Poll: LMFAO!!!!
- Thread starter Killa_ken
- Start date
correct, I am no homo.
Both theoretical and empirical evidence indicate that the growth of marine bacterioplankton is mostly unaffected by turbulence (27, 40, 46). This is mainly due to the small size of bacteria, which precludes significant gains in bacterial nutrient uptake even with relatively high turbulence. Our control experiment without phytoplankton confirmed that the structures of the bacterial assemblages growing under turbulent or still conditions were generally similar. Nevertheless, some differences in bacterial abundance were observed, similar to those found in a recent freshwater study (2). Many phytoplankton groups, however, are sufficiently large to be directly affected by turbulence, and the mixing regimen plays an important role in structuring phytoplankton communities (1, 3, 13, 23). In accordance with previous studies (1, 13), we found that diatoms and phytoflagellates increased their share of the total phytoplankton biomass under turbulent and still conditions, respectively. Although the direct effect of turbulence on bacteria is limited, significant effects of turbulence on gross bacterial production and abundance are observed in the presence of phytoplankton (38, 40, 46). Here we show that changes in the phytoplankton composition between microcosms maintained under turbulent or still conditions were paralleled by shifts in the composition of the bacterial community. The differences in bacterioplankton were apparent from both the appearance and disappearance of unique phylotypes and changes in the relative abundance (i.e., band intensity) of ubiquitous phylotypes. This implies that changes in phytoplankton community composition and other subsequent associated changes in the microbial food web caused the differences in the bacterioplankton species composition. Our results support previous speculations that the composition of algal assemblages is an important factor in determining the development of different bacterial populations in waters with contrasting phytoplankton (28, 51).
Algal classes differ substantially in their biochemical composition, in terms of C/N/P ratios and in terms of relative proportions of cellular protein, fatty acids, and nucleic acids (53, 70). Differences in the biochemical composition of dominant phytoplankton could cause differences in the stoichiometry of particulate and dissolved organic matter and in the availability of mineral nutrients in seawater, all of which could profoundly affect the growth of bacteria (37). Studies of algal cultures, including diatoms and dinoflagellates, have suggested the existence of specific associations between phytoplankton and bacterioplankton species, possibly due to the differential release of organic matter from the algae (25, 60). To this end, van Hannen et al. showed that enrichment of lake water continuous cultures with detritus from either a green alga or cyanobacterium resulted in the growth of different bacterial assemblages (71). These findings are in agreement with general conclusions concerning the importance of the quality of the organic matter for bacterial community composition and activity (10, 11, 32, 48, 49). This suggests the possibility of finding common patterns in the distribution of particular bacterial groups or species during blooms dominated by different phytoplankton.
Quantitative and qualitative differences in planktonic grazer populations have important consequences both for the pattern of nutrient regeneration and the release of dissolved organic matter. Furthermore, higher nutrient recycling rates resulting from increased grazing rates on phytoplankton under turbulent conditions have been suggested to affect bacterial growth, possibly in combination with decreased grazing rates on bacteria (46, 47). We observed greater microzooplankton biomass in the microcosms dominated by diatoms (turbulent microcosms) than in the microcosms with a higher proportion of phytoflagellates (still microcosms). Moreover, ciliates accounted for a majority of the microzooplankton in the diatom blooms, while heterotrophic dinoflagellates were the dominant grazers in blooms with higher proportion of phytoflagellates. Thus, variation in substrate supply to bacteria due to differences in phytoplankton community composition could have been further amplified by different grazer assemblages.
A majority of the bacterial phylotypes identified in our study belonged to the Roseobacter group (Alphaproteobacteria) or the Bacteroidetes phylum. Phylotypes belonging to these groups had different patterns in our microcosms. Whereas most of the Roseobacter phylotypes were ubiquitous, pronounced differences were observed in the occurrence of Bacteroidetes phylotypes between the microcosms dominated by diatoms and those with a higher proportion of phytoflagellates. This could indicate that these bacterial groups responded to different stimuli in our experiments. Possibly, Roseobacter phylotypes represented a response to the nutrient additions, while the Bacteroidetes phylotypes were responding more to the turbulence-induced differences in the phytoplankton.
