4.3.2. Gamma-2 characteristics
Gamma-2 are facultative anaerobic, but will not grow in fully aerobic conditions (PE, unpublished data). These bacteria produce smooth, round, flat, semi-transparent colonies of ~1mm diameter in about 3 days (Fig. 4). Cells are rod-shaped and may form filaments or chains. Gamma-2 can obtain carbon through fermentation of glucose, fructose, and mannose. They are positive for catalase and negative for nitrate reductase and oxidase.
The sole strain described for this group is PEB0191, a member of the family Orbaceae and class Gammaproteobacteria. Although in the same family as Gilliamella, its closest relatives are in the Orbus genus. This bacteria is referred to as “Gamma-2” or “Gammaproteobacteria-2” (Babendreier et al., 2007; Martinson et al., 2011; Moran et al., 2012), pending publication of a formal species name. Gamma-2 has been isolated from A. mellifera but has not been detected in bumble bees (Koch and Schmid-Hempel, 2011). The type strain is PEB0191T and can be procured from bacterial culture collections (accession BAA-2450T at ATCC, or 14821T at NCIMB). Gamma-2 is present in most adult workers and has been estimated to comprise up to 13% of the gut bacteria (Moran et al., 2012).