Studies on the Development of a consortium of fungi and bacteria for efficient composting

Abstract

Composting is the microbial degradation of organic waste material into a useful product that can provide nutrient to plants. Composts containing biocontrol agents can be useful in reducing the use of chemical fertilizer and pesticides since these composts not only increase the plant growth but also provide better suppression in root colonization by soil borne pathogens. During the present studies, microorganisms isolated from various composts were evaluated for their enzymatic and biocontrol activities in order to develop consortia of microorganisms that can reduce the time required for composting, and also provide protection to roots against soil-borne pathogens. A total number of 15 bacteria including six mesophilic, five thermotolerant and four thermophilic, and 44 fungi including 13 mesophilic, 11 thermotolerant and 20 thermophilic species isolated from cow dung, goat pellet, poultry manure and plant debris. Thermophilic fungi viz., Annelophora africana, Conidiobolus thermophilus and Haplotrichum croceum have been reported for the first time from Pakistan. The highest population of thermophilic microorganisms was observed in cow dung followed by goat pellet poultry manure and plant debris. The highest population of thermotolerant microorganisms was recorded from goat pellet followed by poultry manure, cow dung and plant debris. Similarly, the x highest population of mesophilic microorganisms was in plant debris followed by poultry manure, goat pellet and cow dung. The growth of thermophilic fungi was better on yeast starch agar as compared to potato sucrose agar medium. Similarly, the thermotolerant fungi showed better growth on PSA. Among the mesophilic fungi, Aspergillus flavus, Penicillium dipodomyis, Stachybotrys chartarum and Syncephalastrum racemosum showed better growth on YSA medium, PSA was more suitable for the remaining mesophilic fungi. During the present study, 33 fungi and 7 bacteria exhibited amylase activity. Of these, no previous report on amylase activity of Mucor fragilis, Aspergillus floccosus, Aspergillus nidulans (Teleomorph) and Aspergillus rugulosus is available. Similarly, 40 fungi and 6 bacteria showed cellulase activity that included Annelophora africana, Haplotrichum croceum, Aspergillus floccosus, Trichoderma virens and Micrococcus varians as now sources for cullulase enzymes. A total of 17 fungi and 7 bacteria showed chitinase activity and 20 fungi and 5 bacteria showed pectinase activity. No previous report on pectinase activity of Aspergillus rugulosus and Micrococcus varians is available. Furthermore 27 fungi and 6 bacteria showed protease activity. xi In vitro compatibility interactions showed that Acremonium thermophilum, Annelophora africana and Haplotrichum croceum were compatible with 10 fungi. Similarly, Bacillus cerreus and B. megaterium were compatible with 11 different fungi. Individual inoculations of the 44 fungi and15 bacteria into the composting materials showed that rate of degradation of grass clipping was the highest, followed by fruit waste, leave and wheat straw in descending order. The mesophilic microorganisms showed no composting at 50°C but composting activity was very good in thermopole boxes. The thermotolerant microorganisms were less effective at 50°C but in thermopole boxes these activities was very good. The thermophilic microorganisms were equally effective both at 50°C and in thermopole boxes. During single inoculations, the efficient thermophilic microorganisms took 7-8 days to completely degrade the grass clippings into compost. The time taken by the efficient thermotolerant and mesophilic microorganisms was 8 and 12 days, respectively. Combined use of two microorganisms degraded the grass clippings within five to eight days. Combinations of Isaria fumosorosea with Thermomyces lanuginosus, and Bacillus licheniformis with Aureobasidium pullulans were the most efficient. Based on the compatibility between the different microorganisms, three consortia with 17 members in each, developed to evaluate their xii composting ability. Consortium-1 showed the most efficient composting followed by consortia 2 and 3. The populations of the microorganisms were higher in compost developed by consortium-1 followed by consortia 2 and 3. The population densities in all the composts increased after four days whereas after 14 days, the populations of the microorganisms reduced and no bad smell was observed. It indicated the complete degradation of grass clippings. In case of the control, the bad smell continued even after 14 days, that indicates slow degradation. During pit composting, the initial average temperature of the composting material was 20°C. Only the mesophilic microbes isolated during the initial three weeks. The thermotolerant microbes thrived during 4th and 5th weeks. Thermophilic microbes grew from 6th to 8th week and finally disappeared. The peak heating phases (50oC) was at 8th week of composting, and during phase, the highest numbers of thermophilic microorganisms were isolated. Thereafter, the temperature gradually reduced to 40°C by the 9th and 10th weeks; the thermotolerant microbes reappear and later mesophilic microbes re-colonized the compost at 11th and 12th weeks when temperature reduced to 28°C. In pot and field experiments, composts developed by the consortia of microorganisms increased plant growth and reduced root colonization by soil borne pathogen viz., Fusarium solani, Macrophomina phaseolina, xiii Pythium aphanidermatum, Rhizoctonia solani and Sclerotium rolfsii. Use of consortia composts @ 10% w/w gave the highest increase in growth parameters followed by 5% and 1% treatments. Compost developed by consortium-1 was more effective as compared to consortia 2 and 3; consortium-3 compost being the least effective. The efficacy of the composts was greater in pot experiment as compared to field experiments. Plants treated with consortium-1 compost at 5% and 10% showed flowering within one month. Plants treated with consortia 2 and 3 composts flowered after one month only in 10% treatments. No flowering observed in one month old control plants. This early flowering occurred in pot experiments but not in field experiments. In field experiments, soil amendment with consortia composts showed persistence of the efficacy. Mungbean plants grown in the same micro plots without further addition of the composts showed a slight reduction in plant growth promotion and suppression in root colonization by soil-borne pathogens. Planting for the third time without adding consortia composts resulted in further reduction in the efficacy of the compost. However, the plant growth and suppression in root colonization was still better than that in control plants.