Bacteria in the Roseobacter group are widespread and abundant in the oceans and coastal areas of the world (20, 64). Members of the Roseobacter group have 16S rRNA gene sequence similarities of ≥90% (21), and novel genera in this group are continuously being described. Many characteristics have been ascribed to the marine members of the Alphaproteobacteria. For example, they are important in mediating transformations of dimethylated sulfur compounds (41), and members of the Roseobacter group have been suggested to be active colonizers of particles under algal bloom conditions (55). Pinhassi and Berman (49) found that several Roseobacter species became dominant in cultures of unamended seawater collected from the oligotrophic eastern Mediterranean Sea and the Red Sea, suggesting that these bacteria are good competitors under low-nutrient conditions. Most of the Roseobacter phylotypes detected in the present study were found throughout our microcosms and were affiliated with different representatives of the group, such as Roseobacter gallaeciensis, Sulfitobacter pontiacus, and the Atlantic Ocean clone library sequence NAC11-3. The persistence and growth of a substantial subset of Roseobacter phylotypes in our microcosms may at first suggest that these are generalist bacteria. However, in a detailed study of a Roseobacter clade-affiliated cluster, which includes the clone NAC11-3, Selje et al. (64) described significant differences in the geographic distribution of phylotypes that differed by only a few base pairs in the 16S rRNA gene. Future comprehensive phylogenetic analyses and genome comparisons of members of the Roseobacter group will clarify whether the large variety of characteristics ascribed to these bacteria can be explained by a high degree of phenotypic differentiation by phylogenetically relatively closely related bacteria.
The Bacteroidetes phylum is highly diverse; at this time, it consists of 12 families and 79 described genera. Several of these taxa contain representatives from marine environments, documented by culture-independent techniques or by cultured isolates. Bacteria belonging to the Bacteroidetes are abundant in seawater (12, 19, 30), and previous studies have emphasized their importance under algal bloom conditions (48, 55). However, it remains unclear whether particular taxa within the Bacteroidetes are more commonly found than others in the marine environment (31, 44) and whether certain growth conditions selectively favor certain taxa in this phylum. Two phylotypes (MED-S4 and -S5) belonging to the family Cryomorphaceae were unique to the microcosms with a higher proportion of phytoflagellates, although they formed relatively faint bands on the DGGEs. The most intense bands in the upper region of the DGGE were identified as phylotypes belonging to the family Flavobacteriaceae. Two Flavobacteriaceae phylotypes (MED-S1 and -S2) were dominant in the microcosms with a higher proportion of phytoflagellates. Two other members of this family were dominant in the microcosms dominated by diatoms. These phylotypes, MED-T6 and -T7, were identical to the BY-65 and BY-66 phylotypes, respectively (Fig. 6), which were originally detected in 1996 during a diatom bloom experiment performed 200 km northeast of the site of the present experiment (61). This surprisingly consistent response to diatom bloom conditions of a few Flavobacteriaceae phylotypes in the Mediterranean Sea could indicate that some bacteria in this family harbor physiological or ecological traits that make them tightly coupled to diatom species.
Bacteria responding to experimental treatments in a single location may be particular to that location rather than representing general trends in the growth potential of different bacteria. Therefore, we extended our phylogenetic analysis to include 16S rRNA gene sequences of Bacteroidetes phylotypes and isolates from all published studies of marine bacterioplankton diversity associated with natural or experimental algal blooms (Table 3 and Fig. 6). Our analyses showed that even though the Bacteroidetes phylum can be divided into at least 12 families, as much as 80% of the Bacteroidetes phylotypes in these studies (among a total of 63 sequences) belonged to one single family, the Flavobacteriaceae. In particular, phylotypes affiliated with the Tenacibaculum and Cellulophaga or Zobellia genera were frequently found. Other recurrently detected genera in this family included Chryseobacterium, Polaribacter, Gelidibacter, and Psychroserpens. Therefore, we suggest that members of the family Flavobacteriaceae represent bacterial populations that play particularly important roles during and after algal bloom events.
TABLE 3. TABLE 3.
