Picoplankton Community Structure Research Articles

Spatial variation of picoplankton communities along a cascade reservoir system in Patagonia, Argentina

In this study we explored how picoplankton community structure and diversity varied along three cascade oligo-mesotrophic reservoirs of the Limay River (Patagonia, Argentina): Alicura, Piedra del Águila and Ramos Mexía. We analyzed the spatial changes, covering lotic and lentic stretches along a gradient of 262 km from Andes to steppe, and we also sampled the main affluent of the Limay River (Collon Cura). In all sampling sites the main limnological variables were measured, and the picoplankton abundance (autotrophic and heterotrophic) was analyzed by flow cytometry. The bacterial biodiversity was assessed using high throughput sequencing Illumina MiSeq. We expected an increase in the trophic state along this series of cascade reservoirs, which would determine spatial differences in the structure of the picoplankton communities. We also hypothesized that the lotic and lentic conditions along the system would influence the bacterial composition. The results showed a slight increase in trophic state together with an increase in overall picoplankton abundance downstream, towards Ramos Mexía Reservoir. Picocyanobacteria were represented by phycoerythrin-rich cells all along the system, in accordance to the pattern described for oligotrophic aquatic ecosystems. Multivariate analyses based on bacterial OTU composition and environmental variables showed a spatial ordination of sites following the trend of increasing trophic state downstream. Molecular analyses of bacterial OTU diversity also showed an increase in richness and a decrease in evenness at the lotic stretches, and the opposite pattern in the reservoirs, suggesting that water retention time may play a role in structuring the community composition.

Occurrence of enhanced herbivory in the microbial food web of a tropical estuary during southwest monsoon

Tropical monsoonal estuaries have a significant role in global fishery as they act as rich feeding and breeding grounds for many commercial species. Food web dynamic studies in these coastal ecosystems are mainly focused on the classic food chain which assumes that microbial food webs contribute more towards the recycling of organic carbon and nutrients rather than production. But recently it is observed that phyto-microbial food web which is largely dependent on pico-autotrophs can contribute significantly towards the higher trophic level. Based on these observations we have analysed phyto-microbial pathway of food web in a highly productive tropical monsoonal estuary. We assessed the grazer-prey interaction in the microbial food web of Cochin estuary during spring intermonsoon and southwest monsoon seasons. Our results show that during spring intermonsoon the food web is dependent more on heterotrophic bacteria, but in southwest monsoon the dependency of grazers switches over to autotrophic picoplankton. We also analysed the growth rate, grazing rate and carbon contribution of autotrophic picoplankton experimentally during both seasons and found that autotrophic picoplankton show higher growth rate during southwest monsoon. The higher grazing rate and clearance rate of autotrophic picoplankton recorded during southwest monsoon indicate the efficient consumption of autotrophic picoplankton crop during the season. We could also observe a change in autotrophic picoplankton community structure between the seasons with the dominance of picocyanobacteria during spring intermonsoon and that of picoeukaryotes during southwest monsoon. Thus we infer that high freshwater influx into the estuary during monsoon results in high turbid and low saline (mesohaline to oligohaline) environment which increases the growth rate of low light adapted autotrophic picoplankton populations and in turn enhances herbivory (phyto-microbial pathway) in the microbial food web. Apart from protists, autotrophic picoplankton were found to be widely consumed by many larval forms of mesozooplankton, gastropods, bivalves, rotifers and large sized filter feeders either as aggregates or as unicellular forms. Thus monsoon enhanced herbivory can have a significant role in the growth and survival of larval forms recruited into the estuary during monsoon season and in turn the fishery.

Changes in Heterotrophic Picoplankton Community Structure after Induction of a Phytoplankton Bloom under Different Light Regimes

Bacterial and archaeal diversity and succession were studied during a mesocosm experiment that investigated whether changing light regimes could affect the onset of phytoplankton blooms. For this, 454-pyrosequencing of the bacterial V1-V3 and archaeal V3-V9 16S rRNA regions was performed in samples collected from four mesocosms receiving different light irradiances at the beginning and the end of the experiment and during phytoplankton growth. In total, 46 bacterial operational taxonomic units (OTUs) with ≥1% relative abundance occurred (22–34 OTUs per mesocosm). OTUs were affiliated mainly with Rhodobacteraceae, Flavobacteriaceae and Alteromonadaceae. The four mesocosms shared 11 abundant OTUs. Dominance increased at the beginning of phytoplankton growth in all treatments and decreased thereafter. Maximum dominance was found in the mesocosms with high irradiances. Overall, specific bacterial OTUs had different responses in terms of relative abundance under in situ and high light intensities, and an early phytoplankton bloom resulted in different bacterial community structures both at high (family) and low (OTU) taxonomic levels. Thus, bacterial community structure and succession are affected by light regime, both directly and indirectly, which may have implications for an ecosystem’s response to environmental changes.

