1.  Don Yoder, ed.  1936/45/47/51.  Pennsylvania German Immigrants, 1709-1786: Lists Consolidated from Yearbooks of the Pennsylvania German Folklore Society.  2 vols. (Reprinted 1980/98 Genealogical Publ. Co., Baltimore, MD; Broderbund CD-267).  Under the heading, "Emigrants from Wuerttemberg: The Adolf Gerber Lists," on p. 124:

STRAUB, JOHANN GEORG (1)--Neuffen Wf: ANNA CATHARINA. Ch: (I) Johann Georg, b. 8-5-1749. // JERG STRAUB, Two Brothers, September 21, 1751, Hinke, I, 446.

Gerber's lists were based on records in Württemburg.  The "(1)" means Vol. 1.  Neuffen is the town of origin.  Information after the "//" is supplied by the editor (i.e., it was not Gerber's work).

2.  Israel Daniel Rupp.  1876.  A Collection of upwards of Thirty Thousand Names of German, Swiss, Dutch, French, and Other Immigrants in Pennsylvania from 1727 to 1776... Leary, Stuart, & Co., Philadelphia, PA (reprinted 1965/75 by Genealogical Publ. Co., Baltimore, MD; Broderbund CD-267).

p. 258	Sept. 21, 1751.  Ship Two Brothers, Thomas Arnet, Master, from Rotterdam, last from Cowes.--239 passengers...
p. 259	Georg Straub...

3.  William Henry Egle.  1890.  Names of Foreigners Who Took the Oath of Allegiance to the Province and State of Pennsylvania, 1727-1775, with the Foreign Arrivals, 1786-1808.  Pennsylvania Archives, Vol. XVII, 2nd Ser., Harrisburg, PA (reprinted 1967/94, Genealogical Publ. Co., Baltimore, MD; Broderbund CD-267):

p. 339	List of Foreigners Imported in the Ship Two Brothers, Thomas Arnot, Master, From Rotterdam. Qualified Sept. 21, 1751...
p. 340	Georg Straub...

4.  Ralph Beaver Strassburger.  1934.  Pennsylvania German Pioneers: a Publication of the Original Lists of Arrivals in the Port of Philadelphia, from 1727 to 1808.  Pennsylvania German Society, Norristown, PA (reprinted 1966/92 Genealogical Publ Co., Baltimore, MD; Broderbund CD-267).  Under the heading, "Two Brothers 1751":

p. 465	Present: William Plumsted, Esquire, Mayor. The Foreigners whose Names are underwritten, imported in the Ship Two Brothers, Thomas Arnot, Master, from Rotterdam and last from Cowes, did this day take the Qualifications to the Government. Freights 239. No. 112. Messrs Shoemaker...
p. 466	Jerg Straub...

There appears to be a publisher's error here (i.e., a line missing) because the format of the entries normally includes the list number and date on the first line; however, we know from the sources above that the date was 21 Sep 1751.