Fred C. Dobbs

Global spread of microorganisms by ships

Commercial ships have spread many species around the world, but little is known of the extent and potential significance of ship-mediated transfer of microorganisms. Here we show that the global movement of ballast water by ships creates a long-distance dispersal mechanism for human pathogens and may be important in the worldwide distribution of microorganisms, as well as for the epidemiology of waterborne diseases affecting plants and animals.

Phytodetritus at the abyssal seafloor across 10 of latitude in the central equatorial Pacific

Fresh phytoplankton detritus (or phytodetritus) has been reported from numerous deep seafloor sites in the temperate North Atlantic and Pacific Oceans following seasonal phytoplankton blooms. Here we report the first strong evidence for abyssal accumulations of phytodetritus in the tropics, in the central equatorial Pacific. In November–December 1992 we obtained photographs and/or sediment-core samples from 61 abyssal stations (water depths of 4280–5012 m) between 12°S and 9°N along ∼ 140°W. Greenish flocculent material was recovered from the top of multiple-core samples from 5°S to 5°N; this material was most abundant from 2°S to 2°N, in some areas forming continuous layers at least 5 mm thick, and individual aggregates > 1 cm in diameter. The greenish material was clearly visible in bottom photographs as a green veneer that covered >95% of the seafloor near the equator, and as individual cm-scale aggregates covering <1% of the seafloor. Occasionally, thick accumulations of cm-scale aggregates occurred in biogenic pits. Cleared trails and feeding traces suggest that surface-deposit-feeding holothurians and echiurans grazed the greenish material. Microscopic examination of greenish material recovered from core tops and a burrow lumen revealed relatively intact diatoms (including Rhizosolenia sp.) and other microalgae with chloroplasts containing chlorophyll. The greenish material was 1–12.5% organic carbon by weight, i.e. 5–39 times richer than associated seafloor sediments. It also contained high excess activities of 234Th, suggesting arrival from the water column in the previous 100 days. Samples of the greenish flocculent material from 0° and 5°N incubated at simulated environmental pressure and temperature with 14C-labeled glutamate exhibited ⩾ 5-fold higher rates of microbial activity than underlying sediments or brown floc from 9°N. Surface-sediment samples (which included the greenish flocculent material) from 5°S to 5°N also contained significant concentrations of chlorophyll a and other chloropigments; the chloropigment concentrations were roughly comparable to deep-sea phytodetritus collected in the North Atlantic. We conclude that fresh, organic-rich phytodetritus was present on the seafloor from 5°S to 5°N along 140°W in November–December 1992, with highest concentrations within 2–3° of the equator. This material is likely to be a concentrated, high-quality food resource for deep-sea microbes and metazoans. We estimate an upper limit for the standing stock of this phytodetritus to be ∼2.6 mmol Corg/m2; this corresponds to ∼3% of the annual flux of organic carbon to the seafloor at these latitudes in 1992. Because the degradation rate of this material appears to be very high, its presence at the seafloor for several months per year could yield significant phytodetrital contributions to the annual seafloor organic-carbon budget. We also suggest that the phytodetrital aggregates are formed at intense convergence zones resulting from seasonal passage of tropical instability waves within 5° of the equator; if so, phytodetrital accumulations are likely to recur seasonally over broad areas of the abyssal equatorial Pacific.

Comparison of two kinds of Biolog microplates (GN and ECO) in their ability to distinguish among aquatic microbial communities.

We compared the abilities of Biologs GN and ECO plates to distinguish among aerobic and heterotrophic bacterial communities in samples from six aquatic environments. The Biolog system is based on interpreting patterns of sole-carbon substrate utilization indicated by color development in a 96-well microtiter plate. Whether of fresh or saltwater origin, bacterial communities utilized > 95% of substrates in both types of plates. Samples from any one environment exhibited similar time courses of average well color development (AWCD) in both GN and ECO plates. Principal component analysis was performed on data sets resulting from combinations of algorithms (AWCD and curve-integration methods) and levels of color development (end-point and set-point approaches). In all cases, the two types of plates demonstrated an equal capacity to discriminate among the heterotrophic expressions of the six microbial communities. Substantial deviation from an anticipated 1:1 correspondence occurred when color development of 25 substrates common to both types of plates was compared. The discrepancies likely are related to the different formulations of low-nutrient media in GN and ECO plates.

