Remarkably low temperature optima for extracellular enzyme activity from Arctic bacteria and sea ice

Abstract

Extracellular degradative enzymes released by psychrophilic marine bacteria (growing optimally at or below 15 degrees C and maximally at 20 degrees C) typically express activity optima at temperatures well above the upper growth limit of the producing strain. In the present study, we investigated whether or not near-zero Arctic environments contain extracellular enzymes with activity optimized to temperatures lower than previously reported. By applying fluorescently tagged substrate analogues to measure leucine-aminopeptidase and chitobiase activity, the occurrence of extracellular enzymatic activity (EEA) with remarkably low temperature optima (15 degrees C) was documented in sea-ice samples. An extremely psychrophilic bacterial isolate, strain 34H, yielded an extract of cell-free protease with activity optimized at 20 degrees C, the lowest optimum yet reported for cell-free EEA from a pure culture. The use of zymogram gels revealed the presence of three proteolytic bands (between 37 and 45 kDa) in the extract and the release of the greatest quantities of the proteases when the strain was grown at -1 degrees C, suggesting a bacterial strategy for counteracting the effects of very cold temperatures on the catalytic efficiency of released enzymes. The detection of unusually cold-adapted EEA in environmental samples has ramifications not only to polar ecosystems and carbon cycling but also to protein evolution, biotechnology and bioremediation.

Structure of Phenylalanine Hydroxylase from Colwellia psychrerythraea 34H, a Monomeric Cold Active Enzyme with Local Flexibility around the Active Site and High Overall Stability

“…Dielectric constants of 4.0 and 78.5 were used for the protein and the aqueous solvent, respectively. In this study, we calculated the energy of charge-charge interactions of group i with the rest of the ionizable groups in the protein ͗W i ͘, which can be used to estimate the total charge-charge interaction energy in the proteins (͗W q-q ͘), as shown in Equation 1.…”

Persistence of labile organic matter and microbial biomass in Antarctic shelf sediments: evidence of a sediment ‘food bank’

“…saturating) concentrations of substrate, both in polar shelf sediments (Arnosti 1998, Arnosti et al 1998, Fabiano & Danovaro 1998 and in the deep sea (Meyer-Reil & Koster 1992, Boetius & Lochte 1996. Further, the temperature optima of at least some of the enzymes from permanently cold sediments are significantly higher than ambient environmental temperatures, and warming of the sediment greatly increases extracellular enzyme activity (EEA) at sub-saturating concentrations of substrate (Helmke & Weyland 1991, MeyerReil & Koster 1992, Nedwell & Rutter 1994, Huston et al 2000, Arnosti & Jørgensen 2003, Bowman et al 2003. Thus, it appears that extracellular hydrolysis is not inherently limited by low temperature if sufficient (i.e.…”

The psychrophilic lifestyle as revealed by the genome sequence of Colwellia psychrerythraea 34H through genomic and proteomic analyses

“…Colwellia psychrerythraea 34H isolated from Arctic marine sediments (8) represents the type species of the genus Colwellia (3). It grows reliably in heterotrophic media over a temperature range of approximately Ϫ1°C to 10°C, with cardinal growth temperatures (optimum of 8°C, maximum of 19°C, and extrapolated minimum of Ϫ14.5°C) (5) ranking among the lowest for all characterized bacteria (2).…”