Radziah Othman

Isolation and characterization of phosphate-solubilizing bacteria from aerobic rice

Phosphate-solubilizing bacteria are frequently used as plant growth promoters. A study was conducted to isolate phosphate-solubilizing bacteria (PSB) from aerobic rice grown in Penang Malaysia and to determine some biochemical properties of the isolates such as, organic acids, enzymes, indoleacetic acid (IAA), siderophore production and its antagonistic effect against pathogen Rhizoctonia solani. Selective media used for the isolation were; Pseudomonas aeruginosa (PA), national botanical research institutes phosphate growth medium (NBRIP), Pikovskaya and Pseudomonas spp. (PS). Organic acid production was determined using high performance liquid chromatography (HPLC). The PSB populations were higher in rhizosphere than non-rhizospheric soil and the highest population was found in PS and Pikovskaya, while the lowest was found in PA media plates. The highest P solubilizing activity (69.58%) was found in PSB9 strain grown in NBRIP plate. Isolated PSB were able to produce different organic acids and growth hormone such as IAA. A number of PSB isolates belong to the Bacillus sp. and proved for the antagonistic effect against R. solani (sheath blight) even though most of the isolated strains can grow in nitrogen, free semi-solid medium and able to produce siderophore. PSB inoculants with their beneficial traits would be considered as potential biofertilizer for the sustainable aerobic rice cultivation system.

Plant Growth-Promoting Rhizobacteria Inoculation to Enhance Vegetative Growth, Nitrogen Fixation and Nitrogen Remobilisation of Maize under Greenhouse Conditions.

Plant growth-promoting rhizobacteria (PGPR) may provide a biological alternative to fix atmospheric N2 and delay N remobilisation in maize plant to increase crop yield, based on an understanding that plant-N remobilisation is directly correlated to its plant senescence. Thus, four PGPR strains were selected from a series of bacterial strains isolated from maize roots at two locations in Malaysia. The PGPR strains were screened in vitro for their biochemical plant growth-promoting (PGP) abilities and plant growth promotion assays. These strains were identified as Klebsiella sp. Br1, Klebsiella pneumoniae Fr1, Bacillus pumilus S1r1 and Acinetobacter sp. S3r2 and a reference strain used was Bacillus subtilis UPMB10. All the PGPR strains were tested positive for N2 fixation, phosphate solubilisation and auxin production by in vitro tests. In a greenhouse experiment with reduced fertiliser-N input (a third of recommended fertiliser-N rate), the N2 fixation abilities of PGPR in association with maize were determined by 15N isotope dilution technique at two harvests, namely, prior to anthesis (D50) and ear harvest (D65). The results indicated that dry biomass of top, root and ear, total N content and bacterial colonisations in non-rhizosphere, rhizosphere and endosphere of maize roots were influenced by PGPR inoculation. In particular, the plants inoculated with B. pumilus S1r1 generally outperformed those with the other treatments. They produced the highest N2 fixing capacity of 30.5% (262 mg N2 fixed plant−1) and 25.5% (304 mg N2 fixed plant−1) of the total N requirement of maize top at D50 and D65, respectively. N remobilisation and plant senescence in maize were delayed by PGPR inoculation, which is an indicative of greater grain production. This is indicated by significant interactions between PGPR strains and time of harvests for parameters on N uptake and at. % 15Ne of tassel. The phenomenon is also supported by the lower N content in tassels of maize treated with PGPR, namely, B. pumilus S1r1, K. pneumoniae Fr1, B. subtilis UPMB10 and Acinetobacter sp. S3r2 at D65 harvest. This study provides evidence that PGPR inoculation, namely, B. pumilus S1r1 can biologically fix atmospheric N2 and provide an alternative technique, besides plant breeding, to delay N remobilisation in maize plant for higher ear yield (up to 30.9%) with reduced fertiliser-N input.

Physiological and Growth Responses of Six Turfgrass Species Relative to Salinity Tolerance

The demand for salinity-tolerant turfgrasses is increasing due to augmented use of effluent or low-quality water (sea water) for turf irrigation and the growing turfgrass industry in coastal areas. Experimental plants, grown in plastic pots filled with a mixture of river sand and KOSASR peat (9 : 1), were irrigated with sea water at different dilutions imparting salinity levels of 0, 8, 16, 24, 32, 40, or 48 dS m−1. Salinity tolerance was evaluated on the basis of leaf firing, shoot and root growth reduction, proline content, and relative water content. Paspalum vaginatum was found to be most salt tolerant followed by Zoysia japonica and Zoysia matrella, while Digitaria didactyla, Cynodon dactylon “Tifdwarf,” and Cynodon dactylon “Satiri” were moderately tolerant. The results indicate the importance of turfgrass varietal selection for saline environments.

Biochemical and molecular characterization of potential phosphate-solubilizing bacteria in acid sulfate soils and their beneficial effects on rice growth.

