2-n-Pentyl-4-quinolinol produced by a marine Alteromonas sp. and its potential ecological and biogeochemical roles

Bacterium-bacterium interactions occur at intimate spatial scales on the order of micrometers, but our knowledge of interactions at this level is rudimentary. Antagonism is a potential interaction in such microenvironments. To study the ecological role of antibiosis, we developed a model system involving an antibiotic-producing isolate (SWAT5) derived from a marine particle and its dominant antibiotic product, 2-n-pentyl-4-quinolinol (PQ). This system was used to address questions about the significance of this antibiotic for microbial ecology and carbon cycling on particles. We characterized the chemical and inhibitory properties of PQ in relation to the mechanisms used by particle-associated bacteria in interacting with particles and with other attached bacteria. PQ was produced by SWAT5 only on surfaces. When SWAT5 was grown in polysaccharide matrices, PQ diffused within the matrices but not into the surrounding seawater. SWAT5 might thus be able to generate a localized zone of high antibiotic concentration on particles suspended or sinking through seawater. Target bacterial respiration was most sensitive to PQ (75 nM), while inhibition of DNA synthesis, protein synthesis, and bacterial motility required higher (micromolar) PQ levels. The presence of PQ altered the composition of the bacterial community that colonized and developed in a model particle system. PQ also inhibited Synechococcus and phytoplankton growth. Our results suggest that antibiosis may significantly influence community composition and activities of attached bacterial and thus regulate the biogeochemical fate of particulate organic matter in the ocean.     

Bacterial Colonization and Ectoenzymatic Activity in Phytoplankton-Derived Model Particles: Cleavage of Peptides and Uptake of Amino Acids

Abstract Phytoplankton-derived model particles were created in laboratory from a mixture of autoclaved diatom cultures. These particles were colonized by a marine bacterial community and incubated in rolling tanks in order to examine the relationship between aminopeptidase activity and leucine uptake. Bacteria inhabiting particles and ambient water were characterized for abundance, biovolume, aminopeptidase activity, leucine uptake, and growth rate. Particles were a less favorable habitat than ambient water for bacterial growth since growth rates of particle-attached bacteria were similar or even lower than those of free-living bacteria. During the first ∼100 h of the particle decomposition process, there were not statistically significant differences in the aminopeptidase activity:leucine uptake ratio between attached and free-living bacteria. From ∼100 h to ∼200 h, this ratio was higher for attached bacteria than for free-living bacteria. This indicates an uncoupling of aminopeptidase activity and leucine uptake. During this period, attached and free-living bacteria showed similar hydrolytic activities on a cell-specific basis. In the free-living bacterial community, variations in aminopeptidase activity per cell were associated with variations in leucine uptake per cell and growth rates. However, in the attached bacterial community, when leucine uptake and growth rates decreased, aminopeptidase activity remained constant. Thus, after ∼100 h, particle-attached bacteria were not taking advantage of their high aminopeptidase activity; consequently the hydrolysed amino acids were released into the ambient water, supporting the growth of free-living bacteria. These results demonstrate that over the particle decomposition process, the relationship between hydrolysis and uptake of the protein fraction shows different patterns of variation for attached and free-living bacterial communities. However, in our experiments, this uncoupling was not based on a hyperproduction of enzymes by attached bacteria, but on lower uptake rates when compared to the free-living bacteria. Received: 4 February 1997; Accepted: 9 May 1997     

Effects of Inorganic Particles on Metabolism by a Periphytic Marine Bacterium

Measurements were made of adsorption of a periphytic marine bacterium, glucose, and glutamic acid to inorganic particles in seawater and defined bacterial growth medium. Measurements of the metabolism of bacteria were made in the presence and absence of particles by microcalorimetry and radiorespirometry. It was found that hydroxyapatite adsorbs glutamic acid, but not glucose, from the experimental medium. It was also found that hydroxyapatite adsorbs essentially all of the bacteria from the medium when the bacterial concentration is approximately 6 × 10⁵ bacteria per ml. If the bacterial concentration is approximately 6 × 10⁷, then only a small fraction of cells become attached. It was therefore possible to select bacterial concentrations and organic nutrients so that bacterial attachment, organic nutrient adsorption, or both would occur in different experiments. In this experimental system the metabolism by attached and nonattached bacteria of adsorbing and nonadsorbing organic nutrients was measured. The results show that bacterial activity in this model system was not enhanced by the particles, regardless of whether the bacteria, the organic nutrient, or both were associated with the surface. In fact, the respiratory activity of the attached bacteria was diminished in comparison with that of free bacteria.     

