Production Of Heterotrophic Bacteria Research Articles

A Qualitative and Biochemical Analysis of Biofloc from an Indoor Biofloc Technology System Culturing Oreochromis Karongae

The structure of microbial communities in a Biofloc Technology (BFT) system has a great influence on the optimal functioning of the system. This makes understanding the microbial composition in BFT of paramount importance. A study was conducted to characterize the microorganisms in an indoor biofloc technology system. The microorganisms were qualitatively and biochemically analyzed. Qualitative analysis of microorganisms in BFT was carried out using microscopy and plate culture of bacteria and fungi. Isolated bacteria were identified by colony morphology, gram staining and microscopic observation. Catalase test, as a biochemical test, was also used in identifying bacteria. Biochemical analysis of the bio floc was achieved through proximate analysis of nutrients following AOAC (2002) methods. The bio floc sample used in the present study was obtained from culture water of three 1000l circular fibreglass tanks with a working volume of 580l of bio floc water per tank. Oreochromis karongae fingerlings were stocked in the three tanks at a stocking density of 6kg/m3 per tank and cultured for 12 weeks. The fish were fed 30% CP on-farm formulated feed (2mm pelleted) with a feeding rate of 1.5% of the total estimated fish biomass. Maize flour was added in tanks to maintain an optimum C/N ratio (above 10) for heterotrophic bacteria production. Microscopy of the biofloc water revealed various types of microorganisms, which included Protozoa (e.g. ciliates), Zooplanktons (e.g. Rotifers and copepods) and nematodes, heterotrophic bacteria and fungi. It was noted that the bacteria were all heterotrophic bacteria, which confirmed their utilisation of organic carbon in the BFT system to produce microbial protein. The biochemical composition of biofloc showed that the nutritional quality of biofloc was appropriate for tilapia with the exception of lipid content, which was found to be (3.25%). This value is considered low for aquaculture feed as a range of 5- 10% lipid content in feed is recommended. BFT is a promising field which will enable aquaculture to grow towards an environmentally friendly approach because of the ability of microorganisms to recycle nutrients in the system.

Distribution and Relationship between Heterotrophic Organisms and Viruses on the East Siberian Sea Shelf

The distribution of heterotrophic bacteria, viruses, and heterotrophic nanoflagellates was studied in the shelf waters of the East Siberian Sea along the meridional transect from the Kolyma River delta in September. The production of heterotrophic bacteria and their mortality as a result of protozoan grazing and lysis of viruses were also determined. The patterns of the spatial distribution of microorganisms and viruses varied: the number of bacterioplankton decreased with increasing distance from the Kolyma delta, while, on the contrary, its size and biomass increased to the shelf areas with negative water temperatures. The highest abundance and biomass of virioplankton were recorded at the extreme southern and northern stations of the transect and the abundance and biomass of heterotrophic nanoflagellates increased from the south to the north. The studied shelf waters were characterized by a high concentration of fine-textured detrital particles, and, as a consequence, a relatively large number of viruses attached to detritus. The mortality of heterotrophic bacterioplankton accounted for most of its daily production. Protozoan grazing was the main cause of bacterial mortality that significantly exceeded their mortality due to viral lysis.

Population, biomass, and production of heterotrophic bacteria in reservoirs of the Upper Volga

Populations, biomasses, and production rates of planktonic, epiphytic, and benthic bacterial communities were defined in two reservoirs of the upper Volga, and their contributions to total numbers of bacteria and productivity were estimated. Populations and production rates of heterotrophic bacteria in 1-cm3 samples of bottom sediments exceed fouling of higher aquatic plants by a factor of 101–102, and in the water layers by a factor of 103–104. In mesotrophic Rybinsk and eutrophic Ivankovskoye reservoirs, benthic bacteria account for 90.4% and 98.8% of the total biomass, and 99.5% and 95.8% of total heterotrophic bacterial products, respectively. In these reservoirs, dissolved organic carbon accounts for 9.55% and 1.19% of the biomass and 4.12% and 0.45% of production, and epiphytic bacteria account for 0.05% and 0.03% of the biomass and 0.03% and 0.02% of production. These findings suggest important roles of benthic bacterial populations in reservoirs of the upper Volga.

