Biomass Of Heterotrophic Bacteria Research Articles

Micro-scale spatial distribution of bacterioplankton in the Priplotinny (Near-dam) Reach of the Kuibyshev Reservoir in the early autumn period 2020

A detailed study of the distribution of bacterioplankton and photosynthetic pigments of the Priplotinny Reach of the Kuibyshev Reservoir was carried out in early autumn 2020. The bacterioplankton cell numbers were 0.8-2.1 106 cells ml−1, and the biomass varied from 7 to 56 μg C L−1. The average chlorophyll a concentration of in the integral samples was 2.91 μg L−1, varying in the range of 1.1-9.6 μg L−1 (CV 30.7%). The pheophytin content was relatively low, 19.2 ± 10.4% of chlorophyll concentration, indicating the continued active phytoplankton development in the seston in the fall of 2020. From September 17 to October 3, a weak trend for an increase in bacterioplankton abundance as well as for a decrease in the chlorophyll a concentration and in the average cell volume was revealed. A significant (p < 0.05) correlation between the Chl a concentration in the total biomass of heterotrophic bacteria (r = 0.48) was observed. Under conditions of intense wind mixing, anthropogenic sources of pollution and the inflow of the inflow did not have a significant effect on the size structure of bacterioplankton. No pronounced local spatial complexes of stations were revealed in terms of quantitative and structural parameters of bacterioplankton and chlorophyll concentrations in the investigated part of the reservoir. In general, the concentration of pigments and the abundance and biomass of bacterioplankton correspond to the mesotrophic status of the Reach. Both the total number of bacterioplankton and the chlorophyll content in Pryplotinny Reach at the beginning of autumn 2020 are within the range of long-term monitoring values. While in the summer there is a clear long-term increasing trend of the bacterioplankton abundance, in the autumn the bacterioplankton numbers remain stable throughout the entire reservoir existence period.

Effects of Copper Availability on the Physiology of Marine Heterotrophic Bacteria

Marine heterotrophic bacteria play a crucial role in the cycling of energy and nutrients in the ocean. Copper (Cu) belongs to the repertoire of essential trace nutrients for bacterial growth, yet physiological responses of marine heterotrophic bacteria to Cu deficiency remain unexplored. Here, we examined these responses in oceanic and coastal isolates of heterotrophic bacteria from ecologically significant microbial clades (Flavobacteriia [Bacteroidetes], Roseobacter clade [Alphaproteobacteria] and Alteromonadales [Gammaproteobacteria]). Bacterial growth, Cu quotas (Cu:P), macronutrient content and stoichiometry (cellular C, N, P, S and C:N, S:P), as well as carbon metabolism (respiration, productivity, carbon demand, growth efficiency) were monitored across a gradient of Cu conditions, characteristic of coastal and open-ocean surface waters. Cu deficiency had most severe effects on a Flavobacteriia member Dokdonia sp. strain Dokd-P16 for which we observed significant reductions in growth, C metabolism and Cu quotas. Other strains did not significantly reduce their growth rate, but adjusted their Cu content and some C metabolic rates (Ruegeria pomeroyi DSS-3, Roseobacter clade) or were unaffected (Pseudoalteromonas sp. strains PAlt-P26 and PAlt-P2, Alteromonadales clade). These diverse bacterial responses were accompanied by constant cellular composition of major elements and stoichiometric ratios. Changes in bacterial Cu quotas occurred within a modest range (~5-fold range) relative to the 50-fold variation in total Cu in the media. We hypothesize that this may reflect a well-controlled Cu homeostasis in marine heterotrophic bacteria. In a preliminary assessment, we found that Cu quotas of our bacteria and those of eukaryotic phytoplankton are not statistically different. However, compared to eukaryotic phytoplankton, the variability of Cu quotas in marine heterotrophic bacteria is smaller, which could reflect differences in their Cu homeostasis. Using Cu quotas obtained in our study, we assessed the contribution of bacterial Cu to the biogenic Cu pool in an oceanic euphotic zone in the NE Pacific. These preliminary estimates suggest that up to 50 % of the biogenic Cu could be contained in the heterotrophic bacteria biomass. Our study sheds light on the interactions between Cu and marine heterotrophic bacteria, and expands the understanding of factors influencing microbial ecology and bacterial role in Cu cycle.

