Image analysis and processing of an imperfect two-dimensional crystal: the surface layer of the archaebacterium Sulfolobus acidocaldarius re-investigated

The surface layer of the archaebacterium Sulfolobus acidocaldarius has been re-investigated exploring various image analysis and image processing strategies. Straightforward correlation averaging correcting for translational disorder only, and lattice unbending in conjunction with filtration in the Fourier domain gave equivalent results. Careful examination of cross-correlation functions as well as multivariate statistical analysis of individual unit cells revealed the existence of interpenetrating domains with intrinsic p3 symmetry but rotated with respect to each other by 60 degrees and separated by twin boundaries. Non-discriminative averaging over twinned crystal patches generates a higher (p6) class of symmetry emphasizing the importance of selective averaging. (22 References)