Assessing the Abundance, Biomass, and Production of Heterotrophic Bacteria in Upper Volga Reservoirs

Two reservoirs in the Upper Volga were studied to determine the abundance, biomass, and production of planktonic, epiphyte, and benthos bacterial communities and to assess their contribution to the formation of the total abundance and productivity of bacteria. The abundance and production of heterotrophic bacteria per 1 cm3 of bottom sediments were 10–102 times greater than those in epibioses of higher aquatic plants and 103–104 times greater than those in water mass. In the mesoeutrophic Rybinsk Reservoir and eutrophic Ivan’kovo Reservoir, bacteriobenthos accounts for 90.4 and 98.8% of the total biomass and 95.8 and 99.5% of the total production of heterotrophic bacteria; bacterioplankton, for 9.55 and 1.19% of biomass and 4.12 and 0.45% of production; and bacterioepiphyton, for 0.05 and 0.03% of biomass and 0.03 and 0.02% of production. The obtained data demonstrate the important role of benthic bacterial communities in the Upper Volga reservoirs.

Abundance, biomass, and production of heterotrophic bacteria in a large plain reservoir during the ice-covered period

The abundance, biomass, production, and size and morphological structure of heterotrophic bacteria have been determined and their contribution to the total plankton biomass has been assessed in the Rybinsk Reservoir (the Upper Volga) during the ice-covered period. Structural and functional characteristics of bacteria, except for their cell sizes in winter, are lower than those in the growing season. However, heterotrophic bacteria have made the main contribution (89.3%) to the total biomass of plankton community in winter. During the growing season, phytoplankton is a major component of plankton (48.8%), while the bacteria average 36.5%. The total plankton biomass under the ice averages 148 mg C/m3, which is 2.6 times lower than in the period of open water. During the ice-covered period, the number of protists is small and they consume an insignificant part of the bacterial production; viral lysis is the main reason for bacterial mortality.

Abundance, Biomass and Production of Heterotrophic Bacteria in a Large Plain Reservoir During the Ice-Covered Period

Abundance, Biomass and Production of Heterotrophic Bacteria in a Large Plain Reservoir During the Ice-Covered Period

Structure and functioning of the microbial loop in a boreal reservoir

The abundance and biomass of the main components of the microbial plankton food web (“microbial loop”)—heterotrophic bacteria, phototrophic picoplankton and nanoplankton, heterotrophic nanoflagellates, ciliates and viruses, production of phytoplankton and bacterioplankton, bacterivory of nanoflagellates, bacterial lysis by viruses, and the species composition of protists—have been determined in summer time in the Sheksna Reservoir (the Upper Volga basin). A total of 34 species of heterotrophic nanoflagellates from 15 taxa and 15 species of ciliates from 4 classes are identified. In different parts of the reservoir, the biomass of the microbial community varies from 26.2 to 64.3% (on average 45.5%) of the total plankton biomass. Heterotrophic bacteria are the main component of the microbial community, averaging 63.9% of the total microbial biomass. They are the second (after the phytoplankton) component of the plankton and contribute on average 28.6% to the plankton biomass. The high ratio of the production of heterotrophic bacteria to the production of phytoplankton indicates the important role of bacteria, which transfer carbon of allochthonous dissolved organic substances to a food web of the reservoir.

