Particle-attached Bacteria Research Articles

Use of fallout radionuclides ((7)Be, (210)Pb) to estimate resuspension of Escherichia coli from streambed sediments during floods in a tropical montane catchment.

Consumption of water polluted by faecal contaminants is responsible for 2 million deaths annually, most of which occur in developing countries without adequate sanitation. In tropical aquatic systems, streambeds can be reservoirs of persistent pathogenic bacteria and high rainfall can lead to contaminated soils entering streams and to the resuspension of sediment-bound microbes in the streambed. Here, we present a novel method using fallout radionuclides ((7)Be and (210)Pbxs) to estimate the proportions of Escherichia coli, an indicator of faecal contamination, associated with recently eroded soil particles and with the resuspension of streambed sediments. We show that using these radionuclides and hydrograph separations we are able to characterize the proportion of particles originating from highly contaminated soils and that from the resuspension of particle-attached bacteria within the streambed. We also found that although overland flow represented just over one tenth of the total flood volume, it was responsible for more than two thirds of the downstream transfer of E. coli. We propose that data obtained using this method can be used to understand the dynamics of faecal indicator bacteria (FIB) in streams thereby providing information for adapted management plans that reduce the health risks to local populations. Graphical Abstract Graphical abstract showing (1) the main water flow processes (i.e. overland flow, groundwater return flow, blue arrows) and sediment flow components (i.e. resuspension and soil erosion, black arrows) during floods in the Houay Pano catchment; (2) the general principle of the method using fallout radionuclide markers (i.e. (7)Be and (210)Pbxs) to estimate E. coli load from the two main sources (i.e. streambed resuspension vs soil surface washoff); and 3) the main results obtained during the 15 May 2012 storm event (i.e. relative percentage contribution of each process to the total streamflow, values in parentheses).

Differentiating the role of different-sized microorganisms in peptide decomposition during incubations using size-fractioned coastal seawater

Peptide decomposition by different-sized microorganisms was compared by incubating tetrapeptide alanine–valine–phenylalanine–alanine (AVFA), a fragment of RuBisCO, in coastal seawater after size-fraction by filtration. The size-fractioned seawater included <0.8-μm filtered (free-living bacteria), <5-μm filtered (free-living bacteria+heterotrophic nanoflagellates), <20-μm filtered (free-living and particle-attached bacteria+heterotrophic nanoflagellates+other small protists), and unfiltered whole water collected from Texas coast in the western Gulf of Mexico. Decomposition rates of AVFA in the <20-μm and unfiltered seawater were significantly higher than those in the <0.8-μm and <5-μm seawater in the December 2011 incubation. The higher decomposition rate in the large size fractions can be attributed to activities of particle-attached bacteria and/or large-size microorganisms, such as osmotrophic protists. However, the role of particle-attached bacteria in explaining this decomposition difference might be limited, as bacterial abundance and community structure did not differ much among the 4 treatments. Consistently, the June 2013 incubation indicated that AVFA decomposed most rapidly in the unfiltered seawater with >20-μm microorganisms. This study provides insights into the relative role of different-sized microorganisms in regulating the recycling of labile organic matter in coastal waters.

Variation in abundance and community structure of particle-attached and free-living bacteria in the South China Sea

Bacteria play a crucial role in the biological transfer of carbon in the ocean, especially in the transformation of particulate organic carbon (POC) to dissolved organic carbon (DOC), yet little information is available for their abundance and community structures in mesopelagic and bathypelagic waters. Here we present results of our investigation on the spatial variations of abundance and community composition of the particle-attached (PA) and free-living (FL) bacterial assemblages at different depths (500m, 800m, and 1500m) in the South China Sea (SCS). Our results showed that the abundance of FL bacteria was an order of magnitude higher than that of PA bacteria. The relative abundance of FL bacteria increased from 82% at 500m to 93% at 1500m. In all cases, the FL bacteria assemblages were more diverse than the PA fraction. The PA bacterial assemblage was dominated by members of the Rhodobacterales of the α-Proteobacteria and the Alteromonadales of the γ-Proteobacteria. In contrast, the FL bacteria assemblages displayed distinctive spatial heterogeneity and were dominant by different phylotypes at different depths. However, certain bacterial taxa of the α- and γ-Proteobacteria co-occurred in both the FL and PA fractions, with proportions being varied with depth. These results highlight the coexistence of particle-attached and free-living bacteria specialists and generalists, and provide valuable information in understanding the role of different bacterial assemblages in the deep-ocean carbon cycle.

