FIG. 5.

H. volcanii Ca²⁺-induced aggregation in a defined medium. Adding 10 mM Ca²⁺ induced aggregation of H. volcanii (H98) in mid-log phase cultures. While the majority of cells aggregated within 20 min after Ca²⁺ addition in defined medium (CA), aggregation was not apparent when Mg²⁺ was added to the cultures or in complex medium (CX). No aggregation was observed when Ca²⁺ was added to medium lacking H. volcanii (*Ca²⁺).