Cell envelope components contributing to biofilm growth and survival of Pseudomonas putida in low‐water‐content habitats

Abstract

SummaryBacteria in terrestrial habitats frequently reside as biofilm communities on surfaces that are unsaturated, i.e. biofilms are covered in water films varying in thickness depending on the environmental conditions. Water availability in these habitats is influenced by the osmolarity of the water (solute stress) and by cellular dehydration imposed by matric stress, which increases as water content decreases. Unfortunately, we understand relatively little about the molecular mechanisms required for bacterial growth in lowwater-content habitats. Here, we describe the use of mini-Tn 5 -¢ ¢ ¢ ¢ pho A to identify genes in Pseudomonas putida that are matric water stress controlled and to generate mutants defective in desiccation tolerance. We identified 20 genes that were induced by a matric stress but not by a thermodynamically equivalent solute stress, 11 genes were induced by both a matric and a solute stress, three genes were induced by a solute stress and three genes were repressed by a matric stress. Their patterns of expression were analysed in laboratory media, and their contribution to desiccation tolerance was evaluated. Twenty-six genes were homologous to sequences present in the completed P. putida KT2440 genome sequence or plasmid pWWO sequence that are involved in protein fate, nutrient or solute acquisition, energy generation, motility, alginate biosynthesis or cell envelope structure, and the function of five could not be predicted from the sequence. Together, these genes and their importance to desiccation tolerance provide a view of the environment perceived by bacteria in low-watercontent habitats, and suggest that the mechanisms for adaptation for growth in low-water-content habitats are different from those for growth in highosmolarity habitats.

Analysis of Pseudomonas putida KT2440 Gene Expression in the Maize Rhizosphere: In Vitro Expression Technology Capture and Identification of Root-Activated Promoters

“…It was recently reported that algA, the last gene in the algD-A operon, is controlled by water stress in P. putida (49). Nelson and coworkers (36) suggested that the absence of the regulatory gene mucC from the algT-mucC operon might explain the P. putida nonmucoid morphotype under standard culturing conditions.…”

Physiological and Transcriptional Responses to Osmotic Stress of Two Pseudomonas syringae Strains That Differ in Epiphytic Fitness and Osmotolerance

“…Similar to the porins, osmotic stress did not alter flagellar gene expression in P. aeruginosa cells (39) but reduced the expression and protein levels of the flagellar subunit FliC and reduced the motility of P. fluorescens cells (50). Whereas osmotic stress reduced many flagellar gene transcripts in P. syringae (see Table S2) and matric stress reduced at least flgC and fliE in P. putida (51), suggesting reduced motility of pseudomonads in response to water stress, osmotic stress did not affect flagellar gene transcripts in Desulfovibrio vulgaris (52), indicating that this is not a generalized bacterial response to water limitation.…”

Alginate Production by Pseudomonas putida Creates a Hydrated Microenvironment and Contributes to Biofilm Architecture and Stress Tolerance under Water-Limiting Conditions

“…Although deletion of the global regulator U decreased the EPS production and desiccation tolerance of Pseudomonas fluorescens (39), the extent to which the lack of EPS production or of a particular EPS constituent was responsible for the decreased tolerance was not demonstrated. We recently showed that the alginate biosynthesis structural genes were induced by water limitation, but not by high osmolarity, in the soil bacterium Pseudomonas putida (46).…”

“…Despite the nearly universal ability of Pseudomonas species to produce alginate, a class of polymers comprising the uronic acids D-mannuronic and/or its epimer L-guluronic acid assembled into ␤-1,4-linked blocks that can be O acetylated (37,44), the exact benefits of alginate production have been elusive. Potential functions have been indicated by examining alginate biosynthesis structural (22,53) or regulatory (39,49) mutants or by identifying environmental factors influencing the expression of alginate genes (9,21,34,46). Pseudomonas aeruginosa and Pseudomonas syringae share conserved signals, including elevated osmolarity and elevated levels of reactive oxygen species, for activating transcription from alginate promoters, yet neither requires alginate for biofilm formation in flowthrough systems (25,49).…”