Effect of low temperature on microbial growth: lowered affinity for substrates limits growth at low temperature

Abstract

The effect of environmental temperature on the affinity of microorganisms for substrates is discussed in relation to measurements of affinity by either K(s) values or specific affinity (a(A)). It can be shown for psychrophiles, mesophiles and thermophiles that when a(A) is used as the measure of affinity, affinity decreases consistently as temperature drops below the optimum temperature for growth. This effect may be because of stiffening of the lipids of the membrane below the temperature optimum, leading to decreased efficiency of transport proteins embedded in the membrane. The lower temperature limit for growth is, therefore, that temperature at which an organism is no longer able to supply the maintenance requirement of the growth rate-limiting nutrient because of loss of affinity for that substrate. This linking of temperature and affinity for substrates taken up by active transport (a temperature-modulated substrate affinity model) includes uptake of both organic and inorganic substrates. This effect of decreased substrate affinity at low temperature may have profound implications on the availability of substrates in the natural environment as environmental temperatures change. At temperatures below their optimum for growth microorganisms will become increasingly unable to sequester substrates from their environment because of lowered affinity, exacerbating the anyway near-starvation conditions in many natural environments.

Toward a mechanistic understanding of how natural bacterial communities respond to changes in temperature in aquatic ecosystems

“…Although we recognize that the half-saturation constant is most likely not independent of changes in temperature, previous researchers who attempted to find the relationship between K and temperature were unable to illustrate a consistent trend (Tilman et al, 1981;Mechling and Kilham, 1983;Ellis-Evans and Wynn-Williams, 1985). However, because n max in our model is an increasing function of temperature, holding K constant results in a decreasing specific affinity (n max /K) with a decreasing temperature, which is consistent with how bacterial physiology has been shown to respond to temperature (Nedwell, 1999).…”

Dissimilatory reduction of nitrate to ammonium, not denitrification or anammox, dominates benthic nitrate reduction in tropical estuaries

“…These results suggest that DN but not DNRA was simultaneously limited by both electron donor and electron acceptor availability. The low organic C contents of the sediments (Table 2) in all three estuaries tended to indicate low concentrations of electron donors, particularly as the pool of available sedimentary organic matter is usually only a very small proportion of the total benthic organic matter (Nedwell 1987), although benthic oxygen uptake rates were still akin to those reported in more highly organic sediments (see below). Tropical soils and sediments, compared to their temperate equivalents, tend to be characterized by small pool sizes of organic matter and nutrients such as nitrate, which are at low concentrations and turn over rapidly (Holmboe et al 2001).…”

“…It is not known whether nitrate ammonifiers also have a higher affinity for nitrate than denitrifiers, particularly at higher environmental temperatures. Although Jørgensen (1989) m , where V max is the maximum rate of reaction) is much more robust (Nedwell 1999). Although there is no data specifically on tropical isolates, previous work in temperate European estuarine sediments (King and Nedwell 1984;Jørgensen 1989) have shown that nitrate ammonifiers predominate over denitrifiers during higher temperature summer periods, but denitrifiers predominate during autumn and winter.…”

“…An and Gardner (2002) also reported that addition of nitrate increased DNRA more than DN in Baffin Bay and Laguna Madre sediments. The reason for DNRA's predominating over DN in tropical estuaries is important, as it means that nitrogen will be conserved within the tropical estuarine and coastal environment to a greater extent than may be the case in temperate or subtropical estuaries where DN is significant (Nedwell et al 1999). The balance of processes may also affect the extent of formation of other end products such as N 2 O, an important greenhouse gas, which is produced by DN but apparently not by DNRA.…”

“…Such increased loads of nutrients may have a greater effect on biogeochemical cycling in normally low nutrient tropical estuaries and coastal zones than in temperate estuaries. It is now well known that temperate estuaries are major sites of nutrient processing, particularly of N, where denitrification (DN) to either N 2 or N 2 O in bottom sediments may, depending upon estuary retention time (Nixon et al 1996), remove up to half of the nitrate load from catchments before it reaches the coastal seas (Nedwell et al 1999). Alternatively, dissimilatory nitrate reduction to ammonium (DNRA) may occur, particularly where there is high availability of organic electron donors and low nitrate (King and Nedwell 1985), in which case nitrate reduction does not result in N loss as gases from the aquatic system.…”