The influence of sorption on polyaromatic hydrocarbon biodegradation in the presence of modified nonionic surfactant organoclays

This study examined naphthalene (NAP) biodegradation in the presence of organoclays (Ca-Mon) modified by two nonionic surfactants (TX-100 and Brij 35). The nonionic surfactants are adsorbed onto the clay and this provides extra organic matter, which then generates a partition effect that affects NAP biodegradation. NAP biodegradation was found to be affected by the presence of monomer (MN) or micelle (CMC) surfactant-modified organoclays. The pseudo first-order rate constants for NAP biodegradation were as follows: NAP-Brij35-MN > NAP-Brij35-CMC > NAP > NAP-TX-100-MN > NAP-TX-100-CMC, exactly opposite to the soil organic carbon–water partitioning coefficient (koc) values for NAP in the presence of different nonionic surfactants. The bacterial community and physiological characteristics of PAH biodegradation were different between the free-living bacteria and the particle-attached bacteria and was not associated with the surfactant used. The dominant free-living bacteria involved in NAP biodegradation were Brevundimonas diminuta, Caulobacter spp., Mycoplana bullata, Acidovorax spp. and Pseudomonas aeruginosa. Community-level physiological profiling showed significant differences between free-living bacteria and particle-attached bacteria. Significant extracellular enzyme activities, such as esterases and phosphatases, were associated with the TX-100-MN/CMC modified organoclays. Practically, the results suggest that Brij 35 MN-modified organoclay is the most suitable substrate when using a nonionic surfactant for NAP bioremediation.

Impact of freshwater inflow on bacterial abundance and activity in the estuarine system Ria de Aveiro

The influence of freshwater flow on bacterial communities in the estuarine system Ria de Aveiro (Portugal) was investigated at two sites differently impacted by river inputs, representative of the marine and brackish water zones of the estuary. Sampling events were clustered based on hydrological features. The hydrodynamic was simulated with a Lagrangian model and related to microbiological parameters. Estuarine bacteria responded to different freshwater regimes developing distinct patterns of abundance and activity at the marine and brackish water zones. A circulation pattern induced by high river inflow produced vertical stratification in the marine zone, promoting a seaward flux of bacterioplankton, and stimulating the import of riverine phytoplankton and particle-attached bacteria to the brackish water zone. Advective transport and resuspension processes contributed to a 3-times increase in abundance of particle-attached bacteria during intense freshwater inputs. Additionally, bacterial activity in the estuary was controlled by inorganic nitrogen, responding to different freshwater inputs, which, in association with different prevailing sources of organic substrates induced significant changes in bacterial production. The dynamic and main controlling factors of bacterial communities are clearly impacted by freshwater inputs. Therefore, significant changes in the recycling of nutrients by microbial activities can be expected from alterations in freshwater inputs either related to global climate change or regional hydrological regimes.

Bacterial community structure in cooling water and biofilm in an industrial recirculating cooling water system

Microbial fouling is a serious problem in open recirculating cooling water systems. The bacterial communities that cause it have not been fully understood. In this study, we analyzed the community structure of free-living bacteria and particle-attached bacteria in cooling water, and bacteria in biofilm collected from the wall of the water reservoir in an industrial recirculating cooling water system by construction of a 16S rRNA gene clone library. Based on amplified ribosomal DNA restriction analysis, clones of all three libraries were clustered into 45 operational taxonomic units (OTUs). Thirteen OTUs displaying 91-96% sequence similarity to a type strain might be novel bacterial species. Noted differences in community structure were observed among the three libraries. The relative species richness of the free-living bacteria in cooling water was much lower than that of particle-attached bacteria and bacteria in biofilm. The majority of the free-living bacterial community (99.0%) was Betaproteobacteria. The predominant bacteria in the particle-attached bacterial community were Alphaproteobacteria (20.5%), Betaproteobacteria (27.8%) and Planctomycetes (42.0%), while those in the biofilm bacterial community were Alphaproteobacteria (47.9%), Betaproteobacteria (11.7%), Acidobacteria (13.1%) and Gemmatimonadetes (11.3%). To control microbial fouling in industrial recirculating cooling water systems, additional physiological and ecological studies of these species will be essential.

