Scott T. Kendall

Bactericidal Activity of Different Forms of Lactoferrin

Mucosal surfaces provide the portal of entry for most pathogenic microorganisms. In protection the mammalian host has concentrated a number of defense factors in the exocrine secretions that bathe mucosal surfaces. Understanding how these factors operate to prevent pathologic consequences of microbial challenge and what mechanisms a pathogen uses to evade this host defense is essential to the development of interventive approaches. Lactoferrin (LF) and secretory IgA (slgA) are both secreted in significant quantities at most mucosal surfaces and in milk. Both of these factors are reported to have bacteriostatic activity (1–8) and interact with each other and other defense factors (including lysozyme, complement, and lactoperoxidase) to modify their effectiveness (9, 10). In addition purified iron-free LF has been shown to have microbicidal activity against a variety of bacteria and yeast via mechanisms that are not reversed by the addition of free iron (11–16). A factor present in many commercial LF-enriched preparations, which co-purifies with slgA, has been reported to result in syner-gistic bactericidal activity and these impure LF preparations are able to kill bacterial strains that are resistant to purified LF (17).

Benthic Bacterial Diversity in Submerged Sinkhole Ecosystems

ABSTRACT Physicochemical characterization, automated ribosomal intergenic spacer analysis (ARISA) community profiling, and 16S rRNA gene sequencing approaches were used to study bacterial communities inhabiting submerged Lake Huron sinkholes inundated with hypoxic, sulfate-rich groundwater. Photosynthetic cyanobacterial mats on the sediment surface were dominated by Phormidium autumnale, while deeper, organically rich sediments contained diverse and active bacterial communities.

Observations of the Middle Island Sinkhole in Lake Huron: A Unique Hydrologic and Glacial Creation of 400 Million Years

In the northern Great Lakes region, limestone sediments deposited some 400 million ybp during the Devonian era have experienced erosion, creating karst features such as caves and sinkholes. The groundwater chemical constituents of the shallow seas that produced these rock formations now contribute to the formation of a unique physical (sharp density gradients), chemical (dissolved oxygen-depleted, sulfate-rich) and biological (microbe-dominated) environment in a submerged sinkhole near Middle Island in freshwater Lake Huron. A variety of methods including aerial photography, physico-chemical mapping, time series measurements, remotely operated vehicle (ROV) survey, diver observations and bathymetric mapping were employed to obtain a preliminary understanding of sinkhole features and to observe physical interactions of the system’s groundwater with Lake Huron. High conductivity ground water of relatively constant temperature hugs the sinkhole floor creating a distinct sub-ecosystem within this Great Lakes ecosystem. Extensive photosynthetic purple cyanobacterial benthic mats that characterize the benthos of this shallow sinkhole were strictly limited to the zone of ground water influence. tions of chloride, and 100-fold higher concentrations of sulfate (Ruberg et al., 2005). A variety of non-photosynthetic benthic microbial mats were observed in this deepwater aphotic sinkhole system. Water samples collected from the sinkhole plume contained bacterial concentrations (~9x109 cells l-1) an order of magnitude higher than ambient lake concentrations (~1x109 cells l-1), and showed evidence for the occurrence of significant chemosynthesis in this lightless deep water environment (Biddanda et al., 2006). These rates of chemosynthesis occurring in the Lake Huron Isolated sinkhole were comparable to those measured in thermal vents in Yellowstone Lake (Cuhel et al., 2002). Understanding the nature of the groundwater emerging in Lake Huron’s sinkholes requires an introduction P A P E R

Great Lakes Sinkholes: A Microbiogeochemical Frontier

Recent underwater explorations have revealed unique hot spots of biogeochemical activity at several submerged groundwater vents in Lake Huron, the third largest of the Laurentian Great Lakes. Fueled by venting groundwater containing high sulfate and low dissolved oxygen, these underwater ecosystems are characterized by sharp physical and chemical gradients and spectacularly colorful benthic mats that overlie carbon-rich sediments. Here, typical lake inhabitants such as fish and phytoplankton are replaced by communities dominated by microorganisms: bacteria and archaea that perform unique ecosystem functions. Shallow, sunlit sinkholes are dominated by photosynthetic microorganisms and processes, while food webs in deep aphotic sinkholes are supported primarily by chemosynthesis.

Systematically variable planktonic carbon metabolism along a land-to-lake gradient in a Great Lakes coastal zone

During the summers of 2002–2013, we measured rates of carbon metabolism in surface waters of six sites across a land-to-lake gradient from the upstream end of drowned river-mouth Muskegon Lake (ML) (freshwater estuary) to 19 km offshore in Lake Michigan (LM) (a Great Lake). Despite considerable inter-year variability, the average rates of gross production (GP), respiration (R) and net production (NP) across ML (604 ± 58, 222 ± 22 and 381 ± 52 µg C L−1 day−1, respectively) decreased steeply in the furthest offshore LM site (22 ± 3, 55 ± 17 and −33 ± 15 µg C L−1day−1, respectively). Along this land-to-lake gradient, GP decreased by 96 ± 1%, whereas R only decreased by 75 ± 9%, variably influencing the carbon balance along this coastal zone. All ML sites were consistently net autotrophic (mean GP:R = 2.7), while the furthest offshore LM site was net heterotrophic (mean GP:R = 0.4). Our study suggests that pelagic waters of this Great Lakes coastal estuary are net carbon sinks that transition into net carbon sources offshore. Reactive and dynamic estuarine coastal zones everywhere may contribute similarly to regional and global carbon cycles.

Nutrient Bioassays of Plankton Biomass and Metabolism in an Urbanized Drowned River-mouth Lake (Mona Lake, Michigan)

ABSTRACT A variety of short-term responses were observed in inorganic nutrient enrichment bioassays on the plankton of Mona Lake—an urbanized and eutrophic drowned river-mouth lake that drains directly to Lake Michigan (USA). Chlorophyll a and phytoplankton production data indicated phosphorus (P) limitation in spring, nitrogen (N) and P co-limitation in summer, and no N or P limitation in autumn. Heterotrophic bacterial abundance, dissolved organic carbon levels, and plankton respiration were not stimulated by nutrient enrichment. Autotrophic biomass and production, but not heterotrophic biomass or respiration, were seasonally stimulated by the availability of P and/or N. Such imbalance between autotrophic and heterotrophic processes may contribute to the accumulation of phytoplankton biomass during the growing season. Cyanobacterial abundance in the lake increased from 22% of the plankton biomass in the spring when the TN:TP ratio was high to 68% in the autumn when the TN:TP ratio was low, suggesting that P availability helps drive a seasonal succession towards cyanobacterial dominance.