2020. 2. 18. 21:10ㆍ카테고리 없음
AbstractSeveral biological roles have been demonstrated for surfactants expressed by soil and rhizosphere Pseudomonas spp., but the impact of these powerful surface-active agents on the local soil–water distribution within the partially saturated soil pore network has not been examined. To investigate this potential hydrological role, the liquid surface tension (γ)-reducing activities (LSTRA) of 72 pseudomonads isolated from a sandy loam soil by tensiometry of culture supernatants were characterized. Of these, 67% exhibited LSTRA, reducing γ to a minimum (γ Min) of 24 mN m −1 established by individual distribution identification analysis. Soil microcosms were then used to examine the impact of surfactant expression on the local soil–water distribution. The volumetric water content (θ) of soil microcosms was significantly lowered (0.78 ×) by Pseudomonas fluorescens SBW25 expressing the surfactant viscosin compared with a surfactant-deficient mutant ( P. Many SP isolates demonstrate an ability to reduce liquid surface tension. SP isolates were cultured in KB medium and the liquid surface tension (γ) of cell-free supernatants was determined by tensiometry.
Isolates are ranked along the y-axis. Sterile γ KB is indicated by the vertical line; SP isolates showing a clear LSTRA are indicated by white bars (from SP-1 to SP-56); and the rest, shown by grey bars (SP-69 to SP-43), are the non-LSTRA group SP isolates.
Mean γ ± SE are shown. The bimodal distribution of γ is shown by the histogram inset. Data were combined after a comparison of controls indicated that there were no significant differences between batches ( anova, P. Many SP isolates demonstrate an ability to reduce liquid surface tension. SP isolates were cultured in KB medium and the liquid surface tension (γ) of cell-free supernatants was determined by tensiometry. Isolates are ranked along the y-axis.
Sterile γ KB is indicated by the vertical line; SP isolates showing a clear LSTRA are indicated by white bars (from SP-1 to SP-56); and the rest, shown by grey bars (SP-69 to SP-43), are the non-LSTRA group SP isolates. Mean γ ± SE are shown. The bimodal distribution of γ is shown by the histogram inset. Data were combined after a comparison of controls indicated that there were no significant differences between batches ( anova, P0.05). This increase might be attributable to changes in the composition of the medium and the release of cell compounds by lysis during bacterial growth. The inability of these non-LSTR SP isolates to lower γ KB could not be explained by poor or delayed growth in KB medium, as GLM analysis confirmed that growth had no effect on γ ( P=0.078), whereas there was a significant isolate-dependent effect ( P0.05). This estimated a γ Min threshold value of 24.16 mN m −1, which was in agreement with the log-normal and log-logistic predictions, adding confidence that the true LSTRA γ Min for this collection of SPs is close to 24 mN m −1.
The LSTRA of SPs is similar to that seen for other Pseudomonas spp.In order to determine whether the observed LSTRA distribution was unique to this set of SPs, a further 37 Pseudomonas spp. Were assayed, from a mixed collection including soil- and plant-associated strains.
The distribution of these was similar to that found for the SP collection, with 22 (60%) showing a significant LSTRA and a minimum γ KB of 25.4 ± 0.1 mN m −1 (the LSTRA of key strains are listed in). The similarity of the two LSTRA distributions suggests that the ability of the SP isolates to alter the γ of experimental cultures is not unique to this collection, but is a general feature of environmental pseudomonads. Pseudomonas spp.Activityγ (mN m −1)OriginP. Aeruginosa PA01LSTRA32.9 ± 0.2Opportunistic human pathogen (USA)P. Corrugata NCPPB 2445LSTRA39.7 ± 0.2Tomato pathogen (UK)P. Fluorescens Pf0-1Non-LSTRA54.0 ± 0.3Soil (USA)P.
Fluorescens Pf-5LSTRA27.9 ± 0.1Cotton rhizosphere (USA)P. Fluorescens SBW25LSTRA32.5 ± 0.4Sugar beet phyllosphere (UK)P. Fluorescens SS101LSTRA25.6 ± 0.2Wheat rhizosphere (the Netherlands)P. Marginalis NCPPB 2644Non-LSTRA51.2 ± 1.6Alfalfa pathogen (USA)P. Putida KT2440Non-LSTRA51.6 ± 0.3Contaminated soil (Japan)P.
Savastanoi NCPPB 64Non-LSTRA53.1 ± 0.4Olive pathogen (Portugal)P. Syringae DC3000Non-LSTRA52.5 ± 0.5Tomato pathogen (Canada)P. Tolaasii NCPPB 2192LSTRA29.7 ± 0.2Mushroom pathogen (UK). Pseudomonas spp.Activityγ (mN m −1)OriginP.
