So I have 454 sequences from several samples which I would like to compare. No separate 16S data was generated. What would be the best way for OTU diversity analysis? I do have MG-RAST results for these data, including GreenGenes/RDP/Silva. My concern is that the number of OTUs identified this way is rather small. And yes, I did denoise the data.
Clarification, prompted by Casey's response: yes, i only have shotgun 454. I used MG-RAST, but very few 16S reads (300-800 / sample) hit the 16S database (GreenGenes). Thresholded with a minimum length of 100, 97% ID