ONGOING RESEARCH PROJECTS: Decho Laboratory

• Quorum Sensing in Marine bacteria
• Marine Stromatolite Studies
• Optical Properties of Marine Biofilms
  
• Anydrophilic Halotolerant Microbial Mats
• Coastal Pathogen/ Bioavailability Studies
  
• Biofilms of Colon Cancer
  

• Deep-UV Irradiation of Biofilms using LED MicroChips

(1) Marine Stromatolite Studies (Sponsor: NSF - BioComplexity Program).

Marine Stromatolites are finely-laminated rock structures, consisting of fine layers of calcium carbonate precipitate. They are produced through the organized activities cyanobacteria,aerobic heterotrophs, and sulfate-reducing  bacteria (SRB). Today, actively growing marine stromatolites only occur in an isolated area of the Exuma Cay islands in the Bahamas.

Our studies of marine stromatolites are through a five-year project, funded by the NSF BioComplexity Program. Our laboratory's role is to investigate how the EPS matrix interacts with physical factors, chemical processes and microbial groups within biofilm communities ultimately to influence the organized precipitation of calcium carbonate into the resulting stromatolite macrostructure. The microbial mat communities of stromatolites offer a unique, but, fundamental platform from which to examine bacterial interactions.

We are investigating chemical communication by SRB; and developing signatures of CaCO3 precipation using Raman-confocal and Fluorescence lifetime imaging microscopy (FLIM). This project is in collaboration with researchers from the Universities of Miami, Connecticut, Maryland, Duquesne, and St. Andrews (Scotland); and scientists at the NASA. For further information see the Stromatolite website (RIBS): http://www.home.duq.edu/~stolz/RIBS/menu.htm'

Top figure shows study site in Bahamas. Stromatolites (not visible) occur in shallow subtidal waters.

Bottom figure shows a confocal scanning laser micrograph of a stromatolite biofilm. Note accumulating layer (red) calcium carbonate precipitated. The yellow objects are 'ooids' (CaCO3 sediment grains).

(2)Optical Properties of Biofilms in Marine Sediments
(Sponsor: Office of Naval Research (ONR), Environmental Optics Program)

Biofilms, form coatings on virtually all surfaces placed in seawater. Their presence alters the optical signatures (e.g. reflectance, scattering, absorbance, fluorescence) of those surfaces. These processes are of importance to a basic understanding of light and primary production in oceans, and of applied importance to optical sensing by the Navy. The goal of our work, funded through the Office of Naval Research, is to determine how biofilm EPS, and its associated cells, detritus and molecules, change the optical properties of surfaces, such as sediments, in a predictable manner, so that these changes may be incorporated into modeling of shallow water sediments. The EPS matrix forms pliant gels that enhance the relative spacing of sediment grains (see Figures). The EPS gel itself, additionally alters the refractive index of the medium surrounding the grains. The net effect of these ‘microscopic’ processes is a reduction in overall sediment reflectance, that may be detectable from remote sensing platforms.

Image on left shows 'clean' (absence of EPS) carbonate sand grains (red), called ooids, in seawater, and illustrates how natural sediments with little or no-biofilm may be packed at a microscopic scale. The addition of EPS gels (right image, green) changes the relative spacing of ooids, reducing surface reflectance and channeling light deeper into sediments. This 'microscopic' process reduces bottom reflectance off of sediments that is measurable at much larger scales.

