Total Aerobic Heterotrophs Research Articles

Microbial O-Methylation of the Flame Retardant Tetrabromobisphenol-A

We demonstrated the O-methylation of tetrabromobisphenol-A (TBBPA) [4,4'-isopropylidenebis (2,6-dibromophenol)] to its mono- and dimethyl ether derivatives by microorganisms present in different sediments. A most probable number assay of a marsh sediment suggested that up to 10% of the total aerobic heterotrophs may be capable of O-methylation. Although TBBPA dimethyl ether is not produced in industry, it has been detected in terrestrial and aquatic sediments. Our study supports the hypothesis that TBBPA dimethyl ether is a product of microbial O-methylation. The O-methylation of TBBPA, as well as its analog, tetrachlorobisphenol-A (TCBPA), was also demonstrated in cultures of two chlorophenol-metabolizing bacteria, Mycobacterium fortuitum CG-2 and Mycobacterium chlorophenolicum PCP-1. These strains also mediated the O-methylation of 2,6-dibromophenol and 2,6-dichlorophenol, analogs of TBBPA and TCBPA, to their corresponding anisoles, but 2,6-fluorophenol was not transformed. Due to the addition of hydrophobic methyl groups, O-methylated derivatives are more lipophilic, increasing the probability of bioaccumulation in the food chain. Future research regarding the toxicological effects of the O-methylated derivatives of TBBPA is recommended and will further elucidate potential risks to environmental and human health.

Aerobic heterotrophic bacteria and petroleum-utilizing bacteria from cow dung and poultry manure

In this study, enumeration and identification of total aerobic heterotrophic bacteria and petroleum-utilizing bacteria as well as the degradative potential of petroleum-utilizing bacterial isolates were carried out. The average counts of total aerobic heterotrophic bacteria in cow dung and poultry manure were 74.25 × 105 c.f.u. g−1 and 138.75 × 105 c.f.u. g−1 respectively. Acinetobacter sp, Bacillus sp, Pseudomonas sp, and Serratia spp. occurred as aerobic heterotrophs in both cow dung and poultry manure. However, Alcaligenes spp. occurred only in cow dung while, Flavobacterium sp, Klebsiella sp, Micrococcus sp, and Nocardia spp. occurred only in poultry manure as aerobic heterotrophs. The average counts of petroleum-utilizing bacteria in cow dung and poultry manure were 9.25 × 105 c.f.u. g−1 and 17.25 × 105 c.f.u. g−1 respectively. Pseudomonas spp. occurred as petroleum utilizer in both cow dung and poultry manure. However, Bacillus spp. occurred only in cow dung while Acinetobacter spp. and Micrococcus spp. occurred only in poultry manure as petroleum utilizers. Relative abundance of petroleum utilizers in total aerobic heterotrophs ranged from 6.38% to 20.00% for cow dung and from 9.38% to 17.29% for poultry manure. Introduction of pure cultures of petroleum-utilizing bacteria from cow dung and poultry manure into sterile oil-polluted soil revealed oil degradation in one week period.

Bedding and Within‐Pen Location Effects on Feedlot Pen Runoff Quality Using a Rainfall Simulator

Soluble salts, nutrients, and pathogenic bacteria in feedlot-pen runoff have the potential to cause pollution of the environment. A 2-yr study (1998-1999) was conducted at a beef cattle (Bos taurus) feedlot in southern Alberta, Canada, to determine the effect of bedding material [barley (Hordeum vulgare L.) straw versus wood chips] and within-pen location on the chemical and bacterial properties of pen-floor runoff. Runoff was generated with a portable rainfall simulator and analyzed for chemical content (nitrogen [N], phosphorus [P], soluble salts, electrical conductivity [EC], sodium adsorption ratio [SAR], dissolved oxygen [DO], and pH) and populations of three groups of bacteria (Escherichia coli, total coliforms, total aerobic heterotrophs at 27 degrees C) in 1998 and 1999. Bedding had a significant (P < or = 0.05) effect on NH4-N concentration and load in 1999, SO4 load in 1998, SO4 concentration and load in 1999, and total coliforms in both years; where these three variables were higher in wood than straw pens. Location had a significant effect on EC and concentrations of total Kjeldahl nitrogen (TKN), Na, K, SO4, and Cl in 1998, and total coliforms in both years. These seven variables were higher at the bedding pack than pen floor location, indicating that bedding packs were major reservoirs of TKN, soluble salts, and total coliforms. Significantly higher dissolved reactive phosphorus (DRP), total P, and NH4-N concentrations and loads at the bedding pack location in wood pens in 1998, and a similar trend for TKN concentration in 1999, indicated that this bedding-location treatment was a greater source of nutrients to runoff than the other three bedding-location treatments. Bedding, location, and their interaction may therefore be a potential tool to manage nutrients, soluble salts, and bacteria in feedlot runoff.