Ocean acidification and desalination: climate-driven change in a Baltic Sea summer microplanktonic community

Helcom scenario modelling suggests that the Baltic Sea, one of the largest brackish-water bodies in the world, could expect increased precipitation (decreased salinity) and increased concentration of atmospheric CO2 over the next 100 years. These changes are expected to affect the microplanktonic food web, and thereby nutrient and carbon cycling, in a complex and possibly synergistic manner. In the Baltic Proper, the extensive summer blooms dominated by the filamentous cyanobacteria Aphanizomenon sp., Dolichospermum spp. and the toxic Nodularia spumigena contribute up to 30% of the yearly new nitrogen and carbon exported to the sediment. In a 12 days outdoor microcosm experiment, we tested the combined effects of decreased salinity (from 6 to 3) and elevated CO2 concentrations (380 and 960 µatm) on a natural summer microplanktonic community, focusing on diazotrophic filamentous cyanobacteria. Elevated pCO2 had no significant effects on the natural microplanktonic community except for higher biovolume of Dolichospermum spp. and lower biomass of heterotrophic bacteria. At the end of the experimental period, heterotrophic bacterial abundance was correlated to the biovolume of N. spumigena. Lower salinity significantly affected cyanobacteria together with biovolumes of dinoflagellates, diatoms, ciliates and heterotrophic bacteria, with higher biovolume of Dolichospermum spp. and lower biovolume of N. spumigena, dinoflagellates, diatoms, ciliates and heterotrophic bacteria in reduced salinity. Although the salinity effects on diatoms were apparent, they could not clearly be separated from the influence of inorganic nutrients. We found a clear diurnal cycle in photosynthetic activity and pH, but without significant treatment effects. The same diurnal pattern was also observed in situ (pCO2, pH). Thus, considering the Baltic Proper, we do not expect any dramatic effects of increased pCO2 in combination with decreased salinity on the microplanktonic food web. However, long-term effects of the experimental treatments need to be further studied, and indirect effects of the lower salinity treatments could not be ruled out. Our study adds one piece to the complicated puzzle to reveal the combined effects of increased pCO2 and reduced salinity levels on the Baltic microplanktonic community.

Biomass and composition of protistan grazers and heterotrophic bacteria in the Costa Rica Dome during summer 2010.

We investigated biomass and composition of heterotrophic microbes in the Costa Rica Dome during June-July 2010 as part of a broader study of plankton trophic dynamics. Because picophytoplankton (<2 μm) are known to dominate in this unique upwelling region, we hypothesized tight biomass relationships between size-determined predator-prey pairs (i.e. picoplankton-nano-grazers, nanoplankton-micro-grazers) within the microbial community. Integrated biomass of heterotrophic bacteria ranged from 180 to 487 mg C m-2 and was significantly correlated with total autotrophic carbon. Heterotrophic protist (H-protist) biomass ranged more narrowly from 488 to 545 mg C m-2, and was comprised of 60% dinoflagellates, 30% other flagellates and 11% ciliates. Nano-sized (<20 μm) protists accounted for the majority (57%) of grazer biomass and were positively correlated with picoplankton, partially supporting our hypothesis, but nanoplankton and micro-grazers (>20 μm) were not significantly correlated. The relative constancy of H-protist biomass among locations despite clear changes in integrated autotrophic biomass, Chl a, and primary production suggests that mesozooplankton may exert a tight top-down control on micro-grazers. Biomass-specific consumption rates of phytoplankton by protistan grazers suggest an instantaneous growth rate of 0.52 day-1 for H-protists, similar to the growth rate of phytoplankton and consistent with a trophically balanced ecosystem dominated by pico-nanoplankton interactions.