For further information see our website:

http://www.psicorp.com/mazel/research/cobop/lsi/cobop2.html

(3) Anydrophilic, Halotolerant Microbial Mats of San Salvador Island Bahamas
(Sponsor: NSF - Microbial Observatories Program)

The highly-hydrated EPS slime matrix of bacteria provide a mechanism to resist and survive extreme stressors, such as desiccation and extreme salinity fluctuations; a process that occurs in both natural and artificial systems. Bacterial mats growing in hypersaline ponds in the Bahamas, typically receive intermittent rainfall followed by prolonged dry periods. The mats often go to near-complete dryness. However, bacteria in these mats can be revived from a dry, hardened state to an actively-metabolizing state within hours after exposure to (rain) water. In a five-year project, funded by the National Science Foundation (NSF), we are collaborating with researchers at the Universities of North Carolina and Texas A&M, to understand how the EPS matrix, secreted by these mats, may aid in the binding of ions and the conservation of water for cells. The results of this study will provide insight into how bacteria in nature, and even pathogenic (disease-causing) bacteria in artificial systems, may survive extreme environmental conditions.

Fig. 1. Light-microscopy cross-section of a hypersaline microbial mat from Salt Pond, San Salvador. Note distinct layering (with depth) of microbial communities. The mat surface (gold) has a dense array of 'Polymer towers' (see below) that likely influence the mats overall resiliency to changing ionic conditions.

For further information go to our project website at: http://www.marine.unc.edu/Paerllab/research/sansal_site/pages/index.htm

(4) Bioavailability Studies
(Sponsor: National Oceanic and Atmospheric Association (NOAA))

Biofilm coatings on particles are both 'protective' and ' highly-sorptive' matrices for bacterial cells. Their sorptive properties facilitate the binding and concentration of environmental contaminants, such as metals and pesticides. Their extracellular polymers (EPS) also form colloids suspended in the overlying water. The coincidental (and active) ingestion of biofilm-coated particles (and colloids) by small marine animals provide a vehicle for the efficient trophic-transfer of contaminants to animals. We are investigating the roles of bioavailability of metals and pesticides to a range of coastal marine animals, such as harpacticoid copepods (see image below), polychaetes, amphipods, and other marine/estuarine invertebrates.

These same animals often harbor 'commensal' microbial communities on the surface of the integument. Copepods have biofilm communities localized in certain areas that may be highly-active. This provides a potential mechanism for pathogenic bacteria to remain 'cryptic', during water sampling and disperse harmful bacteria between the water-column and sediments.

(5)Biofilms and the Development of Colon Cancer
(Sponsor: SOM/SPH Joint Funding Initiative, USC)

The human colon is a challenging environment for bacteria to attach. Material passing through the colon contains some of the highest densities of bacteria ever measured. Thus, it is a site where rapid bacterial growth, and biotransformations of organics occurs. It is also a site where many environmental toxins (e.g. potential carcinogens) are transformed and/or absorbed by the body. Recent evidence suggests that the activities of specific types of bacteria in the colon may influence the early stages of colon cancer progression. This will likely occur on the surface of colon epithelial tissue, called “crypts”.

We are beginning studies investigating bacterial biofilms on the “specific sites” of colon tissue, called “aberrant crypts” where the initial stages of colon cancers typically develop. We hypothesize that specific types of bacteria may exert effects that influence either the initiation and/or progression of early colon cancer. We are collaborating with researchers in the USC Cancer Center using rodents to model the initial events in this process.

(6)Deep-UV Interactions with Biofilms (DUVO)

Biofilms, owing to their resilient nature, often resist chlorination, antibiotics, and other conventional antimicrobial approaches. Biofilms and their pathogenic consequences, are an extremely costly impediment to society affecting the safety of water supplies, causing medical-implant and nosocomial (hospital-acquired) infections, and represent a 'link between environment and public health'. Ultraviolet irradiation (UV) is a effective means to kill many bacteria. However, UV- mercury lamps are not practical for many applications owing to their large size and environmental risks. Recently, engineers have designed UV-emitting 'microchips'. Such microchip technology can be tuned to emit at specific wavelengths (e.g. 265 and 280 nm) that may specifically target vital bacterial functions (e.g. DNA, proteins, etc) and hence optimize their disinfection potential. We have recently begun collaborations with colleagues in the Department of Electrical Engineering (USC) to understand and develop UV-emitting microchip technology for use in fine-scale control of biofilm populations.