Effects of hydraulic retention time and carbon to nitrogen ratio on micro-pollutant biodegradation in membrane bioreactor for leachate treatment

This research investigated the biodegradation of the micro-pollutants in leachate by the membrane bioreactor (MBR) system under six treatment conditions, comprising two C/N ratios (6, 10) and three hydraulic retention time (HRT) durations (6, 12, 24h). The experimental results indicated that the C/N 6 environment was more advantageous to the bacterial growth. The bacterial communities residing in the sludge were those of heterotrophic bacteria (HB), heterotrophic nitrifying bacteria (HNB) and ammonia oxidizing bacteria (AOB). It was found that HB and HNB produced phenol hydroxylase (PH), esterase (EST), phthalate dioxygenase (PDO) and laccase (LAC) and also enhanced the biodegradation rate constants (k) in the system. At the same time, AOB promoted the production of HB and HNB. The findings also revealed that the 12h HRT was the optimal condition with regard to the highest growth of the bacteria responsible for the biodegradation of phenols and phthalates. Meanwhile, the longer HRT duration (i.e. 24h) was required to effectively bio-degrade carbamazepine (CBZ), N,N-diethyl-m-toluamide (DEET) and diclofenac (DCF).

Performance of biofilters in GAC-sand and anthracite-sand dual-media filters in a water treatment plant in Abadan, Iran

AbstractBiological water treatment using granular activated carbon (GAC) and anthracite improves water quality by reducing total organic carbon (TOC), colour, nitrogen content and turbidity. This study investigated the operation of aerobic biofilm on two pilot biofilters designed to remove turbidity, TOC, and in water. The results show that the GAC-sand pilot filter at a low hydraulic loading rate (HLR) increased the empty bed contact time and recorded the highest production of heterotrophic bacteria and biofilm, which increased the efficiency of treatment. Breakthrough occurred in the GAC-sand pilot filter at 72 h and low HLR, but occurred sooner for medium and high HLRs at 48 and 24 h, respectively. The run-time for the anthracite-sand pilot filter at high, medium and low HLRs was 70, 46 and 22 h, respectively. The microorganisms Pseudomonas, Bacillus and Citrobacter were identified in the GAC-sand filter.

Effect of different biofloc levels on microbial activity, water quality and performance of Litopenaeus vannamei in a tank system operated with no water exchange

In zero-exchange superintensive culture systems, flocculated particles (bioflocs) accumulate in the water column. Consequently, some control over the concentration of these particles must be performed. The objective of this study is to evaluate the effects of three concentrations of bioflocs on microbial activity, selected water quality indicators and performance of Litopenaeus vannamei in a tank system operated with no water exchange. A 44-day study was conducted with juvenile (6.8g) shrimp stocked in twelve 850L tanks at a stocking density of 459shrimpm−3. Biofloc levels were expressed as three presets of total suspended solids (TSS) concentrations, as follows: 200mgL−1 (T200), 400–600mgL−1 (T400–600), and 800–1000mgL−1 (T800–1000). TSS levels were controlled by attaching a 40L settling tank to each culture tank. Reduction of TSS to concentrations close to 200mgL−1 decreased the time of bacterial cell residence and significantly reduced the nitrification rates in the water (P<0.05). The tanks in the T200 treatment had a greater variability of ammonia and nitrite (P<0.05), which led to the need to increase the C:N ratio of the organic substrate to control ammonia through its assimilation into heterotrophic bacterial biomass. But the higher production of heterotrophic bacteria in T200 (P<0.05) increased the dissolved oxygen demand. Nitrification rates were higher (P<0.05) in tanks with TSS concentrations above 400mgL−1, and ammonia and nitrite were significantly lower than in the T200 tanks. We suggest that ammonia and nitrite in the T400–600 and T800–1000 tanks were controlled primarily by nitrifying bacteria, which provided higher stability of these parameters and of dissolved oxygen. Regarding shrimp performance, the reduction of TSS to levels close to 200mgL−1 was associated with better nutritional quality of bioflocs. Nevertheless, differences in biofloc levels and nutritional quality were not sufficient to affect the weight gain by shrimp. The rate of shrimp survival and the final shrimp biomass were lower (P<0.05) when the TSS concentrations were higher than 800mgL−1. Analysis of the shrimps’ gills showed a higher degree of occlusion in the T800–1000 treatment (P<0.05), which suggests that the shrimp have an intolerance to environments with a solids concentration above 800mgL−1. Our results show that intermediate levels of bioflocs (TSS between 400 and 600mgL−1) appear to be more suitable to superintensive culture of L. vannamei since they create factors propitious for maintaining the system’s productivity and stability