Links between Phytoplankton and Bacterial Community Dynamics in a Coastal Marine Environment

Bacteria and phytoplankton dynamics are thought to be closely linked in coastal marine environments, with correlations frequently observed between bacterial and phytoplankton biomass. In contrast, little is known about how these communities interact with each other at the species composition level. The purpose of the current study was to analyze bacterial community dynamics in a productive, coastal ecosystem and to determine whether they were related to phytoplankton community dynamics. Near-surface seawater samples were collected in February, May, July, and September 2000 from several stations in the Bay of Fundy. Savin et al. (M.C. Savin et al., Microb Ecol 48: 51-65) analyzed the phytoplankton community in simultaneously collected samples. The attached and free-living bacterial communities were collected by successive filtration onto 5 m and 0.22 m pore-size filters, respectively. DNA was extracted from filters and bacterial 16S rRNA gene fragments were amplified and analyzed by denaturing gradient gel electrophoresis (DGGE). DGGE revealed that diversity and temporal variability were lower in the free-living than the attached bacterial community. Both attached and free-living communities were dominated by members of the Roseobacter and Cytophaga groups. Correspondence analysis (CA) ordination diagrams showed similar patterns for the phytoplankton and attached bacterial communities, indicating that shifts in the species composition of these communities were linked. Similarly, canonical CA revealed that the diversity, abundance, and percentage of diatoms in the phytoplankton community accounted for a significant amount of the variability in the attached bacterial community composition. In contrast, ordination analyses did not reveal an association between free-living bacteria and phytoplankton. These results suggest that there are specific interactions between phytoplankton and the bacteria attached to them, and that these interactions influence the composition of both communities.     

Attached and Free-Floating Bacterioplankton in Howe Sound, British Columbia, a Coastal Marine Fjord-Embayment

Factors which influence the attachment of bacterioplankton to particles (including phytoplankton) were investigated by using (i) water samples removed from a coastal temperate fjord over an annual cycle and (ii) unialgal cultures of Prorocentrum minimum, Dunaliella tertiolecta, and Skeletonema costatum. Silt and salinity levels in this fjord seawater did not appear to influence bacterial attachment, but the percent attached bacteria was inversely related to both chlorophyll a concentrations and primary productivities. During periods of high primary productivities the percent attached bacteria was low, whereas during periods of low, increasing, and declining primary productivities the percent attached bacteria was high. A similar pattern of bacterial attachment was observed when the three phytoplankton were grown as batch cultures. The percent attached bacterial numbers increased upon the initiation of algal growth and after these cells stopped growing, but not while the algae were growing. We suggest that a major factor influencing the attachment of bacterioplankton is the physiological condition of their major nutrient source, the phytoplankton; mainly free-living bacteria are associated with growing phytoplankton, whereas a much greater proportion of the bacteria are attached among senescent phytoplankton populations.     

Host-Specificity and Dynamics in Bacterial Communities Associated with Bloom-Forming Freshwater Phytoplankton