Effects of nonequilibrium atmospheric pressure plasmas on the heterotrophic pathways of bacteria and on their cell morphology

To date, most research on the interaction of nonequilibrium, atmospheric pressure plasma discharges with bacteria has concentrated on the germicidal effects. Therefore, published results deal mainly with killing efficacy and little attention is given to physical mechanisms and biochemical pathways and their potential alterations when cells of microorganisms are exposed to the plasma. In this letter, an attempt to investigate the effects of plasma exposure on the biochemical pathways of bacteria is presented. In addition, using electron microscopy, we investigate if any gross morphological changes take place when cells are exposed to a lethal dose of plasma. We are testing the hypothesis that disruption of the cell membrane, sometimes to the point of cell lysis, is the mechanism whereby plasma kills cells.

Latitudinal variations in benthic processes in the abyssal equatorial Pacific : control by biogenic particle flux

Abstract The equatorial Pacific forms a band of high, globally significant primary production. This productivity drops off steeply with distance from equatorial upwelling, yielding large latitudinal gradients in biogenic particle flux to the abyssal seafloor. As part of the US JGOFS Program, we studied the translation of these particle-flux gradients into the benthic ecosystem from 12°S to 9°N along 135–140°W to evaluate their control of key benthic processes, and to evaluate sediment proxies of export production from overlying waters. In October–December 1992 the remineralization rates of organic carbon, calcium carbonate and biogenic opal roughly matched the rain rates of these materials into deep sediment traps, exhibiting peak values within 3° of the equator. Rates of bioturbation near the equator were about ten-fold greater than at 9°N, and appeared to exhibit substantial dependence on particulate-organic-carbon flux, tracer time scale (i.e. age-dependent mixing), and pulsed mixing from burrowing urchins. Organic-carbon degradation within sediments near the equator was dominated by a very labile component (reaction rate constant, k approximately 15 per year) that appeared to be derived from greenish phytodetritus accumulated on the seafloor. Organic-carbon degradation at the highest latitudes was controlled by a less reactive component, with a mean k of approximately 0.075 per year. Where measured, megafaunal and macrofaunal abundances were strongly correlated with annual particulate-organic carbon flux; macrofaunal abundance in particular might potentially serve as a proxy for export production in low-energy abyssal habitats. Sedimentary microbial biomass also was correlated with the rain rate of organic carbon, but less strongly than larger biota and on shorter time scales (i.e. approximately 100 days). We conclude that the vertical flux of biogenic particlues exerts tight control on the nature and rates of benthic biological and chemical processes in the abyssal equatorial Pacific, and suggest that global changes in productivity on decadal or greater time scales could yield profound changes in deep-sea benthic ecoystems.

EPIBIOTIC MICROORGANISMS ON COPEPODS AND OTHER MARINE CRUSTACEANS

Although the occurrence of microbial (algal, protozoan, bacterial, and fungal) epibionts on marine crustaceans and other invertebrates has been documented repeatedly, the ecological context and significance of these relationships generally are not well understood. Recently, several studies have examined the population and community ecology of algal and protozoan epibionts on freshwater crustaceans. Even so, the study of microbial epibionts in aquatic environments is still in its infancy. In this review, we summarize associations of microalgae, protozoans, and bacteria with marine crustaceans, especially copepods. We note differences and commonalities across epibiont taxa, consider host‐epibiont cycling of nutrients, generate hypotheses relevant to the ecology of the host and the epibiont, and suggest future research opportunities. Microsc. Res. Tech. 37:116–135, 1997.

Bacterial decontamination of water by means of pulsed-corona discharges

By using a tungsten wire with 75-/spl mu/m diameter, 2 cm apart from a plane cathode, and applying a 600-ns, 120-kV square wave pulse, we were able to obtain a pulsed-water corona discharge (PWC). The effect of these discharges on bacteria was studied using water contaminated with Escherichia coli or Bacillus subtilis, the latter in both the vegetative and spore state. The strongest effect was obtained on E. coli. The concentration of E. coli could be reduced by three orders of magnitude after applying eight corona discharges to the water. The corresponding energy expenditure is 10 J/cm/sup 3/. The decontamination rate had the largest values at the beginning, and decreased considerably after 15 electrical discharges, reaching a constant residual concentration value of 10/sup -4/ of the initial concentration. For B. subtilis in the vegetative state, it took almost 30 discharges to reach the same result, corresponding to an energy expenditure of 40 J/cm/sup 3/. There was no effect on B. subtilis spores. Comparisons with the pulsed-electric field (PEF) method indicate that the decontamination efficiency of the PWC method is slightly higher than that of the PEF method.