Picoplankton distribution influenced by thermohaline circulation in the southern Adriatic

In this study, we focus on the interactive dynamics between physico-chemical processes and picoplankton distribution in order to advance our current understanding of the roles of various parameters in regulating picoplankton community structure in highly dynamic marine system such as the South Adriatic Sea. The research was carried out between October 2011 and September 2012 along the transect in the northern part of the South Adriatic Pit. The deep water convection occurred in the southern Adriatic during February 2012, with vertical mixing reaching the depth of 500 m. The picoplankton community was highly affected by this mixing event, whilst its compartments each responded differently. During deep water convection low nucleic acid heterotrophic bacteria (LNA HB) and Synechococcus had their lowest abundances (4 × 105 cell ml−1 and 8 × 102 cell ml−1, respectively), picoeucaryotes had their highest abundances (104 cell ml−1), while Prochlorococcus was absent from the area, most likely due to intense cooling and vertical mixing. In March 2012 Eastern Adriatic Current (EAC) brought warm and saline water with more nutrients, which resulted in the proliferation of high nucleic acid heterotrophic bacteria (HNA HB), having maximal abundance (4 × 105 cell ml−1). The re-establishment of Levantine Intermediate Water (LIW) intrusion after the deep water convection resulted in the re-appearance of Prochlorococcus and maximal abundances of Synechococcus (4 × 104 cell ml−1) in May 2012. The distribution of picoheterotrophs was mainly explained by the season, while the distribution of picophytoplankton was explained by the depth. Aside from nutrients, salinity was an important parameter, affecting particularly Prochlorococcus. The re-appearance of Prochlorococcus in the southern Adriatic during the period of LIW intrusion, together with their correlation with salinity, indicates their potential association with LIW. The relationship between Prochloroccocus distribution and physico-chemical environmental parameters provides an important insight into the ecological roles and niche preferences of this group.

Nutrient supply controls picoplankton community structure during three contrasting seasons in the northwestern Mediterranean Sea

We investigated the influence of ocean mix- ing and nutrient supply dynamics on picoplankton com- munity composition in the context of Margalef's Mandala (Margalef 1978). Simultaneous measurements of micro- turbulence, nutrient concentration, and autotrophic and heterotrophic picoplankton properties, were collected during 3 cruises carried out in the northwestern Medi- terranean Sea in March (F1), April/May (F2) and Sep- tember (F3) 2009. The 3 cruises sampled different oceanographic conditions, starting with early stages of the late winter-early spring bloom, followed by the late stage of the bloom, and finally summer stratification. As a result of the variability in vertical diffusivity and the ni- trate gradient across the nitracline, nitrate vertical fluxes were higher during F1 (23 ± 35 mmol m �2 d �1 ), compared to F2 (0.4 ± 0.2 mmol m �2 d �1 ) and F3 (0.09 ± 0.09 mmol m �2 d �1 ). Prochlorococcus abundance was low when ni- trate supply was high, Synechococcus exhibited the highest abundances at intermediate levels of nitrate sup- ply and highest irradiance during F2, and large and small picoeukaryotic groups increased their abundance under high nutrient supply in F1. No significant relation- ships between the abundance of high and low nucleic acid heterotrophic bacteria and nitrate supply were found. In agreement with Margalef's model, our results show different responses of picophytoplankton groups to nitrate supply (probably reflecting differences in nu- trient uptake abilities), and that the ratio of prokaryotic to picoeukaryotic photoautotrophic biomass decreases with increasing nitrate supply.