Microbiological parameters as indicators of compost maturity

The objectives of this study were to determine the changes of microbial properties of pig manure collected from pens with different management strategies and composted using different turning and moisture regimes; relate their association with humification parameters and compost temperature; and identify the most suitable microbial indicators of compost maturity. Six different microbial parameters, including total bacterial count, oxygen consumption rate, ATP content, dehydrogenase activity, and microbial biomass C and N, along with humification parameters [humic acid (HA), fulvic acid (FA) and HA : FA ratio] and compost temperature were monitored during composting. Significant positive correlations were found between temperature and microbial properties, including O2 consumption rate, ATP content, dehydrogenase activity, and microbial biomass N. The humification parameters also showed significant correlations with microbial properties of the manure compost. For instance, HA contents of pig manures was positively correlated with total aerobic heterotrophs, and microbial biomass N and C; and negatively correlated with O2 consumption rate, ATP content, and dehydrogenase activity. Among the six microbial parameters examined, dehydrogenase activity was the most important factor affecting compost temperature and humification parameters. Composting strategies employed in this study affected the speed of composting and time of maturation. If the moisture content is maintained weekly at 60% with a 4-day turning frequency, the pig manure will reach maturity in 56 days. The composting process went through predictable changes in temperature, microbial properties and chemical components despite differences in the initial pig manure and composting strategies used. Among the six microbial parameters used, dehydrogenase activity is the most suitable indicator of compost maturity. Compared with respiration rate, ATP content and microbial biomass procedures, dehydrogenase activity is the simplest, quickest, and cheapest method that can be used to monitor the stability and maturity of composts. The results presented here show that microbial parameters can be used in revealing differences between composts and compost maturity. The statistical relationship established between humification parameters and microbial parameters, particularly dehydrogenase activity, demonstrates that it is possible to monitor the composting process more easily and rapidly by avoiding longer and more expensive analytical procedures.

Bedding and Seasonal Effects on Chemical and Bacterial Properties of Feedlot Cattle Manure

Nutrients, soluble salts, and pathogenic bacteria in feedlot-pen manure have the potential to cause pollution of the environment. A three-year study (1998-2000) was conducted at a beef cattle (Bos taurus) feedlot in southern Alberta, Canada to determine the effect of bedding material [barley (Hordeum vulgare L.) straw versus wood chips] and season on the chemical and bacterial properties of pen-floor manure. Manure was sampled for chemical content (N, P, soluble salts, electrical conductivity, and pH) and populations of four groups of bacteria (Escherichia coli, total coliforms, and total aerobic heterotrophs at 27 and 39 degrees C). More chemical parameters of manure were significantly (P < or = 0.05) affected by season (SO4, Na, Mg, K, Ca, sodium adsorption ratio [SAR], total C, NO3-N, NH4-N, total P, and available P) than by bedding (K, pH, total C, C to N ratio, NH4-N, and available P). Bedding had no significant (P > 0.05) effect on the four bacterial groups whereas season affected all four groups. Numbers of E. coli and total coliforms (TC) were significantly higher by 1.72 to 2.02 log10 units in the summer than the other three seasons, which was consistent with a strong positive correlation of E. coli and TC with air temperature. The low ratio of bedding to manure in the pens was probably the major cause of the lack of significant bedding effects. Bedding material and seasonal timing of cleaning feedlot pens and land application of manure may be a potential tool to manage nutrients, soluble salts, and pathogens in manure.

