization, possibly L-rhamnose. We show that B11221 more readily assimilates and utilizes D-galactose and L-rhamnose. B11221 exhibits increased adherence and drug resistance compared to B11220 when grown in these sugars. Transcriptomic analysis of both strains grown on glucose or galactose showed that genes associated with translation were upregulated in B11221. These findings reinforce the growing evidence of a link between metabolism and tolerance. We characterized cell wall composition and macrophage evasion for the two strains. We found that B11221 has far less β-1,3-glucan exposure and resists phagocytosis by macrophages compared to B11220. In a transcriptomic analysis of both strains co-cultured with macrophages we found that B11221 upregulates genes associated with early stages of growth and transcription factors that regulate transport. These key differences in growth and membrane composition could explain the resistance to phagocytosis and increased stress tolerance in general of B11221 and indicates another connection between metabolism and immune system evasion.

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