Bacterial Growth Efficiency in a Tropical Estuary: Seasonal Variability Subsidized by Allochthonous Carbon

Abstract

Bacterial growth efficiency (BGE) is a key factor in understanding bacterial influence on carbon flow in aquatic ecosystems. We report intra annual variability in BGE, and bacteria mediated carbon flow in the tropical Mandovi and Zuari estuaries (southwest India) and the adjoining coastal waters (Arabian Sea). BGE ranged from 3 to 61% and showed clear temporal variability with significantly (ANOVA, p < 0.01) higher values in the estuaries (mean, 28 ± 14%) than coastal waters (mean 12 ± 6%). The greater variability of BGE in the estuaries than coastal waters suggest some systematic response to nutrient composition and the variability of dissolved organic matter pools, as BGE was governed by bacterial secondary production (BP). Monsoonal rains and its accompanied changes brought significant variability in BGE and bacterial productivity to primary productivity (BP/PP) ratio when compared to non-monsoon seasons in the estuaries and coastal waters. High BP/PP ratio (> 1) together with high carbon flux through bacteria (> 100% of primary productivity) in the estuarine and coastal waters suggests that bacterioplankton consumed dissolved organic carbon in excess of the amount produced in situ by phytoplankton of this region, which led to the mismatch between primary production of carbon and amount of carbon consumed by bacteria. Despite the two systems being subsidized by allochthonous inputs, the low BGE in the coastal waters may be due to the nature and time interval in the supply of allochthonous carbon.

Incorporation and mineralization of TNT and other anthropogenic organics by natural microbial assemblages from a small, tropical estuary

“…4). Though this is not unexpected for tropical estuaries (Pradeep Ram et al, 2003, it does suggest that bacterial production may be responsible for DOC removal observed at lower salinity (5 PSU).…”

“…It may not be possible to directly compare results of the mixed treatment to rates from those of similar salinity in the field because the residence time of the water mass at a particular salinity is not known and there is evidence (above) that these results are time dependent. However, it does appear that mixing the water masses of estuarine end members does have an effect on rates of bacterial metabolism or may be even bacterial growth efficiency on these substrates (Pradeep Ram et al, 2007).…”

Viral-Induced Mortality of Prokaryotes in a Tropical Monsoonal Estuary

“…Radioactivity was measured using a liquid scintillation counter (Beckman Coulter, LS 6500, USA). BP, calculated in moles of TdR incorporated into DNA, was converted into the number of bacterial cells produced by applying a conversion factor of 1.96 × 10 18 cells mol −1 (Pradeep Ram et al, 2007) and to carbon using a factor of 2 × 10 −14 gC cell −1 (Bell, 1993). …”

Influence of incubation conditions on bacterial production estimates in an estuarine system

“…Since bacteria play a crucial role in the organic matter transformation in aquatic systems (Valencia et al 2003;Ghiglione et al 2007;Ram et al 2007), inaccurate determinations of bacterial production (BP) have implications on budget estimations (Buesing and Marxsen 2005). The incorporation of radiolabeled substrates under laboratory dark condition is the methodology typically used to determine bacterial production in aquatic ecosystems.…”

“…Heterotrophic bacterioplankton plays a vital function in the dissolved organic matter incorporation (''microbial loop'') and in the mineralization of organic carbon and nutrients; thus, they are essential players in the organic matter processing in aquatic ecosystems (Valencia et al 2003;Ghiglione et al 2007;Ram et al 2007). True estimates of the contribution of the microbial loop to the aquatic carbon cycle can only be achieved upon an accurate estimation of the fraction of organic matter incorporated, assimilated and respired by heterotrophic bacterioplankton (Morán et al 2001).…”