We carry out a lot of 16S sequencing - almost daily - with customer prepared samples. If you generate barcoded amplicons yourself, we will be happy to add Illumina adapters (required by some protocols) and sequence them on our AVITI sequencer.
We don't generate 16S libraries in-house, because UC Davis has a facility specializing in 16S analysis: The Host Microbe Biology Systems Core (HSMBC). The HSMBC offers a complete service ranging from DNA isolation, 16S amplification, sequencing (performed in the DNA Tech Core), to data analysis. You can certainly also choose select parts of their services according to your needs. Please contact the HSMBC manager for details.