Mohammad Mozammel Hoq

Genomic diversity of 2010 Haitian cholera outbreak strains

The millions of deaths from cholera during the past 200 y, coupled with the morbidity and mortality of cholera in Haiti since October 2010, are grim reminders that Vibrio cholerae, the etiologic agent of cholera, remains a scourge. We report the isolation of both V. cholerae O1 and non-O1/O139 early in the Haiti cholera epidemic from samples collected from victims in 18 towns across eight Arrondissements of Haiti. The results showed two distinct populations of V. cholerae coexisted in Haiti early in the epidemic. As non-O1/O139 V. cholerae was the sole pathogen isolated from 21% of the clinical specimens, its role in this epidemic, either alone or in concert with V. cholerae O1, cannot be dismissed. A genomic approach was used to examine similarities and differences among the Haitian V. cholerae O1 and V. cholerae non-O1/O139 strains. A total of 47 V. cholerae O1 and 29 V. cholerae non-O1/O139 isolates from patients and the environment were sequenced. Comparative genome analyses of the 76 genomes and eight reference strains of V. cholerae isolated in concurrent epidemics outside Haiti and 27 V. cholerae genomes available in the public database demonstrated substantial diversity of V. cholerae and ongoing flux within its genome.

Production and characterization of thermostable xylanases by Thermomyces lanuginosus and Thermoascus aurantiacus grown on lignocelluloses

Thermomyces lanuginosus and Thermoascus aurantiacus isolated from self-heated jute fiber stalk were studied for xylanase production using various lignocelluloses under solid-state fermentation. Both organisms performed creditably well with unsupplemented wheat bran at 55°C. T. lanuginosus produced cellulase-free xylanase, whereas T. aurantiacus produced a small amount of cellulase in addition. Xylan (0.7%) also induced xylanase production in T. lanuginosus, leading to a 28.0% increase. The effect of initial moisture level was optimized for the fungi. T. lanuginosus and T. aurantiacus performed best at 80 and 50% initial moisture, respectively. Characterization of the enzymes reveals that xylanases from T. lanuginosus and T. aurantiacus were most active at 70°C, but at pH 6.0 and 5.0, respectively. Both xylanases displayed remarkable pH (5.0 to 11.0) and thermal stabilities by retaining most of their activities even after having been subjected to temperatures much higher than their optimal. Furthermore, they remained active under prolonged storage, having no loss of activity after 1 month of storage at 4°C and retaining up to about 90% after 10 days at 55°C. Xylanase from T. lanuginosus was better and produced a softer and mechanically stronger final product than that from T. aurantiacus when both were applied to low-quality jute fiber. The findings in this study have great implications for the future applications of xylanase.

Cellulase-free xylanase by Thermomyces lanuginosus RT9: Effect of agitation, aeration, and medium components on production

Several carbohydrates were examined for their ability to induce xylanase in Thermomyces lanuginosus RT9 at 50°C in shake flask cultures. It was found that xylan or xylan containing substrates, such as corn cobs, induced maximum and comparable level of xylanase free of cellulase, while the easily metabolisable sugars (glucose, xylose, and sucrose) appeared to repress xylanase synthesis. Low level of constitutive enzyme was produced as evident from the culture medium without carbon source addition. Initial culture pH significantly influenced both growth and xylanase production, exhibiting a maximum at 6.5 on xylan. The effects of agitation and aeration rates were investigated in a bioreactor. Both influenced significantly the growth, cultivation time and enzymes (xylanase and β-xylosidase) production. The highest level of xylanase productivity (41 630 U l−1 h−1) was achieved at an agitation of 200 rpm and 1.0 vvm aeration rate. At these conditions, the specific xylanase activity in the shake flask could be reproduced. Variation of nitrogen components demonstrated that a combination of yeast extract and (NH4)2HPO4 supported the best biomass growth, extracellular protein and xylanase production. At a C/N ratio of about 6.0 using yeast extract and (NH4)2HPO4 containing medium (yeast extract medium), a 3-fold higher xylanase production compared with the peptone medium was achieved in shake flask. However, in bioreactor system, the improved specific xylanase activity could not be reproduced due to rheological problem under higher biomass formation with accompanying viscosity and consequent oxygen transfer efficiency. Hence, the peptone medium with xylan (2.0%) is more appropriate to achieve high productivity of xylanase in bioreactor system.

