Control of chitin nanofiber production by the lipid‐producing diatom Cyclotella Sp. through fed‐batch addition of dissolved silicon and nitrate in a bubble‐column photobioreactor

Abstract

Diatoms are single-celled algae that make cell walls of nanopatterned biogenic silica called frustules through metabolic uptake of dissolved silicon and its templated condensation into biosilica. The centric marine diatom Cyclotella sp. also produces intracellular lipids and the valued coproduct chitin, an N-acetyl glucosamine biopolymer that is extruded from selected frustule pores as pure nanofibers. The goal of this study was to develop a nutrient feeding strategy to control the production of chitin nanofibers from Cyclotella with the coproduction of biofuel lipids. A two-stage phototrophic cultivation process was developed where Stage I set the cell suspension to a silicon-starved state under batch operation, and Stage II continuously added silicon and nitrate to the silicon-starved cells to enable one more cell doubling to 4 × 10 cells mL . The silicon delivery rate was set to enable a silicon-limited cell division rate under cumulative delivery of 0.8 mM Si and 1.2 mM nitrate (1.5:1 mol N/mol Si) over a 4- to 14-day addition period. In Stage II, both cell number and chitin production were linear with time. Cell number and the specific chitin production rate increased linearly with increasing silicon delivery rate to achieve cumulative product yields of 13 ± 1 mg chitin/10 cells and 33 ± 3 mg lipid/10 cells. Therefore, chitin production is controlled through cell division, which is externally controlled through silicon delivery. Lipid production was not linearly correlated to silicon delivery and occurred primarily during Stage I, just after the complete co-consumption of both dissolved silicon and nitrate. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:407-415, 2017.

The dynamic response to hypo‐osmotic stress reveals distinct stages of freshwater acclimation by a euryhaline diatom

“…Increased chitin production could strengthen the cell wall in response to increased intracellular turgor pressure. Extracellular chitin threads also promote increased buoyancy in the water column (Chiriboga & Rorrer, 2017; Morin et al, 1986). This might help diatoms optimize environmental light and temperature conditions (Boyd & Gradmann, 2002; Falciatore et al, 2000; Falciatore & Bowler, 2002), so one hypothesis is that diatoms also regulate buoyancy in response to salinity stress.…”

Multiple Routes to Smart Nanostructured Materials from Diatom Microalgae: A Chemical Perspective

“…Another very interesting example of the application of diatoms cells as living biofactories was provided in 2017 by Chirinboga and Rorrer . The two algal species Cyclotella and Thalassiosira have the specific ability of producing chitin, the N‐acetyl glucosamine biopolymer with biomedical properties, which is extruded from the diatom cell as rigid microfibrils with a diameter of 50 nm and high purity in the β‐crystalline form.…”

“…Chitin fibers are shown emanating from pores lining frustule valve rim. Reproduced with permission . Copyright 2017, Wiley‐VCH.…”

In Vivo Biosynthesis of Inorganic Nanomaterials Using Eukaryotes—A Review

“…The cell surface chemistry plays a vital role in NP production since the cell surface adsorption-reduction of metal cations contributes more to NP synthesis than intracellular NP formation following the metal uptake [ 12 ]. Many studies have reported the cell surface involvement in the production of NPs, as presented in Table 1 [ 72 , 73 , 74 , 75 , 76 , 77 ]. The negatively charged surface groups of the cells, such as hydroxyl, carboxyl, and phosphate, have an affinity for metal cations [ 78 , 79 ].…”