Many freshwater phytoplankton species have the potential to form transient nuisance blooms that affect water quality and other aquatic biota. Heterotrophic bacteria can influence such blooms via nutrient regeneration but also via antagonism and other biotic interactions. We studied the composition of bacterial communities associated with three bloom-forming freshwater phytoplankton species, the diatom Aulacoseira granulata and the cyanobacteria Microcystis aeruginosa and Cylindrospermopsis raciborskii. Experimental cultures incubated with and without lake bacteria were sampled in three different growth phases and bacterial community composition was assessed by 454-Pyrosequencing of 16S rRNA gene amplicons. Betaproteobacteria were dominant in all cultures inoculated with lake bacteria, but decreased during the experiment. In contrast, Alphaproteobacteria, which made up the second most abundant class of bacteria, increased overall during the course of the experiment. Other bacterial classes responded in contrasting ways to the experimental incubations causing significantly different bacterial communities to develop in response to host phytoplankton species, growth phase and between attached and free-living fractions. Differences in bacterial community composition between cyanobacteria and diatom cultures were greater than between the two cyanobacteria. Despite the significance, major differences between phytoplankton cultures were in the proportion of the OTUs rather than in the absence or presence of specific taxa. Different phytoplankton species favoring different bacterial communities may have important consequences for the fate of organic matter in systems where these bloom forming species occur. The dynamics and development of transient blooms may also be affected as bacterial communities seem to influence phytoplankton species growth in contrasting ways.     

Bacterial Community Structure of Biofilms on Artificial Surfaces in an Estuary

This study examined bacterial community structure of biofilms on stainless steel and polycarbonate in seawater from the Delaware Bay. Free-living bacteria in the surrounding seawater were compared to the attached bacteria during the first few weeks of biofilm growth. Surfaces exposed to seawater were analyzed by using 16S rDNA libraries, fluorescence in situ hybridization (FISH), and denaturing gradient gel electrophoresis (DGGE). Community structure of the free-living bacterial community was different from that of the attached bacteria according to FISH and DGGE. In particular, alpha-proteobacteria dominated the attached communities. Libraries of 16S rRNA genes revealed that representatives of the Rhodobacterales clade were the most abundant members of biofilm communities. Changes in community structure during biofilm growth were also examined by DGGE analysis. We hypothesized that bacterial communities on dissimilar surfaces would initially differ and become more similar over time. In contrast, the compositions of stainless steel and polycarbonate biofilms were initially the same, but differed after about 1 week of biofilm growth. These data suggest that the relationship between surface properties and biofilm community structure changes as biofilms grow on surfaces such as stainless steel and polycarbonate in estuarine water.     

Phylogenetic Differences in Attached and Free-Living Bacterial Communities in a Temperate Coastal Lagoon during Summer,Revealed via High-Throughput 16S rRNA Gene Sequencing

Most of what is known about coastal free-living and attached bacterial diversity is based on open coasts, with high particulate and nutrient riverine supply, terrestrial runoffs, and anthropogenic activities. The Magdalen Islands in the Gulf of St. Lawrence (Canada) are dominated by shallow lagoons with small, relatively pristine catchments and no freshwater input apart from rain. Such conditions provided an opportunity to investigate coastal free-living and attached marine bacterial diversity in the absence of confounding effects of steep freshwater gradients. We found significant differences between the two communities and marked temporal patterns in both. Taxonomic richness and diversity were greater in the attached than in the free-living community, increasing over summer, especially within the least abundant bacterial phyla. The highest number of reads fell within the SAR 11 clade (Pelagibacter, Alphaproteobacteria), which dominated free-living communities. The attached communities had deeper phylum-level diversity than the free-living fraction. Distance-based redundancy analysis indicated that the particulate organic matter (POM) concentration was the main variable separating early and late summer samples with salinity and temperature changes also significantly correlated to bacterial community structure. Our approach using high-throughput sequencing detected differences in free-living versus attached bacteria in the absence of riverine input, in keeping with the concept that marine attached communities are distinct from cooccurring free-living taxa. This diversity likely reflects the diverse microhabitats of available particles, implying that the total bacterial diversity in coastal systems is linked to particle supply and variability, with implications for understanding microbial biodiversity in marine systems.     