Number of 16S rRNA gene sequences affiliated with the family Flavobacteriaceae compared to other families in the phylum Bacteroidetesa
At this time, efforts are being made to revise the taxonomy of the Bacteroidetes phylum using phylogenetic analysis of the 16S rRNA gene. This has contributed to the recent redefinition of the family Flavobacteriaceae (4). As a consequence of this revision, bacteria previously named Cytophaga and found throughout the phylum have been renamed, and the type species of the genus Cytophaga is actually well separated from the Flavobacteriaceae. Bacteria in the Flavobacteriaceae have menaquinone 6 (MK-6) as a major respiratory quinone, and this family has therefore been called the marine MK-6 group (67). Suzuki et al. (67) observed that the members of Flavobacteriaceae in their study were unable to use nitrate or ammonium as nitrogen sources, indicating that they required an organic nitrogen source for growth. If confirmed, this observation would substantiate previous findings that bacteria in this group show a high growth capacity when dissolved proteins are abundant (9, 48), which may contribute to explaining why bacteria in the family Flavobacteriaceae are recurrently found during the decay of algal blooms.
We have interpreted the changes in bacterioplankton species composition primarily as a consequence of the differences in dominant phytoplankton groups, which in turn were dependent on the mixing regimen. It is also possible that the total phytoplankton biomass played a role, since nearly three- to sevenfold-higher peaks in Chl a were recorded under turbulent conditions compared to still conditions. Even though the higher bacterial abundance in the final samples in the microcosms with pronounced diatom blooms could have resulted from the higher phytoplankton biomass achieved under turbulence, cell-specific bacterial growth rates and enzymatic activities reached relatively similar levels in all microcosms. Differences in the structure of the bacterial assemblage were also evident in our second bloom experiment, where peak Chl a concentrations were only 50% higher under turbulent conditions compared to still conditions. We note that studies of horizontal variability in bacterial community structure repeatedly find relatively similar bacterial assemblages over substantial distances despite apparent differences in Chl a concentrations (54, 56). At the same time, considerable variability in bacterial diversity is commonly found with depth, which may depend largely on the stratification of phytoplankton populations (see reference 51 and references therein).
For most of the year, the growth of bacteria in northwestern Mediterranean waters is primarily limited by the availability of P (59, 69). The first peak in bacterial production and abundance observed in phytoplankton bloom experiment 1 may therefore be interpreted as a direct effect of the addition of nutrients. The subsequent increase in bacterial production and abundance from day 5 on coincided with the peak and subsequent senescence of the algal blooms. Concomitantly, alpha- and beta-glucosidase and aminopeptidase activities indicated an increase of nearly an order of magnitude or more in the rate of bacterial utilization of carbohydrates and protein. The increase in phosphatase activity could result from the depletion of inorganic phosphate (data not shown) coupled with increased availability of organically bound P. Monitoring bacterioplankton species composition during the experiment showed that the initial bacterial assemblage evolved into different final assemblages in the microcosms dominated by diatoms (turbulent microcosms) and in the microcosms with a greater proportion of phytoflagellates (still microcosms). These findings corroborate previous results obtained primarily from mesocosm experiments with water collected off Scripps Pier, California (39, 48, 55), which showed that changes in bacterial growth and activity during algal blooms were due mainly to shifts in bacterioplankton species composition.
Experimental phytoplankton bloom cycles usually take place within a week or two. The rapid shifts in bacterial activity and community composition during such experiments result from a rapid release of large quantities of organic matter and nutrients due to algal lysis and/or intense grazing during the decay phase of the blooms. Although sudden mass lysis of phytoplankton blooms in the sea has been reported (43), phytoplankton succession is mostly a gradual process, with changes taking place on a time scale of several weeks (23). As a consequence, the opportunity for rapid shifts in bacterioplankton species composition could be limited by a relatively low supply rate of organic matter and/or inorganic nutrients to bacteria under natural algal bloom conditions. This could explain in part why the rate of seasonal succession in bacterioplankton is relatively slow (i.e., several weeks), despite the high growth potential of marine bacteria (50, 62). Still, we find it likely that a sustained release of organic matter and nutrients by live algal cells or by grazers in the long term could profoundly influence the growth of particular bacterial populations, whether under algal bloom or nonbloom conditions. Thus, the greater length of time that natural phytoplankton blooms persist compared to that of experimental phytoplankton blooms could result in larger differences in the bacterioplankton species associated with natural than with experimental blooms.
