Sterile Compost Research Articles

Transcriptional reprogramming of tomato (Solanum lycopersicum L.) roots treated with humic acids and filter sterilized compost tea

BackgroundTo counteract soil degradation, it is important to convert conventional agricultural practices to environmentally sustainable management practices. To this end, the application of biostimulants could be considered a good strategy. Compost, produced by the composting of biodegradable organic compounds, is a source of natural biostimulants, such as humic acids, which are naturally occurring organic compounds that arise from the decomposition and transformation of organic residues, and compost tea, a compost-derived liquid formulated produced by compost water-phase extraction. This study aimed to determine the molecular responses of the roots of tomato plants (cv. Crovarese) grown under hydroponic conditions and subjected to biostimulation with humic substances (HSs) and filtered sterile compost tea (SCT).ResultsThe 13C CPMAS NMR of humic acids (HA) and SCT revealed strong O-alkyl-C signals, indicating a high content of polysaccharides.Thermochemolysis identified over 100 molecules, predominantly from lignin, fatty acids, and biopolymers. RNA-Seq analysis of tomato roots treated with HA or SCT revealed differentially expressed genes (DEGs) with distinct patterns of transcriptional reprogramming.Notably, HA treatment affected carbohydrate metabolism and secondary metabolism, particularly phenylpropanoids and flavonoids, while SCT had a broader impact on hormone and redox metabolism. Both biostimulants induced significant gene expression changes within 24 h, including a reduction in cell wall degradation activity and an increase in the expression of hemicellulose synthesis genes, suggesting that the treatments prompted proactive cell wall development.ConclusionsThe results demonstrate that HS and SCT can mitigate stress by activating specific molecular mechanisms and modifying root metabolic pathways, particularly those involved in cell wall synthesis. However, gene regulation in response to these treatments is complex and influenced by various factors. These findings highlight the biostimulatory effects of HS and SCT, suggesting their potential application in crop biofertilization and the development of innovative breeding strategies to maximize the benefits of humic substances for crops. Further research is needed to fully elucidate these mechanisms across various contexts and plant species.

Glomus mosseae AND Pseudomonas fluorescens AGAINST Soybean mosaic virus UNDER DRIP IRRIGATION SYSTEM

ARTICLE HIGLIGHTS- Glomus mosseae and Pseudomonas fluorescens enhance soybean resistance to SMV.- Ten-day drip irrigation stop at bloom stage boosts seed yield and weight.- Treatment reduces disease severity and increases P. fluorescens population.- Water-saving irrigation method improves soybean performance in dry seasons.- Combining G. mosseae and P. fluorescens increases soybean productivity. ABSTRACTSoybeans [Glycine max (L.) Merr.] require much water, especially in the early stages of growth, flowering, and pod formation and filling. Drought stress on soybeans will increase with global climate change. The research aimed to evaluate the efficacy of Glomus mosseae and Pseudomonas fluorescens in inducing systemic resistance to control Soybean Mosaic Virus (SMV) and the performance of soybean plants with drip irrigation in the dry season. The drip irrigation was stopped for ten days at the beginning of bloom, full bloom, beginning pod, and regular drip irrigation. The application of G. mosseae inoculants used 100 g of sterile compost mixed with 30 spores. The liquid inoculum of P. fluorescens was applied on cotyledonary leaves using the watering method. The plants were inoculated with SMV 6 and 12 days after the P. fluorescens treatment. The symptoms of SMV were recorded two weeks after inoculation, and Indirect ELISA detected the virus. The results showed the combination of G. mosseae and P. fluorescens under drip irrigation stopped at the beginning of bloom for ten days on ELISA absorbance values and disease severity of 0.259 and 3.72 %, respectively. Moreover, this treatment showed the highest values for the 100-seed weight, seed yield, and fresh weight of leaves. The technique of giving water by stopping drip irrigation at the beginning of bloom for ten days will help save water and increase the P. fluorescens population optimally in Alfisols with a pH of between 4.5 and 5.1 with incredibly low fertility. The combination of G. mosseae and P. fluorescens population resulted in a significant increase in the number of G. mosseae’s spores by stopping drip irrigation at the beginning of bloom for ten days.

