A comparison of the ecology of planktonic bacteria in fresh and salt water

Abstract

The planktonic bacteria inhabiting fresh and salt waters are not physiologically identical; most marine bacteria, for example, require sodium and some marine forms can thrive at 1,000 atm of pressure in the deep sea. Despite this difference, the conclusion of this review is that the ecology of planktonic bacteria is virtually identical in fresh and salt waters.The differences are small and mostly a matter of relative proportion of various processes. That is, similar bacterial processes occur in fresh and salt waters but in each environment, one process may be more important than another. For example, bacteria in freshwaters are exposed to high amounts of refractory dissolved organic carbon from soil and stream runoff, while many marine bacteria are exposed to relatively more of the labile organic matter from decaying algae. Also, under anaerobic conditions the sulfur cycle will be dominant in the sea while the carbon-methane cycle will be more important in freshwaters. In spite of the presence of relatively high amounts of methane in the sea, there is thus far little evidence that ,a significant amount of methane is being oxidized.Not enough is yet known to determine if there are dilfcrences in the grazing of bacteria in the two systems. Small, flagellated protozoans are very important grazers in freshwater and marine systems but there is some evidence from salt waters that ciliates are also important grazers. Marine ecosystems also contain large animals that can filter out bacteria. Sponges are the dominant suspension feeders on coral reefs, mussels and oysters are dominant in estuarine and marsh systems, and a large appendicularian may filter significant amounts of bacteria through a mucous net. Ecological understanding of the aquatic bacteria has advanced rapidly in the past two decades. One reason is the basic similarity between microbial ecology in fresh and salt waters and the consequent interchangeability of techniques.

Selective consumption and metabolic allocation of terrestrial and algal carbon determine allochthony in lake bacteria

“…Our results are also consistent with a recent hypothesis, suggesting that the rapid transfer and efficient incorporation of compounds exported from soils and leaf litter, or produced via photochemical degradation, may account for a large share of total bacterial production in boreal streams and lakes (up to 80%) (Berggren et al, 2010a, b). These past studies, together with the observations presented here, are in stark contrast with the common assumption that terrestrially derived C is of poor nutritional quality or not particularly suited to support bacterial growth (Hobbie, 1988). The relative constancy (76 ± 6%, Figure 1) of the terrestrial signature in bacterial biomass across lakes is also remarkable given the range in lake productivity (Table 1), and in the proportion of terrestrial C consumed along this gradient (42-71%).…”

“…A widespread view in aquatic ecology and carbon (C) biogeochemistry is that bacterial communities exposed to a mix of algal and terrestrial compounds should develop a strategy of resource utilization whereby algal C is preferentially consumed and incorporated into biomass over terrestrial C owing to its greater accessibility and nutritional quality (Hobbie, 1988;Bianchi, 2011;Guillemette et al, 2013). However, the preferential consumption of algal C and its subsequent allocation to growth rather than to respiration remain to be empirically tested, as past studies have never simultaneously quantified the sources of DOC that support these different metabolic pathways.…”

Prokaryotic community structure and heterotrophic production in a river-influenced coastal arctic ecosystem

“…They are often the dominant fraction in freshwater lakes, whereas they are nearly absent in the marine environment (Methé et al 1998) and have been considered as a tracer of terrigenous inputs in coastal studies (Hobbie 1988). Clone library analysis of β-Proteobacteria in a temperate latitude estuary showed that they were identical to clones from groundwater, freshwater sediments and soils (Crump et al 2004).…”

Bacteria and phytoplankton production rates in eight river stretches of the middle Rio Doce hidrographic basin (southeast Brazil)

“…Studies of BSP, together with PPP in lotic ecosystems, and of the factors that affect these processes are very scarce (Hobbie, 1988;Currie, 1990;di Sierve et al, 1995), especially in Brazil. For example, the importance of rains in determining seasonality in tropical aquatic ecosystems is well known (Norris and Thoms 1999), but the effects of this functioning force upon BSP and PPP in tropical rivers are poorly understood.…”