Photochemical transformation of terrestrial dissolved organic matter supports hetero- and autotrophic production in coastal waters

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 423:1-14 (2011) - DOI: https://doi.org/10.3354/meps09010 FEATURE ARTICLE Photochemical transformation of terrestrial dissolved organic matter supports hetero- and autotrophic production in coastal waters Anssi V. Vähätalo1,2,*, Hanna Aarnos1,3, Laura Hoikkala1,4, Risto Lignell1,4 1Tvärminne Zoological Station, University of Helsinki, Hanko, Finland 2Present address: ARONIA Coastal Zone Research Team, Åbo Akademi University & Novia University of Applied Sciences, Ekenäs, Finland 3Present address: Department of Environmental Sciences, University of Helsinki, Helsinki, Finland 4Present address: Marine Center, Finnish Environmental Institute, Helsinki, Finland *Email: anssi.vahatalo@helsinki.fi ABSTRACT: We assessed the responses of a nitrogen (N)-limited <10 µm plankton community from the Baltic Sea to the 12 d photochemical transformation of dissolved organic matter (DOM). The photochemical transformation of DOM increased the biomass and the production of heterotrophic bacteria, flagellates, and ciliates in the following 10 d bioassay. The succession of heterotrophic plankton indicated a 3-level trophic transfer of photoproduced bioavailable DOM through bacteria and flagellates to ciliates. The photochemical transformation of DOM also stimulated the biomass and the production of phytoplankton through the photoproduction of bioavailable N initially incorporated into bacterial biomass. The grazing of bacterioplankton supplied N to phytoplankton directly, presumably due to mixotrophy, and indirectly by releasing dissolved N. The carbon stable isotope signature of plankton biomass was similar to that of allochthonous carbon, indicating that the photochemical transformations concerned primarily terrestrial DOM and therefore represented a microbial link between terrestrial DOM and planktonic production. The bacterial production stimulated by the photochemically produced labile DOM was related to the number of photons absorbed during the photochemical transformation of DOM for the determination of apparent quantum yield. According to the apparent quantum yield, the calculated summertime photoproduction of labile substrates contributes 2 to 5% to total bacterial production in the northern Baltic Sea. According to this study, the photochemical transformation of terrestrial DOM influences not only the initial production of bacterioplankton but can also stimulate higher trophic levels and autotrophic plankton in coastal waters. KEY WORDS: Dissolved organic nitrogen · Apparent quantum yield · Trophic transfer · Photochemistry · Bacterioplankton · Phytoplankton Full text in pdf format Information about this Feature Article NextCite this article as: Vähätalo AV, Aarnos H, Hoikkala L, Lignell R (2011) Photochemical transformation of terrestrial dissolved organic matter supports hetero- and autotrophic production in coastal waters. Mar Ecol Prog Ser 423:1-14. https://doi.org/10.3354/meps09010 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 423. Online publication date: February 10, 2011 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2011 Inter-Research.

Eutrophication in a tropical pond: Understanding the bacterioplankton and phytoplankton dynamics during a vibriosis outbreak using flow cytometric analyses