Taxonomic composition of the particle‐attached and free‐living bacterial assemblages in the Northwest Mediterranean Sea analyzed by pyrosequencing of the 16S rRNA

Free-living (FL) and particle-attached (PA) bacterial assemblages in the Northwest Mediterranean Sea were studied using pyrosequencing data of the 16S rRNA. We have described and compared the richness, the distribution of Operational Taxonomic Units (OTUs) within the two fractions, the spatial distribution, and the taxonomic composition of FL and PA bacterial assemblages. The number of OTUs in the present work was two orders of magnitude higher than in previous studies. Only 25% of the total OTUs were common to both fractions, whereas 49% OTUs were exclusive to the PA fraction and 26% to the FL fraction. The OTUs exclusively present in PA or FL assemblages were very low in abundance (6% of total abundance). Detection of the rare OTUs revealed the larger richness of PA bacteria that was hidden in previous studies. Alpha-Proteobacteria dominated the FL bacterial assemblage and gamma-Proteobacteria dominated the PA fraction. Bacteroidetes were important in the PA fraction mainly at the coast. The high number of sequences in this study detected additional phyla from the PA fraction, such as Actinobacteria, Firmicutes, and Verrucomicrobia.

Bacterial community dominance of particle-attached bacteria in lakes of the Mackenzie River Delta: transparent exopolymer particle contribution

Bacterial community dominance of particle-attached bacteria in lakes of the Mackenzie River Delta: transparent exopolymer particle contribution

Role of free-living and particle-attached bacteria in the recycling and export of organic material in the Hudson Bay system

This study investigates, for the first time, the role of free-living and particle-attached bacteria in the sinking export and recycling of organic matter in the Hudson Bay system (i.e. Hudson Bay, Hudson Strait, and Foxe Basin), a large subarctic estuarine system. During the late summers of 2005 and 2006, the abundance, cell size, nucleic acid content, and sinking velocity of free-living and particle-attached bacteria were studied simultaneously, using a new approach that combines the settling column method with flow cytometry. Biomass, production, and respiration of both types of bacteria were estimated using published models. Our results showed that particle-attached bacteria were, on average, twice as large as and contained 1.3 times more nucleic acid than free-living bacteria. Particle-attached bacteria also sank faster than predicted by Stoke's Law, with estimated sinking velocities comparable to those of chlorophyll a biomass and protist cells. Each individual cell of the particle-attached bacterial community had high carbon demand, but their low abundances (< 3% of total bacterial numbers) resulted in low total carbon demand. Therefore, the main contributors to POC recycling were found to be free-living bacteria using the non-sinking dissolved organic material, which is released from particles due to the hydrolytic activity of particle-attached bacteria.

Characterizations of Environmental Factors in Conjugated Linoleic Acid Production by Mixed Rumen Bacteria

Conjugated linoleic acid (CLA) production by rumen bacteria is closely related to biohydrogenation of linoleic acid (LA) and affected by various environmental factors. Ruminal biohydrogenation and isomerization were characterized in view of incubation conditions using a mixed culture of microorganisms obtained from surgically prepared cows. Free-floating bacteria (FFB) produced more CLA than particle-attached bacteria (PAB). Some major factors affecting the ruminal environment such as diet, concentrations of fat substrates, incubation time, pre-incubation, and the presence of glucose in the medium were found to be important determinants for the ruminal production of CLA and in a close relationship with biohydrogenation. The mixed bacterial culture, which was pre-exposed to LA, produced more CLA than an unexposed control in a medium containing 30% rumen fluid. The rate of conversion of fat substrate (LA) to hydrogenated products (trans-C18:1, C18:0) was negatively correlated with the initial LA concentration. Overall, the present study showed that CLA accumulation can be increased by modification of diet-induced environmental conditions, which affect changes in ruminal microflora.

