Research Interests—Craig J. Plante

Role of Disturbance in the Structuring of Benthic Microalgal Communities

Benthic microalgae (BMA) are important primary producers in coastal sediments, serving as a vital food resource for heterotrophs. BMA also release extracellular polymeric secretions (EPS) that inhibit resuspension and stabilize sediments. Key ecological parameters such as abundance, production, and species composition each contribute to the character of these roles. The objective of recent research was to determine the roles of disturbance in structuring benthic microalgal assemblages. The most prominent types of biological and physical disturbance on BMA, and potential interactions between these processes, were studied in intertidal and shallow subtidal settings. Using field comparative studies, we examined the nature of disturbance and recovery following macroinvertebrate ingestion. BMA biomass and composition in fecal materials and sediments were followed through time using fluorometry, microscopy, and molecular techniques (PCR-DGGE analysis of 18S rDNA and sequencing). We’ve also taken an experimental approach to determine mechanisms and rates of recolonization of disturbed sediments, comparing the importance of regrowth, recruitment and immigration. In the future, we will manipulate field densities of deposit feeders to test for their effects on spatial patterns of BMA biomass, diversity, and composition of the larger sedimentary landscape. Under certain situations, e.g., during ebb and flood tides in the intertidal, sediment resuspension appears to homogenize sediments and erase the influence of deposit feeders on BMA. Neutral community models (NCMs) are potentially applicable under such conditions of high dispersal and environmental homogeneity. The primary objectives of ongoing research are to (1) describe the role of biotic disturbance (deposit feeding) in structuring microalgal communities under varied hydrodynamic regimes, and (2) determine the relative influence of stochastic and deterministic factors on BMA diversity and species dynamics. We will employ natural variation in disturbance frequency and dispersal limitation (i.e., tidal resuspension) found over small spatial scales to test the relative roles of neutral assembly and species sorting in this system.

Bacterial Antagonism in Marine Sediments: Ecological Importance and Potential for Novel Antimicrobial Compounds

Sedimentary bacteria are vital to benthic (sea bottom) ecosystems in that they are the primary remineralizers of organic matter and are central players in microbial food webs. The fundamental processes that structure benthic microbial communities are not well known. Several lines of evidence suggest that competition, particularly interference competition employing secreted antimicrobial compounds, may play a key role. In fact, antagonistic bacteria may be keystone species, disproportionately influencing community composition and diversity. Our recent work has identified sedimentary bacteria capable of antagonistic behavior in sediments. Currently, we are developing a method (fluorescence in situ hybridization, FISH) to assess the abundance and distribution of antibiotic-producing bacteria in local marine sediments. The constructed “probes” (fluorescently-labeled oligonucleotides) will allow in situ enumeration of the most potent antibiotic-producing sedimentary bacteria. Future research on antagonistic interactions will 1) identify the inhibitory compounds produced by these bacteria, and 2) test for the effects of these compounds on bacterial composition, species richness and diversity in microcosms or in situ. An additional goal will be to determine minimum inhibitory concentrations (MICs) of these compounds against standard clinical bacterial strains, to test whether they show promise as sources of new antibiotics for the treatment of human or animal diseases.

Surfactant-Resistant Bacteria from Marine Habitats for Use in Bioremediation

Environmental remediation efforts often separately utilize biodegradative microbes or surfactants. Coupling both strategies holds the potential to dramatically increase the rate and extent of remediation as surfactants can enhance bioavailability of contaminants to microbes. However, many surfactants permeabilize bacterial cell membranes and are effective disinfectants. An important goal then is to find or genetically modify microorganisms that possess both desirable degradative capabilities and the ability to thrive in the presence of surfactants. The guts of some marine invertebrates, particularly deposit feeders, have previously been shown to contain high levels of biosurfactants. The primary aim of this work is to mine these natural, surfactant-rich habitats for surfactant-resistant bacteria. Relative to sediment porewaters, the gut contents of two polychaete deposit feeders, Nereis succinea and Amphitrite ornata, exhibit a significantly higher ratio of bacteria resistant to both cationic (CTAB) and anionic (SDS) surfactants. Analyses of 16S rDNA gene sequences revealed that the majority of surfactant-resistant isolates were previously undescribed species of the genus Vibrio, or were of a group most closely related to Kistimonas spp. A number of these novel strains are currently being fully characterized. We also tested resistant bacteria for production of biosurfactants and the majority show some level of production. Next steps, are to 1) screen additional marine microhabitats (e.g., mucus) for surfactant-resistant bacteria, 2) examine the effect of different growth conditions (e.g., anaerobiosis and different carbon sources) on surfactant resistance and biosurfactant production, important to the in situ utilization of bacteria in bioremediation, and 3) elucidate the mechanisms of resistance. This work will expand our understanding of the metabolic potential and physiology of marine bacteria catalyzing contaminant transformations.