Aeruginosa PA01LSTRA32.9 ± 0.2Opportunistic human pathogen (USA)P. Corrugata NCPPB 2445LSTRA39.7 ± 0.2Tomato pathogen (UK)P. Fluorescens Pf0-1Non-LSTRA54.0 ± 0.3Soil (USA)P. Fluorescens Pf-5LSTRA27.9 ± 0.1Cotton rhizosphere (USA)P. Fluorescens SBW25LSTRA32.5 ± 0.4Sugar beet phyllosphere (UK)P. Fluorescens SS101LSTRA25.6 ± 0.2Wheat rhizosphere (the Netherlands)P. Marginalis NCPPB 2644Non-LSTRA51.2 ± 1.6Alfalfa pathogen (USA)P.
Putida KT2440Non-LSTRA51.6 ± 0.3Contaminated soil (Japan)P. Savastanoi NCPPB 64Non-LSTRA53.1 ± 0.4Olive pathogen (Portugal)P.
Syringae DC3000Non-LSTRA52.5 ± 0.5Tomato pathogen (Canada)P. Tolaasii NCPPB 2192LSTRA29.7 ± 0.2Mushroom pathogen (UK). Pseudomonas spp.Activityγ (mN m −1)OriginP. Aeruginosa PA01LSTRA32.9 ± 0.2Opportunistic human pathogen (USA)P.
Corrugata NCPPB 2445LSTRA39.7 ± 0.2Tomato pathogen (UK)P. Fluorescens Pf0-1Non-LSTRA54.0 ± 0.3Soil (USA)P. Fluorescens Pf-5LSTRA27.9 ± 0.1Cotton rhizosphere (USA)P. Fluorescens SBW25LSTRA32.5 ± 0.4Sugar beet phyllosphere (UK)P.
Fluorescens SS101LSTRA25.6 ± 0.2Wheat rhizosphere (the Netherlands)P. Marginalis NCPPB 2644Non-LSTRA51.2 ± 1.6Alfalfa pathogen (USA)P. Putida KT2440Non-LSTRA51.6 ± 0.3Contaminated soil (Japan)P.
Savastanoi NCPPB 64Non-LSTRA53.1 ± 0.4Olive pathogen (Portugal)P. Syringae DC3000Non-LSTRA52.5 ± 0.5Tomato pathogen (Canada)P. Tolaasii NCPPB 2192LSTRA29.7 ± 0.2Mushroom pathogen (UK).
Pseudomonas spp.Activityγ (mN m −1)OriginP. Aeruginosa PA01LSTRA32.9 ± 0.2Opportunistic human pathogen (USA)P. Corrugata NCPPB 2445LSTRA39.7 ± 0.2Tomato pathogen (UK)P. Fluorescens Pf0-1Non-LSTRA54.0 ± 0.3Soil (USA)P. Fluorescens Pf-5LSTRA27.9 ± 0.1Cotton rhizosphere (USA)P. Fluorescens SBW25LSTRA32.5 ± 0.4Sugar beet phyllosphere (UK)P. Fluorescens SS101LSTRA25.6 ± 0.2Wheat rhizosphere (the Netherlands)P.
Marginalis NCPPB 2644Non-LSTRA51.2 ± 1.6Alfalfa pathogen (USA)P. Putida KT2440Non-LSTRA51.6 ± 0.3Contaminated soil (Japan)P. Savastanoi NCPPB 64Non-LSTRA53.1 ± 0.4Olive pathogen (Portugal)P. Syringae DC3000Non-LSTRA52.5 ± 0.5Tomato pathogen (Canada)P.
Tolaasii NCPPB 2192LSTRA29.7 ± 0.2Mushroom pathogen (UK). Some pseudomonads can alter the water content of soil microcosmsThe impact of SBW25 and SS101 in soil microcosms, in direct comparison with their surfactant-deficient mutants, was determined by investigating whether pseudomonads capable of LSTRA could alter the local soil–water distribution in soil, measured by volumetric moisture content (θ) changes due to the expression of surfactants.
Kruss Tensiometer
Based on the t-test results, the mean volumetric water content of SBW25 microcosms was significantly lower (0.78 ×) than SBW25Δ viscA microcosms (SBW25: 0.225 ± 0.005 m 3 m −3; SBW25Δ viscA: 0.290 ± 0.007 m 3 m −3; P. Volumetric water content of soil microcosms can be altered by pseudomonads. The impact of SP isolates on the local water content was investigated using soil microcosms where the volumetric water content (θ) of inoculated microcosms was compared with sterile controls (Ctrl). Previously, SP-1, 7, 10, 19, 21, 27, 42, 57, 65 and 68 were found in KB cultures while SP-15, 17, 36, 38 and 43 were not. Mean θ ± SE are shown.Significant difference from the Ctrl was tested by a comparison of means using Dunnett's method ( P.
Volumetric water content of soil microcosms can be altered by pseudomonads. The impact of SP isolates on the local water content was investigated using soil microcosms where the volumetric water content (θ) of inoculated microcosms was compared with sterile controls (Ctrl). Previously, SP-1, 7, 10, 19, 21, 27, 42, 57, 65 and 68 were found in KB cultures while SP-15, 17, 36, 38 and 43 were not.
