Seasonal variability of metabolically active bacterioplankton in the euphotic zone of a hypertrophic lake

Although detailed temporal studies of marine planktonic cyanobacteria have been reported, relatively little is known about variation of other marine picoplankton groups on time scales on the order of months to years. In this study, we followed vanation in relative abundance of planktonic archaeal rRNA at 5 depths in the upper 300 m of the Santa Barbara Channel (SBC) over 32 mo. Small subunit rRNA targeted oligonucleotide probes were used to quantify archaeal, bacterial, and eucaryal rRNA relative abundance. Archaea subgroups were quantified using probes specific to 2 planktonic archaeal groups, termed G1 and G11 The archaeal rRNA signal in the upper 20 m was characterized by intermittent 'blooms' that coincided with increases in the relatlvc ab.undance of GII rRNA as well as decreases in chlorophyll a (chl a). At greater depths, archaeal rRNA abundance was consistently elevated, approaching bacterial rRNA abundance. The G1 rRNA accounted for the majority of the deeper archaeal rRNA signal throughout the time series. Consistent with a previous report, the 2 groups of archaea had maximal rRNA abundance at different depths. The lnajolity of the variability in the G1 archaeal slgnal in the upper 75 m (77 %) could be attributed to a positive relat~onship with nutrients and negative relationships with prokaryotic abundance, chl a, and temperature; although, at most, 41% of the variability at each depth could be explained. Only 21 % of the variability in the G11 rRNA signal could be explained by the variables included in the model. Leucine incorporation rates and, to a lesser extent, prokaryote abundance, were highly correlated with chl a and POC levels. Only weak relationships were observed between prokaryote abundance or leucine incorporation and incredses in temperature. The results of linear regressions between prokaryote abundance and leucine incorporation suggest that top-down ecological controls may regulate prokaryotic assemblages in this dynamic coastal system. The distribution of the 2 archaeal groups suggested that they responded independently to environmental conditions, are physiologically different, and likely participate in different environmental processes.

Section: Discussionsupporting

confidence: 71%

A time series assessment of planktonic archaeal variability in the Santa Barbara Channel

Murray¹,

Blakis²,

Massana³

et al. 1999

“…As in other studies (Tabor & Neihof 1984, Robarts & Sephton 1988, Sommaruga & Conde 1997, the water temperature in the Sep Reservoir was significantly correlated with the number of metabolically active bacteria (Table 1). In the surface waters of the Gulf of St. Lawrence in Canada, the low proportions of CTC-active bacteria observed by Lovejoy et al (1996) were between 1 and 2% during summer stratification and fell to <1% in winter.…”

Section: Relations With the Other Parameters Measuredsupporting

confidence: 81%

“…2C). Similarly, in a comparative review of published data, Sommaruga & Conde (1997) concluded that in conditions where resources are not limiting, warming the water leads to an increase in the abundance of metabolically active bacteria. For example, in Lake Rodo (Uruguay), those authors calculated that the numbers of CTC-positive bacteria were increased by more than an order of magnitude, parallel to an increase in temperature from 8 to 28°C.…”

Section: Relations With the Other Parameters Measuredmentioning

confidence: 99%

Variations in the number of active bacteria in the euphotic zone of a recently flooded reservoir

Jugnia¹,

Richardot²,

Debroas³

et al. 2000

Using the CTC (5-cyano-2, 3-ditolyl tetrazolium chloride) method, we estimated the active fraction of bacterioplankton in the euphotic zone of the recently flooded Sep Reservoir, France, with the aim of evaluating its importance and dynamics in relation to temperature and some components of dissolved organic matter (DOM) (i.e. dissolved combined amino acids: DCAA; dissolved free monosaccharides: DFCHO; dissolved combined monosaccharides: DCCHO), and its metabolic significance in conjunction with a bacterial growth indicator:14 C-glucose uptake. From our results, it appears that only a small fraction (0.04 to 3.23%) of total bacterial count in this reservoir was metabolically active. Recorded correlations and multivariate regression analysis suggest that temporal variations in the number of active bacteria are mainly (80%) governed by temperature, together with the high concentrations of those components of DOM, which were present in this ecosystem but which apparently were not always available for bacterial metabolism. We also found a positive relation between the number of active bacteria and the potential heterotrophic activity, which suggest that CTC-positive bacteria are responsible for the bulk of bacterial community metabolism in this recently formed reservoir.KEY WORDS: Active bacteria · CTC · Dissolved organic matter · Temperature · Bacterial activity · New reservoir Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 22: [251][252][253][254][255][256][257][258][259] 2000 fraction of bacterioplankton (e.g. Thom et al. 1993), whereas others have suggested temperature (Tabor & Neihof 1984, Robarts & Sephton 1988, Sommaruga & Conde 1997, lysis (Proctor & Fuhrman 1990), grazing (Gasol et al. 1995) and resource availability (del Giorgio & Scarborough 1995, Choi et al. 1999. In terms of resource availability, a wide variety of sources including phytoplankton excretion and lysis (Cole et al. 1988, Maurin et al. 1997) and grazing and release by zooplankton (e.g. Hygum et al. 1997) have been identified as producing dissolved organic matter (DOM) that fuels bacterioplankton metabolism. Inputs of allochthonous DOM and physical disaggregation of detrital particles (Hadas et al. 1990) are also likely to be significant energy sources for bacterial activities. However, nearly all these studies have been conducted in natural or stabilized artificial lake ecosystems. To our knowledge, no information is available on fluctuations in the number of active bacteria in recently flooded reservoirs that are expected to contain large quantities of terrestrial detritus and organic matter, which is known to efficiently regulate bacterial activity (Paterson et al. 1997).The aim of this study was to determine the importance of the active fraction of bacterioplankton in a recently flooded reservoir, the main variables controlling their abundance (especially temperature and DOM) and their metabolic significance in conjunction with a growth indicator:14 C-glucose uptake. The numbe...