Distribution pattern of picoplankton carbon biomass linked to mesoscale dynamics in the southern gulf of Mexico during winter conditions

In order to characterize the carbon biomass spatial distribution of autotrophic and heterotrophic picoplankton populations linked to mesoscale dynamics, an investigation over an extensive open-ocean region of the southern Gulf of Mexico (GM) was conducted. Seawater samples from the mixed layer were collected during wintertime (February–March 2013). Picoplankton populations were counted and sorted using flow cytometry analyses. Carbon biomass was assessed based on in situ cell abundances and conversion factors from the literature. Approximately 46% of the total picoplankton biomass was composed of three autotrophic populations (Prochlorococcus, Synechococcus, and pico-eukaryotes), while 54% consisted of heterotrophic bacteria populations. Prochlorococcus spp. was the most abundant pico-primary producer (>80%), and accounted for more than 60% of the total pico-autotrophic biomass. The distribution patterns of picoplankton biomass were strongly associated with the mesoscale dynamics that modulated the hydrographic conditions of the surface mixed layer. The main features of the carbon distribution pattern were: (1) the deepening of picoplankton biomass to layers closer to the nitracline base in anticyclonic eddies; (2) the shoaling of picoplankton biomass in cyclonic eddies, constraining the autoprokaryote biomasses to the upper layers, as well as accumulating the pico-eukaryote biomass in the cold core of the eddies; and (3) the increase of heterotrophic bacteria biomass in frontal regions between counter-paired anticyclonic and cyclonic eddies. Factors related to nutrient preferences and light conditions may as well have contributed to the distribution pattern of the microbial populations. The findings reveal the great influence of the mesoscale dynamics on the distribution of picoplankton populations within the mixed layer. Moreover, the significance of microbial components (especially Prochlorococcus) in the southern GM during winter conditions was revealed, indicating that they may play an important role in the pelagic food web, and that they may have a substantial impact on the carbon cycle in oligotrophic regions.

Bacterial carbon dependence on freshly produced phytoplankton exudates under different nutrient availability and grazing pressure conditions in coastal marine waters.

The effects of grazing pressure and inorganic nutrient availability on the direct carbon transfer from freshly produced phytoplankton exudates to heterotrophic bacteria biomass production were studied in Mediterranean coastal waters. The short-term incorporation of ¹³C (H¹³CO₃) in phytoplankton and bacterial lipid biomarkers was measured as well as the total bacterial carbon production (BP), viral lysis and the microbial community structure under three experimental conditions: (1) High inorganic Nutrient and High Grazing (HN + HG), (2) High inorganic Nutrient and Low Grazing (HN + LG) and (3) under natural in situ conditions with Low inorganic Nutrient and High Grazing (LN + HG) during spring. Under phytoplankton bloom conditions (HN + LG), the bacterial use of freshly produced phytoplankton exudates as a source of carbon, estimated from ¹³C enrichment of bacterial lipids, contributed more than half of the total bacterial production. However, under conditions of high grazing pressure on phytoplankton with or without the addition of inorganic nutrients (HN + HG and LN + HG), the ¹³C enrichment of bacterial lipids was low compared with the high total bacterial production. BP therefore seems to depend mainly on freshly produced phytoplankton exudates during the early phase of phytoplankton bloom period. However, BP seems mainly relying on recycled carbon from viral lysis and predators under high grazing pressure.

Red tides in Masan Bay, Korea, in 2004–2005: III. Daily variations in the abundance of mesozooplankton and their grazing impacts on red-tide organisms

