Use of Iron Powder to Obtain High Yields of Leptothrix Sheaths in Culture

Abstract

Abstract:The Leptothrix species, Fe-oxidizing bacteria, produce an extracellular, microtubular sheath with a complicated organic-inorganic hybrid nature. We have discovered diverse industrial functions for this material, e.g., electrode material for Li-ion batteries, catalyst enhancers, pigments, plant growth promoters, and plant protectants. To consistently obtain material with the qualitative and quantitative stability needed for industrial applications, we focused on developing an optimum culture system for sheath synthesis by the Leptothrix sp. strain OUMS1. Although we have used Fe plates as an Fe source in the liquid silicon-glucose-peptone medium (SGP), the plates do not yield a consistent quality or precise mass, and formation of Fe-encrusted sheath is restricted to a surface of the plates, which limits harvest yield. In this study, to obtain a high yield of sheaths, we cultured OUMS1 in SGP supplemented with Fe powders. The addition of Fe powders to the medium (up to 14.0 g/L) did not adversely influence growth of OUMS1. The final yield of sheaths was about 10-fold greater than in the Fe plate culture. The sheaths also maintained a microtubular form and crystalline texture similar to those produced on Fe plates

Perspectives on the Biogenesis of Iron Oxide Complexes Produced by Leptothrix, an Iron-oxidizing Bacterium and Promising Industrial Applications for their Functions

“…In SEM images the outer surface layer of the microtubules is covered with tightly or loosely woven fibrils, while the inner surface has a globular appearance (Figure 1b). The thickness of both layers is largely affected by nutrient status [2]: both are relatively thin in nutrient-poor groundwater but very thick in a nutrient-rich culture medium [19,20].…”

“…To date, many researchers have cultured several isolated strains of Leptothrix in media with varied Fe sources such as ferric compounds (FeCl 2 , Fe-ammonium citrate, or FeSO 4 ), FeCl 3 , and Fe plates or powder [6,20,49,54] toward understanding the mechanism of Fe oxidization and deposition on sheaths. Emerson et al [13] emphasized that abiotic Fe oxidation in fully oxygenated water at circumneutral pH is very rapid (half-life <1 min) and that the instantaneous precipitation of Fe oxyhydroxides that resulted from Fe oxidation could potentially entomb a cell in a metal oxide cluster.…”

Abiotic Deposition of Fe Complexes onto Leptothrix Sheaths

“…Multiple researchers have cultured isolated strains of Leptothrix in media with various Fe sources such as FeCl 2 , FeSO 4 , ferric ammonium citrate, FeCl 3 , Fe plate, and Fe powder [ 17 , 18 , 19 , 20 , 21 ] for understanding the mechanism of the Fe oxidation and deposition on sheaths. Since abiotic Fe oxidation in fully oxygenated water at circumneutral pH is very rapid (half-life < 1 min), this instantaneous precipitation of Fe oxyhydroxides could potentially encase a cell in a metal oxide cluster [ 14 , 22 ].…”

Direct Adherence of Fe(III) Particles onto Sheaths of Leptothrix sp. Strain OUMS1 in Culture

“…Suzuki et al [31] reported that yellowish brown sheaths with attached Fe particles formed when OUMS1 cells were cultured in SGP + Fe, while those cultured in SGP lacking an Fe source remained whitish, suggesting that in SGP + Fe, metal iron, Fe(0), could be oxidized to Fe(III), which was deposited onto the sheaths. In this study, the uninoculated SGP + Fe medium looked clear immediately after preparation but became turbid within 5 h ( Figure 1A).…”

“…Single colonies were transferred to 25 mL of SGP broth in 50 mL conical tubes and incubated on a rotary shaker (EYELA FMC-1000, Tokyo Rikakikai, Tokyo, Japan) at 20˝C and 70 rpm. After two to three days, 1-5 mL of the cell suspension (adjusted to 10 cfu/mL by densitometry (Nanodrop 2000C, Thermo Fisher Scientific, Waltham, MA, USA)) was transferred to 100-500 mL of SGP or SGP broth containing 14 g/L Fe(0) powder (~150 µm diameter) (Wako Pure Chemical, Osaka, Japan) (hereafter referred to as SGP + Fe) in glass flasks [31], then incubated for 2-14 days.…”