Presence Of Indigenous Microflora Research Articles

Bioaugmentation of a polychlorobiphenyl contaminated soil with two aerobic bacterial strains

The consortium of aerobic bacterial strains Rhodococcus ruber P25 and Microbacterium sp. B51 was bioaugmented in natural and industrial soils, contaminated by commercial mixture of polychlorinated biphenyls (PCBs) Sovol. The results showed that the bioaugmentation of bacterial strains led to PCBs degradation in soil. Sovol at the initial concentration of about 100mgkg−1 was removed by 72.2% in the bioaugmented system with natural soil within 90 days, while the system with industrial soil removed 96.4% of this compound within the same period. The biodegradation kinetics of PCBs in the bioaugmented soil systems was not dependent on the presence of indigenous microflora. It was found that the growth dynamics of the strains R. ruber P25 and Microbacterium sp. B51 correlated with the specific degradation of Sovol. The strains R. ruber P25 and Microbacterium sp. B51 displayed high degradative activity to all congeners (ortho-, meta- and para-substituent) contained in Sovol. Removal percentage for each congeners amounted to 59–100% in the bioaugmented systems. This study suggests that augmentation of PCB-contaminated soils with strain R. ruber P25 and Microbacterium sp. B51 is promising in PCB bioremediation.

Control of rice sheath blight by phyllosphere epiphytic microbial antagonists

Epiphytic microorganisms on the phyllosphere of traditional and high-yielding rice varieties were isolated from different agroecological zones of Sri Lanka and screened for theirin vitro andin vivo antagonism againstRhizoctonia solani Kuhn AG-1 1A, the sheath blight pathogen of rice. Among a total of 196 bacterial and 91 fungal isolates, 12 bacterial and two fungal isolates which showed more than 50% growth inhibition ofR. solani were tested for theirin vivo antagonism. Among the 14 antagonists tested, six bacterial and one fungal isolate substantially reduced the incidence of sheath blight (by more than 82%) and severity (by more than 92%) of the rice varieties BG94-1 and IR8 grown in a pot experiment under open field conditions. Using five antagonists that showed the bestin vitro antagonism, a pot experiment was conducted to determine whether the presence of indigenous microflora on the rice sheath had any effect on the effectiveness of antagonism. Three isolates (B4, GbB5 and HMWB4) controlled sheath blight incidence and severity equally well in the presence and absence of indigenous microflora. Two isolates (BG352B1 and BG300B1) were more effective when they were introduced into the rice sheath without indigenous microflora. Among the effective antagonists determined by the pot experiment, isolates B4, B16, BG94-1B5, GbB5, HMWB4 and BG379-F2 were tested under field conditions for two consecutive growing seasons. Under field conditions, severity of rice sheath blight was significantly reduced by the application of all the tested antagonists as a spray on rice sheath at a concentration of 108 cfu ml−1, starting 3 days after the development of symptoms and continuing for three applications at 10-day intervals. Antagonistic performances were consistent in the two seasons under field conditions andB. megatarium A (isolate B16) andAspergillus niger (isolate BG379-F2) performed as the most effective antagonists in both seasons. When disease severity was quantified as percentage sheath area covered by the disease lesions, the respective reductions in disease severity were greater than 50% and 61% byB. megaterium A (isolate B16) andAspergillus niger (isolate BG379-F2), respectively, in both seasons.

Survival and naphthalene-degrading activity of Rhodococcus sp. strain 1BN in soil microcosms.

The survival and activity of Rhodococcus sp. strain 1BN, inoculated into naphthalene-contaminated sandy-loam soil microcosms, were studied using classical and molecular methods. The naphthalene-degrading activity of 1BN in microcosms was examined through viable counts, CO2 production and naphthalene consumption, while its survival after inoculation was monitored by detecting the contemporary presence of alkane and naphthalene degradative genes and by analysing the 16S rDNA specific restriction profile. The inoculation of 1BN did not significantly enhance naphthalene degradation in the naphthalene-contaminated native soil, where 1BN maintained its catabolic activity also when in the presence of indigenous microflora. Instead the rate of naphthalene degradation by the inoculated 1BN was greater in sterile naphthalene-contaminated soil. The level of 1BN was only slightly higher after inoculation regardless of whether indigenous naphthalene-degrading bacteria were present or not and 1BN remained viable even when the substrate was depleted. This study documents the colonization and growth of 1BN in a non-sterile, naphthalene-added, sandy-loam soil having an active indigenous naphthalene-degrading population. An active and well-established naphthalene-degrading bacterial population in the native soil did not hamper the survival of the introduced 1BN that, through its activity, enhanced the mineralization rate of naphthalene.

Natural attenuation potential of cyanide via microbial activity in mine tailings.

Biological removal by indigenous microflora of cyanide, contained in old (6-9 years) and fresh tailings (3 months), was studied in order to assess its natural attenuation potential via biodegradation. To investigate the presence of indigenous microflora in tailings, total heterotrophic and cyanide resistant bacteria were counted using the spread-plate method. The free cyanide mineralization potential was estimated using K14CN in the presence of various unlabeled cyanide concentrations (0, 5, and 10 mg CN/kg). The biodegradation of cyanide contained initially in the samples was also investigated by monitoring formate, formamide, ammonia and total cyanide (CNT) concentrations over 111 days. The enumeration of total heterotrophic and cyanide-resistant bacteria in old tailings showed an average population of 105 cfu/g. However, no growth was detected in fresh tailings. Nevertheless, cyanide mineralization tests indicated the presence, in both old and fresh tailings, of a cyanide-degrading microflora. In old tailings, maximum mineralization percentages of free cyanide ranging from 85% to 100% were obtained after 65 days at all concentrations tested. A mineralization percentage of 83% after 170 days was also observed in fresh tailings. No decrease of total cyanide concentration in old tailings was observed when the biodegradation of endogenous cyanide was tested whereas a significant decrease was recorded in fresh tailings after 96 days. The presence of strong metal-cyanide complexes resistant to biodegradation could explain the absence of biodegradation in old tailings. This study demonstrated the presence of an indigenous free cyanide-degrading microflora in both old and fresh tailings, and suggests that natural attenuation of cyanide in gold mine tailings is likely to occur via microbial activity.