Abundance and production of bacteria, and relationship to phytoplankton production, in a large tropical lake (Lake Tanganyika)

Abstract

1. Abundance and bacterial production (BP) of heterotrophic bacteria (HBact) were measured in the north and south basins of Lake Tanganyika, East Africa, during seasonal sampling series between 2002 and 2007. The major objective of the study was to assess whether BP can supplement phytoplankton particulate primary production (particulate PP) in the pelagic waters, and whether BP and particulate PP are related in this large lake. HBact were enumerated in the 0-100 m surface layer by epifluorescence microscopy and flow cytometry; BP was quantified using 3 H-thymidine incorporation, usually in three mixolimnion layers (0-40, 40-60 and 60-100 m). 2. Flow cytometry allowed three subpopulations to be distinguished: low nucleic acid content bacteria (LNA), high nucleic acid content bacteria (HNA) and Synechococcus-like picocyanobacteria (PCya). The proportion of HNA was on average 67% of total bacterial abundance, and tended to increase with depth. HBact abundance was between 1.2 · 10 5 and 4.8 · 10 6 cells mL )1 , and was maximal in the 0-40 m layer (i.e. roughly, the euphotic layer). Using a single conversion factor of 15 fg C cell )1 , estimated from biovolume measurements, average HBact biomass (integrated over a 100-m water column depth) was 1.89 ± 1.05 g C m )2 . 3. Significant differences in BP appeared between seasons, especially in the south basin. The range of BP integrated over the 0-100 m layer was 93-735 mg C m )2 day )1 , and overlapped with the range of particulate PP (150-1687 mg C m )2 day )1 ) measured in the same period of time at the same sites. 4. Depth-integrated BP was significantly correlated to particulate PP and chlorophyll-a, and BP in the euphotic layer was on average 25% of PP. 5. These results suggest that HBact contribute substantially to the particulate organic carbon available to consumers in Lake Tanganyika, and that BP may be sustained by phytoplankton-derived organic carbon in the pelagic waters.

Microbial Ecology of Lake Kivu

“…In 2008, the mean BP in the mixed layer off Kibuye was 336 mg C m −2 day −1 and ranged between 34 and 902 mg C m −2 day −1 (n = 10, Nzavuga Izere 2008 ) . This range was similar to that of Lake Tanganyika (Stenuite et al 2009b ) . In Lake Kivu, BP was relatively low during the dry season, when the mixed layer was deep (Fig.…”

“…Several estimates of planktonic bacterial production (BP) were recently performed using 3 H-thymidine uptake (Fuhrman and Azam 1980 ) following the protocol and conversion factors of Stenuite et al ( 2009b ) described for Lake Tanganyika. Some results are shown in Fig.…”

Relationships between pelagic bacteria and phytoplankton abundances in contrasting tropical freshwaters

“…A strong relationship is taken as an indication that the growth of bacterioplankton is directly dependent on phytoplankton (Cole et al 1988, Jeppesen et al 1997, Gasol & Duarte 2000. However, this bacterial dependence on phytoplankton has been the focus of recent debate (Lee & Bong 2008, Sarmento et al 2008, Stenuite et al 2009). Recent literature provides support for both strong (Sarmento et al 2008, Stenuite et al 2009) and weak dependence (Canosa & Pinilla 2007, Lee & Bong 2008 of bacterial growth on phytoplankton activity.…”

“…However, this bacterial dependence on phytoplankton has been the focus of recent debate (Lee & Bong 2008, Sarmento et al 2008, Stenuite et al 2009). Recent literature provides support for both strong (Sarmento et al 2008, Stenuite et al 2009) and weak dependence (Canosa & Pinilla 2007, Lee & Bong 2008 of bacterial growth on phytoplankton activity.When expressed mathematically as a regression equation between bacteria and algae, the parameters that define the relationships (the slope and the y-intercept) can describe important ecological parameters. The slope of the equation between the bacterial and phytoplankton attributes (either abundance or biomass) indicates the proportion of phytoplankton carbon that is transformed into bacterial carbon, while the y-intercept estimates the fraction of the bacterial standing stock that appears to be independent of phytoplankton (Currie 1990, Simon et al 1992, del Giorgio & Peters 1993.…”

Connecting silvan and lacustrine ecosystems: transport of carbon from forests to adjacent water bodies

“…Taking into account the primary production and input from precipitation (1.6 g C m -2 yr -1 ), the terrestrial input (DOC+DIC) forms 76% of the total carbon input in Valkea-Kotinen. For lakes in other regions besides the boreal zone, the importance of terrestrial carbon can be smaller, because their own autochthonous production is higher (Stenuite et al 2009). …”