Seasonal variations of metabolically active bacteria in a hypertrophic lake (Hartbeespoort Dam, South Africa)

Abstract

The number of metabolically active bacteria was measured with nalidixic acid over two annual cycles at three depths in the epilimnion of hypertrophic Hartbeespoort Dam, South Africa. Concurrent measurements were made of water temperature, DOC, phytoplankton production of dissolved (EDOC) and particulate organic carbon, chlorophyll a and the uptake of glucose (Vma,,). The objective was to determine the dominant factors correlated to the number of metabolically active bacteria and the relationship between active bacterial numbers and heterotrophic activity.The number of active bacteria was usually highest at the surface and ranged between 0.70 and 6.82 x 106 cells ml-' . The dominant factors correlated to the number of bacteria at the surface were water temperature (r = 0.65, n = 54, p<0.001), primary production (r = 0.53, n = 51, p < 0.001) and EDOC (r = 0.37, n = 45, p = 0.005). Surface Vm,, for glucose ranged between 0.11 and 4.0 ItgC 1-1 h -1 and was positively correlated to the number of active bacteria (r = 0.61, n = 53, p < 0.001). The specific activity index (10-12 gC cell-' h-l) varied between 80 and 2290 at the surface and was most strongly correlated to EDOC (r = 0.70, n = 48, p < 0.001). Relationships between active bacterial numbers, water temperature, phytoplankton activity and glucose uptake were also found at two additional depths within the epilimnion. These data suggest that bacterial populations in nutrient enriched lakes contain a large number of metabolically active cells with high individual activity as a result of enhanced phytoplankton growth.

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

“…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.…”

“…This observation agrees with that of Sommaruga & Conde (1997), and also puts the temperature dependence of our results in line with other recent reports 256 The multiple regression analysis showed that 80% of the total variance associated with the numbers of CTCpositive bacteria could be explained by temperature and DOM and the correlation with the dissolved organic carbon stemming from the protein and carbohydrate pool (Table 1) show that, in this ecosystem, temperature is not the only factor involved in controlling the abundance of CTC-positive bacteria. Moreover, as in numerous studies that have already reported a good relation between metabolically active bacteria and bacterial activities, particularly bacterial 14 C-glucose uptake (Robarts & Sephton 1988, Dufour et al 1990), we also showed, in this study, a relation between active bacteria and the uptake of a directly usable component, namely glucose. Such a relation suggests that CTC-positive bacteria are responsible for the bulk of bacterial community metabolism in this recently formed reservoir.…”

“…Kogure et al (1980) concluded from their survey of metabolically active bacteria in the water around Japan that the numbers increased in relation to the particulate and dissolved organic carbon concentrations. In Hartbeespoort Dam, Robarts & Sephton (1988) did not observe any correlation between the number of metabolically active bacteria and the dissolved organic carbon concentration. However, few in situ simultaneous estimates of DOM concentrations and active bacteria are sufficiently complete to permit accurate comparisons.…”

“…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.…”

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

“…Phytoplankton of this warm-water system was dominated by the cyanobacterium Microcystis aeruginosa, which reached chl a concentrations of up to 6530 1-19 I-' and attained primary production rates which were the highest ever reported for aquatic systems (Robarts & Wicks 1990). Surprisingly, the maximum percentage of active bacteria estimated by the nalidixic method was only 48% (Robarts & Sephton 1988 (Robarts & Wicks 1990). In Lake Rodo, the rapid bacterial turnover times which ranged from 5 to 42 h (Sornmaruga 1995) contrasted with the fact that, with the exception of the period between February 26 and March 26 (>85% of active bacteria), the proportion of inactive bacteria was always significant.…”