Identification of secreted proteins during the growth cycle of Nocardia asteroides strain GUH-2

The nocardiae are Gram positive bacteria that are ubiquitous in soil and water worldwide. Many strains of nocardiae are pathogenic to animals including humans. This study was performed to identify secreted proteins of the bacteria which might be virulence factors. Nocardia asteroides has two distinct phases of growth. In logarithmic phase, the bacteria have a filamentous morphology and are significantly more virulent than the later phases of growth. In stationary phase, the N. asteroides fragment into a pleomorphic bacillary form with decreased virulence. Using cultures from two growth stages, which differ in virulence, the filtrate was isolated, concentrated and separated using two-dimensional gel electrophoresis. The secreted proteins of two N. asteroides strains, GUH-2 and ATCC 19247, a viruluent and avirulent strain, were used as an additional comparison of the secreted protein profile and to refine protein selection. Proteins of interest were sequenced using mass spectrophotometry and identified. Many of the proteins identified have known functions in the glycolytic pathway and the tricarboxylic acid cycle. The nocardiae are extremely resistant to cell lysis and literature searches revealed the presence of possible multifunctional or moonlighting proteins. The proteins identified include enolase, fructose bisphosphate aldolase, ATP sulfurylase, electron transfer flavoprotein, tellurium resistance protein, thiosulfate sulfotransferase, and succinyl CoA synthetase.