>4 - 5 µm
||Protozoa Cyclidium spp.
||Young KD. The selective value of bacterial shape. Microbiol Mol Biol Rev. 2006 Sep70(3):660-703 DOI: 10.1128/MMBR.00001-06 p.685 right column 2nd paragraphPubMed ID16959965
|| Shikano S, Luckinbill LS, Kurihara Y. Changes of traits in a bacterial population associated with protozoal predation. Microb Ecol. 1990 Dec20(1):75-84. doi: 10.1007/BF02543868PubMed ID24193965
||Primary source abstract: "In an attempt to understand the significance of predation in the evolution of prey species, the ecological and morphological characteristics of bacterial species under predation by a ciliated protozoa, Cyclidium sp., were investigated. Serial transfer at 7 day intervals was applied to the bacterial populations in the presence or absence of Cyclidium."
||P.685 right column 2nd paragraph: "Ciliated protozoa of the genus Cyclidium have difficulty feeding on bacterial cells longer than 4 to 5 μm (primary source), so when these protozoa are fed a 1.5-μm-long gram-negative rod, 7% of the surviving bacterial population is 12 to 20 μm long (primary source). Interestingly, these filaments lack septa, as though cell division is inhibited temporarily, and when Cyclidium is removed the elongated cells are replaced by cells of normal length (primary source)."