Variation of mechanical properties with amino acid content in the silk of Nephila clavipes.

In this paper, we explore the impact of dietary deprivation, where spiders are provided diets missing one or more of the amino acids, on the properties of the spider dragline silk spun after one month on the diet. Cohorts of female N. clavipes spiders were selected for diets deprived of alanine (Ala) and glycine (Gly), arginine (Arg), leucine (Leu), or tyrosine (Tyr), and their silk was harvested twice weekly during the one-month course of the diet. Significant mechanical differences are observed after as little as 6 days on the diet. Utilizing conventional tensile testing methods, single fibers were strained to break so as to study the influence of diet on the stress/strain properties. Diets deprived of Ala and Gly appear to most directly impact the load-bearing foundation of dragline silk. Diets deprived of Arg, Tyr, and possibly Leu reduce the strength of the silk, and diets missing Tyr and Leu reduce the strain-to-failure. Observations obtained from ESEM photos of the fracture interfaces after tensile testing illustrate the fracture mechanics of spider silk. Both solid-state NMR and amino acid analysis of the digested protein suggest, however, that the relationship between diet and amino acid incorporation into the silk fiber is not straightforward.