Diversity of deep-sea hydrothermal vent Archaea from Loihi Seamount, Hawaii

Abstract Through an examination of SSU rDNA (genes coding for SSU rRNA), the molecular phylogeny of the domain Archaea (e.g. one of the three major lineages of life) was analyzed from a microbial mat at an active, deep-sea hydrothermal vent ecosystem located at Pele’s Vents on the summit of Loihi Seamount, Hawaii. These SSU rDNAs were amplified from extracted microbial mat genomic DNA by PCR, cloned into a plasmid vector, and sequenced. The derived archaeal sequences were then used to infer the evolutionary relationships between these microbial mat community members and their closest known relatives. Of the four clones initially chosen for sequence analysis, a cluster of three phylogenetically similar PVA (Pele’s Vents Archaea) clones all contained in the archaeal group I lineage of the marine Crenarchaeota were detected. A single PVA clone was contained in the archaeal group II lineage of the marine Euryarchaeota. All four of the PVA clones are novel and constitute the discovery of new archaeal taxa. From further rarefaction results of 75 archaeal SSU rDNA clones, we estimate the organismal diversity of this domain from the microbial mats located at Pele’s Vents to be significantly greater than that of the bacterial domain from this same ecosystem. Analyses of archaeal diversity at both the organismal (i.e. rarefaction) and phylogenetic level suggest that hydrothermal vents, such as Pele’s Vents, are intimately linked with marine archaeoplankton (a recently discovered component of marine picoplankton) detected from oceans around the world.

Extended tailing of bacteria following breakthrough at the Narrow Channel Focus Area, Oyster, Virginia

Extended tailing of low bacterial concentrations following breakthrough at the Narrow Channel focus area was observed for 4 months. Bacterial attachment and detachment kinetics associated with breakthrough and extended tailing were determined by fitting a one-dimensional transport model to the field breakthrough-tailing data. Spatial variations in attachment rate coefficient (kf) were observed under forced gradient conditions (i.e., k f decreased as travel distance increased), possibly because of decreased bacterial adhesion with increased transport distance. When pore water velocity decreased by an order of magnitude at 9 days following injection, apparent bacterial attachment rate coefficients did not decrease with velocity as expected from filtration theory, but, instead, increased greatly for most of the wells. The coincidence of the increase in apparent attachment rate coefficient with the occurrence of protist blooms suggested that the loss of bacteria from the aqueous phase during the protist blooms was not governed by filtration but rather was governed by predation. Simulations were performed to examine the transport distances achieved with and without detachment, using attachment and detachment rate coefficients similar to those obtained in this field study. Simulations that included detachment showed that transport distances of bacteria may significantly increase because of detachment under the conditions examined.

Potential invasion of microorganisms and pathogens via ‘interior hull fouling’: biofilms inside ballast water tanks

Surfaces submerged in an aquatic milieu are covered to some degree with biofilms – organic matrices that can contain bacteria, microalgae, and protozoans, sometimes including disease-causing forms. One unquantified risk of aquatic biological invasions is the potential for biofilms within ships’ ballast water tanks to harbor pathogens, and, in turn, seed other waters. To begin to evaluate this vector, we collected biofilm samples from tanks’ surfaces and deployed controlled-surface sampling units within tanks. We then measured a variety of microbial metrics within the biofilms to test the hypotheses that pathogens are present in biofilms and that biofilms have higher microbial densities compared to ballast water. Field experiments and sampling of coastwise and oceangoing ships arriving at ports in Chesapeake Bay and the North American Great Lakes showed the presence of abundant microorganisms, including pathogens, in biofilms. These results suggest that ballast-tank biofilms represent an additional risk of microbial invasion, provided they release cells into the water or they are sloughed off during normal ballasting operations.