Bacterial activity during early winter mixing (Gulf of St. Lawrence, Canada)

Lovejoy, Connie; Legendre, Louis; Klein, Bert; Jé, Tremblay; Rg, Ingram; Jc, Therriault

doi:10.3354/ame010001

Cited by 65 publications

(77 citation statements)

References 28 publications

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“…For example, during the period when the water column was mixed, temperature seemed to play the most dominant role in regulating the APA with DO not playing an important role, probably as a consequence of the fact that mixed water column coincided with relatively low temperature and high DO regimes. Shiah & Ducklow (1994), and Lovejoy et al (1996) have reported temperature as a dominant regulating factor for heterotrophic activity especially in a low water situation. Furthermore, relatively low DIN or DIP contents in the water column during this period may have facilitated APA.…”

Section: Discussionmentioning

confidence: 99%

“…Although in recent years several studof effluents into the inlet, leading to eutrophication of ies have been undertaken to estimate the rate of enzythe site. Average depth near the sampling station is 16 matic hydrolysis of protein in a variety of ecosystems to 17 m. (Hollibaugh & Azam 1983, Somville & Billen 1983 Samples of surface (2 m) and bottom (16 m) waters Lovejoy et al 1996), relationships between the hydrowere collected on a weekly to biweekly basis using lytic rates and ecological factors are still not clear Kitahara (1 1) or Niskin (5 1) water samplers. Samples (Rosso & Azam 1987).…”

Section: Methodsmentioning

confidence: 99%

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Regulation of seasonal variability of aminopeptidase activities in surface and bottom waters of Uranouchi Inlet, Japan

Patel¹,

Fukami²,

Nishijima³

2000

Aquat. Microb. Ecol.

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The potential aminopeptidase activity (APA) vis-a-vis important ecological parameters of surface and bottom waters of Uranouchi Inlet (Japan), a semi-enclosed eutrophic coastal ecosystem, were studied on a weekly to biweekly basis from mid-August 1996 to early November 1997. The aim of this study was to investigate the main factors regulating the annual and seasonal dynamics of APA in the inlet. APA was estimated in short-term incubations as the V, , of the rate of enzymatic hydrolysis of a fluorophore 7-L-leucyl-4-methyl couomarinylarnide under conditions close to those of in situ. The water column structure at the study site changed considerably during the study period as the ecological parameters such as temperature, dissolved oxygen (DO), nutrient contents, and bacterial abundance exhibited pronounced seasonal stratification (May to September). When the water column was mixed (October to March), surface and bottom waters possessed similar APA . But when the water column became stratified, pronounced differences became apparent, with surface water showing considerably higher APA. On extreme days, surface water possessed as much as -20 times higher APA than that of bottom water. Thus, APA of surface water demonstrated strong seasonality and varied by almost 40-fold compared to that of bottom water, which varied only about 12-fold during the study period. Notably, bacterial abundances of both waters showed limited seasonality and varied only -3-fold during the same period. These results imply that changes in APA are not merely a function of bacterial abundance but rather more of per-cell activity. On an annual basis, APA in both waters were positively correlated (p < 0.001) with temperature and bacterial abundance, and negatively correlated with s M i t y (p c 0.001 for surface and p < 0.01 for bottom water) but were not correlated (p > 0.05) with DO, chlorophyll a (p < 0.05; only for surface water), inorganic or organic forms of nitrogen (DIN, DON) or inorganic phosphorous (DIP) contents. Furthermore, when the water column was mixed, APA correlated strongly with temperature (p < 0.001; r = 0.87), and marginally (p < 0.05) with DIN (r = 0.43) and DIP (r = 0.40) content but not with DO (p > 0.05) content. In contrast, when the water column became stratified, APA correlated only marginally with temperature (0.01 c p < 0.05; r = 0.33) but strongly with DO (p c 0.001; r = 0.73), and negatively (p c 0.001) with DIN (r = -0.61) and DIP (r = -0.70) content. DON content did not show any correlation (p > 0.05) with APA regardless of whether the water column was mixed or stratified. These correlations suggest that temperature played a critical role in regulating the APA when the water column was mixed (October to March), and DO or inorganic nutrient contents (May to September) when the water colun~n was stratified.

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Regulation of seasonal variability of aminopeptidase activities in surface and bottom waters of Uranouchi Inlet, Japan

Patel¹,

Fukami²,

Nishijima³

2000

Aquat. Microb. Ecol.

