Insights into biological delignification of rice straw by Trametes hirsuta and Myrothecium roridum and comparison of saccharification yields with dilute acid pretreatment

Rice straw is the most abundant agricultural residue on a global scale and is widely available as feedstock for cellulosic fuel production. However, it is highly recalcitrant to biochemical deconstruction and also generates inhibitors that affect enzymatic saccharification. Rice straw from eastern Arkansas was subjected to dilute acid pretreatment (160 °C, 48 min and 1.0% sulfuric acid) and solid-state fermentation with two lignocellulolytic fungi, Trametes hirsuta and Myrothecium roridum, and their saccharification efficacies were compared. T. hirsuta and M. roridum were tested separately; pretreatment of rice straw with either strain for seven days resulted in 19 and 70% enrichment of its holocellulose content, respectively. However, liquid chromatography analysis of the alkali extracts showed significant differences in cell wall degradation by T. hirsuta and M. roridum. T. hirsuta removed 15% more phenolic compounds and 38% more glucan than M. roridum, while M. roridum removed 77% more xylan than T. hirsuta. Fungal and dilute acid pretreated biomass was then hydrolyzed using Accellerase^® 1500, a saccharification cocktail. Saccharification efficiency of M. roridum was 37% higher than that of dilute acid pretreatment of rice straw, requiring 8% lower enzyme loading and 50% shorter enzymatic hydrolysis duration. Alkali extraction of fungal pretreated biomass also yielded 10–15 g kg⁻¹ of acid precipitable polymeric lignin (APPL), which is a valuable co-product for biorefineries. In comparison to dilute acid pretreatment, fungal pretreatment could be a cost-effective alternative for the degradation of recalcitrant biomass, such as rice straw.     

Genetically modified starter and protective cultures

Modern approaches towards starter and protective culture improvement rely on advances in molecular biology. For most microorganisms used for food production, gene technological methods have been well developed. By recombinant DNA technology, ‘tailor-made’ starter and protective cultures may be constructed so as to combine technically desirable features. A single strain which normally would fail to accomplish a given ‘wtask’ may now be improved so as to meet a set of requirements necessary for a specific production or preservation process (e.g. wholesomeness, no off-flavour production, overproduction of bacteriocins or particular enzymes). In addition, undesirable properties (e.g. mycotoxin or antibiotic production by cheese moulds) may be eliminated by techniques such as ‘gene disruption’.     

Mycological and physical parameters for selecting suitable packaging material for pre- and post-irradiation storage of cereal grains in Ghana

Owing to the rough warehouse handling of storage sacks in tropical areas in Africa, a suitable storage sack should not support de novo growth of fungal spores because this would reduce the tensile strength of the packaging material and act as a springboard for infecting grain contents. This paper reports the effect of activity of saprophytic fungi on the tensile strength of jute and woven polypropylene sacks. New woven polypropylene sacks carried lower levels of fungal spores (1.3×10¹ cfu/72 cm²) than jute sacks (3.0×10³ cfu/72 cm²). The natural mould penetration and growth was examined on sections (4×5 cm) of both jute and woven polypropylene after previous incubation at relative humidities of 55, 60, 65, 70, 75, 80, 90 and 95% for 10 weeks by placing them on Sabouraud's Agar. There was a significant difference (P = 0.05 level of significance) between the higher penetration of mould growth on jute sacks and that obtained on woven polypropylene sacks. Saprophytic fungi (Aspergillus candidus, A. flavus, A. fumigatus, A. niger, A. japonicus, A. parasiticus, A. ustus, Fusarium oxysporium, F. moniliforme, Penicillium verucosum var. cyclopium, Rhizopus oryzae and Trichoderma viride) isolated from jute sacks reduced tensile strength, measured by an Instron Model 1026, by 50–75% after 10 weeks at 90% R.H. Same fungal species on woven polypropylene sacks did not alter the tensile strength. Woven polypropylene sacks did not absorb moisture whilst the moisture content of jute sacks increased by 5.3–6.0% in 10 weeks at 90% R.H. with concomitant increase in mould and yeast counts by 1–2 log cycles. Evidence is presented to show that there was a positive correlation between the final mycoflora on jute sacks and loss in tensile strength. No correlation, however, was found between the total aerobic bacteria on jute sacks and the concomitant reduction in tensile strength. Fungi therefore play a major role in the reduction of tensile strength of jute sacks. Sterilization by gamma irradiation (8.0 kGy) of jute and woven polypropylene sacks did not affect their intrinsic tensile strength. Woven polypropylene sacks therefore have many microbiological and physical advantages over the traditional jute sacks to merit their use for grain storage in tropical areas like Ghana.     