Picoplankton community structure before, during and after convection event in the offshore waters of the Southern Adriatic Sea

Abstract. This paper documents the picoplankton community's response to changes in oceanographic conditions in the period between October 2011 and September 2012 at two stations belonging to the South Adriatic Pit (SAP). The recorded data include the community's abundance, composition, prokaryotic production rates and bacterial metabolic capacity. The sampling period included an intense sea cooling with formation of exceptional, record-breaking dense water. We documented an especially intense winter convection episode that completely diluted the core of Levantine intermediate waters (LIW) in a large area encompassing the SAP's center and its margin. During this convection event the whole picoplankton community had significantly higher abundances with a recorded picoeukaryotic peak at the SAP margin. In the post-convection phase in March, prokaryotic heterotrophic production strongly increased in the entire SAP area (up to 50 times; 456.8 nM C day−1). An autotrophic biomass increase (up to 5 times; 4.86 μg L−1) and a disruption of a close correspondence between prokaryotic heterotrophic biomass production and cell replication rates were observed only in the center of the SAP, which was not under the influence of LIW. At the SAP's margin such an effect was attenuated by LIW, since the waters affected by LIW were characterized by decreased concentrations of dissolved inorganic nitrogen, decreased autotrophic biomasses, and by increased bacterial biomass production balanced with cell replication rates as well as by the domination of Synechococcus among autotrophic picoplankton. The metabolic capacity was lowest in spring when autotrophic biomass largely increased, while the highest levels found in the pre-convection phase (October 2011) suggest that the system was more oligotrophic before than after the convection event. Furthermore, we showed that metabolic capacity is a trait of bacterial community independent of environmental conditions and tightly linked to cell replication and substrate availability. In contrast, the bacterial community composition appears to be strongly influenced by physico-chemical characteristics of waters (e.g., temperature and nutrients) and environmental forcing (e.g., convection and LIW). Our results showed that the two oceanographic phenomena of the Southern Adriatic, strongly relevant for the total production of the Adriatic Sea, winter convection and LIW intrusion, regulate the changes in picoplankton community structure and activities.

Short-time scale coupling of picoplankton community structure and single-cell heterotrophic activity in winter in coastal NW Mediterranean Sea waters

We used flow cytometry to follow the diel variations of picoplankton community structure (PCS) and heterotrophic activity in coastal North Western Mediterranean surface waters during two successive 72 h cycles in winter 2007. Photosynthetic picoeukaryotes (pPeuk) dominated the photosynthetic fraction of the PCS during the first cycle, while Synechococcus (Syn) dominated during the second. For each group, pronounced and significant diel patterns were observed in flow cytometrically determined proxies of cell size (side scatter) and pigment content (fluorescence). Syn and pPeuk grew during the light period and divided at night; opposite patterns were observed in Prochlorococcus. The diel patterns of the overall PCS were strongly disrupted before the second cycle by a wind change event with associated rainfall and increased turbulence, suggesting that the shift observed in PCS resulted from the imbalances between growth and loss processes. During the first cycle, heterotrophic activity was higher at night than during the light period, indicating that bacterial growth was phased with the diel variations of PCS. During the second cycle, no diel patterns were observed. However, similar increasing trends in bacterial activity and small grazer abundance suggested that grazing activity was a possible source of dissolved organic matter (DOM) release that likely drove bacterial activity.

Flow cytometry investigation of picoplankton across latitudes and along the circum Antarctic Ocean

Using a flow cytometer (FCM) onboard the R/V Xuelong during the 24th Chinese Antarctic cruise, picoplankton community structure and biomass in the surface water were examined along the latitude and around the Antarctic Ocean. Salinity and temperature were automatically recorded and total Chl a was determined. Along the cruise, the abundance of Synechococcus, Prochlorococcus, pico-eukaryotes and heterotrophic bacteria ranged in 0.001–1.855×108 ind./L, 0.000–2.778×108 ind./L, 0.002–1.060×108 ind./L and 0.132–27.073×108 ind./L, respectively. Major oceanic distribution of Synechococcus and Prochlorococcus appeared between latitudes 30°N and 30°S. Prochlorococcus was mainly influenced by water temperature, water mass combination and freshwater inflow. Meanwhile, Synechococcus distribution was significantly associated with landing freshwater inflow. Pico-eukaryotes and heterotrophic bacteria were distributed all over the oceans, but with a relatively low abundance in the high latitudes of the Antarctic Ocean. Principal Component Analysis showed that at same latitude of Atlantic Ocean and Indian Ocean, picoplankton distribution and constitution were totally different, geographical location and different water masses combination would be main reasons.

