Novel Essential Role of Ethanol Oxidation Genes at Low Temperature Revealed by Transcriptome Analysis in the Antarctic Bacterium Pseudomonas extremaustralis

Abstract

Temperature is one of the most important factors for bacterial growth and development. Cold environments are widely distributed on earth, and psychrotolerant and psychrophilic microorganisms have developed different adaptation strategies to cope with the stress derived from low temperatures. Pseudomonas extremaustralis is an Antarctic bacterium able to grow under low temperatures and to produce high amounts of polyhydroxyalkanoates (PHAs). In this work, we analyzed the genome-wide transcriptome by RNA deep-sequencing technology of early exponential cultures of P. extremaustralis growing in LB (Luria Broth) supplemented with sodium octanoate to favor PHA accumulation at 8°C and 30°C. We found that genes involved in primary metabolism, including tricarboxylic acid cycle (TCA) related genes, as well as cytochromes and amino acid metabolism coding genes, were repressed at low temperature. Among up-regulated genes, those coding for transcriptional regulatory and signal transduction proteins were over-represented at cold conditions. Remarkably, we found that genes involved in ethanol oxidation, exaA, exaB and exaC, encoding a pyrroloquinoline quinone (PQQ)-dependent ethanol dehydrogenase, the cytochrome c550 and an aldehyde dehydrogenase respectively, were up-regulated. Along with RNA-seq experiments, analysis of mutant strains for pqqB (PQQ biosynthesis protein B) and exaA were carried out. We found that the exaA and pqqB genes are essential for growth under low temperature in LB supplemented with sodium octanoate. Additionally, p-rosaniline assay measurements showed the presence of alcohol dehydrogenase activity at both 8°C and 30°C, while the activity was abolished in a pqqB mutant strain. These results together with the detection of ethanol by gas chromatography in P. extremaustralis cultures grown at 8°C support the conclusion that this pathway is important under cold conditions. The obtained results have led to the identification of novel components involved in cold adaptation mechanisms in this bacterium, suggesting for the first time a role of the ethanol oxidation pathway for bacterial growth at low temperatures.

LaoABCR, a Novel System for Oxidation of Long-Chain Alcohols Derived from SDS and Alkane Degradation in Pseudomonas aeruginosa

“…Transcription of exaA is activated during growth with ethanol and other short-chain alcohols, but long-chain alcohols were not tested (48). In the psychrophilic species Pseudomonas extremaustralis, the ethanol oxidation system, including QEDH, is induced during growth with octanoate at 8°C (49). After oxidation of this C 8 fatty acid, acetyl-CoA is apparently further reduced to ethanol, as detected by gas chromatography.…”

Mechanisms of subzero growth in the cryophile Planococcus halocryophilus determined through proteomic analysis

“…Production of proteins involved in energy metabolism has been shown to decrease at low temperatures in several psychrophilic/psychrotrophic organisms (Gao et al, 2006;Bergholz et al, 2009;Campanaro et al, 2011;Tribelli et al, 2015) but increases in others (Kawamoto et al, 2007;Cacace et al, 2010), especially in 'true psychrophiles' (stenopsychrophiles), which grow faster and are more active at lower temperatures (Mock and Hoch, 2005;Hwang et al, 2008;Chong et al, 2011). P. halocryophilus exhibits a mixed response (Fig.…”

Discovery of functional gene markers of bacteria for monitoring hydrocarbon pollution in the marine environment - a metatranscriptomics approach

“…Such co-occurrence was not observed in our dataset. Some PQQ-dependent ethanol dehydrogenases (exaA) and aldehyde dehydrogenases (exaC) taking part in the ethanol oxidation pathway, were shown to be essential for survival and growth at cold temperatures (Tribelli, Solar Venero et al 2015). Hence, these dominant proteins could also reflect an essential aspect of the cold-adapted lifestyle of the active bacterioplankton in the oil exposed tank.…”