Summary In order to obtain insights into the evolution of colorless (apochlorotic) diatoms, we investigated newly established apochlorotic strains of Nitzschia spp. using light and electron microscopy and molecular phylogenetic analyses. Fluorescence microscopic observations demonstrated that the apochlorotic diatoms lack chlorophylls. Transmission electron microscopy of two apochlorotic strains also demonstrated that their plastids lacked thylakoids; instead, having four‐membrane‐bound organelles without thylakoids, similar to nonphotosynthetic plastid remnants. From the apochlorotic strains, we also found plastid small subunit rRNA genes that were unusually long branched in phylogenetic analyses, as observed in other nonphotosynthetic plastids. Molecular phylogenetic analysis of the nucleus‐encoded large subunit rRNA genes showed eight distinct lineages for apochlorotic diatoms. The eight apochlorotic lineages were not monophyletic, suggesting that the loss of photosynthesis took place multiple times independently within Nitzschia. Several diatoms, including Nitzschia spp., are mixotrophic, which is an expected mode of nutrition that would help explain the evolutionary switch from a photosynthetic lifestyle to a heterotrophic lifestyle.

Inheritance of spheroid body and plastid in the raphid diatom Epithemia (Bacillariophyta) during sexual reproduction". Phycologia 60 (3). 265-273. Taylor and Francis.

Recently, the use of brackish diatoms has been proposed to remove various inorganic constituents, such as dissolved silica, nutrients, calcium, and bicarbonate, to enhance the freshwater recovery in reverse osmosis (RO). In this study, nine strains of brackish diatoms isolated from water and sediment samples from several evaporation ponds in California and Arizona were examined for their ability to assimilate silica and remove other constituents from RO concentrate. In addition to two previously reported strains, namely Gedaniella flavovirens PEWL001 and Nitzschia communis PEWL002, several new isolates including Halamphora sydowii PEWL004, Nitzschia sp. PEWL008, and Halamphora sp. PEWL011 were found to remove more than 95% of silica, 95% of ammonia and orthophosphate, and more than 50% of calcium and carbonate within 6 days. Two additional G. flavovirens strains (Psetr3 and Psetr7) collected from a brackish lake in Aomori, Japan, also showed rapid dissolved silica uptake (32 mg L−1 day−1) comparable to the one isolated from an agricultural drainage water evaporation pond in the Central Valley, California. This study demonstrated that the brackish diatoms isolated from the evaporation ponds could be useful for the treatment of RO concentrate, which would possibly enable more sustainable desalination processes.