To investigate the role of mesozooplankton in the dynamics of red tides in Masan Bay, Korea, we measured the abundance of mesozooplankton in daily samples collected from June 1, 2004 to May 31, 2005. Mesozooplankton were abundant in the winter, but rare in the summer, and had a range of abundance of 3–52,843ind.m−3. Similarly, both copepods and cladocerans were abundant in the winter, but rare in the summer, and had ranges of abundance of 0–48,817ind.m−3 and 0–10,951ind.m−3, respectively. Invertebrate larvae were abundant in the fall but not in other seasons. The biomass of copepods was significantly positively correlated with salinity, dissolved oxygen, the biomass of the phototrophic dinoflagellates Heterocapsa triquetra and Prorocentrum minimum, and the biomass of the heterotrophic dinoflagellate Gyrodinium glaucum, but negatively correlated with water temperature and the biomass of heterotrophic bacteria and small algae. In addition, the biomass of cladocerans was significantly positively correlated with salinity and the biomass of euglenophytes and G. glaucum, but negatively correlated with water temperature. The biomass of invertebrate larvae was significantly positively correlated with water temperature, but negatively correlated with dissolved oxygen. These observations suggest that copepods and cladocerans may increase their populations by feeding on large phytoplankton in cold water, whereas invertebrate larvae may prefer warm water. The grazing coefficients for the copepods Acartia spp. on co-occurring Pfiesteria-like dinoflagellates (PLDs), P. minimum, Skeletonema costatum, H. triquetra, Heterosigma akashiwo, and Scrippsiella trochoidea were 0.104, 0.083, 0.042, 0.034, 0.033, and 0.030d−1, respectively. These results suggest that grazing by Acartia populations in Masan Bay can have a considerable impact on the populations of PLDs and P. minimum, but only a moderate impact on S. costatum, H. triquetra, S. trochoidea, and H. akashiwo.

Effects of calcium and magnesium addition on the start-up of sequencing batch reactor using biofloc technology treating solid aquaculture waste

The present study investigated the effects of calcium and magnesium addition on biofloc technology (BFT) treating solid aquaculture waste in sequencing batch reactors. The concentrations of calcium and magnesium for treatment reactors were 400mg/L and 800mg/L. The dissolved inorganic nitrogen concentration in treatment is lower than that of control during the start-up period of reactors. The bio-flocs’ settle-ability was improved significantly for the treatment with calcium and magnesium addition. And, calcium and magnesium addition increased bio-flocs’ saturated fatty acid, polysaccharide, and monounsaturated fatty acid content, and decreased crude protein content. Bacteria production in the treatments was 415.00±4.38g MLVSS (mixed liquor violate suspended solids)/(kg aquaculture solids waste), which is 1.3 times higher than that of control. The average chemical oxygen demand (COD) removal rate was 71.80±0.54mg carbon/(Lday) for control. 79% and 67% of nitrogen in aquacultural sludge was converted into heterotrophic bacteria biomass for control and treatment. The calcium and magnesium content of flocs in treatment was 188.76±0.15 and 11.09±0.02mg/g MLSS (mixed liquor suspended solids) at the end of the experiment.

Temporal variation of picoplankton in the spring bloom of Yellow Sea, China

Temporal variation of Synechococcus, picoeukaryote and heterotrophic bacteria abundance and depth integrated biomass during three spring blooms in 2007 and 2009 were investigated in the Yellow Sea, China. Synechococcus and picoeukaryote responded differently to different types and course of spring blooms. During the diatom blooms of 2007 and Bloom B20 in 2009, Synechococcus and picoeukaryote abundances decreased sharply during the bloom period. However, during a mixed dinoflagellate and diatom bloom of Bloom B23 in 2009, Synechococcus and picoeukaryote increased in abundance and biomass along the bloom. During all three spring blooms, heterotrophic bacteria biomass had a similar increasing trend. Ciliate and heterotrophic nanoflagellate grazing could be responsible for Synechococcus and picoeukaryote abundance and biomass decrease during the spring blooms.

Spatial and temporal variations of picoplankton in three contrasting periods in the Pearl River Estuary, South China