A study was conducted to determine the total microbial population, the occurrence of growth promoting bacteria and their beneficial traits in acid sulfate soils. The mechanisms by which the bacteria enhance rice seedlings grown under high Al and low pH stress were investigated. Soils and rice root samples were randomly collected from four sites in the study area (Kelantan, Malaysia). The topsoil pH and exchangeable Al ranged from 3.3 to 4.7 and 1.24 to 4.25 cmolc kg−1, respectively, which are considered unsuitable for rice production. Total bacterial and actinomycetes population in the acidic soils were found to be higher than fungal populations. A total of 21 phosphate-solubilizing bacteria (PSB) including 19 N2-fixing strains were isolated from the acid sulfate soil. Using 16S rRNA gene sequence analysis, three potential PSB strains based on their beneficial characteristics were identified (Burkholderia thailandensis, Sphingomonas pituitosa and Burkholderia seminalis). The isolated strains were capable of producing indoleacetic acid (IAA) and organic acids that were able to reduce Al availability via a chelation process. These PSB isolates solubilized P (43.65%) existing in the growth media within 72 hours of incubation. Seedling of rice variety, MR 219, grown at pH 4, and with different concentrations of Al (0, 50 and 100 µM) was inoculated with these PSB strains. Results showed that the bacteria increased the pH with a concomitant reduction in Al concentration, which translated into better rice growth. The improved root volume and seedling dry weight of the inoculated plants indicated the potential of these isolates to be used in a bio-fertilizer formulation for rice cultivation on acid sulfate soils.

Symbiotic interaction of endophytic bacteria with arbuscular mycorrhizal fungi and its antagonistic effect on Ganoderma boninense.

Endophytic bacteria (Pseudomonas aeruginosa UPMP3 and Burkholderia cepacia UMPB3), isolated from within roots of oil palm (Elaeis guineensis Jacq.) were tested for their presymbiotic effects on two arbuscular mcorrhizal fungi, Glomus intraradices UT126 and Glomus clarum BR152B). These endophytic bacteria were also tested for antagonistic effects on Ganoderma boninense PER 71, a white wood rot fungal pathogen that causes a serious disease in oil palm. Spore germination and hyphal length of each arbuscular mycorrhizal fungal (AMF) pairing with endophytic bacteria was found to be significantly higher than spores plated in the absence of bacteria. Scanning electron microscopy (SEM) showed that the endophytic bacteria were scattered, resting or embedded on the surface hyaline layer or on the degraded walls of AMF spores, possibly feeding on the outer hyaline spore wall. The antagonistic effect of the endophytic bacteria was expressed as severe morphological abnormalities in the hyphal structures of G. boninense PER 71. The effects of the endophytic bacteria on G. boninense PER 71 hyphal structures were observed clearly under SEM. Severe inter-twisting, distortion, lysis and shriveling of the hyphal structures were observed. This study found that the effect of endophytic bacteria on G. intraradices UT126 and G. clarum BR152B resembled that of a mycorrhiza helper bacteria (MHB) association because the association significantly promoted AMF spore germination and hyphal length. However, the endophytic bacteria were extremely damaging to G. boninense PER 71.

Application of potential phosphate-solubilizing bacteria and organic acids on phosphate solubilization from phosphate rock in aerobic rice.

A study was conducted at Universiti Putra Malaysia to determine the effect of phosphate-solubilizing bacteria (PSB) and organic acids (oxalic & malic) on phosphate (P) solubilization from phosphate rock (PR) and growth of aerobic rice. Four rates of each organic acid (0, 10, 20, and 30 mM), and PSB strain (Bacillus sp.) were applied to aerobic rice. Total bacterial populations, amount of P solubilization, P uptake, soil pH, and root morphology were determined. The results of the study showed significantly high P solubilization in PSB with organic acid treatments. Among the two organic acids, oxalic acid was found more effective compared to malic acid. Application of oxalic acid at 20 mM along with PSB16 significantly increased soluble soil P (28.39 mg kg−1), plant P uptake (0.78 P pot−1), and plant biomass (33.26 mg). Addition of organic acids with PSB and PR had no influence on soil pH during the planting period. A higher bacterial population was found in rhizosphere (8.78 log10 cfu g−1) compared to the nonrhizosphere and endosphere regions. The application of organic acids along with PSB enhanced soluble P in the soil solution, improved root growth, and increased plant biomass of aerobic rice seedlings without affecting soil pH.

