Mass spectrometry enumeration of filamentous M13 bacteriophage

In the last decade, filamentous M13 bacteriophage has emerged into numerous biotechnological applications as a promising nontoxic and self-assembling biomaterial with specific binding properties. This raises a question about its upscale production that consequently requires an accurate phage enumeration during the various protocol developments. However, traditional methods of measuring phage concentration are mainly biological in nature and therefore time and labor intensive. These traditional methods also demonstrate poor reproducibility and are semi-quantitative at best. In the present work, we capitalized on mass spectrometry based absolute protein quantitation. We have optimized the quantitation conditions for a major coat protein, pVIII. Enumeration of M13 bacteriophage can be further performed using the determined molar concentration of pVIII, Avogadro's number, and known copy number of pVIII per phage. Since many different phages have well-defined copy number of capsid proteins, the proposed approach can be simply applied to any phage with known copy number of a specific capsid protein.