Diversity of total and active free-living vs. particle-attached bacteria in the euphotic zone of the NW Mediterranean Sea

The structure of the total and metabolically active communities of attached and free-living bacteria were analysed in the euphotic zone in the NW Mediterranean Sea with the use of DNA- and RNA-derived capillary electrophoresis single-strand conformation polymorphism fingerprinting. More than half (between 52% and 69%) of the DNA-derived operational taxonomic units (OTUs) were common in both attached and free-living fractions in the euphotic layer, suggesting an exchange or co-occurrence between them. However, analysis targeting 16S rRNA showed that only some of them were found in the dominant active bacterial pool. Especially at the deep chlorophyll maximum, less than half of the attached bacterial populations were found to be active, with regard to the high proportion of OTUs present at the DNA level, but not at the RNA level. These results suggest that even if colonization on and detachment of particles appear to be ubiquitous, most of the particulate organic carbon remineralization appeared to be mediated by a rather low number of dominant active OTUs specialized in exploiting such specific microenvironment.

Seasonal to hour variation scales in abundance and production of total and particle-attached bacteria in the open NW Mediterranean Sea (0–1000 m)

Abstract. We present the vertical and temporal dynamics of total vs. particle-attached bacterial abundance and activity over a 5 week period under summer to autumn transition in NW Mediterranean Sea. At a weekly time scale, total bacterial biomass and production in the euphotic layers was significantly correlated with phytoplanktonic biomass. At an hourly time scale, total bacterial biomass responded very rapidly to chlorophyll a fluctuations, suggesting a tight coupling between phytoplankton and bacteria for resource partitioning during the summer-autumn transition. In contrast, no influence of diel changes on bacterial parameters was detected. Episodic events such as coastal water intrusions had a significant positive effect on total bacterial abundance and production, whereas we could not detect any influence of short wind events whatever the magnitude. Finally, we show that particle-attached bacteria can represent a large proportion (up to 49%) of the total bacterial activity in the euphotic layer but display rapid and sporadic changes at hourly time scales. In the mesopelagic layers, bacterial abundance and production linearly decreased with depth, except some production peaks at 400–750 m. This study underlines the value of large datasets covering different temporal scales to clarify the biogeochemical role of bacteria in the cycling of organic matter in open seawater.

Gradients of coastal fish farm effluents and their effect on coral reef microbes

Coastal milkfish (Chanos chanos) farming may be a source of organic matter enrichment for coral reefs in Bolinao, Republic of the Philippines. Interactions among microbial communities associated with the water column, corals and milkfish feces can provide insight into the ecosystem's response to enrichment. Samples were collected at sites along a transect that extended from suspended milkfish pens into the coral reef. Water was characterized by steep gradients in the concentrations of dissolved organic carbon (70-160 microM), total dissolved nitrogen (7-40 microM), chlorophyll a (0.25-10 microg l(-1)), particulate matter (106-832 microg l(-1)), bacteria (5 x 10(5)-1 x 10(6) cells ml(-1)) and viruses (1-7 x 10(7) ml(-1)) that correlated with distance from the fish cages. Particle-attached bacteria, which were observed by scanning laser confocal microscopy, increased across the gradient from < 0.1% to 5.6% of total bacteria at the fish pens. Analyses of 16S rRNA genes by denaturing gradient gel electrophoresis and environmental clone libraries revealed distinct microbial communities for each sample type. Coral libraries had the greatest number of phyla represented (range: 6-8) while fish feces contained the lowest number (3). Coral libraries also had the greatest number of 'novel' sequences (defined as < 93% similar to any sequence in the NCBI nt database; 29% compared with 3% and 5% in the feces and seawater libraries respectively). Despite the differences in microbial community composition, some 16S rRNA sequences co-occurred across sample types including Acinetobacter sp. and Ralstonia sp. Such patterns raise the question of whether bacteria might be transported from the fish pens to corals or if microenvironments at the fish pens and on the corals select for the same phylotypes. Understanding the underlying mechanisms of effluent-coral interactions will help predict the ability of coral reef ecosystems to resist and rebound from organic matter enrichment.