In tropical shrimp ponds, the increasing of feed input, concomitantly with the stocking shrimp biomass, induces an eutrophication of the ecosystem. Although difficult to maintain, its stability is required to guarantee the success of the culture. A 110-day period of phytoplankton and bacterioplankton stock and dynamics in an earthen pond (1.2 ha area, 1 m depth) was monitored using flow cytometry to provide baseline information on community characteristics and ecosystem instability. Seven autotrophic cell types were identified over the whole sampling period. Prokaryotic cells included Synechococcus sp., a group named UNK which presented an atypical new flow cytometric signature and picoeukaryotes (PEUK). Nanophytoplankton cells were represented by 4 groups: NAN1, NAN2, NAN3 and Cryptophytes. During the first part of the survey, picophytoplankton dominated the phytoplanktonic assemblage. The mean abundance of total cells (up to 8 × 10 6 cells mL −1) was among the highest recorded in marine and brackish waters. Bacterial abundance and production ranged from 0.8 to 5.1 × 10 7 cells mL −1 and from 30 to 110 μg C L −1 h −1. A shift from pico to nanophytoplankton abundance was observed for a few days from d 96. During this period, heterotrophic bacteria production and abundance suddenly dropped, implying a change in the functioning of the microbial loop. This shift was concomitant with a significant shrimp mortality outbreak due to Vibrio penaeicida, the etiological agent of a disease known as Syndrome 93, which affects the shrimp industry in New Caledonia. This survey suggests that flow cytometric analysis could be used for the monitoring of aquaculture systems to improve our understanding of the complex phytoplankton and bacterial dynamics of these systems and its potential influence on disease development.

Spatial variability in biomass and production of heterotrophic bacteria in the East China Sea and the Yellow Sea

The distributions of heterotrophic bacterial abundance and production were investigated in the East China Sea and the Yellow Sea during the autumn of 2000 and spring of 2001. Bacterial abundance varied in the range 3.2-15.7 (averaging 5.7) x 10(5) and 2.3-13.6 (averaging 6.2) x 10(5) cells cm(-3) in the spring and autumn, respectively. During autumn, bacterial production (BP) (0.27-7.77 mg C m(-3) day(-1)) was on average 3 fold that in spring (0.001-2.04 mg C m(-3) day(-1)). Bacterial average turnover rate (ratio of bacterial production:bacterial biomass, mu=0.21 day(-1)) in autumn was 3 times as high as in spring (0.07 day(-1)). The ratio of integrated bacterial biomass to integrated phytoplankton biomass in the euphotic zone ranged from 4 to 101% (averaging 35%) in spring and 24 to 556% (averaging 121%) in autumn. The results indicate that the distributions of heterotrophic bacteria were controlled generally by temperature in spring and additionally by substrate supply in autumn. (C) 2010 Elsevier Ltd. All rights reserved.

Empirical Leucine-to-Carbon Conversion Factors for Estimating Heterotrophic Bacterial Production: Seasonality and Predictability in a Temperate Coastal Ecosystem

Leucine-to-carbon conversion factors (CFs) are needed for converting substrate incorporation into biomass production of heterotrophic bacteria. During 2006 we performed 20 dilution experiments for determining the spatiotemporal variability of empirical CFs in temperate Atlantic coastal waters. Values (0.49 to 1.92 kg C mol Leu(-1)) showed maxima in autumn to early winter and minima in summer. Spatially averaged CFs were significantly negatively correlated with in situ leucine incorporation rates (r = -0.91) and positively correlated with phosphate concentrations (r = 0.76). These relationships, together with a strong positive covariation between cell-specific leucine incorporation rates and carbon contents (r = 0.85), were interpreted as a strategy to maximize survival through protein synthesis and low growth rates under nutrient limitation (low CFs) until favorable conditions stimulate cell division relative to protein synthesis (high CFs). A multiple regression with in situ leucine incorporation rates and cellular carbon contents explained 96% of CF variance in our ecosystem, suggesting their potential prediction from more easily measurable routine variables. The use of the theoretical CF of 1.55 kg C mol Leu(-1) would have resulted in a serious overestimation (73%) of annual bacterial production rates. Our results emphasize the need for considering the temporal scale in CFs for bacterial production studies.

