Selective Isolation of Bacillus sphaericus from Soil by Use of Acetate as the Only Major Source of Carbon

Mechanisms of Anaerobic Soil Disinfestation: Volatile Fatty Acids Reduce Viability of Athelia (Sclerotium) rolfsii Sclerotia in Acidic Soil Conditions and Have Limited Effects on Endemic Trichoderma spp

Volatile fatty acids (VFAs), such as acetic and n-butyric acid, released during anaerobic decomposition of organic soil amendments during anaerobic soil disinfestation (ASD) likely play a role in soilborne plant pathogen inoculum suppression. However, research is limited on the direct effects of soil VFA exposure on fungal plant pathogen inoculum, effects on pathogen antagonists such as Trichoderma spp., and the role of soil microbial VFA metabolism on reducing exposure effects. The present study addresses these limitations through a series of studies evaluating the effects of VFA (acetic or n-butyric acid), VFA concentration (4, 8, or 16 mmol/kg soil), soil sterilization by autoclaving, and soil amendment on the viability of Athelia rolfsii (Sclerotium rolfsii) sclerotia post VFA exposure, and soil populations of Trichoderma spp. HCl and water-only controls were included. After 4-days exposure in an acidic, anaerobic environment, sclerotial viability, and colonization by culturable fungi or bacteria were assessed with standard procedures. Greenhouse experiments were similarly conducted to evaluate endemic soil populations of Trichoderma spp. following soil exposure to VFAs and Trichoderma spp. populations assessed with standard soil dilution plating onto semi-selective medium. Sclerotial germination was generally reduced by soil exposure to acetic (35.1% germination) or n-butyric (21.9% germination) acids compared to water (74.3% germination) and HCl (62.7% germination). Germination was reduced as VFA concentration increased from 4 to 8 and 16 mmol/kg (39.5, 29.1, and 16.9%, respectively). In amended soils, there was no difference in sclerotial germination compared to non-amended soils, but in the greenhouse experiment there was a Trichoderma spp. population increase of over 300% in amended soil [3.4 × 106 colony forming units (CFU)/g soil] compared to the non-amended soil (9.6 × 105 CFU/g soil). Soil autoclaving had no effect on sclerotial germination at low VFA concentrations, but sclerotial germination was reduced at higher VFA concentrations compared to non-autoclaved soil. Our results suggest that VFAs contribute to sclerotial mortality in strongly acidic soil environments, and mortality is influenced by VFA components and environment. Antifungal activity is less for acetic acid than for n-butyric, and less in non-sterile soil environments more typical of field conditions than in sterile laboratory conditions.

The Use of Response Surface Methodology as a Statistical Tool for the Optimisation of Waste and Pure Canola Oil Biodegradation by Antarctic Soil Bacteria

Hydrocarbons can cause pollution to Antarctic terrestrial and aquatic ecosystems, both through accidental release and the discharge of waste cooking oil in grey water. Such pollutants can persist for long periods in cold environments. The native microbial community may play a role in their biodegradation. In this study, using mixed native Antarctic bacterial communities, several environmental factors influencing biodegradation of waste canola oil (WCO) and pure canola oil (PCO) were optimised using established one-factor-at-a-time (OFAT) and response surface methodology (RSM) approaches. The factors include salinity, pH, type of nitrogen and concentration, temperature, yeast extract and initial substrate concentration in OFAT and only the significant factors proceeded for the statistical optimisation through RSM. High concentration of substrate targeted for degradation activity through RSM compared to OFAT method. As for the result, all factors were significant in PBD, while only 4 factors were significant in biodegradation of PCO (pH, nitrogen concentration, yeast extract and initial substrate concentration). Using OFAT, the most effective microbial community examined was able to degrade 94.42% and 86.83% (from an initial concentration of 0.5% (v/v)) of WCO and PCO, respectively, within 7 days. Using RSM, 94.99% and 79.77% degradation of WCO and PCO was achieved in 6 days. The significant interaction for the RSM in biodegradation activity between temperature and WCO concentration in WCO media were exhibited. Meanwhile, in biodegradation of PCO the significant factors were between (1) pH and PCO concentration, (2) nitrogen concentration and yeast extract, (3) nitrogen concentration and PCO concentration. The models for the RSM were validated for both WCO and PCO media and it showed no significant difference between experimental and predicted values. The efficiency of canola oil biodegradation achieved in this study provides support for the development of practical strategies for efficient bioremediation in the Antarctic environment.

Selective leaching of copper and zinc from primary ores and secondary mineral residues using biogenic ammonia

With the number of easily accessible ores depleting, alternate primary and secondary sources are required to meet the increasing demand of economically important metals. Whilst highly abundant, these materials are of lower grade with respect to traditional ores, thus highly selective and sustainable metal extraction technologies are needed to reduce processing costs. Here, we investigated the metal leaching potential of biogenic ammonia produced by a ureolytic strain of Lysinibacillus sphaericus on eight primary and secondary materials, comprised of mining and metallurgical residues, sludges and automotive shredder residues (ASR). For the majority of materials, moderate to high yields (30-70%) and very high selectivity (>97% against iron) of copper and zinc were obtained with 1 mol L^-1 total ammonia. Optimal leaching was achieved and further refined for the ASR in a two-step indirect leaching system with biogenic ammonia. Copper leaching was the result of local corrosion and differences in leaching against the synthetic (NH₄)₂CO₃ control could be accounted for by pH shifts from microbial metabolism, subsequently altering free NH₃ required for coordination. These results provide important findings for future sustainable metal recovery technologies from secondary materials.

Egg yolk enhances early sporulation and toxicity of Bacillus sphaericus H5a5b for small-scale production of a mosquito control agent

Bacillus sphaericus has been widely used in mosquito control programs, but the production of this bacterium is a little tricky as it does not utilize carbohydrates and requires proteinaceous substrates, which are expensive. In this study, we developed a cost-effective medium that resulted in a lower cost and shorter fermentation time. The locally available raw material, egg yolk was used and the level of sporulation, toxicity and biomass were compared with the conventional medium. Use of the egg yolk culture medium significantly shortened fermentation time to 15 h and yielded high activity, equivalent to that of conventional medium against 3rd instar Culex quinquefasciatus. Conventional NYSM medium required 21 h to attain the maximum activity and biomass. Hence, the egg yolk-based culture medium appears to be suitable and economical for the small-scale production of B. sphaericus.

Identification, cloning and sequence analysis of the Bacillus sphaericus 1593 41.9 kD larvicidal toxin gene

A number of strains of the widespread aerobic soil bacterium, Bacillus sphaericus, possess crystalline inclusions of a toxin lethal to a variety of insect (larvae) which are vectors of major tropical diseases. Partial amino acid sequence data from one strain, B. sphaericus 2362 have permitted us to design oligonucleotide probes for identifying the toxin gene in the closely related B. sphaericus 1593. The gene was found to be contained within an EcoRI-HindIII fragment and was cloned in its entirety in the bacterial plasmid pUC12. The DNA sequence was determined together with the upstream and downstream controlling elements, and a sequence of 370 amino acids was deduced for the toxin protein. This is the first reported sequence of a B. sphaericus toxin gene and will facilitate further work in characterizing the genes from other strains of different virulence and host range. The data do not support the suggestion that the toxin is derived by proteolysis of a protoxin precursor.