Semi-Arid-Habitat-Adapted Plant-Growth-Promoting Rhizobacteria Allows Efficient Wheat Growth Promotion

Plant-growth-promoting rhizobacteria (PGPR) introduced into agricultural ecosystems positively affect agricultural production and constitute an ecological method for sustainable agriculture. The present study demonstrated the effects of two PGPR, Pantoea agglomerans strain Pa and Bacillus thuringiensis strain B25, on seed germination, on the plant growth of two durum wheat varieties, Bousselam and Boutaleb, and on the frequency of the cultivable beneficial bacterial community. The bacterial strains were used as seed primers (individually or in consortia) by coating them with carboxymethyl cellulose (CMC 1%). The effect of PGPR was negligible on germinative ability but improved seed vigor in the Boutaleb variety after inoculation with the Pa strain alone or in combination with the B25 strain. The results showed that the germination capacity depends on the wheat variety. It seemed to be better in the Bousselam variety. Analysis of the results of morphological plant parameters in sterile compost after 75 days under controlled conditions (16 h light, 26/16 °C day/night) showed a significant improvement in plant growth in both wheat varieties with the Pa strain alone or in combination. Chlorophyll (a, and total), carotenoid, and total soluble sugars were significantly increased, while proline and MDA were strongly reduced by inoculation of the Bousselam variety. Bacterial survival of the Pa and B25 strains in the rhizosphere of sterile compost was appreciable (105–107 CFU/g) for both the Pa and B25 strains. Only the Pa strain was endophytic and able to colonize roots. Contrary to sterile compost, the different inoculation treatments in natural soil (after 114 days) significantly improved all morphological parameters and chlorophyll pigments in both wheat varieties. The reduction of proline contents at the leaf level was observed with Pa, mainly in Bousselam. Bacterial densities of the rhizosphere and endophyte cultivable communities did not differ significantly. However, the number of cultivable beneficial bacteria isolated from roots and rhizosphere with multiple PGP traits was significantly increased. Bacterial survival of CMC-coated seed inoculum was appreciable and remained constant, especially for the Pa strain, during 21 months at room temperature. Based on these results, the PGPR used after seed priming would be a feasible and sustainable strategy to improve soil fertility and promote growth of durum wheat in stressful and non-stressful environments.

Treatment of compost as a source of organic material for bacterial consortium in the removal of sulfate and heavy metal lead (Pb) from acid mine drainage

Acid mine drainage can pollute the environment because it is acidic and contains toxic heavy metals. The purpose of this research was the application of a bacterial consortium to remove sulfate and reduce heavy metal lead (Pb) in acid mine drainage. The application was done in the bioreactor for acid mine drainage treatment that was treated with compost. Observations were made every five days and included observation of total bacterial growth using the Standard Plate Count (SPC) method, determination of sulfate content by gravimetry, determination of pH by use of pH meter, and determination of the concentration of heavy metal Pb using the AAS method. As a result, it was obtained that the treatment of non-sterile compost in acid mine drainage was able to reduce the initial heavy metal concentration of Pb of 84% and reduce the sulfate content by 72%, along with increasing pH and an increase in total bacterial growth. Meanwhile, sterile compost treatment was only able to reduce the Pb content by 63% and sulfate by 54%. This result indicates that the addition of compost is more effective than the treatment of sterile compost.

An improved micropropagation protocol for lentisk (Pistacia lentiscus L.)

Abstract This study presents an efficient improvement in the in vitro propagation protocol for one cloned genotype of lentisk (Pistacia lentiscus L.) by assessing the effects of gibberellic acid (GA3) concentrations, different cytokinins and amino acids and their concentrations on shoot proliferation, the effects of shoot length on rooting and the effects of compost type (sterile and non-sterile) on acclimatization. The best growth medium for multiple shoot induction was the MS medium supplemented with a combination of 1 mg l−1 BA, 100 mg l−1 tryptophan and 0.5 mg l-1 GA3, which gave a mean shoot length of 1.64 ± 0.07 cm and a mean bud number of 5.46 ± 0.16. The best results in terms of root length, rooting rate and the number of roots per shoot were obtained with 2 cm long shoots. The rooted plantlets were readily acclimatized in the sterile compost. In conclusion, the micropropagation protocol developed in this study can be used for large-scale propagation of P. lentiscus L. in reforestation programmes.