Role of environment and hydrography in determining the picoplankton community structure of Sagami Bay, Japan

Seasonal variations in the picoplankton community were investigated from June 2002 to March 2004 within the photic zone of Sagami Bay, Japan. The study area was mostly dominated by coastal waters during the warm period (mixed layer water temperature ≥ 18°C). During the cold period (mixed layer water temperature ≤ 18°C), the water mass was characterized by low temperature and high saline waters indicative of the North Pacific Subtropical Mode Water (NPSTMW). Occasionally, a third type of water mass characterized by high temperature and low saline properties was observed, which could be evidence of the intrusion of warm Kuroshio waters. Synechococcus was the dominant picophytoplankton (5−28 × 1011 cells m−2) followed by Prochlorococcus (1−5 × 1011 cells m−2) and picoeukaryotes during the warm period. Heterotrophic bacteria dominated the picoplankton community throughout the year, especially in the warm period. During the Kuroshio Current advection, cyanobacterial abundance was high whereas that of picoeukaryotes and heterotrophic bacteria was low. During the cold period, homogeneously distributed, lower picophytoplankton cell densities were observed. The dominance of Synechococcus in the warm period reflects the importance of high temperature, low salinity and high Photosynthetically Active Radiation (PAR) on its distribution. Cyanobacterial and heterotrophic bacterial abundance showed a positive correlation with temperature. Prochlorococcus and picoeukaryotes showed a positive correlation with nutrients. Picoeukaryotes were the major contributors to the picophytoplankton carbon biomass. The annual picophytoplankton contribution to the photosynthetic biomass was 32 ± 4%. These observations suggest that the environmental conditions, combined with the seasonal variability in the source of the water mass, determines the community structure of picoplankton, which contributes substantially to the phytoplankton biomass and can play a very important role in the food web dynamics of Sagami Bay.

Picoplankton community structure at a coastal front region in the northern part of the South China Sea

Abundances of picoplankton groups were determined by flow cytometry in the Northern South China Sea (SCS) in winter 2004 to study the dynamics of picoplankton at a coastal front region. Prochlorococcus is more abundant in relatively high temperature and salinity waters than in nearshore area. Heterotrophic bacteria dominate in total picoplanktonic biomass but keep rather stable in biomass and surface/bottom biomass ratio on both sides of the front. Increases of picophytoplanktonic biomass and their surface/bottom biomass ratio are remarkable mainly owing to the contribution of Synechococcus on the offshore open SCS waters. Temperature is found to limit the growth of Synechococcus and Prochlorococcus. Picoeukaryotes and heterotrophic bacteria are less sensitive to the change in hydrographic conditions across the front. The autotrophic/heterotrophic biomass ratio of picoplankton is lower in eutrophic coastal waters on the nearshore side relative to the offshore and oligotrophic open SCS.

Seasonal dynamics of picoplankton in shelf waters of the southern Bay of Biscay

Seasonal variations in autotrophic and heterotrophic picoplankton community structure were studied by flow cytometry at 3 shelf stations in the central Cantabrian Sea (southern Bay of Biscay), from April 2002 to April 2003. A marked seasonality was found for autotrophs, with cyanobacteria (Synechococcus and Prochlorococcus) being more important in nutrient-depleted waters (June to October, 75 ± 3% of picophytoplanktonic cells) whereas picoeukaryotes clearly dom- inated in terms of biomass during the rest of the year (82 ± 2%). The absence of Prochlorococcus in spring and summer seems to be related to hydrology rather than to nutrient conditions. Under strati- fication the maximum abundance of cyanobacteria was found above the nutricline, in contrast to picoeukaryotes. Autotrophic groups cell size was strongly influenced by nutrient conditions while chlorophyll a fluorescence varied in parallel to irradiance. Heterotrophic bacteria were less variable than picophytoplankton and high nucleic acid content (HNA) cells dominated the community in win- ter and spring (64 ± 1%) but only at depth during the rest of the year. A similar response of low nucleic acid content (LNA) bacteria to environmental conditions suggests they are, at least partially, metabolically active, in contrast to the commonly held view that they are a homogeneous group of dead or dormant cells. A larger mean size of LNA compared with HNA bacteria was consistently observed in winter and spring. Regardless of variations in abundance and group composition, the great constancy of the picoplanktonic contribution to integrated algal biomass (17 ± 2%) over the seasonal cycle outlines the importance of picophytoplankton also in coastal zones.

