A Culture Based Study of Non-Fungal Heterotrophic Microbial Eukaryotes from Hawaiian Marine Sediments

Abstract

Non-fungal heterotrophic eukaryotic microorganisms have been cultured from marine sediment samples from Kāneʻohe Bay, Oahu, Hawaiʻi, USA between 2011 and 2014. Of these, several are new to science and represent novel lineages within their respected classes. Phylogenetically and ultrastructurally novel eukaryotes belonging to the Labyrinthulomycetes, Oomycota, Dermocystida (of the class mesomycetozoea), and likely the Bacillariophyceae (diatoms) were among those cultured. Several cultured organisms appear to represent basal members of genera and even classes. Of ten Labyrinthulomycetes cultured, Oblongichytrium sp. KB9/16, and novel Thraustochytriidae spp. KB8, NK55, and NK58 were investigated in terms of cellular ultrastructure, fatty acid production, and carotenoid pigment production. Also from the stramenopile clade, novel oomycete sp. NK401 was studied in the same manner. The polyunsaturated fatty acid profiles and growth characteristics of these organisms indicates they are unlikely candidates for commercial PUFA production. Carotenoid pigment production was variable and uncertain in some instances. The phylogenetic relationships of the Labyrinthulomycetes were extensively analyzed by maximum-likelihood inference and a most likely phylogeny for the class has been established. On the opposite side of the phylogenetic tree of eukaryotic life, an isolate of Corallochytrium limacisporum and a novel member of the order Dermocystida, sp. NK52, were cultured and studied. These organisms are among the closest unicellular relatives of the Metazoa. Other members of the order Dermocystida are important pathogens of humans and animals, and have only been cultivated by infecting cell cultures. It is hoped that NK52 will provide researchers with material for the by-proxy study of the human and animal pathogens that comprise the rest of the order and in the study of the origins of multi-cellular animals. The diatom that NK52 was co-isolated with also appears to be novel based on examination of its frustule morphology. Investigations into the relationship between NK52 and the diatom it was co-isolated with are ongoing, as is the molecular identification of the diatom. Attempted environmental enumeration efforts for Corallochytrium limacisporum and the Labyrinthulomycetes via correlation with cultured organism standards (qPCR) were generally unreliable when applied to sediment samples, and were likely hindered by non-specific binding, amplification of ton-target DNA, and/or other chemical interference. Had the qPCR assay for C. limacisporum withstood scrutiny, it would have indicated an increased presence of C. limacisporum in sediment sampled, compared to estimates from direct plating of sediment samples.