Community composition and activity of prokaryotes associated to detrital particles in two contrasting lake ecosystems

The composition, distribution and extracellular enzyme activities of bacteria attached to small (2-50 microm in size) transparent exopolymer and Coomassie-stained proteinaceous particles (TEP and CSP) were examined in two lakes of different trophic status located in the Massif Central of France. TEP concentrations (10(4)-10(6) particle per L) were significantly higher in the more productive lake and were significantly related to chlorophyll a concentrations. The majority of TEP and CSP were colonized by bacteria that constituted 2.6% and 7.4% of the total 4',6-diamidino-2-phenylindole-stained bacteria in lakes Pavin and Aydat, respectively. In both lakes, the composition of particle-associated bacteria was different from that of free-living bacteria, the Betaproteobacteria and Bacteroidetes (i.e. former Cytophaga-Flavobacteria group) being the dominant groups on particles. We also found that 2-5 microm TEP were more colonized than 2-5 microm CSP in the two lakes, and that TEP colonization was higher in the less productive lake. Measurements of Leucine aminopeptidase and alpha-glucosidase activities in fractionated lake water (0.2-1.2, 1.2-5 and >5 microm fractions) indicated that proteolytic activity was always higher and that particle-associated bacteria have higher enzymatic activities than free-living bacteria. The glycolytic activities in the 1.2-5 and >5 microm fractions were related to the abundance of TEP. We conclude that small freshwater detrital organic particles constitute microhabitats with high bacterial activities in pelagic environments and, undoubtedly, present significant ecological implications for the prokaryotic community structure and function in aquatic ecosystems.     

The Native Bacterioplankton Community in the Central Baltic Sea Is Influenced by Freshwater Bacterial Species

The Baltic Sea is one of the largest brackish environments on Earth. Despite extensive knowledge about food web interactions and pelagic ecosystem functioning, information about the bacterial community composition in the Baltic Sea is scarce. We hypothesized that due to the eutrophic low-salinity environment and the long water residence time (>5 years), the bacterioplankton community from the Baltic proper shows a native “brackish” composition influenced by both freshwater and marine phylotypes. The bacterial community composition in surface water (3-m depth) was examined at a single station throughout a full year. Denaturing gradient gel electrophoresis (DGGE) showed that the community composition changed over the year. Further, it indicated that at the four extensive samplings (16S rRNA gene clone libraries and bacterial isolates from low- and high-nutrient agar plates and seawater cultures), different bacterial assemblages associated with different environmental conditions were present. Overall, the sequencing of 26 DGGE bands, 160 clones, 209 plate isolates, and 9 dilution culture isolates showed that the bacterial assemblage in surface waters of the central Baltic Sea was dominated by Bacteroidetes but exhibited a pronounced influence of typical freshwater phylogenetic groups within Actinobacteria, Verrucomicrobia, and Betaproteobacteria and a lack of typical marine taxa. This first comprehensive analysis of bacterial community composition in the central Baltic Sea points to the existence of an autochthonous estuarine community uniquely adapted to the environmental conditions prevailing in this brackish environment.     

Bacterial diversity associated with the tunic of the model chordate Ciona intestinalis

The sea squirt Ciona intestinalis is a well-studied model organism in developmental biology, yet little is known about its associated bacterial community. In this study, a combination of 454 pyrosequencing of 16S ribosomal RNA genes, catalyzed reporter deposition-fluorescence in situ hybridization and bacterial culture were used to characterize the bacteria living inside and on the exterior coating, or tunic, of C. intestinalis adults. The 454 sequencing data set demonstrated that the tunic bacterial community structure is different from that of the surrounding seawater. The observed tunic bacterial consortium contained a shared community of <10 abundant bacterial phylotypes across three individuals. Culture experiments yielded four bacterial strains that were also dominant groups in the 454 sequencing data set, including novel representatives of the classes Alphaproteobacteria and Flavobacteria. The relatively simple bacterial community and availability of dominant community members in culture make C. intestinalis a promising system in which to investigate functional interactions between host-associated microbiota and the development of host innate immunity.     

Dynamics of Bacterial Community Composition and Activity during a Mesocosm Diatom Bloom

