A George Alkmus, co E, 91st PA, died on 4 August 1862, and was buried in plot 301 of the Cypress Hill National Cemetery, Brooklyn, Kings County, New York. [source: 1]
However, no George Alkmus appears on the roster, and the only plausible George listed on the company E death register is George Hollick, who died after the war. No George Alkmus appears in Fold3's index to the index to the compiled service records (searched without any restrictions, 16 January 2015). Perhaps he was not actually from the 91st PA.
1 Cypress Hills National Cemetery, Brooklyn, Kings County, NY, interment records ("Alkmus, George, d. 08/04/1862, PVT CO E 91 PA INF, Plot: 301, *")