Rhizosphere Microbiome Recruited from a Suppressive Compost Improves Plant Fitness and Increases Protection against Vascular Wilt Pathogens of Tomato.

Suppressive composts represent a sustainable approach to combat soilborne plant pathogens and an alternative to the ineffective chemical fungicides used against those. Nevertheless, suppressiveness to plant pathogens and reliability of composts are often inconsistent with unpredictable effects. While suppressiveness is usually attributed to the compost’s microorganisms, the mechanisms governing microbial recruitment by the roots and the composition of selected microbial communities are not fully elucidated. Herein, the purpose of the study was to evaluate the impact of a compost on tomato plant growth and its suppressiveness against Fusarium oxysporum f. sp. lycopersici (Foxl) and Verticillium dahliae (Vd). First, growth parameters of tomato plants grown in sterile peat-based substrates including 20 and 30% sterile compost (80P/20C-ST and 70P/30C-ST) or non-sterile compost (80P/20C and 70P/30C) were evaluated in a growth room experiment. Plant height, total leaf surface, and fresh and dry weight of plants grown in the non-sterile compost mixes were increased compared to the plants grown in the sterile compost substrates, indicating the plant growth promoting activity of the compost’s microorganisms. Subsequently, compost’s suppressiveness against Foxl and Vd was evaluated with pathogenicity experiments on tomato plants grown in 70P/30C-ST and 70P/30C substrates. Disease intensity was significantly less in plants grown in the non-sterile compost than in those grown in the sterile compost substrate; AUDPC was 2.3- and 1.4-fold less for Foxl and Vd, respectively. Moreover, fungal quantification in planta demonstrated reduced colonization in plants grown in the non-sterile mixture. To further investigate these findings, we characterized the culturable microbiome attracted by the roots compared to the unplanted compost. Bacteria and fungi isolated from unplanted compost and the rhizosphere of plants were sequence-identified. Community-level analysis revealed differential microbial communities between the compost and the rhizosphere, suggesting a clear effect of the plant in the microbiome assembly. Proteobacteria and Actinobacteria were highly enriched in the rhizosphere whereas Firmicutes were strongly represented in both compartments with Bacillus being the most abundant species. Our results shed light on the composition of a microbial consortium that could protect plants against the wilt pathogens of tomato and improve plant overall health.

In Vitro Propagation of Sambong (Blumea balsamifera Linn.).

Terminal shoot tips of sambong (Blumea balsamifera Linn.) are cultured to initiate and regenerate shoots on Murashige and Skoog (MS) medium containing 1.0 mg/L benzyl adenine (BA). After 1 month, shoots, usually 4.5 cm long are separated and subcultured for multiplication. Regenerated shoots, about 6 cm long are rooted on MS medium supplemented with 1.0 mg/L naphthalene acetic acid (NAA). Exposure of shoots to high humidity for the first 2 weeks and equal proportion (1:1:1) of sterile sand, compost, and coir dust as potting mix favors the development of whole sambong plants. Young shoots from in vitro-derived sambong plants could also be used for propagation.

Enhancing pentachlorophenol degradation by vermicomposting associated bioremediation

Vermicomposting is an effective and environmentally friendly approach for soil organic contamination clean-up. This study investigated the roles and mechanisms of earthworm (Eisenia foetida) on soil pentachlorophenol (PCP) degradation with sterile and non-sterile soil-compost treatment. Limited soil PCP degradation was observed in the control and sterile compost treatments, whereas the synergetic effects of earthworm and compost contributed to the PCP biodegradation acceleration by significantly improving microbial biomass and activities. Sequence analysis and phylogentic classification of soil bacterial and fungal community structure after 42 days treatment identified the dominancy of indigenous bacterial families Pseudomonadaceae, Sphingobacteriaceae and Xanthomonadaceae, and fungal family Trichocomaceae, which were responsible for PCP biodegradation and stimulated by vermicomposting. Further investigation revealed the dominant roles of sterile compost during PCP biodegradation as the formation of humus-PCP in soil rather than neutralizing soil pH and increasing PCP availability. The mechanisms of vermicomposting include humus-PCP complex degradation, humus consumption and soil pH neutralization. This study provides a comprehensive understanding of the synergetic effect of vermicomposting on microbial community functions and PCP degradation enhancement in soils.