Mean θ ± SE are shown.Significant difference from the Ctrl was tested by a comparison of means using Dunnett's method ( P. Reduced soil–water surface tensions alter the soil–water retention curve. The water retention curve determined for soil microcosms assuming γ SW to be ∼73 mN m −1 is shown by (a). The curve is recalculated for γ SW values of 50 mN m −1 (b) and 25 mN m −1 (c).The observation that some SPs are capable of reducing the volumetric moisture content of soil microcosms through expression of surfactants, and the predicted impact of reduced γ SW on the soil–water distribution, suggest that bacterial surfactants may play a significant hydrological role in soils beyond their recognized biological functions. The hydrological model focuses on the impact that surfactant expression may have on partially saturated pores at equilibrium. Under these conditions, surfactants will act to drain pores and uncover microcolonies or biofilms that may have been O 2 limited. The lowered A–L interface, with increased concavity and surface area, would provide these bacterial aggregations with better access to O 2 and allow further growth.
Based on the behaviour of the non-LSTRA SP isolates identified in this work, it is possible that some bacteria may increase γ SW, and raises the possibility that aggregations might antagonistically interact to control the γ SW of local pore spaces. However, we are currently unaware of any other reports of bacteria increasing γ or of mechanisms by which this change might be effected. The reduction of soil–water surface tension (γ SW) in partially saturated soil pores may have a significant ecological impact on colonizing bacteria.
Manual High School Peoria Il
Bacteria (grey areas) colonizing the meniscus region and A–L interface of a partially saturated pore at equilibrium are shown in the left schematic. O 2 diffusing into the liquid column is indicated by the small arrows. The respiration of colonists will establish a strong O 2 gradient indicated in the accompanying box. The particular physical–chemical nature of the pore surface and soil–water solution determines the meniscus curvature and the surface area of the A–L interface. Growth of bacteria below the A–L interface is likely to be O 2 limited and reach the stationary phase earlier than those at the interface.
The impact of the expression of surfactants by bacteria is shown in the right schematic. Surfactants will alter the shape of the A–L interface, with the top edge moving up and the centre moving down (large arrows) (more active surfactants will have a larger impact than less active or stable surfactants). This will expose more pore surface for colonization, allowing further growth upwards as partially saturated colonies, while the increased concavity and surface area of the A–L interface will allow O 2 to diffuse more deeply into the liquid column, allowing additional growth downwards as biofilms. This new colonization of the pore will result in an extended and more complex O 2 gradient as suggested in the accompanying box. The reduction of soil–water surface tension (γ SW) in partially saturated soil pores may have a significant ecological impact on colonizing bacteria. Bacteria (grey areas) colonizing the meniscus region and A–L interface of a partially saturated pore at equilibrium are shown in the left schematic. O 2 diffusing into the liquid column is indicated by the small arrows.
The respiration of colonists will establish a strong O 2 gradient indicated in the accompanying box. The particular physical–chemical nature of the pore surface and soil–water solution determines the meniscus curvature and the surface area of the A–L interface. Growth of bacteria below the A–L interface is likely to be O 2 limited and reach the stationary phase earlier than those at the interface. The impact of the expression of surfactants by bacteria is shown in the right schematic. Surfactants will alter the shape of the A–L interface, with the top edge moving up and the centre moving down (large arrows) (more active surfactants will have a larger impact than less active or stable surfactants). This will expose more pore surface for colonization, allowing further growth upwards as partially saturated colonies, while the increased concavity and surface area of the A–L interface will allow O 2 to diffuse more deeply into the liquid column, allowing additional growth downwards as biofilms. This new colonization of the pore will result in an extended and more complex O 2 gradient as suggested in the accompanying box.Environmental Pseudomonas spp., such as SBW25 and many soil and rhizosphere isolates, have a propensity to produce biofilms at the A–L interface of static liquids in which O 2 is accessed from above and nutrients from below.
Access to O 2 in static liquids also drives the emergence of biofilm-forming mutants of SBW25 and explains the fitness advantage that biofilm formers have over non-biofilm-forming strains. Many of the biofilm-forming Pseudomonas spp.
From tested here showed LSTR activity ( and Table S1), while many of the SP isolates are known to produce A–L interface biofilms (A. Spiers, unpublished data), suggesting a strong link between biofilm formation and surfactant expression.
Surfactants are involved in the initial attachment and biofilm growth of both SBW5 and SS101 (, ), as well as in biofilm development and dispersal for a wide range of other bacteria. Within soils, biofilm formation, often referred to as bioclogging, can significantly reduce porosity and hydraulic conductivity as well as promote preferential flow.
Both biofilm matrix and surfactants are microbial legacies that may influence soil structure and hydrology long after the bacteria that produced them have disappeared. Authors' contributionJ.F.
Contributed equally to this work. AcknowledgementsWe thank Wilfred Otten and Iain Young, as well as the anonymous reviewers, for their helpful comments of our manuscript. Is funded by the University of Abertay Dundee and is a member of the Scottish Alliance for Geoscience Environment and Society (SAGES).
Is a SAGES-associated PhD student. The University of Abertay Dundee is a charity registered in Scotland, No: SC016040.