Bacterial production and microbial food web structure in a large arctic river and the coastal Arctic Ocean

Globally significant quantities of organic carbon are stored in northern permafrost soils, but little is known about how this carbon is processed by microbial communities once it enters rivers and is transported to the coastal Arctic Ocean. As part of the Arctic River-Delta Experiment (ARDEX), we measured environmental and microbiological variables along a 300 km transect in the Mackenzie River and coastal Beaufort Sea, in July–August 2004. Surface bacterial concentrations averaged 6.7 × 10 5 cells mL − 1 with no significant differences between sampling zones. Picocyanobacteria were abundant in the river, and mostly observed as cell colonies. Their concentrations in the surface waters decreased across the salinity gradient, dropping from 51,000 (river) to 30 (sea) cells mL − 1 . There were accompanying shifts in protist community structure, from diatoms, cryptophytes, heterotrophic protists and chrysophytes in the river, to dinoflagellates, prymnesiophytes, chrysophytes, prasinophytes, diatoms and heterotrophic protists in the Beaufort Sea. Size-fractionated bacterial production, as measured by 3H–leucine uptake, varied from 76 to 416 ng C L − 1 h − 1 . The contribution of particle-attached bacteria (> 3 µm fraction) to total bacterial production decreased from > 90% at the Mackenzie River stations to < 20% at an offshore marine site, and the relative importance of this particle-based fraction was inversely correlated with salinity and positively correlated with particulate organic carbon concentrations. Glucose enrichment experiments indicated that bacterial metabolism was carbon limited in the Mackenzie River but not in the coastal ocean. Prior exposure of water samples to full sunlight increased the biolability of dissolved organic carbon (DOC) in the Mackenzie River but decreased it in the Beaufort Sea. Estimated depth-integrated bacterial respiration rates in the Mackenzie River were higher than depth-integrated primary production rates, while at the marine stations bacterial respiration rates were near or below the integrated primary production rates. Consistent with these results, P CO2 measurements showed surface water supersaturation in the river (mean of 146% of air equilibrium values) and subsaturation or near-saturation in the coastal sea. These results show a well-developed microbial food web in the Mackenzie River system that will likely convert tundra carbon to atmospheric CO 2 at increasing rates as the arctic climate continues to warm.

Sediment–water exchange of Vibrio sp. and fecal indicator bacteria: Implications for persistence and transport in the Neuse River Estuary, North Carolina, USA

In estuaries, frequent resuspension and deposition of sediment complicate bacterial transport model development by transporting particle-attached bacteria and possibly inducing bacterial responses, such as growth, degradation, or changes in attachment. In order to better characterize these dynamics, observations were made in the Neuse River Estuary (NRE) using the combination of an in situ sampler to monitor the water column and sediment cores to monitor sediment concentrations. Two allochthonous bacteria, Escherichia coli (EC) and Enterococcus sp. (ENT), were selected as proxies for fecal contamination from stormwater runoff. Vibrio sp. (VIB), native to the NRE, was also observed as an autochthonous bacterial group that includes potentially pathogenic species. Two sampling periods were identified as dominated by different suspension types: runoff and resuspension. Despite this difference, several bacterial measures remained comparable between sampling periods. In bottom water, VIB concentration was correlated with salinity and ENT concentration was correlated with turbidity. Differences were observed for EC, where higher concentrations were found in hypoxic waters and sediment during the resuspension period. In the sediment, EC and VIB concentrations significantly increased following the passage of Hurricane Ophelia in September 2005. Throughout this study, all bacterial groups showed evidence of persistence in sediment, suggesting that sediment resuspension represents a significant source of bacteria to the water column.

