Molecular and Biochemical Mechanisms of Pathogenesis in the Maize Foliar Pathogen Cercospora zeae-maydis

GLS is a serious foliar disease of maize, a major staple crop grown commercially in the USA for both human and animal feed production, and increasingly, for ethanol production. The disease is caused by two Cercospora species, C. zeae-maydis and C. zeina, both of which infect maize in the USA and in other parts of the world, with yield losses potentially greater than 50%, depending on local conditions. In culture, C. zeae-maydis produces a phytotoxic, host non-specific perylenequinone, cercosporin, and abscisic acid (ABA), for which there is no known pathological or physiological function in the fungus. Experimental evidence indicates that cercosporin, is a virulence factor among some species of Cercospora, although evidence from other studies suggests that the phytotoxin may not be universally significant for all species. The overall goal of this project was to determine the biosynthetic regulation and pathological significance of cercosporin and ABA in C. zeae-maydis. To this end, the ortholog of CTB1, a polyketide synthase gene involved in the biosynthesis of cercosporin, was identified and disrupted. Disruption mutants failed to produce cercosporin but were able to infect maize and induce lesions. Furthermore, upon disruption of the nitrogen responsiveness gene AREA and a photoropin-like gene CzmPhot-24 , cercosporin biosynthesis was significantly reduced. However, these two mutants were still able to infect maize, although the AREA mutants were significantly reduced in virulence. AreA is a global regulator of secondary metabolism, thus suggesting that the reduction in virulence may be the result of global down-regulation of other virulence factors. Similarly, deletion of putative ABA biosynthesis pathway genes, which resulted in the loss of ABA biosynthesis, did not affect stomatal infection nor lead to decreased virulence when maize leaves were inoculated with the mutants. Taken together, these findings suggest that cercosporin and ABA individually are not necessary for pathogenesis, but may instead belong to a suite of as-yet unidentified virulence factors produced by C. zeae-maydis during infection of maize

Response surface optimisation of enzymatic hydrolysis of cassava peels without chemical and hydrothermal pretreatment

Cassava peel is a feedstock of significant potential for bioprocessing into industrial products. Its economic utility has however not been explored despite its advantages over traditional first-generation biomass feedstock. We demonstrate in this study that cassava peel can be hydrolysed to produce glucose at very high efficiency without chemical or hydrothermal pretreatment. We evaluated the conversion efficiency of a one-step simultaneous hydrolysis of the peel with mixed enzymes. Response surface methodology was applied to optimise the hydrolysis condition for maximum glucose recovery. Glucose concentration was measured by HPLC-IR and polynomial regression models defining the process parameters fitted to predict the optimal setting of process variables for maximum glucose recovery. Maximum glucose recovery was predicted to occur at pH 4 and 54.75 degrees C with an enzyme mixture containing 10 FPU/g cellulase, 0.5 U/g beta-glucosidase, 50 U/g amyloglucosidase, and 50 U/g alpha-amylase. Validation experiments confirmed that up to 95.48% glucose can be recovered from 0.06 g/ml of cassava peel in 43.15 h at these factor settings. Overall, the empirical models developed present an efficient tool for glucose recovery at high conversion efficiency. This model could be used for large-scale industrial production of glucose from cassava peel without the cost of pretreatment

Effect of organic acid pre-treatment on polyphenol oxidase induced browning and sensory quality of frozen yam chips

Yam Dioscorea spp suffers about 30% postharvest losses annually. Processing into convenience products such as yam chips prolong shelf life although the action of enzymes including polyphenol oxidase (PPO) and peroxidase (POD) may affect the quality if not precluded. Pre-treatment of cut yam with pH modifiers and antioxidants before storage could reduce enzymatic browning. In this study we investigated the effectiveness of ascorbic acid, citric acid and lime juice treatment and 5 weeks (w) of frozen storage in reducing browning in yam chips without affecting sensory quality. PPO and POD activity of freshly prepared yam chips pre-treated with citric acid, ascorbic acid or lime juice and stored frozen at -18 °C for 5 weeks was determined. The yam chips were fried and the moisture, oil content and colour determined. Consumer acceptability sensory evaluation was conducted for the week 0 and 5 of stored samples. POD activity was significantly reduced (50%) by treatment with citric acid after five-weeks of frozen storage while treatment with ascorbic acid and lime juice had no effect on the enzyme activity. There was no significant difference in lightness between the different treatments although treated samples differed significantly from the untreated. Moisture content of all samples were lower after storage while oil content of the various treatments was significantly different. Notwithstanding these differences, consumer acceptability was not different between the various treatment and storage periods. Pre-treated frozen yam chips have a good consumer acceptance and potential for commercial application. Developing this product will add value to yams and reduce huge postharvest losses

Risk of heavy metal ingestion from the consumption of two commercially valuable species of fish from the fresh and coastal waters of Ghana.