We have shown that changes in phytoplankton community composition were accompanied by shifts in the composition of the bacterial assemblages. The most pronounced changes were observed for bacterial populations belonging to the phylum Bacteroidetes, principally members of the family Flavobacteriaceae, indicating that flavobacteria could be particularly important in the processing of organic matter during algal blooms.
Algal classes differ substantially in their biochemical composition, in terms of C/N/P ratios and in terms of relative proportions of cellular protein, fatty acids, and nucleic acids (53, 70). Differences in the biochemical composition of dominant phytoplankton could cause differences in the stoichiometry of particulate and dissolved organic matter and in the availability of mineral nutrients in seawater, all of which could profoundly affect the growth of bacteria (37). Studies of algal cultures, including diatoms and dinoflagellates, have suggested the existence of specific associations between phytoplankton and bacterioplankton species, possibly due to the differential release of organic matter from the algae (25, 60). To this end, van Hannen et al. showed that enrichment of lake water continuous cultures with detritus from either a green alga or cyanobacterium resulted in the growth of different bacterial assemblages (71). These findings are in agreement with general conclusions concerning the importance of the quality of the organic matter for bacterial community composition and activity (10, 11, 32, 48, 49). This suggests the possibility of finding common patterns in the distribution of particular bacterial groups or species during blooms dominated by different phytoplankton.
Quantitative and qualitative differences in planktonic grazer populations have important consequences both for the pattern of nutrient regeneration and the release of dissolved organic matter. Furthermore, higher nutrient recycling rates resulting from increased grazing rates on phytoplankton under turbulent conditions have been suggested to affect bacterial growth, possibly in combination with decreased grazing rates on bacteria (46, 47). We observed greater microzooplankton biomass in the microcosms dominated by diatoms (turbulent microcosms) than in the microcosms with a higher proportion of phytoflagellates (still microcosms). Moreover, ciliates accounted for a majority of the microzooplankton in the diatom blooms, while heterotrophic dinoflagellates were the dominant grazers in blooms with higher proportion of phytoflagellates. Thus, variation in substrate supply to bacteria due to differences in phytoplankton community composition could have been further amplified by different grazer assemblages.
A majority of the bacterial phylotypes identified in our study belonged to the Roseobacter group (Alphaproteobacteria) or the Bacteroidetes phylum. Phylotypes belonging to these groups had different patterns in our microcosms. Whereas most of the Roseobacter phylotypes were ubiquitous, pronounced differences were observed in the occurrence of Bacteroidetes phylotypes between the microcosms dominated by diatoms and those with a higher proportion of phytoflagellates. This could indicate that these bacterial groups responded to different stimuli in our experiments. Possibly, Roseobacter phylotypes represented a response to the nutrient additions, while the Bacteroidetes phylotypes were responding more to the turbulence-induced differences in the phytoplankton.
Bacteria in the Roseobacter group are widespread and abundant in the oceans and coastal areas of the world (20, 64). Members of the Roseobacter group have 16S rRNA gene sequence similarities of ≥90% (21), and novel genera in this group are continuously being described. Many characteristics have been ascribed to the marine members of the Alphaproteobacteria. For example, they are important in mediating transformations of dimethylated sulfur compounds (41), and members of the Roseobacter group have been suggested to be active colonizers of particles under algal bloom conditions (55). Pinhassi and Berman (49) found that several Roseobacter species became dominant in cultures of unamended seawater collected from the oligotrophic eastern Mediterranean Sea and the Red Sea, suggesting that these bacteria are good competitors under low-nutrient conditions. Most of the Roseobacter phylotypes detected in the present study were found throughout our microcosms and were affiliated with different representatives of the group, such as Roseobacter gallaeciensis, Sulfitobacter pontiacus, and the Atlantic Ocean clone library sequence NAC11-3. The persistence and growth of a substantial subset of Roseobacter phylotypes in our microcosms may at first suggest that these are generalist bacteria. However, in a detailed study of a Roseobacter clade-affiliated cluster, which includes the clone NAC11-3, Selje et al. (64) described significant differences in the geographic distribution of phylotypes that differed by only a few base pairs in the 16S rRNA gene. Future comprehensive phylogenetic analyses and genome comparisons of members of the Roseobacter group will clarify whether the large variety of characteristics ascribed to these bacteria can be explained by a high degree of phenotypic differentiation by phylogenetically relatively closely related bacteria.