Direct Organogenesis of Seaside Heliotrope (Heliotropium crassavicum) Using Stem Explants

Heliotropium crassavicum L. is a sand binder salt marsh herb with enormous traditional value and widely found in South Asia America and Europe. In the direct method of regeneration from stem explants, we observed the maximum number of shoot regeneration after four weeks culture of MS elongation medium with 2.0 mg L(-1) of 2, 4-D (17.27 +/- 0.51). It was clear that MS medium with 2.0 mg mL(-1) 2, 4-D alone suitable for shoot multiplication as well as shoot elongation then compared to other combination of auxin and cytokinin. In vitro shoots were excised from shoot clumps and transferred to rooting medium containing 2, 4-dichlorophenoxy acetic acid (0.5-3.0 mg L(-1)). The maximum number of root regeneration (6.4 +/- 0.416) and root length (6.08 +/- 0.07) were observed in MS rooting medium fortified with 2.5 mg L(-1) of 2, 4-D after 2 weeks of culture. 85% of in vitro raised plantlets with well-developed shoots and roots were transferred to ex vivo conditions into polythene bag containing sterile compost with ratio (v/v/v) of organic fertilizer: sand: peat (1:2:2; 3:1:0 or 2:2:1). Sixty five percent of acclimated plants were transferred to the pots under full sun where they grew well without any detectable phenotypic variations.

The influence of biotic and abiotic factors on the rate of degradation of poly(lactic) acid (PLA) coupons buried in compost and soil

Poly(lactic) acid (PLA) is a compostable biopolymer and has been commercialised for the for the manufacture of short-shelf life products. As a result, increasing amounts of PLA are entering waste management systems and the environment; however, the degradation mechanism is unclear. While hydrolysis of the polymer occurs abiotically at elevated temperature in the presence of water, potential catalytic role for microbes in this process is yet to be established. In this study, we examined the degradation of PLA coupons from commercial packaging at a range of temperatures (25°, 37°, 45°, 50° and 55 °C) in soil and compost and compared with the degradation rates in sterile aqueous conditions by measuring loss of tensile strength and molecular weight (Mw). In addition, in order to assess the possible influence of abiotic soluble factors in compost and soil on degradation of PLA, degradation rates in microorganism-rich compost and soil were compared with sterile compost and soil extract at 50 °C. Temperature was determined to be the key parameter in PLA degradation and degradation rates in microorganism-rich compost and soil were faster than in sterile water at temperatures 45° and 50 °C determined by tensile strength and Mw loss. Furthermore, all tensile strength was lost faster after 30 and 36 days in microorganism-rich compost and soil, respectively, than in sterile compost and soil extract, 57 and 54 days, respectively at 50 °C. Significantly more Mw, 68% and 64%, was lost in compost and soil, respectively than in compost extract, Mw, 53%; and in soil extract, 57%. Therefore, degradation rates were faster in microorganism-rich compost and soil than in sterile compost and soil extract, which contained the abiotic soluble factors of compost and soil at 50 °C. These comparative studies support a direct role for microorganisms in PLA degradation at elevated temperatures in humid environments. No change in tensile strength or Mw was observed either 25° or 37 °C after 1 year suggesting that accumulation of PLA in the environment may cause future pollution issues.