The distribution characteristics and biomass composition of three picophytoplankton (PP) groups (Synechococcus, picoeukaryotes and Prochlorococcus) were identified using flow cytometry in three contrasting periods (August 2010, January 2011 and August 2011) in the Pearl River Estuary (PRE), South China. To eliminate the overestimation of heterotrophic bacteria (HBA), HBA were identified by epifluorescence microscopy and flow cytometry. The average biomass in the three observations was as follows: 22.80, 21.04 and 18.72μg C/L of HBA, and 12.92, 0.62 and 15.42μg C/L of PP. The biomass ratio between the PP and HBA measurements increased along the estuarine axis, which suggested the dominance of PP in the outer estuary and HBA in the nearshore waters. The HBA biomass was not related to chlorophyll a or even exhibited a negative correlation with chlorophyll a in the two summer observations; this implied that dissolved organic carbon from other sources or some environmental factors, like suspended solids concentration (SSC), also affected bacterial growth and obscured the relationship between HBA and phytoplankton by shaping phytoplankton distribution. The HBA linked tightly with suspended particles and was mainly shaped by the SSC. We considered that most of the HBA were attached to riverine-originated particulates and consequently exhibited a decreasing trend from the upper estuary to the open shelf waters in the PRE. The low Synechococcus and picoeukaryotes biomass and the undetectability of Prochlorococcus in the winter were probably attributed to high turbidity and low water temperature. The sharp decrease in river flow in the summer of 2011 may have exerted less pressure on Prochlorococcus and resulted in biomass elevation and a further upward distribution scale. Furthermore, Synechococcus and Prochlorococcus exhibited similar distribution patterns and were relevant to the river input. Meanwhile, picoeukaryotes were the least abundant groups among the PP community in our investigations and showed a distinct distribution pattern from that of Synechococcus and Prochlorococcus.

Dynamics of Planktonic Prokaryotes and Dissolved Carbon in a Subtropical Coastal Lake

To understand the dynamics of planktonic prokaryotes in a subtropical lake and its relationship with carbon, we conducted water sampling through four 48-h periods in Peri Lake for 1 year. Planktonic prokaryotes were characterized by the abundance and biomass of heterotrophic bacteria (HB) and of cyanobacteria (coccoid and filamentous cells). During all samplings, we measured wind speed, water temperature (WT), pH, dissolved oxygen (DO), precipitation, dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), and carbon dioxide (CO2). DOC was higher in the summer (average = 465 μM – WT = 27°C) and lower in the winter (average = 235 μM – WT = 17°C), with no significant variability throughout the daily cycles. CO2 concentrations presented a different pattern, with a minimum in the warm waters of the summer period (8.31 μM) and a maximum in the spring (37.13 μM). Daily trends were observed for pH, DO, WT, and CO2. At an annual scale, both biological and physical-chemical controls were important regulators of CO2. HB abundance and biomass were higher in the winter sampling (5.60 × 109 cells L−1 and 20.83 μmol C L−1) and lower in the summer (1.87 × 109 cells L−1 and 3.95 μmol C L−1). Filamentous cyanobacteria (0.23 × 108–0.68 × 108 filaments L−1) produced up to 167.16 μmol C L−1 as biomass (during the warmer period), whereas coccoid cyanobacteria contributed only 0.38 μmol C L−1. Precipitation, temperature, and the biomass of HB were the main regulators of CO2 concentrations. Temperature had a negative effect on the concentration of CO2, which may be indirectly attributed to high heterotroph activity in the autumn and winter periods. DOC was positively correlated with the abundance of total cyanobacteria and negatively with HB. Thus, planktonic prokaryotes have played an important role in the dynamics of both dissolved inorganic and organic carbon in the lake.

Biomass and trophic structure of the plankton community in subtropical and temperate waters of the northwestern Pacific Ocean

This study examined the biomass structure of autotrophic and heterotrophic plankton along a trophic gradient in the northwestern Pacific Ocean in an attempt to understand planktonic food web structure. Autotrophic biomass exceeded that of heterotrophic organisms in all sampling regions, but with lesser contribution to total planktonic biomass at stations of higher phytoplankton biomass, including the northern East China Sea, compared to the regions of lower phytoplankton biomass. The proportion of the biomass of heterotrophic bacteria, nanoflagellates (HNF), and dinoflagellates (HDF) relative to that of phytoplankton was all inversely related to phytoplankton biomass, but positive relationships were observed for both ciliates and mesozooplankton. Mesozooplankton biomass inclined greater than phytoplankton along the gradient of phytoplankton biomass, with biomass rise being most closely associated with ciliate and HDF biomass and, to a lesser degree, with large phytoplankton (>3 μm). Both bacteria and picophytoplankton were significantly and positively related to the biomass ratio of mesozooplankton to the sum of HDF and ciliates (i.e., proxy of mesozooplankton predation on protozoans), but no positive relationship was apparent either for HNF or for large phytoplankton. Such relationships may result from predation relief on lower food webs associated with mesozooplankton feeding on protistan plankton.