Section: Methodsmentioning

confidence: 99%

“…Heterotrophic bacteria. To determine colony forming units (CFU), water samples were plated on agar (Sommaruga & Conde 1997, Bernard et al 2000 and cultivated for 7 d at 25°C (Simon et al 1999, Zhongtang et al 2000.The halotolerance of bacteria was determined by plating on M9 media with different NaCl contents (Miller 1972). The objects of the investigation were 3 groups of heterotrophic bacteria differing in their resistance to osmotic pressure: freshwater bacteria (unable to tolerate more than 3% NaCl), halophile bacteria (able to tolerate 0.05 to 5% NaCl) and moderate halotolerant bacteria (able to tolerate 0.05 to 10% NaCl).…”

mentioning

confidence: 99%

Antibiotic resistance of heterotrophic bacteria in Shira lake: natural and anthropogenic impacts

Lobova¹,

Barkhatov²,

Popova³

2002

Studies were conducted to investigate the antibiotic resistance of freshwater, halophile and moderate halotolerant bacteria isolated from the nearshore part of Shira lake, which is affected by the activity of a health resort, and from the central part of the lake in the summer (June to August) of 1999. It has been shown that the allochthonous microflora, which is brought into the lake with the resort effluent in mid-summer, is the anthropogenic factor contributing to an increase in the number of freshwater bacteria that feature multiple antibiotic resistance in the central part of the lake. It has been found that resistance to ampicillin of freshwater and halophile heterotrophic bacteria is related to the increase in the biomass of blue-green and green algae in the central part of Shira lake between mid-July and the end of August. A mathematical model has been constructed to describe the dynamics of the antibiotic resistance of heterotrophic bacteria in the close-to-resort and the central parts of Shira lake under natural and anthropogenic impacts.KEY WORDS: Heterotrophic bacteria · Halotolerance · Antibiotic resistance · Anthropogenic load · Brackish lake · Mathematical modeling Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 30: [11][12][13][14][15][16][17][18] 2002 upstream (Parnachev 1997). The result of all these processes may be a disturbance of the natural biodiversity of Shira lake.There are various ways to estimate the anthropogenic load on an ecosystem, including chemical analysis, bioindication, bioassays, etc. (Doust et al. 1994, Ostroumov 2000, Lindstron-Seppa et al. 2001, Samecka-Cymerman & Kempers 2001. Bacteria are often used to monitor the state of the environment (Jacobs et al. 1995, Schwedt et al. 1997, Backhaus & Grimme 1999, as their evolution rate is very high, and under the effect of environmental factors they can acquire various specific features, and thus, serve as good indicators for the presence of pollutants. One of the properties of bacteria used to assess the anthropogenic load is their antibiotic resistance (Hagedorn et al. 1999, Goni-Urriza et al. 2000, Mary et al. 2000, McArthur & Tuckfield 2000.Antibiotic resistance in bacteria can be determined both by chromosome genes and by extrachromosome genetic elements (R-plasmids) (Gomes-Lus 1998, Ho et al. 1998. The acquisition of antibiotic resistance is realized as an active process only under the conditions selective for such genes (Chandrasekaran et al. 1998, Guardabassi et al. 1998, Goni-Urriza et al. 2000. Thus, if antibiotic resistance is recorded in a great number of heterotrophic bacteria, a drastic change in the environmental conditions due to direct or indirect impact of non-natural factors may be assumed.The aim of this work is to investigate the dynamics of antibiotic resistance of heterotrophic bacteria varying in halotolerance in the central and the close-to-resort parts of Shira lake. In addition, we determine the relationship between antibiotic resistance of ...