Microbial Population Dynamics and Enzyme Activities During Composting

The changes in population size of different microbial groups (total aerobic heterotrophs, actinomycetes, fungi, fecal coliforms, ammonium- and nitrite-oxidizing bacteria, and denitrifying bacteria) and the activities of 19 different enzymes (three phosphatases, three esterases, two proteases, three amino-peptidases, and eight glycosyl-hydrolases) were examined during cocomposting of poultry litter (a mixture of poultry manure, waste feed, feathers, and wood shavings) and yard trimmings (a mixture of grass clippings, leaves, and wood barks). Three piles with forced aeration were established by mixing 2:1 (v/v) ratio of poultry litter and yard trimmings. During composting, samples were taken at three different locations (top, middle, and bottom) of the forced aeration piles for microbial and enzyme analyses. Results demonstrated that population size of different microbial groups was not a limiting factor in this composting process as the microorganisms in the poultry litter + yard trimmings compost are in great abundance. Although the numbers of these microbial groups were reduced by high temperature, their populations multiplied rapidly as composting progressed. Fecal coliforms were eliminated by day 49, suggesting that the poultry litter + yard trimmings compost showed an overall increase in diversity and relative abundance of extracellular enzymes present as composting progressed. The population of fungi and actinomycetes (microorganisms active in degradation of cellulose, hemicellulose, and lignin) were positively correlated with esterase, valine amino-peptidase, α-galactosidase, β-glucosidase, and lipase. Of all 19 enzymes examined, ß-galactosidase (enzyme involved in the hydrolysis of lactose) had the most significant positive correlation with microbial populations, such as total aerobic heterotrophs, ammonium- and nitrite-oxidizing bacteria, denitrifying bacteria, and fecal coliforms. Cystine amino peptidase, chymotrypsin, and trypsin showed no evidence of activity during the entire period of composting. This composting process represented a combined activity of a wide succession of environments in the compost pile as one microbial group/enzyme overlapped the other and each emerged gradually as a result of the continual change in temperature as well as moisture content, O2 and CO2 level, and progressive breakdown of complex compounds to simpler ones.

Removal of Nigerian light crude oil in soil over a 12-month period

Abstract A study was carried out to aid in understanding the effect of various concentrations (10, 20, 30, 40% v/w) of Nigerian light crude oil (Transniger pipeline crude, TNP) deliberately spilled on soil will have on the indigenous bacterial population and the role of the bacteria in the removal of the oil. The average total counts of aerobic heterotrophs and crude oil utilizing bacteria in oil-impacted soils were 108 and 10 6 CFU/g , respectively, while in the untreated soil the total counts of the two groups of bacteria were low. The counts of the two groups of bacteria decreased with increasing oil concentration in the soil. Significantly higher numbers of total aerobic heterotrophs were recorded between May and July while those of crude oil utilizing bacteria were recorded between February and April probably due to differences in metabolic rates of the organisms as influenced by environmental conditions. The crude oil utilizing bacteria were identified as species of Bacillus, Pseudomonas, Vibrio, Micrococcus and Alcaligenes. The total extent of crude oil degradation by these organisms ranged from 26.7% to 43.3% after 16 days. GC analysis of the crude oil extracted from soil showed that hydrocarbon components C14 to C32 were extensively lowered in soil polluted with 10% and 20% (v/w) crude oil after 12 months but moderately lowered in soil treated with 30% (v/w) crude oil over the same period. In soil contaminated with 40% (v/w) of the same crude oil, minimal degradation of C14 to C32 was observed. The results indicate that the quantity of crude oil spilled in soil and the age of the contamination influence the rate and total extent of disappearance of the oil in the environment.

Plasmid incidence in bacteria from agricultural and industrial soils

Heavy metal contents of agricultural and industrial soils were determined by atomic absorption spectrophotometry. The analysis of the samples collected from two different locations revealed significantly high levels of Fe, Zn, Cu, Cr and Ni. Certain microbiological parameters (total aerobic heterotrophs, asymbiotic N2-fixers, total Actinomycetes and fungi) were also monitored from these soils. A total of 70 bacterial isolates from agricultural and industrial soils were examined for plasmid DNA content and resistance to the antibiotics amoxycillin, cloxacillin, chloramphenicol, doxycycline methicillin, nalidixic acid, and tetracycline. Minimum inhibitory concentrations (MICs) of Cu, Cr, Pb, Cd, Hg, Zn, and Ni for each isolate were also determined. Resistance was most frequent to methicillin (48.5%), cloxacillin (45.7%), and nalidixic acid (40%) for all isolates of bacteria. The highest MICs observed were 100 μg/ml for mercury, 800 μg/ml for Ni and 1600 μg/ml for other metals. The incidences of metal resistance and MICs of metals for bacteria from industrial soil were significantly different to those of agricultural soil. On a percentage basis, 91.4% of the total bacterial isolates from industrial soil were found to harbour plasmids whereas 40% of the isolates from agricultural soil contained plasmids.