Role of oleic acid solubilized in buffer—glycerol solution on adsorbed lipase during continuous hydrolysis of olive oil in a microporous hydrophobic membrane bioreactor

Abstract The cause of the superiority of the countercurrent flow mode of reactions over the cocurrent one during continuous hydrolysis of olive oil in a microporous hydrophobic membrane bioreactor was investigated. Outlet buffer-glycerol solution (BGS) contained an unknown compound which was extracted and identified as oleic acid, the major (84%) component of olive oil hydrolysis which diffused across the membrane and solubilized in the BGS. The estimated content of oleic acid in the outlet BGS of the countercurrent mode was significantly higher and was more homogeneously distributed (in the BGS compartment) than that of cocurrent one, which affected the adsorbed lipase resulting in higher hydrolysis rate at the same flow rate of olive oil.

Novel Toxicity of Bacillus thuringiensis Strains against the Melon Fruit Fly, Bactrocera cucurbitae (Diptera: Tephritidae)

Bactrocera cucurbitae (melon fruit fly) is one of the most detrimental vegetable-damaging pests in Bangladesh. The toxicity of Bacillus thuringiensis (Bt) has been reported against a few genera of Bactrocera in addition to numerous other insect species. Bt strains, harbouring cry1A-type genes were, therefore, assayed in vivo against the 3(rd) instar larvae of B. cucurbitae in this study. The biotype-based prevalence of cry1 and cry1A genes was calculated to be 30.8% and 11.16%, respectively, of the test strains (n=224) while their prevalence was greatest in biotype kurstaki. Though three indigenous Bt strains from biotype kurstaki with close genetic relationship exhibited higher toxicity, maximum mortalities were recorded for Btk HD-73 (96%) and the indigenous Bt JSc1 (93%). LC50 and LC99 values were determined to be 6.81 and 8.32 for Bt JSc1, 7.30 and 7.92 for Bt SSc2, and 6.99 and 7.67 for Btk HD-73, respectively. The cause of toxicity and its variation among the strains was found to be correlated with the synergistic toxic effects of cry1, cry2, cry3 and cry9 gene products, i.e. relevant Cry proteins. The novel toxicity of the B. thuringiensis strains against B. cucurbitae revealed in the present study thus will help in developing efficient and eco-friendly control measures such as Bt biopesticides and transgenic Bt cucurbits.

Short Communication: Effect of agitation rate on the growth and production of xylanase free of cellulase by Thermomyces lanuginosus MH4 in bioreactor

Cellulase-free xylanase production by T. lanuginosus MH4 was investigated in a 3-litre stirred tank bioreactor under different agitation rates and an aeration rate of 1v/v/m. The cultivation time in the bioreactor was reduced significantly over that in shake culture conditions. A xylanase productivity of 0.1 mkat1−1h−1 was achieved on xylan in the bioreactor. This was nearly double to that obtained in shake culture. The agitation rates influenced both growth and enzyme secretion in the bioreactor. The highest level of biomass concentration and activities of both xylanase and β-xylosidase were obtained at 150 revmin−1

Enterotoxicity ofVibrio furnissii isolated from eels

Fourteen strains ofVibrio furnissii, isolated from different ulcerated areas of eel, were tested to check their enterotoxicity in an animal model. Most strains caused fluid accumulation in ileal loop tests after serial passages and culture filtrates of most of the strains caused induration and increase in vascular permeability in rabbit skin. Production of extracellular haemolysin was also detected in all the culture filtrates. All of these observations clearly establish the enterotoxicity of these organisms.