In vitro propagation of Diyarbakır watermelons and comparison of direct-seeded and transplanted watermelon

A rapid protocol using shoot tip explants for micropropagation of Diyarbakır watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] types Sürme, Beyazkış and Karakış was achieved. Shoot tips from 5-day-old in vitro germinated seedlings were cultured on shoot regeneration medium for 3 weeks. The effects of the different concentrations of benzyl adenine (BA) and carbohydrate types on shoot proliferation were examined. The results confirmed that a range of 0.5-1.0 mg/L of BA was almost equally effective in promoting the shoot length of cultures in the 3 genotypes. Sucrose, in the presence of BA, was superior to other carbohydrates for the 3 genotypes studied in terms of the number of proliferated shoots and the average shoot length obtained. The highest percentage of rooting was achieved when medium supplemented with 1.0 mg/L of indole-3-butyric acid (IBA) was used for the 3 genotypes. The highest frequency of acclimatized plantlets for the 3 genotypes was 85%, 85%, and 90%, respectively, in sterile compost, when the shoots of Beyazkış, Karakış, and Sürme were rooted in the IBA-supplemented rooting treatments. The Sürme genotype produced a significantly higher yield and mean fruit weight than the Beyazkış and Karakış genotypes in both direct-seeded and transplanted watermelons. The main soluble sugar of the experimental types was separated, identified, and quantified using high performance liquid chromatography (HPLC). Fructose was found to be the most abundant sugar and was highly detected in Beyazkış for the seeded watermelon and in Karakış for the transplanted watermelon. This demonstrates that in vitro propagation can be used to produce high quality diploid Diyarbakır watermelon for use in breeding lines.

IN VITRO ROOTING IMPROVEMENT OF ADULT PISTACHIO, PISTACIA VERA L. 'ATLI'

Axenic cultures of Pistacia vera L. 'Atli' initiated on agar solidified Murashige and Skoog (MS) medium with Gamborg vitamins supplemented with different concentrations of 6-benzyladenine (BA) and indole-3-acetic-acid (IAA) were proliferated and maintained on an MS medium supplemented with 4.4 μM BA. Using these proliferated cultures, effects of: i) washing of the basal-cut-ends in sterile distilled water; ii) dipping of the basal-cut-ends in the different indole butyric acid (IBA) solutions; iii) cloned shoots; and iv) explant sizes (1.0, 2.0, 3.0 and 4.0 cm long) were assessed for root induction. The highest rooting frequency (92%) of microshoots was recorded at 4.0 cm long cloned and twice washed microshoots. Rooting was apparent within 14 days. The present study also aimed to reduce the occurrence of basal callus production. The microshoots cultured from the cloned shoots produced less calli than the mixed population, and developed roots that resemble the seedling plantlets. Those plantlets that had been rooted and exposed to sterile compost were able to acclimatize readily. Major improvement of the present study over previously published protocols has been achieved with the improvement of the in vitro rooting percentages of adult pistachio plantlets.

Evaluating the Effect of Environmental Factors on Pathogen Regrowth in Compost Extract

Pathogenic microorganisms may survive the composting process in low numbers and subsequently regrow to high levels under favorable conditions. The objective of this study was to investigate the regrowth potential of Salmonella spp., Escherichia coli O157:H7, and Listeria monocytogenes in dairy-based composts under different environmental conditions. Water extract of commercially available dairy compost was used as a model system. Cocktails of five rifampin-resistant strains of each pathogen previously grown in reduced nutrient media (1/2 or 1/10 strength of tryptic soy broth, TSB) were inoculated into water extract of compost of different ratios (1:2,1:5, and 1:10, w/v), and then stored at 35 degrees C or 22 degrees C for 7 days. The strains exhibiting greatest survival or regrowth were identified by pulsed-field gel electrophoresis (PFGE). At 22 degrees C, both E. coli O157:H7 and L. monocytogenes multiplied in all compost extracts, whereas Salmonella spp. regrew in both 1:2 and 1:5 compost extracts but not in 1:10. For all three pathogens, incubation at 22 degrees C provides better conditions for regrowth than at 35 degrees C. Both Salmonella and E. coli O157:H7 previously adapted to nutrient-limited broth (1/10 strength of TSB) regrew in compost extracts to higher populations than the control cultures grown previously in full strength of TSB. In the absence of indigenous microorganisms, all three pathogens regrew even in the most diluted sterile compost extract (1:10) with growth potentials ranging from 2.30 to 3.59 log CFU/ml. In nonsterile compost extract with ca. 5 log CFU/ml of background microorganisms, all three pathogens regrew only in the most concentrated compost extract (1:2) with much less population increases ranging from 0.70 to 1.43 log CFU/ml. Compost extract samples of all ages supported the regrowth of both Salmonella and E. coli O157:H7 with population increases ranging from 0.95 to 2.32 log CFU/ml. The PFGE patterns for E. coli O157:H7 isolates from sterile compost extracts matched with either the spinach outbreak strain or an avirulent B6914 strain. These results demonstrated that compost extract of dairy-based compost contained sufficient nutrients for pathogen regrowth. Cultures previously adapted to low nutrient media regrew to higher populations than control cultures; however, indigenous microflora suppressed the pathogen regrowth in compost extract, especially at 35 degrees C.