Bacterial community composition, enzymatic activities, and carbon dynamics were examined during diatom blooms in four 200-liter laboratory seawater mesocosms. The objective was to determine whether the dramatic shifts in growth rates and ectoenzyme activities, which are commonly observed during the course of phytoplankton blooms and their subsequent demise, could result from shifts in bacterial community composition. Nutrient enrichment of metazoan-free seawater resulted in diatom blooms dominated by a Thalassiosira sp., which peaked 9 days after enrichment (≈24 μg of chlorophyll a liter⁻¹). At this time bacterial abundance abruptly decreased from 2.8 × 10⁶ to 0.75 × 10⁶ ml⁻¹, and an analysis of bacterial community composition, by denaturing gradient gel electrophoresis (DGGE) of PCR-amplified 16S rRNA gene fragments, revealed the disappearance of three dominant phylotypes. Increased viral and flagellate abundances suggested that both lysis and grazing could have played a role in the observed phylotype-specific mortality. Subsequently, new phylotypes appeared and bacterial production, abundance, and enzyme activities shifted from being predominantly associated with the <1.0-μm size fraction towards the >1.0-μm size fraction, indicating a pronounced microbial colonization of particles. Sequencing of DGGE bands suggested that the observed rapid and extensive colonization of particulate matter was mainly by specialized α-Proteobacteria- and Cytophagales-related phylotypes. These particle-associated bacteria had high growth rates as well as high cell-specific aminopeptidase, β-glucosidase, and lipase activities. Rate measurements as well as bacterial population dynamics were almost identical among the mesocosms indicating that the observed bacterial community dynamics were systematic and repeatable responses to the manipulated conditions.     

Impact of hydrology on free-living and particle-associated microorganisms in a river floodplain system (Danube, Austria)

1. A floodplain segment of the Danube River downstream of Vienna was studied during the hydrologically most dynamic phase (spring–summer) to evaluate the significance of connection between the main channel and the floodplain segment for particle abundance and quality as well as for bacterial and viral parameters, both free‐living and attached to particles. 2. Hydrological connectivity between the main channel and its floodplain segment (expressed as water age) influenced particle abundance and quality. Polysaccharide‐containing particles [Alcian positive‐stained particles (ASP)] and protein‐containing particles [Coomassie positive‐stained particles (CSP)] each contributed a substantial fraction to total suspended solids and were both positively related to water age. ASP were about twice as abundant as CSP. 3. Water age influenced bacterial and viral abundance and the bacterioplankton productivity in the surrounding water. Free‐living bacterial abundance and their bacterial secondary production (BSP) increased continuously with water age, best described by a linear regression. Water age also significantly impacted BSP and per cell BSP of bacteria attached to particles. The abundance of attached bacteria and viruses was not influenced by water age. 4. Bacteria and viruses on particles were influenced by particle quality. Their abundance on particles was closely related to particle size. Particle‐attached bacteria accounted on average for 30.34% (± 3.09) of the total bacterial abundance. A variable and occasionally significant proportion of viruses, between 0.43% and 35.06%, were associated with particulate material. 5. Bacteria attached to particles were significantly more productive than their free‐living counterparts. Their per‐cell activity was on average 8.6 times higher than that of the free‐living fraction. 6. Hydrological connectivity between the Danube River and its floodplain is crucial not only for the exchange of water, sediment and nutrients, but also for microbiota, thus influencing microbial life, distribution and activity.     

Host–microbe interactions as a driver of acclimation to salinity gradients in brown algal cultures

Like most eukaryotes, brown algae live in association with bacterial communities that frequently have beneficial effects on their development. Ectocarpus is a genus of small filamentous brown algae, which comprises a strain that has recently colonized freshwater, a rare transition in this lineage. We generated an inventory of bacteria in Ectocarpus cultures and examined the effect they have on acclimation to an environmental change, that is, the transition from seawater to freshwater medium. Our results demonstrate that Ectocarpus depends on bacteria for this transition: cultures that have been deprived of their associated microbiome do not survive a transfer to freshwater, but restoring their microflora also restores the capacity to acclimate to this change. Furthermore, the transition between the two culture media strongly affects the bacterial community composition. Examining a range of other closely related algal strains, we observed that the presence of two bacterial operational taxonomic units correlated significantly with an increase in low salinity tolerance of the algal culture. Despite differences in the community composition, no indications were found for functional differences in the bacterial metagenomes predicted to be associated with algae in the salinities tested, suggesting functional redundancy in the associated bacterial community. Our study provides an example of how microbial communities may impact the acclimation and physiological response of algae to different environments, and thus possibly act as facilitators of speciation. It paves the way for functional examinations of the underlying host–microbe interactions, both in controlled laboratory and natural conditions.     