Development and experimental validation of an overlay mortar with biocide activity

Biodeterioration of concrete by microorganism colonisation may be a problem in several structures, especially in irrigation and hydroelectric canals. The main problem in such structures is the proliferation of algae and cyanobacteria that affect the performance of the structure, increase the maintenance costs and affects its durability. A research was conducted to develop a novel cement-based material with biocide activity that can be used as an overlay mortar in existing structures, such as canals and pipes. With this aim, ten commercial biocides were evaluated in a laboratory campaign to assess the effectiveness of the compounds against the microbial colonisation of concrete. Both mono- and multicomponent formulations were designed from the commercial products, to increase their antimicrobial effect obtaining a set of biocide formulations. The formulations were submitted to a flowchart process to determine their influence on the physical properties of the concrete, evaluate the release of the actives, and their antimicrobial efficiency both before and after accelerated aging processes. During the campaign, some formulations were observed to diminish the strength of the concrete. Such behaviour was normally due to the interaction of the active with the cement hydration process. Other formulations showed a high release of active from the concrete in water, compromising the durability of the treatment. In general, monocomponent formulations did not succeed to fulfill all the requirements, thus multicomponent formulations were analysed. One studied multicomponent formulation presented particularly good results in all properties analysed. This product did not significantly change the properties of concrete and the release of active in water from the concrete was low, while the antimicrobial effects were long lasting.     

Bacteria in a water‐damaged building: associations of actinomycetes and non‐tuberculous mycobacteria with respiratory health in occupants

We examined microbial correlates of health outcomes in building occupants with a sarcoidosis cluster and excess asthma. We offered employees a questionnaire and pulmonary function testing and collected floor dust and liquid/sludge from drain tubing traps of heat pumps that were analyzed for various microbial agents. Forty‐nine percent of participants reported any symptom reflecting possible granulomatous disease (shortness of breath on exertion, flu‐like achiness, or fever and chills) weekly in the last 4 weeks. In multivariate regressions, thermophilic actinomycetes (median = 529 CFU/m²) in dust were associated with FEV₁/FVC [coefficient = ?2.8 per interquartile range change, P = 0.02], percent predicted FEF_25–75% (coefficient = ?12.9, P = 0.01), and any granulomatous disease‐like symptom [odds ratio (OR) = 3.1, 95% confidence interval (CI) = 1.45?6.73]. Mycobacteria (median = 658 CFU/m²) were positively associated with asthma symptoms (OR = 1.5, 95% CI = 0.97?2.43). Composite score (median = 11.5) of total bacteria from heat pumps was negatively associated with asthma (0.8, 0.71?1.00) and positively associated with FEV₁/FVC (coefficient = 0.44, P = 0.095). Endotoxin (median score = 12.0) was negatively associated with two or more granulomatous disease‐like symptoms (OR = 0.8, 95% CI = 0.67?0.98) and asthma (0.8, 0.67?0.96). Fungi or (1→3)‐β‐D‐glucan in dust or heat pump traps was not associated with any health outcomes. Thermophilic actinomycetes and non‐tuberculous mycobacteria may have played a role in the occupants' respiratory outcomes in this water‐damaged building.     

Next‐generation DNA sequencing reveals that low fungal diversity in house dust is associated with childhood asthma development

Dampness and visible mold in homes are associated with asthma development, but causal mechanisms remain unclear. The goal of this research was to explore associations among measured dampness, fungal exposure, and childhood asthma development without the bias of culture‐based microbial analysis. In the low‐income, Latino CHAMACOS birth cohort, house dust was collected at age 12 months, and asthma status was determined at age 7 years. The current analysis included 13 asthma cases and 28 controls. Next‐generation DNA sequencing methods quantified fungal taxa and diversity. Lower fungal diversity (number of fungal operational taxonomic units) was significantly associated with increased risk of asthma development: unadjusted odds ratio (OR) 4.80 (95% confidence interval (CI) 1.04–22.1). Control for potential confounders strengthened this relationship. Decreased diversity within the genus Cryptococcus was significantly associated with increased asthma risk (OR 21.0, 95% CI 2.16–204). No fungal taxon (species, genus, class) was significantly positively associated with asthma development, and one was significantly negatively associated. Elevated moisture was associated with increased fungal diversity, and moisture/mold indicators were associated with four fungal taxa. Next‐generation DNA sequencing provided comprehensive estimates of fungal identity and diversity, demonstrating significant associations between low fungal diversity and childhood asthma development in this community.     