The potential of endomycorrhizal fungi in controlling tomato bacterial wilt Ralstonia solanacearum under glasshouse conditions

The impact of colonization by three mycorrhizal fungi on tomato bacterial wilt caused by Ralstonia solanaceraum was investigated. Three species of arbuscular mycorrhizal fungal (AMF) were tested ( Glomus mosseae , Scutellospora sp. and Gigaspora margarita ). Siginificant differences in tomato growth based on plant hieght was recorded between G. mosseae (125.25 cm) and all treatments. The combination of G. mosseae and R. solanacearum resulted in significantly taller tomato plants than G. margarita + R. solanacearum and Scutelospora sp.+ R. solanacearum . Shoot fresh and dry weight was higher in G. mosseae inoculated plants. No disease symptoms were observed in the combination treatment of G. mosseae and R. solanacearum . The plants treated with Scutellospora sp. showed low incidence of infection (105, 15%) at 15 and 20 days after inoculation, respectively. The combination of G. mosseae and R. solanacearum resulted in more increase in root morphology (root tips (434.75), root length (267.00 cm), root surface area (149.31 cm 2 ), root volume (3.77 cm 3 ), root fresh weight (4.75 g) and root dry weight (2.5 g). The treatment of G. mosseae + R. solanacearum was different significantly when compared to G. margarita and Scutellospora sp. + R. solanacearum treatments in all parameters considered. The highest number of AMF spores was recorded in G. mosseae treatment followed by Scutellospora sp. The concentration of N, P and K in G. mosseae + R. solanacearum treatment was significantly higher (N: 1.69; P: 0.51 and K: 1.65%) compared to G. margarita (N: 1.06 ; P: 0.11 and K: 1.02%) and Scutellospora sp., treatment (N: 1.48; P: 0.44 and K: 1.47%). Generally, the current findings has provided an evedance about the ability of AMF species to control bacterial wilt causal agents with significant differences between the species used. Keywords: Bio-control, wilt disease, tomato, Glomus mosseae

Bioleaching of Heavy Metals from Mine Tailings by Aspergillus fumigatus

ABSTRACT The bioleaching experiment was conducted for the removal of heavy metals from mine tailings. A fungal strain was isolated from the gold mine tailings and it has been identified as Aspergillus fumigatus based on its 18S rDNA analysis. Bioleaching using A. fumigatus was carried out in bioleaching step processes (one-step and two-step) at various tailings concentrations (1%, 2%, 4%, and 8% [w/v]). In the one-step bioleaching process where fungi were cultivated in the presence of the tailings, concentration of oxalic acid was the highest among the organic acids produced. On the other hand, in the two-step bioleaching process where the metabolic products of fungal growth, which have been separated from its biomass, were used, citric acid was dominant. In the one-step process, the highest As (62%), Fe (58%), Mn (100%), and Zn (54%) removals were observed at the lowest tailings concentration (1%). The removal of Pb at 1% tailings concentration in the one-step process was 56%, whereas 88% removal was achieved in the two-step process where citric acid was dominant. In general, heavy metals removal efficiency decreased with increased tailings of the concentration in both bioleaching processes. This study shows the possibility of using A. fumigatus to bioleach hazardous heavy meals from gold mine tailings.

Use of Lignocellulolytic Microbial Consortium and pH Amendment on Composting Efficacy of Rice Straw

ABSTRACT The present study was conducted at the Composting Unit, Universiti Putra Malaysia to determine the physico-chemical changes, microbial dynamics, and enzyme activities during microbial composting of rice straw at different pH conditions. Different treatments comprising of composting substrates (A), substrates with microbial consortium (B), substrates, microbial consortium, and acetic acid (C), substrates, microbial consortium, and sodium hydroxide (D) were used to enhance the composting process of rice straw. In inoculated treatments, the temperature increased rapidly to higher than 50°C by day 5 and remained above 40°C up to day 17, while in the control the temperature increased slowly and peaked (46°C) at day 9 and remained above 40°C until day 23. The results showed that biodegradation was at its maximum in microbial-infused treatments within 14–21 days as indicated by profiles of pH, reduction of C/N ratio, lignocellulolytic (lignin peroxidase, endoglucanase, and exoglucanase) enzyme activities, and lignocellulose bioconversion. After day 21, the C/N ratio of microbial-infused treatment without any pH adjustment (B) was reduced to 17.5 from an initial value of 29.2 suggesting that there were no additive effects of pH adjustment during the microbial composting of rice straw.

Effect of urea-N on growth and indoleacetic acid production of Stenotrophomonas maltophilia (Sb16) isolated from rice growing soils in Malaysia

Growth and activity of N2-fixing bacteria can be affected by N fertilizer application. A study was conducted at Universiti Putra Malaysia, Malaysia, to determine the effect of urea-N on the growth and indoleacetic acid (IAA) production of diazotrophic Stenotrophomonas maltophilia strain Sb16 (accession number, JQ820255), previously isolated from rice (Oryza sativa L.) growing soils of Malaysia. Five rates of N from urea fertilizer were applied (0, 50, 100, 150, and 200 kg ha-1) to the flooded rice soil and incubated in the control environment for 6 wk. Results showed that the population growth increased with increased N rates and highest population (8.2 log10 cfu mL-1) recorded in soil-standing water at the second week of incubation. The population decreased with the reduction of total N. Soil and soil water pH increased from 7.1 to 8.4 at the first week of incubation. Production of indoleacetic acid was significantly reduced with N fertilizer application. The highest indoleacetic acid (2.6 mg mL-1) was produced in the control treatment. Application of high rates of N fertilizer increased the population of diazotrophic strain Sb16 but significantly reduced indoleacetic acid production.