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“…Among these, the detection of actively respiring cells via cellspecific reduction of the fluorogenic dye 5-cyano-2, 3-ditolyl tetrazolium chloride (CTC; Polyscience Europe) is often considered as one of the most universal methods applicable for complex natural communities. Although this method remains controversial (Thom et al 1993, Lovejoy et al 1996, Ullrich et al 1996, Sieracki et al 1999, it has been shown that active cell counts vary in an ecologically interpretable manner (del Giorgio & Scarborough 1995, Smith 1998. The proportion of actively respiring cells is generally below 10% in aquatic ecosystems (Lovejoy et al 1996, Karner & Fuhrman 1997.…”

Section: Resale or Republication Not Permitted Without Written Consenmentioning

confidence: 99%

“…For example, rRNA gene fragments of less-abundant microorganisms tend to be underrepresented in polymerase chain reaction (PCR) amplification. It could be argued that these underrepresented populations are likely to be of minor ecological importance in a given ecosystem, but one should realize that in most aquatic ecosystems, only a small fraction of the community is active at any given time (Lovejoy et al 1996, Karner & Fuhrman 1997, Choi et al 1999. Therefore, the community structure derived from the analysis of the whole DNA includes active, inactive and dead cells.…”

Section: Resale or Republication Not Permitted Without Written Consenmentioning

confidence: 99%

“…Although this method remains controversial (Thom et al 1993, Lovejoy et al 1996, Ullrich et al 1996, Sieracki et al 1999, it has been shown that active cell counts vary in an ecologically interpretable manner (del Giorgio & Scarborough 1995, Smith 1998. The proportion of actively respiring cells is generally below 10% in aquatic ecosystems (Lovejoy et al 1996, Karner & Fuhrman 1997. However, the general acceptance of this method by microbial ecologists requires more investigation.…”

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confidence: 99%

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Genetic diversity of total, active and culturable marine bacteria in coastal seawater

Bernard¹,

Schäfer²,

Joux³

et al. 2000

Aquat. Microb. Ecol.

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The genetic diversity of marine bacteria from coastal Mediterranean water was analyzed using denaturing gradient gel electrophoresis (DGGE) and comparative sequence analysis of PCR-amplified 16S rRNA genes. The diversity of the whole bacterial assemblage was compared to the diversity of the fraction of actively respiring bacterial cells and of culturable bacteria. Culturable bacteria were isolated on agar plates using 4 different culture media, as well as in filtered autoclaved seawater following dilution to extinction. The cell fractions exhibited varied genetic diversity. High similarity between DGGE patterns obtained from the whole bacterial assemblage and those obtained from the active cell fraction (representing only 3% of total cells) indicated the simultaneous presence of both active and inactive cells within populations corresponding to numerous bacterial phylotypes defined as DGGE bands. Furthermore, an important source of genetic diversity corresponding to viable organisms, detected by culturability on agar media and in dilution culture with unamended seawater, was not detectable by DGGE patterns obtained from total cells. Most of the strains isolated by dilution cultures were different from those isolated on solid agar media. These results suggest that studies on the structure of complex marine bacterial communities do not necessarily reflect the physiological heterogeneity of ecologically important populations and may ignore populations present at low relative abundance that can play a key ecological role.KEY WORDS: Activity · Cell sorting · Culturability · Genetic diversity · Marine bacteria · Oligotrophy Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 23: [1][2][3][4][5][6][7][8][9][10][11] 2000 not yet been cultured. Several media with different compositions have been proposed for isolating new species (Martin & MacLeod 1984, Gonzalez & Moran 1997) and a dilution culture technique has been developed to isolate oligotrophic species, which do not grow on nutrient-rich medium . However, culturability is also a function of the physiological state of a cell, and cells of cultured species may become unculturable under adverse environmental conditions (Schut et al. 1997). Recent studies have demonstrated that, even if the CFU proportion remains very low, cultured species sometimes represent a significant part of the community DNA (Pinhassi et al. 1997). This suggests that non-culturable cells of cultured species may represent a numerically important fraction of natural communities.Different culture-independent methods have been developed to quantify metabolically active bacteria in natural communities (Joux & Lebaron 2000). Among these, the detection of actively respiring cells via cellspecific reduction of the fluorogenic dye 5-cyano-2, 3-ditolyl tetrazolium chloride (CTC; Polyscience Europe) is often considered as one of the most universal methods applicable for complex natural communities. Although this method remains controversial (Thom et ...

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