Author:

Keywords:

Science & Technology, Life Sciences & Biomedicine, Biotechnology & Applied Microbiology, Microbiology, ESCHERICHIA-COLI, GENE-EXPRESSION, PSEUDOMONAS-PUTIDA, OSMOTIC-STRESS, SINORHIZOBIUM-MELILOTI, TRANSCRIPTOME ANALYSIS, NONPERMEATING SOLUTES, BACTERIAL BIOFILMS, RESPONSES, WATER, Biofilms, Gene Expression Regulation, Bacterial, Osmotic Pressure, Phenanthrenes, Saline Solution, Hypertonic, Sphingomonas, Stress, Physiological, Transcriptome, 3107 Microbiology, 3207 Medical microbiology

Abstract:

Members of the genus Sphingomonas are important catalysts for removal of polycyclic aromatic hydrocarbons (PAHs) in soil but their activity can be affected by various stress factors. This study examines the physiological and genome-wide transcription response of the phenanthrene-degrading Sphingomonas sp. LH128 in biofilms to solute stress (invoked by 450 mM NaCl solution), either as an acute (4 h) or chronic (3 days) exposure. The degree of membrane fatty acid saturation was increased as a response to chronic stress. Oxygen consumption in the biofilms and phenanthrene mineralization activities of biofilm cells were however not significantly affected, neither after imposing acute nor chronic stress. This was in agreement with the transcriptomic data since genes involved in PAH degradation were not differentially expressed in stressed conditions compared to non-stressed conditions. The transcriptomic data suggest that LH128 adapts to NaCl stress by (i) increasing the expression of genes coping with osmolytic and ionic stress such as biosynthesis of compatible solutes and regulation of ion homeostasis (ii) increasing the expression of genes involved in general stress response, (iii) changing the expression of general and specific regulatory functions, and (iv) decreasing the expression of protein synthesis such as proteins involved in motility. Differences in gene expression between cells under acute and chronic stress suggest that LH128 goes through changes in genome-wide expression to fully adapt to NaCl stress, without significantly changing phenanthrene degrading activity.