The need to evaluate the human health safety of fishery resources remain urgent in the mist of the ever-increasing fear of heavy metal toxicity from the consumption of Ghana's fisheries resource, as a consequence of pollution from several anthropogenic activities including artisanal gold mining. Nevertheless, the bigeye grunt (Brachydeuterus auritus) and Bagrid catfish (Chrysichthys nigrodigitatus) remain commercially valuable fish species in West Africa and continue to attract high patronage.Forty-five specimens each of C. nigrodigitatus and B. auritus collected from the Weija Dam and the Tema Fishing Habour in Ghana, between June and September 2016, were analysed for seven heavy metals using Atomic Absorption Spectrometry.Lead and Cadmium were below detection in all samples while Cu was not detected in B. auritus. Levels of the remaining metals (mg kg-1) were below FAO/WHO maximum permissible limits in fish and occurred in the rank order Se (3.5) > Zn (2.34) > Cu (0.59) > As (0.37) > Hg (0.19) in C. nigrodigitatus and Se (2.97) > Zn (2.28) > Hg (0.31) > As (0.21) in B. auritus. Only As in C. nigrodigitatus recorded Estimated Weekly Intake (EWI) greater than FAO/WHO Provisional Tolerable Weekly Intake (PTWI). Also, As in C. nigrodigitatus and Hg in B. auritus had Targeted Hazard Quotient (THQ) greater than 1 for individuals consuming the fishes on daily basis and therefore, raising concerns. However, for both species of fish, cancer risk of As was 1 in 10,000,000,000 and modified Health Benefits values of Se (HBVSe) were positive indicating the health risks that might accompany Hg exposure would be negated. Since toxicity depends on the concentration and quantity of a pollutant consumed, safe maximum consumption rate of C. nigrodigitatus based on As concentrations was 0.21 mg per day and that of B. auritus was 0.058 mg per day for Hg. With an average of 0.227 kg fish per meal of an adult human, these translated into not more than 24 C. nigrodigitatus and nine (9) B. auritus meals in a month but because fish is consumed at 0.0685 kg per person per day in Ghana, these values respectively translates to 93 and 30 safe days of consumption per month.At the rate of 0.0685 kg fish per person per day that fish is consumed in Ghana, the consumption of the two species of fish in Ghana would essentially be of little or no consequence to consumers

Human health risk assessment parameters of heavy metals from the consumption of <i>Chrysichthys nigrodigitatus</i> and <i>Brachydeuterus auritus</i> respectively from the fresh and coastal waters of Ghana.

<p>Human health risk assessment parameters of heavy metals from the consumption of <i>Chrysichthys nigrodigitatus</i> and <i>Brachydeuterus auritus</i> respectively from the fresh and coastal waters of Ghana.</p

Map of Ghana showing the Weija Dam and the Tema fishing harbour where fish specimens were collected.

<p>Map of Ghana showing the Weija Dam and the Tema fishing harbour where fish specimens were collected.</p

Frequency distribution of metal concentrations in the muscle tissues of <i>Chrysichthys nigrodigitatus</i> and <i>Brachydeuterus auritus</i> from the waters of Ghana.

<p>Note: Pb, Cd and Cu were excluded from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0194682#pone.0194682.g001" target="_blank">Fig 1</a> because Pb and Cd were below detection in all samples while 96% of the C. nigrodigitatus and 100% of the B. auritus samples had Cu levels below detections.</p

Comparison of heavy metals concentrations between the muscle tissues of <i>Chrysichthys nigrodigitatus</i> and <i>Brachydeuterus auritus</i> from the waters of Ghana.

<p>Note: <i>Mean ± SD with different letters in columns are significantly different (Mann–Whitney U test</i>, <i>p > 0</i>.<i>05)</i>.</p

Weight of <i>Chrysichthys nigrodigitatus</i> and <i>Brachydeuterus auritus</i> respectively from the fresh and coastal waters in Ghana.

<p>Weight of <i>Chrysichthys nigrodigitatus</i> and <i>Brachydeuterus auritus</i> respectively from the fresh and coastal waters in Ghana.</p

Trends in the concentration of heavy metals in the muscle tissues of <i>Brachydeuterus auritus</i> from the coastal waters of Ghana.

<p>Note: Pb, Cd and Cu were below detection limits in B. auritus. Also, pairwise comparison indicates concentration of all metals were significantly different except As and Hg (Kruskal-Wallis test with Fisher’s LSD post hoc, H_3,0.05 = 129.618, p < 0.05.</p