Decrease in the Autotrophic-to-Heterotrophic Biomass Ratio of Picoplankton in Oligotrophic Marine Waters Due to Bottle Enclosure

We investigated the effects of bottle enclosure on autotrophic and heterotrophic picoplankton in North and South subtropical Atlantic oligotrophic waters, where the biomass and metabolism of the microbial community are dominated by the picoplankton size class. We measured changes in both autotrophic (Prochlorococcus, Synechococcus, and picoeukaryotes) and heterotrophic picoplankton biomass during three time series experiments and in 16 endpoint experiments over 24 h in light and dark treatments. Our results showed a divergent effect of bottle incubation on the autotrophic and heterotrophic components of the picoplankton community. The biomass of picophytoplankton showed, on average, a >50% decrease, mostly affecting the picoeukaryotes and, to a lesser extent, Prochlorococcus. In contrast, the biomass of heterotrophic bacteria remained constant or increased during the incubations. We also sampled 10 stations during a Lagrangian study in the North Atlantic subtropical gyre, which enabled us to compare the observed changes in the auto- to heterotrophic picoplankton biomass ratio (AB:HB ratio) inside the incubation bottles with those taking place in situ. While the AB:HB ratio in situ remained fairly constant during the Lagrangian study, it decreased significantly during the 24 h of incubation experiments. Thus, the rapid biomass changes observed in the incubations are artifacts resulting from bottle confinement and do not take place in natural conditions. Our results suggest that short (<1 day) bottle incubations in oligotrophic waters may lead to biased estimates of the microbial metabolic balance by underestimating primary production and/or overestimating bacterial respiration.

Morphological and physiological changes in Microcystis aeruginosa as a result of interactions with heterotrophic bacteria

Pg1. To reveal the role of aquatic heterotrophic bacteria in the process of development of Microcystis blooms in natural waters, we cocultured unicellular Microcystis aeruginosa with a natural Microcystis-associated heterotrophic bacterial community. 2. Unicellular M. aeruginosa at different initial cell densities aggregated into colonies in the presence of heterotrophic bacteria, while axenic Microcystis continued to grow as single cells. The specific growth rate, the chl a content, the maximum electron transport rate (ETR(max)) and the synthesis and secretion of extracellular polysaccharide (EPS) were higher in non-axenic M. aeruginosa than in axenic M. aeruginosa after cell aggregation, whereas axenic and non-axenic M. aeruginosa displayed the same physiological characteristic before aggregation. 3. Heterotrophic bacterial community composition was analysed by PCR-denaturing gradient gel electrophoresis (PCR-DGGE) fingerprinting. The biomass of heterotrophic bacteria strongly increased in the coinoculated cultures, but the DGGE banding patterns in coinoculated cultures were distinctly dissimilar to those in control cultures with only heterotrophic bacteria. Sequencing of DGGE bands suggested that Porphyrobacter, Flavobacteriaceae and one uncultured bacterium could be specialist bacteria responsible for the aggregation of M. aeruginosa. 4. The production of EPS in non-axenic M. aeruginosa created microenvironments that probably served to link both cyanobacterial cells and their associated bacterial cells into mutually beneficial colonies. Microcystis colony formation facilitates the maintenance of high biomass for a long time, and the growth of heterotrophic bacteria was enhanced by EPS secretion from M. aeruginosa. 5. The results from our study suggest that natural heterotrophic bacterial communities have a role in the development of Microcystis blooms in natural waters. The mechanisms behind the changes of the bacterial community and interaction between cyanobacteria and heterotrophic bacteria need further investigations.