On-board flow cytometric observation of picoplankton community structure in the East China Sea during the fall of different years

On-board flow cytometric determinations of picoplankton abundance (i.e. Synechococcus spp., Prochlorococcus spp., picoeukaryotes and also heterotrophic bacteria) were obtained in the East China Sea in fall of 2000 and 2003. The average abundances of Synechococcus, Prochlorococcus, picoeukaryotes and heterotrophic bacteria were 10 5, 10 5, 10 4 and 10 6 cells ml −1, respectively. Synechococcus, picoeukaryotes and heterotrophic bacteria were abundant at all the stations and presented higher concentration in the inner shelf where influences from the Changjiang effluent plumes and the coastal upwelling were evident, while Prochlorococcus was absent from the near-shore stations and became the dominant picophytoplankton population in offshore waters, where its abundance was comparable to that for heterotrophic bacteria. All picoplankton groups showed a reduction in cell number with depth, and a positive correlation with water temperature were observed, which reflected the importance of light and temperature on picoplankton growth. A negative relationship with salinity was found for heterotrophic bacteria along two sections across the East China Sea Shelf, and distribution of picoplankton was dominated by different water masses. The fixation could lead to loss in Prochlorococcus cell numbers within one month, and all the picoplankton numbers decreased dramatically after three months.

Picoplankton community structure along the northern Iberian continental margin in late winter-early spring

The surface distribution of autotrophic and heterotrophic picoplankton was assessed in 24 transects perpendicular to the coast along the N and NW Iberian peninsula shelf in late winter and early spring 2002. Community structure was analyzed by flow cytometry (FC) and found to be strongly influenced by hydrography. Typical late winter conditions were found during the survey, characterized by the presence of the poleward Portugal coastal counter current (PCCC) in the west and an increasing stratification eastwards. Cyanobacteria (mostly Synechococcus) dominated at low chlorophyll a (Chl a) concentration whereas both the total and relative abundance of picoeukaryotes generally increased with total phytoplankton biomass. Differences in the cell size of most FC-defined picoplanktonic groups were also observed along the longitudinal and coastal‐offshore gradients. The presence of Prochlorococcus (<10 3 cells mL � 1 ) coincided with the core of the PCCC and its significant correlation with salinity suggests its possible use as a tracer of this current. Two groups of heterotrophic bacteria were distinguished according to their relative DNA content. High DNA bacteria dominated the community (60¯� 1% SE of total numbers), reaching maximum values in areas under riverine influence with presumed higher inputs of organic matter. Picoplankton biomass was dominated by heterotrophic bacteria in the western region (58¯� 3%) while autotrophic groups contributed on average 66¯� 2% in the southern Bay of Biscay. The heterotrophic bacteria to phytoplankton biomass ratio decreased significantly along the measured range. Yet showing regional differences, the estimated contribution of picophytoplankton to total algal biomass was high (mean 59¯� 4%), indicating the important role of small cells at the onset of the spring bloom in these temperate shelf waters.

Picoplankton community structure in the subarctic Pacific Ocean and the Bering Sea during summer 1999