Effects of Refined Petroleum Hydrocarbon on Soil Physicochemical and Bacteriological Characteristics

The physico-chemical and bacteriological characteristics of soils as influenced by the addition of 5% gasoline, kerosene and diesel oil hydrocarbons, were investigated. Soil for study was bulked from around a car park in Port Harcourt. Soil sampling was carried out at weekly intervals for four weeks and subsequently at monthly intervals for four months, between the months of March and July 1998. Physico-chemical parameters such as organic carbon, magnesium, and sodium increased from 1.48% to 2.46%: 0.60 to 3.40meg 100g-1 soil and 0.23 to 0.77meg 100g-1 soil respectively. Nitrogen and phosphorous decreased from 0.15% to 0.07% and 35.1ppm to 10.88pm respectively while ammonium nitrate and nitrite were not affected in all soils. Calcium and potassium decreased beyond the control soil level in gasoline — contaminated soil after week 16. Counts of total viable aerobic heterotrophs ranged from 0.46 x 106 CFGg-1 soil to 1.59 x 106 CFUg-1 soil for the control soil; and from 0.56 x 106 CFUg-1 to 2.40 x 106 CFUg-1 soil for the hydrocarbon — contaminated soils. There was significant difference amongst treatments at P = 1%. (Journal of Applied Sciences & Environmental Management: 2002 6(1): 39-44)

Dynamics of yard trimmings composting as determined by dehydrogenase activity, ATP content, arginine ammonification, and nitrification potential

Microbial activities, numbers, and biomass are key parameters that can be used to elucidate the dynamics of the composting process. In the present study, four different biochemical parameters (dehydrogenase activity, ATP content, arginine ammonification, and nitrification potential) were measured (1) to monitor the dynamics of yard trimmings composting; and (2) to relate these parameters to changes in microbial numbers, physico-chemical properties, and maturity (stability) of yard trimmings compost. The initial yard trimmings was a mixture of leaves, grass clippings, and shredded bark (1:1:1 v/v). Three windrows, each having a dimension of 1.5 m (height)×4 m (length)×0.6 m in (width) were established. The temperature profile showed a rapid self-heating of the compost mass from ambient temperature of 20 to 70 °C in the first 24 h of composting. This thermophilic temperature was sustained until day 14 and then dropped to ambient level towards the end of composting (day 63). The maturation of yard trimmings compost was accompanied by a decline in pile temperature to ambient level, increases in bulk density, (NO 3 −+NO 2 −)–N, population sizes of actinomycetes and fungi, drop in C:N ratio to 20:1, and decreases and stabilisation of biochemical properties (dehydrogenase activity, ATP content, and nitrification potential) to low levels. Dehydrogenase activity, ATP content, and nitrification potential depended on the changes in C and N content during composting. These parameters were correlated with the populations of either total aerobic heterotrophs or actinomycetes, indicating the usefulness of these parameters as indicators of microbial activity and dynamics of the composting process. Arginine ammonification was dependent on the change of neither C nor N. It also did not correlate with microbial numbers, suggesting that this parameter may not be suitable for evaluating microbial activity and dynamics of yard trimmings composting.

Molecular Microbial Diversity of a Spacecraft Assembly Facility

In ongoing investigations to map and archive the microbial footprints in various components of the spacecraft and its accessories, we have examined the microbial populations of the Jet Propulsion Laboratory's Spacecraft Assembly Facility (JPL-SAF). Witness plates made up of spacecraft materials, some painted with spacecraft qualified paints, were exposed for approximately 7 to 9 months at JPL-SAF and examined the particulate materials collected for the incidence of total cultivable aerobic heterotrophs and heat-tolerant (80 degrees C for 15-min.) spore-formers. The results showed that the witness plates coated with spacecraft qualified paints attracted more dust particles than the non-coated stainless steel witness plates. Among the four paints tested, witness plates coated with NS43G accumulated the highest number of particles, and hence attracted more cultivable microbes. The conventional microbiological examination revealed that the JPL-SAF harbors mainly Gram-positive microbes and mostly spore-forming Bacillus species. Most of the isolated microbes were heat resistant to 80 degrees C and proliferate at 60 degrees C. The phylogenetic relationships among 23 cultivable heat-tolerant microbes were examined using a battery of morphological, physiological, molecular and chemotaxonomic characterizations. By 16S rDNA sequence analysis, the isolates fell into seven clades: Bacillus licheniformis, B. pumilus, B. cereus, B. circulans, Staphylococcus capitis, Planococcus sp. and Micrococcus lylae. In contrast to the cultivable approach, direct DNA isolation, cloning and 16S rDNA sequencing analysis revealed equal representation of both Gram-positive and Gram-negative microorganisms.

