Christopher J. McNamara

Microbial deterioration of historic stone

Environmental science has traditionally focused on conservation of natural resources. However, there is a second, little known, branch of environmental science that deals with the conservation of cultural resources. Many historic stone structures, archeological sites, and objects are at risk, and in need of protection, as a result of physical, chemical, and biological weathering. Because these structures are often large and located outdoors, they pose particular conservation challenges that require collaborative efforts between conservators and scientists. Historic stone supports large and diverse communities of microorganisms that colonize both the stone surface and the porous interior. In many cases, microbial processes have been implicated in the deterioration of the stone. The study of the role of microorganisms in this process is in its infancy, but recent findings have important implications for the preservation of cultural resources and for our understanding of weathering in natural systems.

Comparison of Methods for the Concentration of Bacterioplankton for in Situ Hybridization

Three approaches for concentrating stream bacterioplankton were compared for analysis by in situ hybridization: centrifugation; filtration onto a polymer membrane and transfer to a gel-coated slide; and filtration onto an inorganic filter disk. Stream bacterioplankton were hybridized with a species-specific oligonucleotide probe targeted for 23S rRNA of Burkholderia cepacia for analysis of variability among techniques. The inorganic filter technique yielded three to six times higher total cell counts and appeared to be effected less by interfering suspended particles and differences in site conditions than the other two concentration methods. Hybridization of samples with minimum cell loss yielded different, and presumably more accurate, estimates of the relative abundance of B. cepacia than the other methods.

Response of Biofilm Bacteria to Dissolved Organic Matter from Decomposing Maple Leaves

Stream bacteria play an important role in the utilization of dissolved organic matter (DOM) leached from leaves, and in transfer of this DOM to other trophic levels. Leaf leachate is a mixture of labile, recalcitrant, and inhibitory compounds, and bacterial communities vary in their ability to utilize leachate. The purpose of this study was to determine the effects of DOM from sugar maple leaves on bacterial populations in biofilms on decomposing leaf surfaces. Populations of Acinetobacter calcoaceticus, Burkholderia cepacia, and Pseudomonas putida were enumerated on decomposing maple leaves in a northeast Ohio stream using fluorescence in situ hybridization. Additionally, artificial substrata consisting of PVC-end caps filled with agar supplemented with leaf leachate and covered with cellulose filters were used to determine bacterial response to leachate from leaves at different stages of decomposition. Population sizes of bacterial species exhibited different responses. Leachate did not affect A. calcoaceticus. B. cepacia was tolerant of phenolic compounds released from leaves and the population size increased when DOM concentrations were greatest. In contrast, P. putida was inhibited by phenolic components of leachate when total DOM concentrations were greatest. Differences in response of the bacterial species to components of leaf leachate indicate the complexity of microbial population dynamics and interactions with DOM. Differences among species in response to DOM have the potential to influence transport and retention of organic matter in stream ecosystems.

Corrosion of aluminum alloy 2024 by microorganisms isolated from aircraft fuel tanks

Abstract Microorganisms frequently contaminate jet fuel and cause corrosion of fuel tank metals. In the past, jet fuel contaminants included a diverse group of bacteria and fungi. The most common contaminant was the fungus Hormoconis resinae. However, the jet fuel community has been altered by changes in the composition of the fuel and is now dominated by bacterial contaminants. The purpose of this research was to determine the composition of the microbial community found in fuel tanks containing jet propellant-8 (JP-8) and to determine the potential of this community to cause corrosion of aluminum alloy 2024 (AA2024). Isolates cultured from fuel tanks containing JP-8 were closely related to the genus Bacillus and the fungi Aureobasidium and Penicillium. Biocidal activity of the fuel system icing inhibitor diethylene glycol monomethyl ether is the most likely cause of the prevalence of endospore forming bacteria. Electrochemical impedance spectroscopy and metallographic analysis of AA2024 exposed to the fuel tank environment indicated that the isolates caused corrosion of AA2024. Despite the limited taxonomic diversity of microorganisms recovered from jet fuel, the community has the potential to corrode fuel tanks.

Bacterial community composition in biofilms on leaves in a northeastern Ohio stream

Abstract Litterfall is often an important source of organic matter in streams, and biofilms play an essential role in the decomposition and cycling of organic matter in leaves. Biofilms form rapidly on the surfaces of decomposing leaves, but little is known about the taxonomic composition of the bacterial community in leaf-surface biofilms. In addition, it is not known if bacteria in the biofilm colonize leaves from stream water, or if the biofilm forms from growth of bacteria already on the leaf surface. The purposes of our study were to examine the contribution of major taxa of freshwater bacteria to maple-leaf biofilms and to determine if these taxa were present in the biofilm because of colonization from the stream water. Exposed and dialysis-bag-enclosed maple leaves were incubated in a stream in northeastern Ohio during autumn 1998 and 1999. Leaves were collected, the biofilm was removed, and bacteria were counted using 4′,6-diamidino-2-phenylindole (DAPI) staining or fluorescence in situ hybridization (FISH) with probes targeted to Domain Bacteria and to the α-, β-, and γ-Proteobacteria. DAPI-stained cells and Bacteria were more abundant in 1999 than 1998. Differences in abundance between years may have been related to water velocity, which was much lower in 1999 than 1998. The α-Proteobacteria were the most abundant group in the biofilm (up to 40% of Domain Bacteria), whereas the γ-Proteobacteria were the least abundant (generally <10%). Percentages of β-Proteobacteria were much greater in 1999 than 1998 (26% and 15%, respectively). Abundances of biofilm α- and β-Proteobacteria were much greater on exposed leaves than on dialysis-bag-enclosed leaves, suggesting that large numbers of cells may colonize leaf surfaces from stream water. In conclusion, Proteobacteria made up most bacteria on the surface of decomposing maple leaves. Erosion of cells from the biofilm and colonization from stream water may have been important factors controlling biofilm development.