We studied picoplankton community structures in the subarctic Pacific Ocean and the Bering Sea during summer 1999 using flow cytometric analysis. The picoplankton community in the studied area was comprised of Synechococcus spp., eukaryotic ultraplankton and heterotrophic bac- teria. Prochlorococcus spp. were not detected at any station. Abundances of Synechococcus and eukaryotic ultraplankton were at approximately the same level of 10 3 to 10 4 cells ml -1 within the upper euphotic layer in the subarctic gyres. An abundance of Synechococcus spp. higher than 5 · 10 4 cells ml -1 was found at the surface to 40 m depth in the northern Gulf of Alaska, whereas low Synechococcus spp. abundance (about 500 cells ml -1 ) was found in the upper euphotic layer in the Bering Sea. Abundances of heterotrophic bacteria were about 2 orders of magnitude higher than those of Synechococcus spp. and eukaryotic ultraplankton, with higher abundance generally occur- ring in the area of high autotrophic biomass. Although Synechococcus spp. and eukaryotic ultra- plankton occurred at comparable abundance, the latter contributed significantly more to photosyn- thetic carbon biomass, except in the northern Gulf of Alaska, where the biomass of Synechococcus spp. and eukaryotic ultraplankton were approximately equal. Cellular red fluorescence for Synecho- coccus spp. and eukaryotic ultraplankton increased by an average 4- and 2-fold, respectively, from the surface to the bottom of the euphotic layer, with the smallest increase occurring in the Bering Sea. Both the red fluorescence and forward light scatter (FSC, related mainly to cell size) per cell varied more than 2-fold spatially, with the highest value occurring in the Bering Sea. These variations were probably caused by differences in physiological conditions and species compositions. Overall, pico- phytoplankton was the dominant contributor to total autotrophic biomass in the subarctic North Pacific, but contributed only a small fraction to total autotrophic biomass in the Bering Sea. The West- ern Gyre (WG) and the Alaskan Gyre (AG) possess both similarities and differences in biogeochem- ical processes and microbial food-web dynamics. The slightly higher phytoplankton biomass, photo- synthetic efficiencies and growth rates in WG than AG suggests less severe iron limitation in the WG.

Seasonal variability of picophytoplankton and bacteria in the western subarctic Pacific Ocean at station KNOT

Picoplankton community structure in the upper 200 m at Station KNOT in the western subarctic North Pacific was studied by flow cytometric analysis of the time-series samples collected from June 1998 through June 2000. Phototrophic picoplankton, Synechococcus and picoeukaryotes, displayed a clear seasonal cycle in population abundance during the 2-yr period, where chlorophyll a concentration remained relatively low and constant throughout the year, except in spring when the diatom bloom occurred. High picoplankton abundance occurred after the spring diatom bloom when the water column became more stratified. The maximum abundance of Synechococcus occurred in late June to early August, whereas the peak in picoeukaryotes abundance appeared to take place earlier in May and remained high through the summer. Heterotrophic bacteria abundance also displayed a seasonal variation pattern that was closely related to the picoplankton biomass, but not total chlorophyll biomass.

Effects of filtration on bacterial activity and picoplankton community structure as assessed by flow cytometry

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 16:251-264 (1999) - doi:10.3354/ame016251 Effects of filtration on bacterial activity and picoplankton community structure as assessed by flow cytometry Josep M. Gasol*, Xosé A. G. Morán Departament de Biologia Marina i Oceanografia, Institut de Ciències del Mar, CSIC, Passeig Joan de Borbó, s/n, E-08039 Barcelona, Spain *E-mail: pepgasol@icm.csic.es ABSTRACT: We used flow cytometry of autofluorescent and Syto13-stained marine bacteria and the uptake of tritiated leucine to assess the effects of different filter types on picoplankton abundance, community structure and bacterial activity in the filtrate. Coastal and oceanic samples from the NW and SW Mediterranean and the Atlantic coast of Galicia were size-fractionated using polycarbonate (PC), mixed cellulose esters (CE), aluminum oxide (IM) and glass fiber (GF) filters of 0.2 to 1.2 μm nominal pore size from different brands. Flow cytometry of Syto13-stained marine bacteria and autofluorescent photosynthetic prokaryotes was used to analyze picoplankton abundance, size structure and community composition before and after filtration. We combined this capability with the detection of the changes in cell-specific heterotrophic activity in the filtrates. We found that the CE filters retained picoplankton better than the PC filters. The PC filters did not discriminate prokaryotes according to size as much as the GF and the CE filters did. In our hands the IM filters were no better than the CE filters. Bacterial activity in the filtrates increased in the PC and in the CE filtrates and this stimulation of bacterial activity was more important in the less productive environments. We conclude that care must be taken when PC filters are used for generating bacteria-free water, and that the use of CE 0.22 μm filters is the best way of creating picoplankton-free water. However, the picoplankters that will go through the filters may encounter increased nutrient levels. KEY WORDS: Filters · Filtration · Bacteria · Picoalgae · Flow cytometry · Bacterial activity Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 16, No. 3. Publication date: February 24, 1999 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 1999 Inter-Research.