Effects of Acidity on the Exo-enzyme and Recycling Capabilities of a Sediment Microbial Community

ABSTRACT We determined effects of acidification on sediment aerobic heterotrophic exo-amylase and exo-protease producing microbial populations in addition to effects on the total microbial population. Acidification of microcosms to sediment pHs of 6, 5, 4, and 3 followed by plate counts showed that numbers of total aerobic heterotrophic microbes, as well as numbers exo-amylase producers and exo-protease producers, decreased at pH 3. It appears that pH 3 may represent a critical level of damage. Numbers of total aerobic heterotrophs also decreased at pH 4. Numbers of all groups increased at pH 6. An accompanying change in species composition was observed with acidification, in which a type of microbe with little production of exo-amylase or exo-protease became dominant in the microbial community as pH decreased. Analysis of three metals (Al, Pb, Cu) indicated an increased mobilization of metals from the sediments at low pHs.

Composting of spent pig litter at different seasonal temperatures in subtropical climate

To investigate the effects of seasonal temperatures on the composting of spent pig-manure sawdust litter (spent litter), two sets of experiments were carried out: one during winter, the other during summer. Physicochemical and microbial parameters including temperature, pH, inorganic N, humification indicators (HA and FA), heavy metals (Cu and Zn), total aerobic heterotrophs, ATP content and dehydrogenase activity were measured to understand changes in the spent litter during composting. Results demonstrated that the composting was faster during summer than winter. The spent litter during the summer trial reached maturity at day 56 whereas that of the winter trial was still immature at the end of composting (days 91). Microbial activities during the thermophilic stage of composting were much lower in the winter trial. Values began to increase during the latter part of composting, indicating that the spent litter in this winter trial was biologically unstable and must be further composted to reach full maturity. The changes in the microbial activities of the spent litter during summer or winter reflected the changes in their temperatures and chemical properties. The maturation of the spent litter during summer was accompanied by stabilization of the microbial and chemical properties and a drop in temperature to ambient level. Results of correlation analysis showed that temperature correlated not only with the microbial parameters but also with most of the chemical parameters. These parameters also correlated with each other. Among all the parameters measured, the trend of temperature changes is the simplest and most rapid parameter that can be used to evaluate the maturity of spent litter.

Microbial activities during composting of spent pig-manure sawdust litter at different moisture contents

The changes in microbial properties, including total aerobic heterotrophs, O 2-consumption rate, ATP content, dehydrogenase activity and microbial biomass C and N of the spent pig-manure sawdust litter were examined during further compositing. The effects of three moisture levels, 50% (pile A), 60% (pile B) and 70% (pile C), on the composting process were also evaluated. Piles A and B had very similar trends of change in temperature and microbial properties during the composting period but pile C was significantly different. Temperatures in the first two piles increased to a peak of 64–69°C by day 4, while that of pile C rose to a lower peak (58°C) on day 7. The high moisture content (about 70%) of pile C led to early cooling of the pile and decreased the production of microbial activity and biomass. Although water was added frequently to maintain the moisture content of each pile, it was difficult in practice to maintain the moisture content of pile C at 70%, since water leaked out from the pile. Therefore, a moisture content of between 50 and 60% can be considered as the optimal moisture level for further composting of the spent litter. In general, the total aerobic heterotrophs, O 2 consumption rate and ATP content of all piles increased dramatically during the thermophilic stage of composting, but then decreased slowly and were maintained at lower levels at the end of the composting process. Stability of microbial properties was observed at day 60, indicating that two months is enough to convert spent litter to a mature compost. Temperature was found to be correlated with ATP content, dehydrogenase activity and oxygen consumption rate, and so these parameters could be used to indicate microbial activity and degradation of the spent pig-manure sawdust litter.

