Polyploidy and polyteny in the gigantic eubacterium Epulopiscium fishelsoni

Abstract

Content and distribution of basic proteins, histones, acidic proteins and DNA, as well as the interaction of basic proteins with DNA, were studied microfluorometrically within nucleoid bodies of the gigantic eubacterium Epulopiscium fishelsoni living in the guts of the algivorous surgeonfish Acanthurus nigrofuscus. The fine structure of the bacterial nucleoid was studied using transmission electron microscopy (TEM). The mean content of basic proteins, histones and acidic proteins per nucleoid was directly proportional both to cell volume and DNA amount, proving that these proteins are integral components of bacterial chromatin. The maximal DNA quantity of ~1012 base pairs nucleoid−1 was found in the largest specimens of 354,000 µm3 volume (150-fold more then in human lymphocyte). Binding of proteins to DNA was strongest in cup-like nucleoids at the end of the bacterial life cycle, and weakest in enlarged and elongated nucleoids in mid-cycle. Contact fluorescent microscopy and TEM revealed a non-homogenous distribution of these proteins within the nucleoids, as well as the presence of giant polytene chromosome(s). We assume that the unusual genetic and morphological peculiarities, particularly increased polyploidy and polyteny, as revealed in E. fishelsoni, are the results of specific adaptations to the chemical conditions in the host's gut.