Cold stress can enhance the virulence of some bacteria. One such bacteria is Vibrio metschnikovii, which is present in a wide range of seafood. However, little research has investigated the molecular response of V. metschnikovii during adaptation and growth under cold temperatures that allow it to thrive and therefore risk food safety. Jia et al.1 (2015) used comparative proteomics to study V. metschnikovii exposed to cold stress. They also apply a novel proteomics approach to microbial study using nano-flow ultra-high-performance liquid chromatography (nLC) coupled to a high-resolution Q Exactive hybrid quadrupole-Orbitrap mass spectrometer (Thermo Scientific).
To begin with, the investigators isolated V. metschnikovii from American lobsters and cultured the bacteria. They then subjected the bacteria to cold stress at 4ºC for two weeks. Two control (37ºC) and two cold-stressed cultures formed the basis of the experiment. The investigators harvested the cultures and separated the resulting peptide solutions using an EASY-nLC 100 liquid chromatograph (Thermo Scientific). Jia et al. then used the Orbitrap analyzer to perform mass spectrometric scans, querying against a database of V. metschnikovii from UniProt containing 3,079 proteins.
Further quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR) analysis identified and quantified 2,066 proteins with an overlap of 1,743 proteins between the control and cold-stressed bacteria. Of these, they found 288 to be upregulated and 572 to be downregulated. In particular, cold-stressed cells had greater amounts of cold shock and ribosomal proteins, and decreased proteins involved in energy conversion and metabolism. Specifically, cold shock proteins, elongation factors, chaperone proteins, ribosomal proteins, outer membrane proteins, and some proteins related to energy conversion and metabolism were the most abundant. Neither the number nor proportion of proteins in various categories differed significantly, with the exception of proteins categorized by Gene Ontology in pigmentation, biological regulation, transcription regulator activity and transporter activity.
The authors compared their study of V. metschnikovii to other studies of bacteria exposed to cold shock and noted their ribosomal proteins increased similarly. They also noted downregulation of proteins related to energy conversion, consistent with studies of other strains. Jia et al. also assert that the fact that proteins involved in translation in V. metschnikovii remained unchanged under normal conditions but highly expressed under cold stress indicates that the bacteria uses protein synthesis to resist cold stress.
The novel application of proteomics to microbiology by Jia et al. identified a number of unique proteins and changing expression levels in V. metschnikovii exposed to cold shock. This may contribute to present and future understandings of food safety.
1. Jia, J., et al. (2015) “Proteomic analysis of Vibrio metschnikovii under cold stress using a quadrupole Orbitrap mass spectrometer,” Research in Microbiology, 166(8) (pp. 618–625).