Quantitative dominance of seasonally persistent filamentous cyanobacteria (Planktothrix rubescens) in the microbial assemblages of a temperate lake

The spatiotemporal changes in abundance and biomass of heterotrophic bacteria, of three major bacterial phylogenetic groups, and of picocyanobacteria in the upper 20 m of a deep prealpine lake (Lake Zurich, Switzerland) were monitored during a seasonally persistent bloom of the toxigenic filamentous cyanobacterium Planktothrix rubescens. In addition, bacterial 16S ribosomal deoxyribonucleic acid (rDNA) sequences were collected at one instance from the bloom layer and from waters above and below this zone. P. rubescens comprised up to 70% of particulate organic carbon during summer stratification and autumnal mixis and thus by far exceeded the total biomass both of other phytoplankton and of prokaryotes. A strong negative correlation was found between the estimated basin‐wide biomass of P. rubescens and of heterotrophic bacteria, and there was different spatial niche preference of filamentous vs. picocyanobacteria. Only members of the Cytophaga‐Flavobacterium lineage of Bacteroidetes showed an increasing tendency of association with the P. rubescens population, in particular at the onset of autumnal mixing. Although the filamentous cyanobacterium was the dominant primary producer throughout the year, it did not seem to be a carbon source for heterotrophic bacteria at all. We conclude that P. rubescens represents a powerful competitor of autotrophic and heterotrophic prokaryotes, likely due to both its specific physiological (photoheterotrophic) properties and its protection against zooplankton grazing. This competitiveness might be regarded as another reason for its mass occurrence in numerous lakes of the Northern hemisphere.

Differential responses of phytoplankton and heterotrophic bacteria to organic and inorganic nutrient additions in coastal waters off the NW Iberian Peninsula

The short-term effects of inorganic N and P (nitrate, ammonium, phosphate) and organic C and N (glucose, amino acids) input, added separately as well as jointly, on microplankton commu- nity structure and metabolism were studied in 6 microcosm experiments conducted from February to July 2008 in a eutrophic coastal embayment in NW Spain under contrasting hydrographic conditions. The responses of planktonic communities were highly variable. Strong positive effects of combined inorganic and organic nutrient enrichments for phytoplankton and heterotrophic bacteria were found. In most experiments enhanced phytoplankton biomass and productivity (primary production increased up to 5.5-fold) was measured after mixed (inorganic plus organic) additions but phyto- plankton responded only in one of the experiments after inorganic additions. Heterotrophic bacteria responded faster than phytoplankton to the additions but were never affected by inorganic nutrient additions, suggesting a C limitation of bacterial activity in this coastal environment. Heterotrophic bacteria biomass, productivity, and respiration responded to mixed additions (containing C, N, and P) in all the experiments (bacterial production increased from 14- to 34-fold) whereas its response to organic (containing C and N) additions greatly differed among experiments (bacterial production increased from 0.6- to 21-fold), which could be partially related to P availability. A general increase in bacterial growth efficiency occurred only after mixed additions (up to 2-fold). The tendency towards heterotrophy of the microbial plankton community was weaker after the mixed (Production/Respira- tion (P/R) ratio changes from 0.34- to 1.6-fold) than after the organic additions (P/R changes from 0.16- to 0.8-fold). Our results suggest that phytoplankton requirememnts for organic nutrients for growth and P deficiency of bacterial populations intermittently occur in this coastal area.

Kinetics, design and biomass production of a bacteria reactor treating RAS effluent streams

The kinetics and design of a suspended bacteria growth reactor, which can be integrated in a 100MT African catfish farm, were determined. Such a reactor converted nitrogen (N) and phosphorus (P) from RAS effluents into heterotrophic bacteria biomass. The determined kinetics were: yield = 0.537 g VSS/g C; endogenous decay coefficient = 0.033 h −1; maximum specific growth rate = 0.217 h −1; half-velocity constant = 0.025 g/l; maximum rate of substrate utilization = 0.404g C/g VSS h. A reactor integrated in a 100MT farming facility would have a volume of 11 m 3, based on a minimum HRT of 6 h. The kinetics and reactor design were integrated in a model to predict the VSS production (volatile suspended solids as measure of bacteria biomass) and nutrient conversions. The VSS production was on average 187 ± 2 g VSS/kg feed and the inorganic nutrients (N and P) were removed with an efficiency of 85 ± 3.0% and 95 ± 2.5%, respectively. A carbon (C) supplementation level of 455 g C/kg feed was required to ensure optimal C:N ratios for heterotrophic bacteria production. The production of heterotrophic bacteria biomass is, therefore, a prospective tool to lower nutrient discharge and to increase nutrient retention and sustainability of RAS in the future.

