Biology subjects

Hernandez, M. N.

Publications and source records attributed to Hernandez, M. N..

2 recordsLinked to original sources

bioRxiv2020

Contact-dependent traits in Pseudomonas syringae B728a

Production of the biosurfactant syringafactin by the plant pathogen Pseudomonas syringae B728a is a surface contact-dependent trait. Expression of syfA, as measured using a gfp reporter gene fusion was low in planktonic cells in liquid cultures but over 4-fold higher in cells immobilized on surfaces as varied as glass, plastic, paper, parafilm, agar, membrane filters, and leaves. Induction of syfA as measured by GFP fluorescence was rapid, occurring within two hours after immobilization of cells on surfaces. Comparison of the global transcriptome by RNA sequencing of planktonic cells in a nutrient medium with that of cells immobilized for 2 hours on filters placed on this solidified medium revealed that, in addition to syfA, 3156 other genes were differentially expressed. Genes repressed in immobilized cells included those involved in quaternary ammonium compound (QAC) metabolism and transport, compatible solute production, carbohydrate metabolism and transport, organic acid metabolism and transport, phytotoxin synthesis and transport, amino acid metabolism and transport, and secondary metabolism. Genes induced in immobilized cells included syfA plus those involved in translation, siderophore synthesis and transport, nucleotide metabolism and transport, flagellar synthesis and motility, lipopolysaccharide (LPS) synthesis and transport, energy generation, transcription, chemosensing and chemotaxis, replication and DNA repair, iron-sulfur proteins, peptidoglycan/cell wall polymers, terpenoid backbone synthesis, iron metabolism and transport, and cell division. That many genes are rapidly differentially expressed upon transfer of cells from a planktonic to an immobilized state suggests that cells experience the two environments differently. It seems possible that surface contact initiates anticipatory changes in P. syringae gene expression, which enables rapid and appropriate physiological responses to the new environmental conditions. Such responses could help cells survive transitions from aquatic habitats fostering planktonic traits to attachment on surfaces, conditions that alternatively occur on leaves.

microbiology↗

bioRxiv2019

Pseudomonas syringae Increases Water Availability in Leaf Microenvironments via Production of Hygroscopic Syringafactin

The epiphytic bacterium Pseudomonas syringae strain B728a produces the biosurfactant syringafactin which is hygroscopic. The water absorbing potential of syringafactin is high. At high relative humidities, syringafactin attracts 250% of its weight in water but is less hygroscopic at lower relative humidities. This suggests that syringafactins benefit to the producing cells is strongly context-dependent. The contribution of syringafactin to the water availability around cells on different matrices was assessed by examining water availability biosensor strains that express gfp via the water-stress activated proU promoter. Wild-type cells exhibited significantly less GFP fluorescence than a syringafactin-deficient strain, on humid but dry filters as well as on leaf surfaces indicating higher water availability. When infiltrated into the leaf apoplast, wild-type cells also subsequently exhibited less GFP fluorescence than a syringafactin-deficient strain. These results suggest that the apoplast is a dry, but humid environment and that, just as on dry but humid leaf surfaces, syringafactin increases liquid water availability and reduces the water stress experienced by P. syringae.\n\nIMPORTANCEMany microorganisms, including the plant pathogen Pseudomonas syringae, produce amphiphilic compounds known as biosurfactants. While biosurfactants are known to disperse hydrophobic compounds and reduce water tension, they have other properties that can benefit the cells that produce them. Leaf colonizing bacteria experience frequent water stress since liquid water is only transiently present on or in leaf sites that they colonize. The demonstration that syringafactin, a biosurfactant produced by P. syringae, is sufficiently hygroscopic to increase water availability to cells, thus relieving water stress, reveals that P. syringae can modify its local habitat both on leaf surfaces and in the leaf apoplast. Such habitat modification may be a common role for biosurfactants produced by other bacterial species that colonize habitats that are not always water saturated such as soil.

microbiology↗