Occurrence and distribution of phosphate solubilizing bacteria and phosphatase in marine sediments at Porto Novo

The occurrence and distribution of a special group of bacteria, capable of dissolving insoluble phosphates, were studied in marine environments, especially in sediments. The phosphatase activity was also investigated. Clayey sediments contained more phosphate solubilizing bacteria and phosphatase than sandy sediments. There was a positive correlation between the total phosphate content and the phosphatase activity. The phosphatase activity was recorded in all samples, irrespective of salinity variations. The role of various factors of the sediments in maintaining the phosphate availability in the overlying water is discussed.Contribution No. 102, Marine Biological Station, Annamalai University, Porto Novo, Tamil Nadu, South India.     

Alkaline phosphatase activity in subtropical Central North Pacific waters using a sensitive fluorometric method

This paper describes a fluorometric method for assaying low levels of the enzyme alkaline phosphatase in seawater. The assay is based on the hydrolysis of the monophosphate ester bond of 3-0-methylfluorescein phosphate. This enzyme is synthesized by many microorganisms when phosphate becomes limiting. Alkaline phosphatase activity was detected in phytoplankton from the nutrient-impoverished surface waters of the subtropical Central North Pacific Ocean. The presence of naturally occurring phosphatase suggests that phosphorus may be limiting to phytoplankton growth in these waters. The phytoplankton in water samples lacking enzyme activity at the time of collection produced phosphatase within 1 to 2 days of incubation at in situ temperatures.     

黄河上游沉积物对磷酸盐的吸附动力学研究

研究了黄河上游10个不同表层沉积物在黄河水体中对磷酸盐（P）的吸附动力学及其影响因素和吸附机理。结果表明：不同黄河沉积物对P的吸附能力各不相同,但吸附量随时间的变化具有相同的趋势,吸附速率均在前8 h内较快,以后逐渐趋缓,在48 h时基本达到吸附平衡。不同黄河沉积物对P的吸附量均随P初始质量浓度的增加而增大,随沉积物质量浓度增大而减小,且也受水体pH值的影响,在pH为6.0~9.0范围内吸附量比较大。不同沉积物在不同P起始质量浓度下对P的吸附动力学均符合Lagergren二级吸附动力学模型及Weber–Morris扩散方程,求得二级吸附速率常数和扩散速率常数分别在10.85~229.29 g.mg-1.h-1和0.7×10-3~5.2×10-3 mg.g-1？h-1/2）之间,吸附过程由P在沉积物内的扩散控制。     

Factors affecting enumeration and isolation of actinomycetes from Chesapeake Bay and Southeastern Atlantic Ocean sediments

Studies of the seasonal distribution of heterotrophic bacteria in Chesapeake Bay (USA) led us to the observation that fungizone was selective for actinomycetes without appreciably altering the total viable aerobic, heterotrophic bacterial counts. A study of the actinomycete populations in the Bay was undertaken, with several media compared for ability to enrich for actinomycetes: basal, casein, Czapek, starch-casein, glycerol-glycine, chitin and oil agar No. 2. Between 40 and 100% of the colonies appearing on chitin and oil No. 2 media were found to be actinomycetes, compared with <2% for the other media employed. It was also found that if sediment samples are frozen, a practice followed when laboratory facilities are not available in the field, a decrease in the total counts and in the actinomycete colony counts occurred. However, on a proportional basis, a slight increase in the percent actinomycetes was noted. A minimum of 21 days incubation time is recommended for recovery of actinomycetes. Also, the absence of NaCl from the actinomycete isolation media and incubation temperatures ≥15°C should give good recoveries of actinomycetes. A seasonal distribution of actinomycetes was noted for Chesapeake Bay, with maximal populations of actinomycetes observed in March and November. Actinomycetes were isolated in the ocean from depths ranging from 7 to 7,790 m. Greater numbers of actinomycetes were isolated using an incubation temperature of 25°C for the estuarine stations and 15°C for the deep-ocean stations. Greater numbers of actinomycetes were associated with polluted environments close to shore.     

Effects of tetrahydrofuran on dissolved oxygen,pH, culturable aerobic microbes and enzyme activity in wastewater

Tetrahydrofuran (THF) is easy to volatilize and hard to biodegrade. Little is known about the influence and fate of tetrahydrofuran in the environment. The effects of THF were examined on dissolved oxygen, pH, culturable aerobic microbes (bacteria, actinomycetes, and fungi) and four selected enzymes (protease, phosphatase, amylase, and lipase) in wastewater. The wastewater containing some activated sludge was taken from the aeration basin in Sibao sewage plant in Hangzhou, China. THF at lower concentrations of enhanced aerobic respiration and higher concentrations decreased utilization of oxygen in wastewater. The short-term influence of THF on pH was not obvious, but the long-term effect was apparent. Inhibition of THF on culturable aerobic microbes rose with increasing THF concentrations but decreased with prolongation of incubation time. No effect of THF on the activity of protease, phosphatase, amylase, and lipase was found. Data indicate that lower concentrations of THF exert no marked influence on wastewater in an urban sewage plant.     