Distribution and variation of fungi and major mycotoxins in pre- and post-nature drying maize in North China Plain

Forty-four pre- and post-nature drying maize kernels were collected from North China Plain and assessed for fungi infection and mycotoxins contamination. The percentage of fungi infection was significantly higher in pre-nature drying samples than post-nature drying samples except for Fusariuim graminearum, which increases from 6.06% to 24.09%. Fusarium, Aspergillus, Alternaria and Trichoderma were main genera. Fusarium verticillioides (24.77%) and F. graminearum (15.08%) were predominant species, followed by Aspergillus niger (7.51%) and Aspergillus flavus (4.93%). FB₁ and DON were the major mycotoxins presented in the samples, followed by ZEN. All samples showed FB₁ ranging from 16.5 to 315.9 μg/kg. All post-nature drying maize kernels showed DON ranging from 5.8 to 9843.3 μg/kg, while 7 of 22 pre-nature drying samples contaminated with DON ranging from 50.7 to 776.6 μg/kg. The samples contaminated with ZEN in pre- and post-nature drying maize were 3, with the content ranging from 60.5 to 147.6 μg/kg and from 40.7 to 1056.8 μg/kg, respectively. Only 1 sample contaminated with AFB₁ of 148.4 μg/kg. The occurrence of mycotoxins is highly in accordance with the incidence of the corresponding mycotoxin-producing fungi. This is the first comprehensive comparison of fungi infection and mycotoxins contamination between pre- and post-nature drying maize kernels.     

Occurrence of toxigenic fungi and ochratoxin A in Ethiopian coffee for local consumption

Information on the presence of ochratoxin A (OTA) in local Ethiopian coffee is scarce. Therefore, the objective of this study was to type the fungal and mycotoxin contamination levels in Ethiopian coffee consumed by the local community. Coffee samples were collected from six major coffee growing districts in Jimma zone of Oromiya regional state in Ethiopia. Total fungal incidence mounted up to 87% and Aspergillus (79%), Fusarium (8%) and Penicillium (5%) were the predominant toxigenic genera. OTA producing species A. westerdijkiae, Aspergillus ochraceus, and Aspergillus steynii were identified for the first time in Ethiopia and were shown to be the predominant species while aflatoxin (AF) producing Aspergillus species were scarce. Using an in vitro approach, the OTA production potential was assessed under standardized conditions. Based on this experiment, it was concluded that Aspergillus westerdijkiae isolates were clearly the most potent producers of OTA. The median OTA level in the locally sold Ethiopian coffee was 1.53 μg/kg. Notwithstanding this low median value, significant differences in fungal and toxin incidences were observed between the different coffee processing types, coffee sample types, and storage characteristics.     

A field comparison of four fungal aerosol sampling instruments: inter-sampler calibrations and caveats

Four bioaerosol samplers (Reuter Centrifugal, Andersen N6 Single Stage, Surface Air System Super 90, and Air-o-Cell) were used to take c. 300 side-by-side measurements at 75 public building sites. Regression models were developed to examine the relationships between each method pair. The models demonstrate that measurements from these instruments are not directly comparable, requiring inter-instrument calibration. Sampling location (indoor vs. outdoor) was a confounder in all the pairwise comparisons between samplers. In addition, the slopes of the relationships between all method pairs except one differed in indoor vs. outdoor locations. These results emphasize that direct comparisons between methods should not be undergone without prior calibration. Where measurement circumstances are similar to those of this study, the regression models might serve as a basis to convert measurements made with one instrument to those made with another. However, the robustness and generalizability of the models in different measurement settings needs to be assessed. PRACTICAL IMPLICATIONS: Many different bioaerosol sampling devices are in common use for indoor air quality studies. If data from research studies are to be compared, an approximation of the relationships between the equipment would be useful. A comparison of three culturable sampling devices (Andersen N6, SAS 90, RCS) and one particulate sampling device (Air-o-Cell) collecting simultaneous samples under field conditions showed high linear correlations between methods. However, while direct comparisons between sampling data were not possible, the regression models reported here explained 60-85% of the variance in fungal concentrations, and underscored the importance of the effect of environment on measurement.