New insights on the reorganization of gene transcription in Pseudomonas putida KT2440 at elevated pressure

Abstract

BackgroundElevated pressure, elevated oxygen tension (DOT) and elevated carbon dioxide tension (DCT) are readily encountered at the bottom of large industrial bioreactors and during bioprocesses where pressure is applied for enhancing the oxygen transfer. Yet information about their effect on bacteria and on the gene expression thereof is scarce. To shed light on the cellular functions affected by these specific environmental conditions, the transcriptome of Pseudomonas putida KT2440, a bacterium of great relevance for the production of medium-chain-length polyhydroxyalkanoates, was thoroughly investigated using DNA microarrays.ResultsVery well defined chemostat cultivations were carried out with P. putida to produce high quality RNA samples and ensure that differential gene expression was caused exclusively by changes of pressure, DOT and/or DCT. Cellular stress was detected at 7 bar and elevated DCT in the form of heat shock and oxidative stress-like responses, and indicators of cell envelope perturbations were identified as well.Globally, gene transcription was not considerably altered when DOT was increased from 40 ± 5 to 235 ± 20% at 7 bar and elevated DCT. Nevertheless, differential transcription was observed for a few genes linked to iron-sulfur cluster assembly, terminal oxidases, glutamate metabolism and arginine deiminase pathway, which shows their particular sensitivity to variations of DOT.ConclusionsThis study provides a comprehensive overview on the changes occurring in the transcriptome of P. putida upon mild variations of pressure, DOT and DCT. Interestingly, whereas the changes of gene transcription were widespread, the cell physiology was hardly affected, which illustrates how efficient reorganization of the gene transcription is for dealing with environmental changes that may otherwise be harmful. Several particularly sensitive cellular functions were identified, which will certainly contribute to the understanding of the mechanisms involved in stress sensing/response and to finding ways of enhancing the stress tolerance of microorganisms.

Online Monitoring of Crude Oil Biodegradation at Elevated Pressures

“…The culture grew slower on hexadecane at the simulated deep-sea pressure than at the atmospheric pressure and also lost viability in comparison to the one incubated at 1 bar [12]. It was recently reported that even mild variations of pressure (7 bar) elevated oxygen tension and elevated carbon dioxide tension caused widespread changes in the transcriptome of Pseudomonas putida but not in the cell physiology [13].…”

Over‐pressurized bioreactors: Application to microbial cell cultures

“…Cultivations of P. putida carried out at 7 bar revealed the induction of the sigma factor responsible for heat‐shock response (RpoH) and of the heat‐shock proteins (HtpG, GrpE, GroES, and GroEL), as well as the upregulation of ROS detoxification, hypothetical proteins, and transcription genes. In addition, genes coding for sensing proteins and for proteins located in the cell envelope exhibited the highest significant differential expression compared to the control (air pressure, 1 bar) …”

Polyhydroxyalkanoates

“…In Pseudomonas, a transcriptional regulator highly homologous to Fnr in E. coli, named Anr (arginine and nitrate reduction), is known to control a set of genes involved in the aerobic-to-anaerobic transition, encoding, among others, nitrate respiration functions, arginine fermentation, hydrogen cyanide, and heme synthesis in anaerobiosis (Follonier et al, 2013;Galimand, Gamper, Zimmermann, & Haas, 1991;McPhee et al, 2009;Zimmermann, Reimmann, Galimand, & Haas, 1991). A DNA microarray analysis performed in P. putida under conditions of elevated pressure and oxygen availability indicated a decrease in the transcription of anr and, concomitantly, a low level of the transcripts corresponding to terminal oxidases (Follonier et al, 2013).…”

“…A DNA microarray analysis performed in P. putida under conditions of elevated pressure and oxygen availability indicated a decrease in the transcription of anr and, concomitantly, a low level of the transcripts corresponding to terminal oxidases (Follonier et al, 2013). In P. extremaustralis, a bacterium highly resistant to stress which produces PHB and also PHAs of different monomeric composition, the effect of Anr on PHB synthesis was analyzed by means of an anr mutant under different oxygen availability conditions.…”