Effects of phytoplankton bloom in a coastal ecosystem on the composition of bacterial communities

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 48:47-60 (2007) - doi:10.3354/ame048047 Effects of phytoplankton bloom in a coastal ecosystem on the composition of bacterial communities Beate Rink1, Susanne Seeberger1, Torben Martens1, Claus-Dieter Duerselen2, Meinhard Simon1, Thorsten Brinkhoff1,* 1Institute for Chemistry and Biology of the Marine Environment (ICBM), University of Oldenburg, PO Box 2503, 26111 Oldenburg, Germany 2AquaEcology, Marie-Curie-Straße 1, 26129 Oldenburg, Germany *Corresponding author. Email: thorsten.brinkhoff@icbm.de ABSTRACT: We studied the composition of free-living and particle-associated bacterial communities during the course of the phytoplankton succession in spring and early summer in the Wadden Sea, a tidal flat ecosystem in the southern North Sea. We applied the denaturing gradient gel electrophoresis (DGGE) approach based on PCR-amplified 16S rRNA gene fragments and, in addition to Bacteria-specific primers, used primer sets targeting Alphaproteobacteria, the Roseobacter-clade and the Bacteroidetes phylum. Even though the application of the primer sets targeting Bacteria and Alphaproteobacteria detected some changes, they were most pronounced with those targeting the Roseobacter-clade and Bacteroidetes. The changes were supported by a correspondence analysis, which showed a statistically significant correlation of the DGGE banding patterns of the Roseobacter-specific PCR with the composition of the phytoplankton (p = 0.03). This indicates that changes in the phytoplankton composition in this habitat are not reflected by changes in the most abundant or most readily amplifiable phylotypes. The findings rather suggest that few, specialized, heterotrophic bacteria are most responsive to the organic matter supplied by distinct phytoplankton communities and that the main part of organic matter in the Wadden Sea is utilized by generalists. Sequence analyses of excised bands revealed a high diversity for the Bacteria- and Bacteroidetes-targeted approaches. The bacterial community detected by the primer set targeting Alphaproteobacteria, however, was mainly composed of bacteria affiliated to the Roseobacter-clade. KEY WORDS: Free-living bacteria · Particle-attached bacteria · Bacteroidetes · Roseobacter · Phytoplankton · Denaturing gradient gel electrophoresis · Wadden Sea Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 48, No. 1. Online publication date: June 20, 2007 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2007 Inter-Research.

Ectoenzymatic activity and glucose heterotrophic metabolism in a shallow estuary (Ria de Aveiro, Portugal): influence of bed sediments and salt marshes

Abstract Bacterioplankton abundance and activity were studied in the estuarine system of Ria de Aveiro (Portugal) to test if tidal resuspension of sediments and transport of particles from the salt marshes may act as factors of variability of bacterial communities. The total and attached cell abundance, ectoenzymatic activity and the heterotrophic metabolism of glucose, as well as seston, chlorophyll a and particulate organic carbon (POC) were monitored during four 10-h periods along the tidal cycle at four sampling sites across a transect. The variation of particulate materials (seston, POC and chlorophyll a ) along the transect was not significantly correlated with either distance to the margin or distance to the sediment surface. Nevertheless, proximity to the salt marsh or to the bottom sediment surface favoured glucose incorporation and aminopeptidase activity. A multiple stepwise linear regression analysis using temperature, salinity, seston, POC, chlorophyll a , distance to sediment surface and distance to the margin as independent variables explained 66.5% of the variability of the fraction of particle-attached bacteria and only a very small proportion (12–43%) of the observed variability of total bacterial abundance, ectoenzymatic activity and glucose utilization. The spatial patterns of variation of the concentration of particulate material (seston, POC and chlorophyll a) do not clearly indicate the occurrence of sediment resuspension and runoff from the margins. This, together with the poor contribution of these parameters to the transversal and tidal variability of bacterial activity, dismisses the importance of inputs of suspended material across the sediment/water interface and from neighbouring salt marshes in the control of bacterial density and activity.

Is bacterioplankton production in the Ria de Aveiro influenced by salt marshes and bed sediment

The contribution of potential export of materials from bottom sedimentsand salt marshes into the water column of a shallow estuarine system of Ria deAveiro to the observed high bacterial productivity in the mid section of thisestuary was evaluated. Vertical profiles of physical, chemical and bacterialvariables were studied in the marine and brackish water zones, and oftransversal profiles in the brackish zone only. Although the concentrations ofseston (17–241 mg l−1), particulate organiccarbon (3–15.5 mg l−1) and chlorophyll(1.2–7.0 μg l−1) varied widely, thevertical and transversal profiles were without much variation. Total bacterialnumber (0.2–8.5 × 109 cellsl−1) and the number of particle-attached bacteria(0.02–2.50 × 109 cellsl−1)along vertical and transversal profiles did not differ much, but the rate ofbacterial production (0.05–14.2 μg C l−1h−1) and dissolved organic carbon concentration(6.0–69.2 mg l−1) were frequently highernear the salt marsh margin at the brackish water transect. The increase inproductivity could not be associated with runoff of particulate matter butcoincided with the inputs of dissolved organic carbon. The results of verticaland transversal profiles point to a minor role of particulate matter additionsfrom the salt marsh area or from bed sediments.