Effect of the Yellow Sea Cold Water Mass (YSCWM) on distribution of bacterioplankton

Abstract Four surveys were carried out in August 2001, and in August, September and October 2002 in the southern Yellow Sea, China. Bacterioplankton abundance and biomass were quantified along the transects from Qingdao, China to the Korean island of Jeju. In this paper, the author describes the distribution of bacterioplankton and predatory pressures, and also discusses the impact of Yellow Sea Cold Water Mass (YSCWM) on the distribution of bacterioplankton. The range of Synechococcus biomass was 0.78–33.49 mg C/m 3 (on average 6.26 mg C/m 3), and heterotrophic bacteria biomass was 1.58–21.25 mg C/m 3 (on average 5.79 mg C/m 3, n=197). In the vertical direction, the distribution order of Synechococcus biomass was mid-layer>surface>bottom, and the one of heterotrophic bacteria biomass was surface>mid-layer>bottom. The contribution of Synechococcus to the total phytoplankton biomass (SB/PB) ranged from 2% to 99% (on average 42.5%), and the ratio of heterotrophic bacterial biomass to phytoplankton biomass (HBB/PB) was from 5% to 637% (on average 85%). Daily variations of bacterioplankton biomass at anchor stations showed that the maximal Synechococcus biomass was 8.8 times the minimum, and it was 2.8 times in heterotrophic bacterial biomass. The distribution of bacterioplankton accorded with temperature and salinity, and the minimum of bacterioplankton biomass occurred in the YSCWM waters. At the same time, the microzooplankton (20–200 μm) preyed on Synechococcus in these waters, with the ingestion rate of about 0.20–0.42/d.

Effect of nutrient enrichment on bacterioplankton biomass and community composition in mesocosms in the Archipelago Sea, northern Baltic

Effects of nutrient enrichment on the biomass and community composition of heterotrophic bacteria and picocyanobacteria were studied in large (42 m 3 ) mesocosms in the brackish-water Archipelago Sea (Baltic Sea) in late summer 2000 using cell counts and denaturing gradient gel electrophoresis (DGGE) of polymerase chain reaction (PCR)-amplified 16S rRNA gene fragments. The identity of the major DNA bands was determined by sequencing. The obtained sequences were related to α- and γ-proteobacteria, actinobacteria, verrcomicrobia and cyanobacteria. Nitrogen and phosphorus additions increased the biomasses of heterotrophic bacteria and picocyanobacteria and caused significant changes in their community composition judging from the DGGE banding patterns. Most verrucomicrobial bands had their highest relative intensity in the control treatment and their lowest in the higher nutrient addition treatment, whereas most Synechococcus-related bands had their lowest relative intensity in the lower nutrient addition treatment. The responses of proteobacteria and actinobacteria were more variable. The presence of both freshwater and marine sequences among the closest relatives to our sequences highlights the intermediate character of the Archipelago Sea between a freshwater and truly marine environment.

Distribution of biomass of heterotrophic bacterioplankton in the Bohai Sea

Distribution, variation and impact factors of biomass of bacterioplankton from April to May 1999 in Bohai Sea were studied in DAPI method with epifluorescence microscopy. The biomass in surface waters showed a small day-night variation, varying from 0.13 to 2.51 μg/dm3 with an average of 0.84 μg/dm3. The biomass in bottom waters showed, however, a large variation, changing from 0.15 to 4.18 μg/dm3 with an average of 1.36 μg/dm3. The peak values occurred at 5 and 11 a.m. The bottom water biomass showed a significant correlation with particulate organic carbon (r=0.639,P<0.05). Heterotrophic bacterioplankton biomass was high in nearshore waters and low in offshore areas with a high biomass zone around Huanghe (Yellow) River mouth, showing the same distribution of nutrients. In vertical distribution, heterotrophic bacteria biomass in bottom waters was higher than that in surface water.