Microbial plankton abundance and heterotrophic activity across the Central Atlantic Ocean

The role of microorganisms in the transfer of carbon of marine systems is very important in open oligotrophic oceans. Here, we analyze the picoplankton structure, the heterotrophic bacterioplankton activity, and the predator–prey relationships between heterotrophic bacteria and nanoflagellates during two large scale cruises in the Central Atlantic Ocean (∼29°N to ∼40°S). Latitud cruises were performed in 1995 between March–April and October–November. During both cruises we crossed the regions of different trophic statuses; where we measured different biological variables both at the surface and at the deep chlorophyll maximum (DCM). The concentration of chlorophyll a varied between 0.1 and 0.8 mg m −3, the abundance of heterotrophic bacteria varied between <1.0 × 10 5 and >1.0 × 10 6 cells ml −1, and that of heterotrophic nanoflagellates between <100 and >1.0 × 10 4 cells ml −1. The production of heterotrophic bacteria varied more than three orders of magnitude between <0.01 and 24 μgC L −1 d −1; and the growth rates were in the range <0.01–2.1 d −1. In the Latitud-II cruise, Prochlorococcus ranged between <10 3 and >3 × 10 5 cells ml −1, Synechococcus between <100 and >1.0 × 10 4 cells ml −1, and picoeukaryotes between <100 and >10 4 cells ml −1. Two empirical models were used to learn more about the relationship between heterotrophic bacteria and nanoflagellates. Most bacterial production was ingested when this production was low, the heterotrophic nanoflagellates could be controlled by preys during Latitud-I cruise at the DCM, and by predators in the surface and in the Latitud-II cruise. Our results were placed in context with others about the structure and function of auto- and heterotrophic picoplankton and heterotrophic nanoplankton in the Central Atlantic Ocean.

Heterotrophic bacterial production on solid fish waste: TAN and nitrate as nitrogen source under practical RAS conditions

The drumfilter effluent from a recirculation aquaculture system (RAS) can be used as substrate for heterotrophic bacteria production. This biomass can be re-used as aquatic feed. RAS effluents are rich in nitrate and low in total ammonia nitrogen (TAN). This might result in 20% lower bacteria yields, because nitrate conversion into bacteria is less energy efficient than TAN conversion. In this study the influence of TAN concentrations (1, 12, 98, 193, 257 mg TAN/l) and stable nitrate-N concentrations (174 ± 29 mg/l) on bacteria yields and nitrogen conversions was investigated in a RAS under practical conditions. The effluent slurry was supplemented with 1.7 g C/l sodium acetate, due to carbon deficiency, and was converted continuously in a suspended bacteria growth reactor (hydraulic retention time 6 h). TAN utilization did not result in significantly different observed yields than nitrate (0.24–0.32 g VSS/g C, p = 0.763). However, TAN was preferred compared to nitrate and was converted to nearly 100%, independently of TAN concentrations. TAN and nitrate conversions rates were differing significantly for increasing TAN levels ( p < 0.000 and p = 0.012), and were negatively correlated. It seems, therefore, equally possible to supply the nitrogenous substrate for bacteria conversion as nitrate and not as TAN. The bacteria reactor can, as a result, be integrated into an existing RAS as end of pipe treatment.

Molasses as C source for heterotrophic bacteria production on solid fish waste

The drumfilter effluent from a recirculation aquaculture system (RAS) can be used as substrate for heterotrophic bacteria production. These bacteria can be reused as aquatic feed. In RAS drumfilter effluents are organic carbon deficient for bacteria production. This is due to nitrogen accumulation in the system water. In the present experiment, a bacteria growth reactor (3.5l) was connected to the drumfilter (filter mesh size 60 μm) outlet of a recirculation system. To counteract carbon deficiency, different supplementation levels of molasses (organic carbon) were tested (carbon fluxes of 0.0, 3.2, 5.8, 7.8, 9.7 gC molasses/l/d; C:N ratios: 3.4, 6.4, 9.4, 13.0 and 16.5). The hydraulic retention time in the bacteria reactor was 6 h. For the maximum flux, the VSS and crude protein productions were about 168 gVSS and 95 g crude protein per kg feed. The maximum conversion of nitrate and ortho-phosphate was 24 g NO 3−N and 4 gP/kg feed. This equals a conversion of 90% of the inorganic nitrogenous waste and 98% of the ortho-phosphate–P. Furthermore the maximum substrate removal rate and the K s for molasses were determined (1.62 gC/l/h and 0.097 gC/l respectively). The maximum specific removal rate was 0.31 gC/gVSS/h and the related half saturation constant was 0.008 gC/l. The observed growth rate reached a maximum for C fluxes higher than 8 g/l/d. The present integration of heterotrophic bacteria production in RAS represents, therefore, an innovative option to reduce waste discharge by conversion. If the bacteria are reused as feed, system's ecological sustainability increases.