Pelagic Bacteria–Particle Interactions and Community-Specific Growth Rates in Four Lakes along a Trophic Gradient

Abstract The relationships between bacterial concentration, bacterial production, and cell-specific activity of both free and attached bacteria and environmental factors such as suspended solids, nutrients, and temperature were examined in four lakes, two in New Zealand and two in Switzerland. Estimates of cell-specific production were obtained by microautoradiographic counts of [³H]thymidine-labeled cells. Bacteria attached to particles accounted for only 1.3 to 11.6% of the total bacterial abundance, but showed overall 20-fold higher specific growth rates and were relatively more active than their free counterparts. On average, 80 to 100% of epibacteria were attached to organic particles. The abundance and production of free and attached bacteria were positively correlated; however, relationships between these fractions and some environmental variables differed. Cell-specific activities of active bacteria were not equivalent to mean cellular activities of the entire bacterial community and differed in their relationship to trophic state. [³H]Thymidine-positive bacteria were more tightly linked to chlorophyll a than were total bacteria. Our findings indicate that production by attached bacteria, fueled by phytoplankton carbon, supplies ``new' free bacteria to the bacterial community. Our results support the idea that particulate organic matter acts as a source of dissolved nutrients to free bacteria. Bottom-up control of bacterial biomass, as shown by regressions of biomass vs production, appeared to be stronger in two ultraoligotrophic lakes than in two more eutrophic ones. Received: 17 April 1998; Accepted: 24 August 1998     

Interactions of bacteria and microflagellates in sequencing batch reactors exhibiting enhanced mineralization of toxic organic chemicals

Community level interactions were studied in non-axenic sequencing batch reactors (SBRs) being used to treat 2,4-dinitrophenol (DNP). Increasing the influent DNP concentrations from 1 to 10 μg ml⁻¹ eliminated large predatory organisms such as rotifers and ciliated protozoa from the SBRs. Under steady-state conditions at a DNP concentration of 10 μg ml⁻¹, supplemental additions of glucose enhanced DNP degradation and led to the establishment of a microbial community consisting of five species of bacteria and a variety of microflagellates. The bacteria and flagellates exhibited oscillating population dynamics in this system, possibly indicating predator-prey interactions between these two groups. Only two of the five bacteria isolated from this system could utilize glucose as a growth substrate, and one of these two species was the only organism that could mineralize DNP in the system. The other three bacteria could grow using metabolic by-products of one of the glucose-utilizing strains (Bacillus cereus) found in the reactors. Supplemental glucose additions increased the average size of bacterial floc particles to 172 μm, compared with 41 μm in SBRs not receiving glucose. It is theorized that the enhanced mineralization of DNP in this non-axenic system was attributable to increased community interactions resulting in increased bacterial flocculation in SBRs receiving supplemental glucose additions. Offprint requests to: S. K. Schmidt.     

Diel and Seasonal Variations in Abundance,Activity, and Community Structure of Particle-Attached and Free-Living Bacteria in NW Mediterranean Sea

Diel and seasonal variations in abundance, activity, and structure of particle-attached vs free-living bacterial communities were investigated in offshore NW Mediterranean Sea (0–1000 m). Attached bacteria were always less abundant and less diverse but generally more active than free-living bacteria. The most important finding of this study was that the activity of attached bacteria showed pronounced diel variations in the upper mixed water column with higher activities at night. Under mesotrophic conditions, the contribution of attached bacteria to total bacterial activity increased from less than 10% at day time to 83% at night time. At high chlorophyll a concentration, the highest cell-specific activities and contribution to total bacterial activity were due to free-living bacteria at day and to attached bacteria at night. Under summer oligotrophic conditions, free-living bacteria dominated and contributed to the most important part of the bacterial activity at both day and night, whereas attached bacteria were much less abundant but presented the highest cell-specific activities. These diel and seasonal variations in activities were concomitant to changes in bacterial community structure, mainly in the upper layer. The number of attached ribotypes was fairly constant suggesting that particles are colonized by a relatively limited number of ubiquitous ribotypes. Most of these ribotypes were also free-living ribotypes suggesting that attached bacteria probably originate from colonization of newly formed particles by free-living bacteria in the upper layer. These results reinforce the biogeochemical role of attached bacteria in the cycling of particulate organic carbon in the NW Mediterranean Sea and the importance of diel variability in these processes.     

