Characterizing the surface-exposed proteome of Planococcus halocryophilus during cryophilic growth

Abstract

Planococcus halocryophilus OR1 is a bacterial isolate capable of growth at temperatures ranging from -15 to +37 °C. During sub-zero (cryophilic) growth, nodular features appear on its cell surface; however, the biochemical compositions of these features as well as any cold-adaptive benefits they may offer are not understood. This study aimed to identify differences in the cell surface proteome (surfaceome) of P. halocryophilus cells grown under optimal (24 °C, no added salt), low- and mid-salt (5 and 12 % NaCl, respectively) at 24 °C, and low- and mid-salt sub-zero (5 % NaCl at -5 °C and 12 % NaCl at -10 °C) culture conditions, for the purpose of gaining insight into cold-adapted proteomic traits at the cell surface. Mid-log cells were harvested, treated briefly with trypsin and the resultant peptides were purified followed by identification by LC-MS/MS analysis. One hundred and forty-four proteins were subsequently identified in at least one culture condition. Statistically significant differences in amino acid usage, a known indicator of cold adaptation, were identified through in silico analysis. Two proteins with roles in peptidoglycan (PG) metabolism, an N-acetyl-L-alanine amidase and a multimodular transpeptidase-transglycosylase, were detected, though each was only detected under optimal conditions, indicating that high-salt and high-cold stress each affect PG metabolism. Two iron transport-binding proteins, associated with two different iron transport strategies, were identified, indicating that P. halocryophilus uses a different iron acquisition strategy at very low temperatures. Here we present the first set of data that describes bacterial adaptations at the cellular surface that occur as a cryophilic bacterium is transitioned from optimal to near-inhibitory sub-zero culture conditions.

Mechanisms of subzero growth in the cryophile Planococcus halocryophilus determined through proteomic analysis

“…However, it is possible that in this case the amidases may function in enabling the significant remodelling of the peptidoglycan as shown previously by Mykutczuk et al (Mykytczuk et al, 2013;2015) leading, in combination with increased synthesis, to formation of the crust. These findings are somewhat contradictory to those from the surfaceomics study (proteomic analysis of the cell surface) of P. halocryophilus, which did not find a transpeptidase/transglycosylase or N-acetylmuramoyl-L-alanine amidases at subzero temperatures, but this may be due to the more limited number of proteins identified at 2108C in this published study (Ronholm et al, 2015).…”

“…These findings are somewhat contradictory to those from the surfaceomics study (proteomic analysis of the cell surface) of P . halocryophilus , which did not find a transpeptidase/transglycosylase or N‐acetylmuramoyl‐L‐alanine amidases at subzero temperatures, but this may be due to the more limited number of proteins identified at −10°C in this published study (Ronholm et al ., ).…”

“…The same cysteine and ferric iron ABC transporter proteins (gi|495772257| & gi|495773646|) were previously detected at the surface of P . halocryophilus in both cold and salt conditions (Ronholm et al ., ). While the earlier transcriptome study of P .…”

“…discovered unusual cell envelope modifications during subzero growth, leading to production of a crust like envelope composed of peptidoglycan (+ protein), choline and CaCO 3 (Mykytczuk et al ., ). A study looking at the exposed surface proteins in Planococcus halocryophilus at −5°C and −10°°C found differences in the composition of membrane, peptidoglycan and transport proteins present at the surface (Ronholm et al ., ). Interestingly, the composition of fatty acids in P .…”

“…In addition, Mykytczuk et al discovered unusual cell envelope modifications during subzero growth, leading to production of a crust like envelope composed of peptidoglycan (1 protein), choline and CaCO 3 (Mykytczuk et al, 2015). A study looking at the exposed surface proteins in Planococcus halocryophilus at 258C and 21088C found differences in the composition of membrane, peptidoglycan and transport proteins present at the surface (Ronholm et al, 2015). Interestingly, the composition of fatty acids in P. halocryophilus at lower temperatures was found to favour a higher ratio of saturated to branched fatty acids (Mykytczuk et al, 2013), contrary to what is observed in many cold adapted organisms.…”