Changes in Microbiological Properties During In-Situ Composting of Pig Manure

A 10-month study was carried out in an experimental farm in Hong Kong to examine the microbial densities and activities of the mesophilic in-situ composting process of pig manure under a ‘Pig-on-litter’ (POL) system. The effects of the commercial bacterial product recommended by this POL system (treated group) were evaluated and compared with the control pig pens (without any bacterial inoculation). The results show that there was no significant difference between the treated and control groups, both had very high microbial populations, including total aerobic heterotrophs, nitrifying and denitrifying bacteria, and microbial activities, in terms of oxygen consumption rate, content of ATP and microbial biomass C and N. These parameters were low at the beginning of the study as well as during the idle periods when no pigs were kept, but increased rapidly when pigs were kept within the pig pens and the pig manure started to deposit directly onto and mixed with the bedding material. It is clear that the pig m...

Effects Of The Inoculum Size Of A Commercial Bacterial Product And The Age Of Sawdust Bedding On Pig Waste Decomposition In A Pig-on-litter System

A 10 week study was carried out in an experimental farm in Hong Kong to examine the effects of the inoculum sizes of a commercial bacterial product imported from Taiwan on in situ composting of pig manure in a pig-on-litter (POL) system. The pig pens using fresh sawdust as bedding material were also compared with those employing aged sawdust (spent sawdust litter). The results show that high microbial populations were recorded in all pig pens. The organic matter released from the pig manure was mineralized and assimilated into microbial biomass. A process similar to mesophilic composting might have taken place. When comparing the pig pen using full dose of bacterial inoculum with that of half dosage, the densities of total aerobic heterotrophs, total fungi, nitrifying and denitrifying bacteria were not different from each other. However, the pig waste mixtures from a half-dosage pig pen had slightly lower contents of organic nitrogen, total protein, total P and total K, but wider C:N ratio. These small differences suggest that it would be possible to reduce the amount of bacterial inoculation to achieve similar "composting" results. In "fresh" and "aged" pens, the microbial population sizes were also similar. However, the waste mixtures collected from pens using fresh sawdust had lower contents of nutrients (including organic and inorganic N, P and K) but wider C:N ratios than the aged pig pen at the start of this investigation. During the 10 week study, total salts and nutrients of the fresh pens increased rapidly, but their C:N ratios dropped dramatically. On the other hand, in aged pens the changes of the nutrient and protein levels in the waste mixture were small. The bedding material of the aged pig pen was more stable and mature, rendering aged sawdust a better bedding material for the POL system.

Effects of the Inoculum Size of a Commercial Bacterial Product and the Age of Sawdust Bedding On Pig Waste Decomposition in a Pig-On-Litter System

A 10 week study was carried out in an experimental farm in Hong Kong to examine the effects of the inoculum sizes of a commercial bacterial product imported from Taiwan on in situ composting of pig manure in a pig-on-litter (POL) system. The pig pens using fresh sawdust as bedding material were also compared with those employing aged sawdust (spent sawdust litter). The results show that high microbial populations were recorded in all pig pens. The organic matter released from the pig manure was mineralized and assimilated into microbial biomass. A process similar to mesophilic composting might have taken place. When comparing the pig pen using full dose of bacterial inoculum with that of half dosage, the densities of total aerobic heterotrophs, total fungi, nitrifying and denitrifying bacteria were not different from each other. However, the pig waste mixtures from a half-dosage pig pen had slightly lower contents of organic nitrogen, total protein, total P and total K, but wider C:N ratio. These small differences suggest that it would be possible to reduce the amount of bacterial inoculation to achieve similar "composting" results. In "fresh" and "aged" pens, the microbial population sizes were also similar. However, the waste mixtures collected from pens using fresh sawdust had lower contents of nutrients (including organic and inorganic N, P and K) but wider C:N ratios than the aged pig pen at the start of this investigation. During the 10 week study, total salts and nutrients of the fresh pens increased rapidly, but their C:N ratios dropped dramatically. On the other hand, in aged pens the changes of the nutrient and protein levels in the waste mixture were small. The bedding material of the aged pig pen was more stable and mature, rendering aged sawdust a better bedding material for the POL system.

Composition ofAzospirillum species associated with wetland rice plant grown in different soils

Total aerobic heterotrophs and N2-fixing putative azospirilla associated with rice plant grown in long-term unfertilized wetland rice field at 5 sites in the Philippines were enumerated. Several azospirilla isolates were identified based on cellular morphology, biochemical tests and reaction to immunodiffusion. Azospirilla constitute about one percent of the total aerobic heterotrophs. Most (85%) of the Azospirillum isolates belong toA. lipoferum indicating its preferential colonization to the rice plant.