Service files are available through the message board. Use the link above titled, "Military Service Records Research".
Company "G" of Nixon's 48th Tennessee Regiment was taken from Company "B", 54th Tennessee Regiment.
You may also wish to check J. D. Belew of Co. "D", Biffle's 19th Tennessee Cavalry. It may be that Jonathan served in two different commands. Each of the companies mentioned (including the one in Biffle's Cavalry) were recruited in Lawrence County TN.