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.

Phytoplankton, bacterial production and protozoan bacterivory in stratified, brackish-water Lake Shira (Khakasia, Siberia)

Rates of oxygenic and anoxygenic photosynthesis, chemoautotrophic and heterotrophic bacterial production and protozoan bacterivory were measured in the pelagic zone of the stratified brackish-water lake with the purpose to determine the vertical distribution of these processes and to estimate their significance in the functioning of planktonic community of the lake. In midsummer, total daily primary productivity was about 1.3 g C m−2, of which 72% was produced by the phytoplankton, 24% by the chemoautotrophic bacteria, and only 4% by the phototrophic sulphur bacteria. Thus anoxygenic photosynthesis is a negligible source of organic matter in the lake. The production of heterotrophic bacteria averaged 1.5 g C m−2 d−1 and exceeded the total photosynthesis of phytoplankton and photosynthetic bacteria by a factor of 1.5. The estimated total primary production was too low to sustain the bacterial production. Probably the carbon cycle in the lake is dependent on the input of allochthonous organic matter. As a rule, the maximal rates of primary production and heterotrophic bacterial production were found in the chemocline or at the upper boundary of the chemocline. Heterotrophic flagellates dominated among the protozoan populations and were the major consumers of the bacterioplankton production in the lake. They showed maximal ingestion rates from 2.3 to 2.9 mg C m−3 h−1 at the upper boundary of the chemocline, where they consumed from 50 to 54% of the production of heterotrophic bacteria. Data obtained indicate that in Lake Shira the oxic-anoxic interface is the site of the most intensive production and mineralization of organic matter.

Heterotrophic bacterial turnover along the 20°W meridian between 59°N and 37°N in July 1996

Heterotrophic bacteria were enumerated by flow cytometry in samples from 200 m depth profiles along the 20°W meridian between 59°N and 37°N during June and July 1996. Bacterial volume estimates made by size fractionation were used in the determination of heterotrophic bacterial biomass. Concentrations of heterotrophic bacteria in the surface mixed layer were close to 10 6 ml −1 along most of the transect, but decreased to about 0.2×10 6 ml −1 at the southern end; this corresponded with a biomass range between about 2 and 15 mg C m −3. Concentrations also decreased to 0.1–0.3×10 6 ml −1 below the top mixed layer. Production of heterotrophic bacteria was measured in samples from eight profiles by following the simultaneous incorporation of isotopically labelled thymidine and leucine; in the mixed layer it ranged between a maximum of 1.5–2 mg C m −3 d −1 in the region of a frontal system near 50°N and 0.2–0.25 mg C m −3 d −1 at the southern end of the transect, with bacterial growth rates generally about 0.1 d −1. The daily production of heterotrophic bacteria integrated for the euphotic layer ranged between about 5 and 15% of the daily 14C primary production of phytoplankton. Heterotrophic nanoplankton biomass reflected the bacterial biomass and was about half as large; it showed a strong correlation with the production of heterotrophic bacteria. At the station with the highest bacterial biomass, the rate of grazing of bacteria by heterotrophic nanoplankton was 5–6% d −1, but at all other stations it was too low (<5% d −1) to be measured reliably by the techniques used. The data suggest that the nanoplankton grazed at least half of the bacterial production.