Microbial Transport Processes in the Environment: Cells and Solutes II
Presiding: K Searcy, Northwestern University; S Findlay, Institute of Ecosystem Studies; A Packman, Northwestern University
B24A-01 INVITED 15:30h
A Conceptual Model for Migration of Pathogens in Surface and Ground Water
A conceptual model for migration of bacterial cells (i.e. pathogens) in flowing systems will be presented. Key processes include cell transport in the bulk liquid, attachment, growth, detachment, and persistence within microbial biofilms. Emphasis will be placed on the migration of a pathogenic species introduced, either naturally or intentionally, into a surface or ground water supply system. Each process will be discussed and data gaps identified. Interaction among processes will be examined by way of a cellular automata simulation model. Simulation results will be compared with a laboratory data set in which Escherichia coli cells are transported through a capillary flow cell and captured by an established Pseudomonas aeruginosa biofilm. Attachment, growth and persistence of both species observed over a 3 day period will be compared with results from cellular automata simulations.
B24A-02 15:45h
Effects of Starvation of Bacterial Transport in the Subsurface: Impacts on Natural and Engineered Systems
The movement of bacteria in the subsurface is of great importance to many areas of science and engineering including biogeosciences, microbial ecology, public health and bioremediation. Many researchers have studied bacterial transport through natural and engineered porous media systems. However, few have studied how starvation, or survival under extreme oligatrophic conditions, may enhance bacterial transport in the subsurface. The impact of starvation on many types of bacteria was studied to determine how it may impact pathogen transport, in situ bioremediation, and microbial diversity in the subsurface. The studies determined how nutrient starvation changed cell size, cell shape, adhesion efficiency, exo-cellular polysaccharide production, and maintenance of genetic and phenotypic attributes. Results to be presented will demonstrate how starvation physically and physiologically changes bacterial cells to enhance their transport properties regardless of soil type, hydraulic conductivity or bacterial species. The work will also show how bacterial adhesion onto porous media can be reduced by starvation and what impact that has on bacterial transport though various types of soil and aquifer material. The results also show the physiological and genetic consequences of starvation and their potential impact on microbial ecology, degradative potential and over-all survival in the subsurface. Adversely, the results will indicate how the resuscitation of the starved cells within the sub-surface may change the hydraulic characteristics of the aquifer material, resulting in reduced permeability and variable hydraulic flow characteristics.
B24A-03 16:00h
Direct Numerical Simulation of Motile Bacteria and Conjugative Transfer in the Happel Model of Porous Media
Bacterial transport in natural porous media is often addressed with tools from colloid filtration theory (CFT), much of which is based on the idealized Happel Sphere-in-Cell conceptual model. The analysis of colloid and in particular bacterial transport in natural porous media using this model entails several important assumptions. In order to examine the sensitivity of the results of this analysis to the validity or failure of basic assumptions we constructed a direct numerical simulation of colloid transport in the Sphere-in-cell model using a lagrangean framework. In particular we report on use of the numerical solutions to assess the validity of superposition principles previously relied upon to combine advective and diffusive components of the transport, we explore the affect of bacterial motility on transport, and we describe preliminary results in the use of the model in investigating the rates of horizontal conjugative gene transfer in granular porous media.
B24A-04 INVITED 16:15h
Upslope dissolved organic matter controls bacterial activity through shifts in community composition
Water moving through heterogeneous catchments supplies distinct down-slope bacterial communities with dissolved organic matter (DOM) of distinct chemical composition. Yet interactions between DOM sources and bacterial communities are not well understood at the catchment level. To investigate how upslope DOM influences bacterial activity and community composition, we used mesocosm experiments to manipulate DOM source from along a toposequence fed to down-slope bacteria. We measured bacterial production (BP) throughout the experiment and characterized DOM chemistry and bacterial community composition (using denaturing gradient gel electrophoresis of 16S rRNA) at the beginning and end of the experiment. Compared to lake controls, lake bacteria fed soil water DOM had higher integrated BP (420%) and DOC-specific BP (532%). Addition of upslope DOM to lake bacteria shifted community composition in the direction of the community from which the DOM originated relative to controls. Results demonstrated a surprisingly complete functional redundancy among natural soil, stream, and lake water communities, and showed that DOM controlled the level of bacterial activity, but only through alterations in bacterial community composition. We suggest that water flow through catchments will govern these interactions by influencing contact time between DOM and bacterial communities.
B24A-05 16:30h
Algal Community Responses to Substratum Movement in Arctic Headwater Streams
Nutrient availability, invertebrate grazing, and substratum movement are important factors affecting algal community structure in streams. We investigated the effects of substratum movement on algal communities of twenty headwater streams on the North Slope of Alaska. Substratum movement was measured indirectly using estimates of tractive forces and particle size distribution and directly using rocks marked in situ. Algae were sampled from natural and artificial substrata made from natural fiber ropes. In a pilot study of two streams with contrasting levels of substratum movement (low and high), we found that 23 out of 28 algal species were present in both streams. Total chlorophyll was more variable in the high substratum-movement stream (30.7 Μg cm-1 rope) than in the low substratum-movement stream (18.7 Μg cm-1 rope). Variability in total chlorophyll in the high substratum-movement stream was associated with flooding and related bed movement. Chlorophyll in the stable stream remained relatively constant. In the Arctic, structural attributes of algal communities colonizing artificial substrata in high substratum-movement streams are presumably regulated by abiotic factors such as abrasion associated with bed movement, while communities in low substratum-movement streams are controlled by biotic factors such as grazing.
B24A-06 16:45h
Indirect Selection for Antibiotic Resistance in Multiple Stream Microhabitats
One aspect challenging public health efforts to minimize the spread of antibiotic resistance (AR) is the prevalence of resistant bacteria in the environment. Anthropogenic-derived sources of selection are typically implicated as mechanisms for maintaining AR in the environment. Here we report an additional mechanism for maintaining AR in the environment through co- or cross-resistance to heavy metals. Using culture-independent techniques, bacteria isolated from heavy-metal contaminated sites were more tolerant of antibiotics and metals compared to those bacteria from a reference site. This evidence supports our hypothesis that metal contamination directly selects for metal tolerant bacteria while indirectly selecting for antibiotic tolerant bacteria. Additionally, to assess how antibiotic- and metal-tolerance may be transported through a stream network, we studied antibiotic and metal-tolerance patterns over four months in bacteria collected from multiple stream microhabitats including water column, biofilm, sediment, and Corbicula fluminea (Asiatic clam) digestive tracts. Sediment bacteria were the most tolerant to antibiotics and metals, while bacteria from Corbicula were the least tolerant. Differences between these microhabitats may be important for predicting antibiotic resistance transfer and transport in stream environments. Further, temporal dynamics suggest that tolerance patterns within microhabitats are linked to physico-chemical characteristics of the stream.
http://arches.uga.edu/~mswright