FAME analysis

Fatty Acid Methyl Esters (FAME) analysis is one of the traditional methods used for phenotypic classification of bradyrhizobia which have now been replaced by advanced genotypic analyses including 16S, ITS, multilocus sequence analysis (MLSA) and whole genome analysis. This process hydrolyzes fatty acids from phospholipids, triacylglycerols, sterols, and various other lipid structures of a bacterial cell. The fatty acids are converted to FAMEs by adding a methyl group to the fatty acids. Fatty acid profiles for a population of bacteria are then determined using gas chromatography (GC). The retention times for FAMEs are compared to retention times of individual purified standards or secondary standards (well characterized in literature) for identification. Bacteria can be divided into different FAME groups by analyzing the cellular fatty acid profiles.

FAME analysis for University of Delaware Bradyrhizobia Culture Collection
FAME analysis was carried out for all 382 accessions (370 isolates and 12 USDA strains) from UDBCC. In the gas chromatograph for each accession, the percentage contribution of individual fatty acids to the total peak area for a sample was used for cluster analysis performed by the unweighted pair group method with arithmetic averages (UPGMA), and a dendrogram was built to display relationships between the groups (figure 1). The 382 accessions were divided into 11 FAME groups that could be clustered into three categories: A, B, and C. These categories correspond to B. japonicum, B. diazoefficiens, and B. elkanii respectively. Average percentages of different fatty acids in accessions from each species are also summarized for reference (Table 1).