Characterization of a Recombinant Laccase B from Trametes hirsuta MX2 and Its Application for Decolorization of Dyes.

Trametes hirsuta is able to secrete laccase isoenzymes including constitutive and inducible forms, and has potential application for bioremediation of environmental pollutants. Here, an inducible group B laccase from T. hirsuta MX2 was heterologously expressed in Pichia pastoris, and its yield reached 2.59 U/mL after 5 days of methanol inducing culture. The optimal pH and temperature of recombinant laccase (rLac1) to 2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) were 2.5 and 60 °C, respectively. Metal ions showed different effect on rLac1 which Mg2+, Cu2+, and K+ increased enzyme activity as their concentration increased, whereas Zn2+, Na+, and Fe2+ inhibited enzyme activity as their concentration increased. rLac1 showed good tolerance to organic solvents, and more than 42% of its initial activity remained in 10% organic solvents. Additionally, rLac1 exhibited a more efficient decolorization ability for remazol brilliant blue R (RBBR) than for acid red 1 (AR1), crystal violet (CV), and neutral red (NR). Molecular docking results showed RBBR has a stronger binding affinity with laccase than other dyes by interacting with substrate binding cavity of enzyme. The results indicated rLac1 may be a potential candidate for dye removal from textile wastewater.

The complete mitochondrial genome of Reticulitermes ovatilabrum (Isoptera: Rhinotermitidae).

The mitochondrial genome of the Reticulitermes ovatilabrum is 15,913 bp in length and encodes 37 genes including 13 protein-coding genes (PCGs), 22 transfer RNA genes (tRNA), 2 ribosomal RNA genes (rRNA), and a non-coding control region (D-loop). The percentage of A/T (65.59%) is much higher than that of C/G (34.41%). The phylogenetic tree revealed that R. ovatilabrum was closest to R. kanmonensi and R. periflaviceps. The mitochondrial genome of the R. ovatilabrum provides a resource for evolutional analysis within termites especially Reticulitermes.

Purification, characterization, and gene cloning of two laccase isoenzymes (Lac1 and Lac2) from Trametes hirsuta MX2 and their potential in dye decolorization.

In this study, two laccase isoenzymes (Lac1 and Lac2) from the culture supernatant of Trametes hirsuta MX2 were purified, and the genes (Lac1 and Lac2) coding the isoenzymes were cloned. Both Lac1 and Lac2 contained an open reading frame of 1563 bp with an identity of 79%. The two isoenzymes showed significant biochemical differences. The maximal activities of Lac1 and Lac2 were at pH 2.5 with 2-2'-azino-di-(3-ethylbenzthiazoline sulfonic acid) (ABTS), and the optimal temperatures for the activities of Lac1 and Lac2 were 60 and 50 °C, respectively. Lac1 exhibited excellent resistance to acidic conditions and retained 62.17% of its initial activity at pH 2.5 after a 72-h incubation. Lac2 was more thermostable than Lac1 with half-lives (t1/2) of 9.58 and 3.12 h at 50 and 60 °C, respectively; the t1/2 of Lac1 were only 4.19 and 0.88 h, respectively. Both Lac1 and Lac2 isoenzymes have a strong tolerance to Mg2+, Mn2+, Cu2+, and EDTA (50 mM). At a low concentration of 0.05 U mL-1, the enzymes could decolorize towards Remazol Brilliant Blue R, Acid Red 1, Crystal Violet, and Neutral Red in the presence of ABTS. These unusual properties demonstrated that the two laccases have strong potential for specific industrial applications.

Sodium Fluoride for Protection of Wood Against Field Populations of Subterranean Termites.

Sodium fluoride (NaF) is a wood preservative with fungicidal activity and antifeedant activity against termites. In this study, wood blocks of Pinus massoniana were treated with a 0.5% (wt/wt) aqueous solution of NaF, and placed in soil contact under field conditions to evaluate leachability of NaF and resistance to Reticulitermes flaviceps (Oshima). Fluoride leachate levels in soil from wood-soil locations were also determined. After 12-mo outdoor exposure, 91.54% of fluoride was leached from NaF-treated wood and fluoride retention of the wood was 154.28 µg/g wood. In NaF-treated wood-soil locations, soil fluoride residues were significantly higher than locations with the water-treated negative control. Termite activity (presence or occupation) on NaF-treated blocks was 6.25% which was significantly less than 40.00% activity on water-treated control blocks. The mass lost from the wood of NaF-treated blocks was 17.46% which was significantly less than the 45.21% loss from the water-treated blocks. The results show that fluoride is readily leachable from treated wood into surrounding soil. NaF treatment can reduce termite damage to wood under field conditions, and this compound should receive further consideration as a wood preservative to protect timber from termite damage.