The Bacteroidetes phylum is highly diverse; at this time, it consists of 12 families and 79 described genera. Several of these taxa contain representatives from marine environments, documented by culture-independent techniques or by cultured isolates. Bacteria belonging to the Bacteroidetes are abundant in seawater (12, 19, 30), and previous studies have emphasized their importance under algal bloom conditions (48, 55). However, it remains unclear whether particular taxa within the Bacteroidetes are more commonly found than others in the marine environment (31, 44) and whether certain growth conditions selectively favor certain taxa in this phylum. Two phylotypes (MED-S4 and -S5) belonging to the family Cryomorphaceae were unique to the microcosms with a higher proportion of phytoflagellates, although they formed relatively faint bands on the DGGEs. The most intense bands in the upper region of the DGGE were identified as phylotypes belonging to the family Flavobacteriaceae. Two Flavobacteriaceae phylotypes (MED-S1 and -S2) were dominant in the microcosms with a higher proportion of phytoflagellates. Two other members of this family were dominant in the microcosms dominated by diatoms. These phylotypes, MED-T6 and -T7, were identical to the BY-65 and BY-66 phylotypes, respectively (Fig. 6), which were originally detected in 1996 during a diatom bloom experiment performed 200 km northeast of the site of the present experiment (61). This surprisingly consistent response to diatom bloom conditions of a few Flavobacteriaceae phylotypes in the Mediterranean Sea could indicate that some bacteria in this family harbor physiological or ecological traits that make them tightly coupled to diatom species.
Bacteria responding to experimental treatments in a single location may be particular to that location rather than representing general trends in the growth potential of different bacteria. Therefore, we extended our phylogenetic analysis to include 16S rRNA gene sequences of Bacteroidetes phylotypes and isolates from all published studies of marine bacterioplankton diversity associated with natural or experimental algal blooms (Table 3 and Fig. 6). Our analyses showed that even though the Bacteroidetes phylum can be divided into at least 12 families, as much as 80% of the Bacteroidetes phylotypes in these studies (among a total of 63 sequences) belonged to one single family, the Flavobacteriaceae. In particular, phylotypes affiliated with the Tenacibaculum and Cellulophaga or Zobellia genera were frequently found. Other recurrently detected genera in this family included Chryseobacterium, Polaribacter, Gelidibacter, and Psychroserpens. Therefore, we suggest that members of the family Flavobacteriaceae represent bacterial populations that play particularly important roles during and after algal bloom events.
TABLE 3. TABLE 3.
Number of 16S rRNA gene sequences affiliated with the family Flavobacteriaceae compared to other families in the phylum Bacteroidetesa
At this time, efforts are being made to revise the taxonomy of the Bacteroidetes phylum using phylogenetic analysis of the 16S rRNA gene. This has contributed to the recent redefinition of the family Flavobacteriaceae (4). As a consequence of this revision, bacteria previously named Cytophaga and found throughout the phylum have been renamed, and the type species of the genus Cytophaga is actually well separated from the Flavobacteriaceae. Bacteria in the Flavobacteriaceae have menaquinone 6 (MK-6) as a major respiratory quinone, and this family has therefore been called the marine MK-6 group (67). Suzuki et al. (67) observed that the members of Flavobacteriaceae in their study were unable to use nitrate or ammonium as nitrogen sources, indicating that they required an organic nitrogen source for growth. If confirmed, this observation would substantiate previous findings that bacteria in this group show a high growth capacity when dissolved proteins are abundant (9, 48), which may contribute to explaining why bacteria in the family Flavobacteriaceae are recurrently found during the decay of algal blooms.