Chemical properties of compost extracts inhibitory to germination of Sclerotium rolfsii

Suppression of Sclerotium rolfsii by compost has been previously related to colonization of sclerotia by mycoparasitic fungi. Compost which has undergone prolonged curing was shown to lose its suppressive traits. In this work we sought to decouple the effects of the chemical conditions in the compost from the biological effect of antagonists inhabiting it. This was done by examining the direct effect of sterile compost extracts on the germination of sclerotia, and on the colonization of sclerotia by antagonistic fungal isolates. Sterile extracts of non-cured compost were found to completely inhibit sclerotia germination whereas extracts of cured compost allowed germination. Using buffered solutions which mimic the pH, NH 4 + concentration and buffering capacity of the extracts, it was shown that germination inhibition was related to effective NH 3 concentration in the extracts. A concentration of 0.5 mM NH 3 in compost extracts was identified as a threshold level above which sclerotia germination was completely inhibited. Sclerotia placed on compost extracts inhibitory to their germination were more vulnerable to attack by mycoparasites. The opportunistic antagonists Penicillium and Petriella exhibited enhanced colonization of sclerotia on these extracts, while the mycoparasitic fungus Trichoderma was found to behave as a primary antagonist, colonizing sclerotia regardless of the environmental conditions.

EVALUATION OF PRODUCTIVITY AND POSTHARVEST QUALITY DURING STORAGE OF FIVE AGARICUS BISPORUS STRAINS

ABSTRACT Five Agaricus bisporus commercial strains (S100, A15, F56, F40 and F62) were evaluated as regards their colonization rates, yields, quality characters and storability. Concerning their colonization performance, the mycelial growth rates examined in “race tubes” on sterile compost, as well as earliness in fructification did not differ significantly. Significantly lower was the yield of strain S100 compared to the yield of strains F62 and F56, which presented the greatest cumulative biological efficiency values. However, mushroom number and average weight presented negative relation. For the storage and quality study, mushrooms at the “closed‐cap” stage packaged in 500‐g plastic containers were stored for 5 days at 2C and 5 days at 18C (shelf life). The respiration behavior of the five strains was similar with the mass loss not exceeding 15% during storage at 2C and 40–50% at the end of the shelf life. Also, no differences in the whiteness and texture change were detected and a correlation between the period of pileus diameter increase and the respiration rate was found. According to their color and texture quality assessment, mushrooms deriving from the first four strains may be considered well acceptable at the end of the shelf life, whereas these from strain F62 just saleable.

A TRICHODERMA KONINGII SEED TREATMENT IS EFFECTIVE BEFORE AND AFTER SEED STORAGE AGAINST SCLEROTIUM ROLFSII DAMPING OFF OF TOMATO

An isolate of Trichoderma koningii was used for treatment of tomato seeds with a suspension of 106 con/ml in dilute Tween-20 or sterile distilled water. Seeds were stored at 6°C or 20°C and periodically sampled in order to determine the efficacy of Trichoderma koningii as a biocontrol agent against Sclerotium rolfsii damping off in the greenhouse. Seed germination tested in water agar plate showed that T. koningii slightly delayed seed germination over control treatments. Length of storage had a significant effect on the survival of Trichoderma on seeds, which was more pronounced when seeds were stored at 20°C rather than at 6°C. The biocontrol ability of T. koningii, expressed as pre- and post-emergence damping off in artificially infested sterile potting compost, was affected by the length of storage. Storage temperature also excerted a significant (P=0.034) effect on final stand. After each storage period, Trichoderma-treated seed still gave significantly greater seedling counts of plants than uncoated control seed.