Kinetic bias in estimates of coastal picoplankton community structure obtained by measurements of small-subunit rRNA gene PCR amplicon length heterogeneity

Marine bacterioplankton diversity was examined by quantifying natural length variation in the 5' domain of small-subunit (SSU) rRNA genes (rDNA) amplified by PCR from a DNA sample from the Oregon coast. This new technique, length heterogeneity analysis by PCR (LH-PCR), determines the relative proportions of amplicons originating from different organisms by measuring the fluorescence emission of a labeled primer used in the amplification reaction. Relationships between the sizes of amplicons and gene phylogeny were predicted by an analysis of 366 SSU rDNA sequences from cultivated marine bacteria and from bacterial genes cloned directly from environmental samples. LH-PCR was used to compare the distribution of bacterioplankton SSU rDNAs from a coastal water sample with that of an SSU rDNA clone library prepared from the same sample and also to examine the distribution of genes in the PCR products from which the clone library was prepared. The analysis revealed that the relative frequencies of genes amplified from natural communities are highly reproducible for replicate sets of PCRs but that a bias possibly caused by the reannealing kinetics of product molecules can skew gene frequencies when PCR product concentrations exceed threshold values.

Phototrophic picoplankton community structure in three different pelagic regimes in the Arabian Sea

Cell numbers and vertical distribution of Synechococcus, eucaryotic phototrophic picoplankton and prochlorophytes as determined by epifluorescence microscopy are presented from 3 different epipelagic systems (the mesotrophic coast off Oman, the oligotrophic central Arabian Sea and the shelf edge off Pakistan) in the Arabian Sea during the inter-monsoon period 1987. The vertical distribution patterns are described in relation to the epipelagic structure of the respective study sites. Synechococcus dominated phytoplankton in the upper mixed layer and prochlorophytes at the bottom of the euphotic zone in the lower part of and below the deep chlorophyll maximum High pressure liquid chromatography analysis confirmed the presence of prochlorophytes and revealed vertical profiles of characteristic pigments of picoplankton orgamsms, chlorophyll (chl) a and b, dmnyl chl a (chl a;) and zeaxanthin. Cellular pigment concentrations of Synechococcus and prochlorophytes are presented.

Photosynthetic picoplankton community structure in the subtropical North Pacific Ocean near Hawaii (station ALOHA)

The structure of the picoplankton community in the subtropical Pacific was examined on four depth profiles, one from each season, sampled at the Hawaii Ocean Time-series station ALOHA (22°45′N, 158°W). Three cell populations were discriminated by flow cytometry: Prochlorococcus prochlorophytes, Synechococcus cyanobacteria, and picoeukaryotes. Prochlorococcus were the most abundant component (maximum ca 2 × 10 5 cells ml −1). Unlike previous reports, their concentration was almost constant down to roughly 100 m, with a slight maximum at the surface or near the chlorophyll maximum. Cellular chlorophyll fluorescence increased 50-fold between surface and deep populations. One distinguishing feature of the community off Hawaii was the co-occurrence near the chlorophyll maximum of at least two distinct Prochlorococcus populations with different chlorophyll and DNA contents. Throughout the year, Synechococcus abundance was two orders of magnitude lower and there was no seasonal alteration between Prochlorococcus and Synechococcus, as observed in the northern Sargasso Sea. Synechococcus populations did not extend below 120 m and were dominated by high phycourobilin cell types. Picoeukaryote abundance was quite similar to that of Synechococcus, but these cells extended deeper in the water column. Their chlorophyll fluorescence exhibited much less depth variation than Prochlorococcus or Synechococcus. Seasonal variability was small (<2- to 3-fold) for all three components of the picoplankton, not only for cell abundance but also for cellular parameters such as light scatter or pigment fluorescence. Synechococcus populations exhibited the largest seasonal changes (e.g. abundance maximum and chlorophyll fluorescence varied 3-fold). Picoplankton community structure in the Pacific Ocean appears to be distinct from previous reports for other areas. In comparing station ALOHA to the Atlantic Ocean (especially the Sargasso Sea) and the Mediterranean Sea, depth-integrated abundances of Prochlorococcus were higher, that of Synechococcus were lower, and that of picoeukaryotes were similar. We believe this structure, dominated by Prochlorococcus, may be typical for subtropical open-ocean regions.