We have interpreted the changes in bacterioplankton species composition primarily as a consequence of the differences in dominant phytoplankton groups, which in turn were dependent on the mixing regimen. It is also possible that the total phytoplankton biomass played a role, since nearly three- to sevenfold-higher peaks in Chl a were recorded under turbulent conditions compared to still conditions. Even though the higher bacterial abundance in the final samples in the microcosms with pronounced diatom blooms could have resulted from the higher phytoplankton biomass achieved under turbulence, cell-specific bacterial growth rates and enzymatic activities reached relatively similar levels in all microcosms. Differences in the structure of the bacterial assemblage were also evident in our second bloom experiment, where peak Chl a concentrations were only 50% higher under turbulent conditions compared to still conditions. We note that studies of horizontal variability in bacterial community structure repeatedly find relatively similar bacterial assemblages over substantial distances despite apparent differences in Chl a concentrations (54, 56). At the same time, considerable variability in bacterial diversity is commonly found with depth, which may depend largely on the stratification of phytoplankton populations (see reference 51 and references therein).
For most of the year, the growth of bacteria in northwestern Mediterranean waters is primarily limited by the availability of P (59, 69). The first peak in bacterial production and abundance observed in phytoplankton bloom experiment 1 may therefore be interpreted as a direct effect of the addition of nutrients. The subsequent increase in bacterial production and abundance from day 5 on coincided with the peak and subsequent senescence of the algal blooms. Concomitantly, alpha- and beta-glucosidase and aminopeptidase activities indicated an increase of nearly an order of magnitude or more in the rate of bacterial utilization of carbohydrates and protein. The increase in phosphatase activity could result from the depletion of inorganic phosphate (data not shown) coupled with increased availability of organically bound P. Monitoring bacterioplankton species composition during the experiment showed that the initial bacterial assemblage evolved into different final assemblages in the microcosms dominated by diatoms (turbulent microcosms) and in the microcosms with a greater proportion of phytoflagellates (still microcosms). These findings corroborate previous results obtained primarily from mesocosm experiments with water collected off Scripps Pier, California (39, 48, 55), which showed that changes in bacterial growth and activity during algal blooms were due mainly to shifts in bacterioplankton species composition.
Experimental phytoplankton bloom cycles usually take place within a week or two. The rapid shifts in bacterial activity and community composition during such experiments result from a rapid release of large quantities of organic matter and nutrients due to algal lysis and/or intense grazing during the decay phase of the blooms. Although sudden mass lysis of phytoplankton blooms in the sea has been reported (43), phytoplankton succession is mostly a gradual process, with changes taking place on a time scale of several weeks (23). As a consequence, the opportunity for rapid shifts in bacterioplankton species composition could be limited by a relatively low supply rate of organic matter and/or inorganic nutrients to bacteria under natural algal bloom conditions. This could explain in part why the rate of seasonal succession in bacterioplankton is relatively slow (i.e., several weeks), despite the high growth potential of marine bacteria (50, 62). Still, we find it likely that a sustained release of organic matter and nutrients by live algal cells or by grazers in the long term could profoundly influence the growth of particular bacterial populations, whether under algal bloom or nonbloom conditions. Thus, the greater length of time that natural phytoplankton blooms persist compared to that of experimental phytoplankton blooms could result in larger differences in the bacterioplankton species associated with natural than with experimental blooms.
We have shown that changes in phytoplankton community composition were accompanied by shifts in the composition of the bacterial assemblages. The most pronounced changes were observed for bacterial populations belonging to the phylum Bacteroidetes, principally members of the family Flavobacteriaceae, indicating that flavobacteria could be particularly important in the processing of organic matter during algal blooms.
Soldato
- Joined
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- Essex
Aye wtf ban the wall of text guy.
What are you doing all the way out here anyway!? Come on, come back to the Sports Arena, come on... there there.
PS I voted YES
lollers
Me too, because Killa_ken is a pussyLooks like I'm safe then.
Last edited:
Man of Honour
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Me too, because Kill_ken is a pussy
I just got snot on my macbook from scoffing at that.......
Looks like I'm safe then.
I demand you have your name changed to Killa_kens_sidekick
Sort of proved his point there.
Man of Honour
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- Southampton, UK
Oh dear lord please let me be able to retract my vote...
Soldato
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If its good enough for mel gibson, its good enough for me
Are you an alcoholic who hates the Jews?