Production attributes of Agaricus bisporus white and off-white strains and the effect of calcium chloride irrigation on productivity and quality

Five Agaricus bisporus commercial cultivars (one off-white, two white, and two pure-white) were evaluated as regards their colonization rates, production characters, and quality attributes. Although the mycelia growth rates on sterile compost did not differ significantly, an important difference was detected between the lowest (off-white strain) and the highest (white strain) yield value. Average mushroom weight showed the tendency to decrease as yield increased. Irrigation of the white strain 203 (selected among tested strains for its good productivity and quality) with 0.05–0.25% (w/v) calcium chloride did not result in reduced yields, on the contrary increased yields were calculated for 0.10 and 0.15% treatments. Average mushroom weight was positively affected, while firmer mushrooms were produced when crops were treated with 0.05 and 0.10% calcium chloride. Also, color improvement was detected at the dosage of 0.25% calcium chloride.

Flow cytometric detection of viable bacteria in compost

Flow cytometry employing several vital stains was used to study the colonisation of sterile compost by Bacillus subtilis 168 (pAB224). The dyes used included rhodamine 123 (Rh123), carboxyfluorescein diacetate (CFDA) and chemchrome B. The results demonstrated the ability of flow cytometry to detect and enumerate viable bacteria in filtered compost extracts. Flow cytometry was also used to detect and study the viability of an indigenous compost community. Although it was possible to detect a viable bacterial population, the numbers of viable bacteria estimated were significantly different to those estimated from cfu.

Survival of a plasmid-bearing strain of Bacillus subtilis introduced into compost

Survival of Bacillus subtilis strain 168 containing plasmid pAB224, which carries a gene for tetracycline resistance, was studied in mushroom compost under mesophilic and thermophilic conditions. Stable populations of B. subtilis were maintained as spores in both sterile and fresh mushroom compost incubated at 37 degrees C. At 65 degrees C, the introduced B. subtilis populations declined during incubation but spores were still detectable after 28 d. Survival at the higher temperature was greater in fresh than in sterile compost. There was no apparent loss of plasmid pAB224 or plasmid-determined phenotype from the introduced B. subtilis population at either incubation temperature. The frequency of tetracycline resistance in the indigenous Bacillus population was very low (10(-5), but some tetracycline-resistant isolates contained plasmid DNA. Four plasmid DNA profiles were found associated with five Bacillus phenotypes, and some evidence for homology with pAB224 was found. However, pAB224 was found to be a suitable marker for release studies because it was easily recovered, readily distinguished from indigenous plasmids on agarose gels, and was maintained in compost-grown B. subtilis 168 in the absence of any selective pressure.

Growth kinetics of Agaricus bisporus mycelium on solid substrate (mushroom compost)

Growth of Agaricus bisporus was studied on sterile compost and on sterile compost pre-grown with the thermophilic fungus Scytalidium thermophilum. Early growth was characterized by depressed, slowly growing hyphae. The mycelial radius extended exponentially in this stage. Mycelium on sterile compost switched to a fluffy growth type of radially orientated hyphae that extended at a linear rate, K r, of 5 mm d−1. On compost pre-grown with S. thermophilum, early growth continued up to 30 mm, then extension became linear at K r = 7·2 mm d−1. If cultures were well ventilated, K r was higher. A new growth function was derived to combine both growth phases. The width of the peripheral growth zone, w, of A. bisporus mycelium was 3 mm. The exponential specific growth rate, μ, was calculated from K r/w = 2·4 d−1, which is much higher than a previous estimate of 0·19 d−1. In addition to growth-promoting effects, S. thermophilum had inhibitory effects; the period of early growth was reduced if S. thermophilum was inactivated in pre-grown compost. Under commercial conditions, maximum growth rates are not exploited. The introduction of selected strains of thermophilic fungi in compost and the development of a new kind of spawn inoculum of A. bisporus might lead to improvements in commercial practice.