Aggregation, sedimentation and biodegradability of phytoplankton-derived material during spring in the Ross Sea, Antarctica

Abstract The sedimentation rates, aggregation and biodegradability of phytoplankton-derived material were investigated in the Ross Sea Polynya during austral spring, 1997. Planktonic organisms and aggregates were collected using a large volume (100 l) sampler. The phytoplankton assemblages were dominated by diatoms and/or Phaeocystis antarctica, a colonial haptophyte. Total community sinking rates of phytoplankton or derived aggregates were low, ranging between 0 and 1 m d−1, except towards mid-December when the sinking rates increased to 3 m d−1. At this time, the co-occurrence of Phaeocystis colonies and diatoms resulted in the enhanced formation of aggregates. Taxon-specific differences in sinking behaviour were observed, in that diatoms and dinoflagellates had higher sinking rates than P. antarctica. The biodegradability of phytoplankton-derived material was estimated from the enzymatic (ectoprotease, ecto-β-glucosidase) activities of free-living vs. particle-attached bacteria. Bacterial production rates were very low until late November, and from mid-December the bacterial activities increased slowly. At the same time, the proportion of attached bacteria increased; nevertheless, their contribution to the total bacterial activity remained low (less than 19% for ectoprotease, 24% for ecto-β-glucosidase and 18% for bacterial production). In contrast, specific (per cell) activities were higher for particle-attached bacteria than for free-living bacteria. Calculations suggest that 1.4–38.5% of the primary production potentially could be removed from the euphotic zone via sinking during spring, and 0.5–11.6% could be remineralized by bacterial metabolism, with a minor contribution of particle-attached bacteria (less than 2% of the primary production). Thus, during the most active period of phytoplankton growth when grazing losses are nearly non-existent, most of the removal of phytoplankton-derived particulate material is by passive sinking, and only a small amount of the particulate organic carbon is heterotrophically oxidized.

Bacterial and Phytoplankton Dynamics along a Trophic Gradient in a Shallow Temperate Estuary

Heterotrophic bacterial and phytoplankton biomass, production, specific growth rates and growth efficiencies were studied from June to October in 1996 and from February to May in 1997 along the longitudinal axis of the Urdaibai Estuary, a shallow temperate tidal estuary. Both phytoplankton and bacterial biomass showed a distinct lower to upper estuary increasing gradient. Longitudinal variations of phytoplankton biomass were controlled mainly by inorganic nutrient availability and tidal flushing. Longitudinal variations of bacterial biomass were further influenced by allochthonous inputs of organic carbon from a wastewater treatment plant located at the upper estuary. On a temporal scale, the dilution and washout effect of river discharge was a major controlling factor of both bacterial and phytoplankton biomass in the upper estuary. In this zone there were no indications that bacteria were resource limited, and temperature was the variable that explained most of the variability in bacterial specific growth rates. In the lower estuary, however, data suggested bacteria were nitrogen limited. Likewise, phytoplankton growth rates also showed a positive correlation with inorganic nutrients in this area.Free-living bacteria were generally more abundant than attached ones all along the estuary. However, following the longitudinal gradient of turbidity, the proportion of attached bacteria increased from the lower to the upper estuary. Rates of thymidine incorporation per cell were generally higher for particle-attached bacteria than for free-living bacteria.On average, bacteria contributed only 23% of the phytoplankton plus bacterial carbon biomass. Bacterial contribution to total (bacterial plus phytoplankton) net production of organic carbon was on average 17% for surface samples and 39% for bottom samples. Average phytoplankton growth efficiency in the euphotic zone was estimated to be higher (85%) than bacterial growth efficiency (46%).