Growth characterization of non-photosynthetic diatoms, <i>Nitzschia</i> spp., inhabiting estuarine mangrove forests of Ishigaki Island, Japan

Abstract

Abstract:The non-photosynthetic diatoms Nitzschia spp. are known to have evolved from photosynthetic species to heterotrophic species by the loss of photosynthesis. We investigated their ability to tolerate wide ranges of temperatures and salinities. Nitzschia spp. were capable of surviving or thriving even at 5°C and 35°C. In addition, these diatoms were also capable of surviving at salinities of 0.5 and 12.0, while thriving at those from 1.0 to 9.0. Such tolerance to a wide range of temperatures and salinities would allow these non-photosynthetic diatoms to thrive in mangrove estuaries, where environmental conditions often drastically fluctuate. Our experiments revealed that the growth rates of the non-photosynthetic diatoms were larger than those estimated based on cell volumes and temperature, suggesting that these non-photosynthetic diatoms may be an important group of organisms contributing to material circulation by growing heterotrophically in mangrove estuaries.

The genome of a nonphotosynthetic diatom provides insights into the metabolic shift to heterotrophy and constraints on the loss of photosynthesis

“…Nonphotosynthetic Nitzschia are strictly marine and found on coastlines, and they are especially common in mangrove habitats (Ishii & Kamikawa, 2017 ; Onyshchenko et al ., 2019 ). Vascular plants, including mangroves, are a major source of dissolved organic carbon (DOC) in coastal ocean ecosystems (Moran et al ., 1991b ; Moran & Hodson, 1994b ; Hedges et al ., 1997 ).…”

Genome evolution of a nonparasitic secondary heterotroph, the diatomNitzschia putrida

“…The CAZyme compositions suggest that N. putrida might be able to degrade extracellular polysaccharides such as ß-1,3 glucans (e.g., lichenin, paramylon, callose, and laminarin), starches, β-1,2-glucans, pectin, and α-mannan. As N. putrida has been isolated from disintegrating mangrove leaves in a paddle ( 5 , 42 ), this species might play a role in degrading dead leaves and therefore facilitating carbon recycling in mangroves. To gain first insight into how transcription of CAZyme genes is regulated by different carbon sources, we performed comparative transcriptome analyses with starved N. putrida cells in comparison to cells growing on glucose and starch.…”

“…S12B). LRR-containing proteins and VWFDs might play important roles in N. putrida for attaching to disintegrating mangrove leaves ( 5 , 42 , 45 ). Endopeptidases and aromatic compound degradation may facilitate the utilization of their complex carbon compounds.…”

“…The latter requires uptake of dissolved organic compounds by osmosis as realized by bacteria and fungi, for instance ( 40 , 41 ). As N. putrida grows well under axenic conditions ( 5 , 42 ), it is likely an osmotroph, dependent on the uptake of dissolved organic compounds across the silicified cell wall and the plasma membrane. As realized by osmotrophic fungi, N. putrida may even be able to degrade higher–molecular weight compounds extracellularly to be subsequently taken up as individual molecules by specific transporters or even osmosis ( 40 , 41 ).…”

Genome evolution of a non-parasitic secondary heterotroph, the diatomNitzschia putrida

“…A microbial heterotroph either acquires nutrients by phagotrophy, the preferred nutrition of many parasites, or by osmotrophy, which is the uptake of dissolved organic compounds by osmosis as realised by bacteria and fungi, for instance (Richards and Talbot 2013; Richards and Talbot 2018). As N. putrida grows well under axenic conditions (Kamikawa et al 2015;Ishii & Kamikawa 2017), it is likely an osmotroph, dependent on the uptake of dissolved organic compounds across the silicified cell wall and the plasma membrane. As realised by osmotrophic fungi, N. putrida may even be able to degrade higher molecular weight compounds extracellularly to be subsequently taken up as individual molecules by specific transporters or even osmosis (Richards and Talbot 2013; Richards and Talbot 2018).…”