Transcriptomic response of the polycyclic aromatic hydrocarbon-degrading Sphingomonas sp. LH128 upon long-term starvation stress

This study examines genome-wide expression of the phenanthrene-degrading Sphingomonas sp. LH128 as a response to long-term starvation stress. For this purpose, the strain was subjected to complete nutrient starvation for 6 months after growth on a rich medium. Survival was monitored by plating, physiological response was examined by flow cytometry and FAME analysis, and this response was related to transcriptomic response as determined by whole-genome microarray analysis. The data showed that decreased gene functions involved in ribosomal proteins biosynthesis, decreased chromosomal replication, increased gene functions involved in stringent regulation of gene expression, increased gene functions involved in genetic exchange and recombination, increased efflux systems, increased degradation of rRNA, and increased β-oxidation of fatty acids to access stored nutrients. Genes involved in PAH degradations appears to be with decreased expression. Transcriptomic response of phenanthrene degrading Sphingomonas sp. LH128 starved for 6 month in isotonic solution of 0.01 mM MgS04 was studied using genome-wide gene expression analysis. For this purpose, the strain was pregrown in minimal medium to an OD600 of 0.5, washed twice with 0.01 mM MgS04 and resuspended in the same solution to an OD of 0.5. RNA was extracted both from starved cells and from the initial culture (non-starved cells) and cDNA was synthesized and labeled with Cy3. Transcriptomic response of three replicates were analyzed and compared with the initial inoculum