Culturable and non-culturable fractions of bacterial populations in sediments of a South Carolina stream

Population sizes of three bacterial species were examined in stream benthic habitats to assess differences in distribution and culturability among species. Population sizes were determined in sediments (both near bank and mid-channel) from three sites along Four Mile Creek (South Carolina, USA) using both culture-dependent (colony hybridization) and culture-independent (fluorescent in situ hybridization) techniques. The two methods used yielded different results. The numbers of colony forming units (CFU) of each species were similar in pattern to that found when the total number of CFU was enumerated (i.e., greater abundance in bank sediments and at downstream sites). In situ hybridization revealed a different distribution of these bacterial populations. Population sizes of the species were similar among sites. By using both the culture-based method and the culture-independent methods, the culturability of each species could be determined. The culturability of each species was at times much higher than the culturability of the overall assemblage. In spite of this higher culturability, viable but non-culturable cells commonly dominated the populations examined. These findings suggest that not only do bacterial species differ in population size and distribution, but also that cells within a population differ in their physiological state, or response to their environment, as reflected in differences in culturability.

NOVEL METHOD OF MICRONUTRIENT APPLICATION INCREASES RADISH (RAPHANUS SATIVUS) AND SHIRONA (BRASSICA RAPA VAR. PEKINENSIS) BIOMASS

The practice of enriching nutrient-poor soils with large quantities of chemical fertilizer has contributed significantly to the boost in agricultural productivity witnessed over the last century. Plants also require minute quantities of micronutrients, such as iron (Fe), manganese (Mn), and zinc (Zn). Inadequate micronutrient concentrations in the soil are a crucial problem for crop production that can severely reduce yield and nutritional quality of crops. Modern agriculture can further promote micronutrient deficiency through excessive irrigation and imbalanced application of chemical fertilizers. Anecdotal evidence suggested that irrigation of crops with FFC H2O, a commercial product currently utilized by the agriculture, fishery, and food industries in Japan, improved crop yields. Our study quantified the biomass of radish and shirona plants watered with FFC H2O. These plants developed larger leaves, greater dry weight, and longer stems than plants watered with deionized H2O. Inductively coupled plasma mass spectroscopy revealed the presence of several biologically relevant micronutrients in FFC H2O. Radish plants watered with an FFC H2O solution that lacked micronutrients, or nutrient solutions that lacked either iron or zinc failed to increase plant size relative to controls. These results provide quantitative evidence that FFC H2O operates via micronutrient supplementation, and may alleviate micronutrient deficiencies through the addition of critical elements such as Fe and Zn. FFC H2O offers agriculturalists a simple and effective tool for the fortification of irrigation waters with micronutrients.

Bacterial Populations of the Floodplain of a South Carolina (USA) Stream: A Comparison of Two Species

The distributions of two bacterial populations (Acinetobacter calcoaceticus and Pseudomonas putida) across the floodplain of a coastalplain stream (Four Mile Creek in South Carolina) were examined. In addition, populations in two areas of the floodplain with different vegetation were compared. One site (FOU 1) featured a typical bottomland hardwood forest with abundant stocks of leaf litter and the other site (FOU2) featured a plant community dominated by grasses/shrubs/herbs with limited amounts of leaf litter. Despite a higher amount of organic matter in the soil at FOU1, total bacterial numbers were greater at FOU2. A. calcoaceticus numbers peaked in the water saturated portion of the floodplain while P. putida numbers peaked at the more elevated edge of the floodplain. Differences in floodplain populations were not apparently related to differences in populations within the stream channel.

The use of force-volume microscopy to examine bacterial attachment to titanium surfaces

Force-volume microscopy (FVM) was used to study the interfacial and adhesive forces affecting primary bacterial attachment to surfaces. Forces were measured for titanium surfaces immersed either in cation-enriched (CE) solutions of yeast extract amended with phosphate buffer or in control solutions lacking the cation enrichment. The FVM measurements demonstrated that regions of elevated interfacial repulsion covered 72(±2)% of the surfaces immersed in CE solutions, compared to 26(±2)% for immersion in control solutions. Parallel collection of scanning electron micrographs demonstrated that surface densities of attached Pseudomonas aeruginosa were approximately 0.62(±1.3) × 106 cells cm−2 compared to 8.7(±0.8) × 106 cells cm−2 for surfaces immersed in the CE and control solutions, respectively. Interfacial repulsion indicated by FVM measurements therefore served as a predictor of bacterial attachment. Another factor influencing bacterial attachment was the adhesion force. FVM measurements indicated that the upper fifth percentile of surface adhesion was 1784(±40) pN for surfaces immersed in the CE solution compared to 2284(±40) pN for the control solutions. The more extensive regions of elevated interfacial repulsion as well as of decreased surface adhesion provide an explanation for the lower density of attached cells observed for the surfaces immersed in the CE compared to the control solutions. The conclusion is that FVM is a sensitive and informative technique that can be used to measure and explain interactions between microorganisms and surfaces.