Bacterial Colonization of Particles: Growth and Interactions

Marine particles in the ocean are exposed to diverse bacterial communities, and colonization and growth of attached bacteria are important processes in the degradation and transformation of the particles. In an earlier study, we showed that the initial colonization of model particles by individual bacterial strains isolated from marine aggregates was a function of attachment and detachment. In the present study, we have investigated how this colonization process was further affected by growth and interspecific interactions among the bacteria. Long-term incubation experiments showed that growth dominated over attachment and detachment after a few hours in controlling the bacterial population density on agar particles. In the absence of grazing mortality, this growth led to an equilibrium population density consistent with the theoretical limit due to oxygen diffusion. Interspecific interaction experiments showed that the presence of some bacterial strains (“residents”) on the agar particles either increased or decreased the colonization rate of other strains (“newcomers”). Comparison between an antibiotic-producing strain and its antibiotic-free mutant showed no inhibitory effect on the newcomers due to antibiotic production. On the contrary, hydrolytic activity of the antibiotic-producing strain appeared to benefit the newcomers and enhance their colonization rate. These results show that growth- and species-specific interactions have to be taken into account to adequately describe bacterial colonization of marine particles. Changes in colonization pattern due to such small-scale processes may have profound effects on the transformation and fluxes of particulate matter in the ocean.     

Bacterial colonization of particles: growth and interactions

Marine particles in the ocean are exposed to diverse bacterial communities, and colonization and growth of attached bacteria are important processes in the degradation and transformation of the particles. In an earlier study, we showed that the initial colonization of model particles by individual bacterial strains isolated from marine aggregates was a function of attachment and detachment. In the present study, we have investigated how this colonization process was further affected by growth and interspecific interactions among the bacteria. Long-term incubation experiments showed that growth dominated over attachment and detachment after a few hours in controlling the bacterial population density on agar particles. In the absence of grazing mortality, this growth led to an equilibrium population density consistent with the theoretical limit due to oxygen diffusion. Interspecific interaction experiments showed that the presence of some bacterial strains ("residents") on the agar particles either increased or decreased the colonization rate of other strains ("newcomers"). Comparison between an antibiotic-producing strain and its antibiotic-free mutant showed no inhibitory effect on the newcomers due to antibiotic production. On the contrary, hydrolytic activity of the antibiotic-producing strain appeared to benefit the newcomers and enhance their colonization rate. These results show that growth- and species-specific interactions have to be taken into account to adequately describe bacterial colonization of marine particles. Changes in colonization pattern due to such small-scale processes may have profound effects on the transformation and fluxes of particulate matter in the ocean.     

Possible food chain relationships between bacterioplankton,protozoans, and cladocerans in a reservoir

Ingestion of fluorescent particles by natural protozoan assemblage was studied in the Řimov Reservoir (Southern Bohemia) from April to October, 1987. Attached and free-living bacterial abundance, proportion of active bacteria, density of suspended particles and biomass of cladocerans were also monitored. Heterotrophic nanoflagellates (HNF; 5–12.8 10²ml⁻¹) were the dominant bacterial micrograzers during the spring period and consumed 3 to 9% of the total bacteria per day. After the spring phytoplankton bloom maximum densities of suspended particles and attached bacteria (up to 28% of the total counts) were found. Development of cladocerans in May sharply decreased the proportion of attached bacteria and kept them below 5% of the total counts. All the studied components of plankton except Cladocera decreased during the clearwater phase. The most significant drop was observed in the numbers of protozoans, and they were negligible for bacterial elimination. Bacterial losses during that time apparently were due to cladoceran grazing. During the summer period, ciliates (15–142 ml⁻¹) were mostly dominant micrograzers, and protozoan community grazing increased up to 21% of bacterial standing stock per day. The proportion of active bacteria was strongly correlated with protozoan grazing (r=0.83).