Growth of Arthrobacter Sp. ATCC 31012 on fatty acid substrates produces a new class of extracellular microbial protein-associated lipopolysaccharides (the ".alpha.-emulsans"). Deproteinization of .alpha.-emulsans by hot phenol extraction produces the lipopolysaccharide components (the "apo-.alpha.-emulsans") of such emulsans, which components have been shown to be completely N-acylated and partially O-acylated heteropolysaccharides made up of major amounts of D-galactosamine and an aminouronic acid, such apo-.alpha.-emulsans containing at least 5 percent by weight of O-substituted fatty acid esters in which the fatty acids contain from about 10 to about 18 carbon atoms. .alpha.-Emulsans and apo-.alpha.-emulsans, both of which biopolymers are strongly anionic, exhibit a high degree of specificity in the emulsification of hydrocarbon substrates which contain both aliphatic and cyclic components. In addition, these extracellular microbial polysaccharides as well as their O-deacylated and N-deacylated derivatives are adsorbed on and capable of flocculating aluminosilicate ion-exchangers, such as kaolin and bentonite.