Phosphate enrichment in the northern Gulf of Aqaba: Regulation by carbonate sediments and impact on nitrogen elevation

The effect of carbonate sediment in regulating phosphate concentrations in sea water was investigated by laboratory incubation experiments using different sediment types. Incubation experiments were made with two types of sediments: uncontaminated sediment from a marine reserve and contaminated sediment with deposited phosphate powders. Fluxes of inorganic nitrogen and phosphate were estimated from linear regressions of solute concentrations over incubation periods. Ammonium and phosphate fluxes were about twofold higher in the uncontaminated sediment that had significantly lower organic carbon and total phosphate concentrations than in the phosphate-contaminated sediment. To test the effect of dissolved phosphate on increasing nitrogen fixation, additional incubation experiments were carried out using treated carbonate and silicate sediments with added dissolved phosphate (20 μM). Incubations were made under sterile conditions with HgCl₂ added to distinguish between biologically enhanced processes and pure physicochemical processes. The adsorption rate of phosphate onto carbonate sediment was about twice that onto silicate sediments. No nitrogen elevation either as ammonium or as nitrate was observed in the soluble phosphate enrichment incubations. In conclusion, this study demonstrates the importance of the regulation of soluble phosphate concentrations in carbonate sediment environments where the carbonate sediment acts as a buffering system keeping soluble phosphate concentrations at certain steady-state levels. The study also demonstrates the lack of evidence on enhancement of nitrogen concentrations due to the increase phosphate concentrations.     

Characteristics of culturable endophytic bacteria of Xanthoceras sorbifolia Bunge with tumor roots北大核心CSCD

Xanthoceras sorbifolia Bunge with tumor roots was discovered, and the endophytic bacteria that were isolated from the tumor roots were purified and identified. This paper aimed to study the characteristics of endophytic bacteria. The CAS detection plate, Salkowski colorimetry, phosphate solubilizing circle, and molybdenum antimony spectrophotometry were used to analyze endophytic bacteria ability, which produced siderophores, secreted indole-3-acetic acid (IAA), and dissolved phosphorus. Strains were isolated from the tumor roots through morphological and molecular identification, and they were named XSB1-XSB9, of which 6 strains belonged to Bacillus sp., 2 strains belonged to Brevibacillus sp., and 1 strain belonged to Pseudomonas sp. All 9 strains produced siderophores; strains XSB3, XSB4, XSB8, and XSB9 were extremely high yielding, and strains XSB5 and XSB6 were high yielding. The strains with high yields were XSB3, XSB4, XSB5, XSB6, XSB8, and XSB9 and accounted for 66.7% of the tested strains. Nine strains secreted IAA; the concentration of IAA secreted by the strains that contained tryptophan was between 15-50 mg/L, and the concentration of IAA secreted by the one strain without tryptophan was between 10-35 mg/L. The IAA ability of the XSB2, XSB3, XSB4, XSB5, and XSB9 strains were significantly different (P < 0.05) after adding tryptophan. These results indicate that the synthesis of IAA may be the tryptophan synthesis pathway where tryptophan is used as a precursor. All 9 strains had some ability to dissolve phosphorus. The concentration of phosphate in the solubilizing strains, XSB1, XSB2, XSB4, and XSB5, were significantly higher than that in the other strains (P < 0.01), and the concentration of phosphate solubilizing was between 50-90 mg/L; the ability to dissolve phosphate was increased by 19-29 times. The XSB4 and XSB5 strains, which produced siderophores, secreted IAA and had a strong capacity to dissolve phosphorus, may be candidate strains for promoting growth. This research provides the foundation for the development and utilization of rhizosphere microbes to understand the resistance mechanisms and cultivation level of X. sorbifolia. © 2018 Science Press. All rights reserved.     

不同生存环境和磷酸盐对4株溶磷菌溶磷能力的影响

利用液体培养法研究了不同NaCl浓度、碳源、氮源、溶解氧及磷酸盐对分离自小麦(Triticum aestivum)、苜蓿(Medicago sativa)根际的4株优良溶磷细菌(Lx81、Jm92、Dm84、Lx191)溶磷能力的影响.结果表明:(1)4株溶磷菌均为高耐盐菌株,其中Jm92和Din84维持较高溶磷量的NaCl浓度最高阈值分别为4%和8%,Lx81、Lx191在NaCl浓度超过5%时溶磷活性受到抑制.(2)Lx81的最佳碳源是葡萄糖,其次为蔗糖;另外3株菌在葡萄糖和蔗糖为碳源时,均有较高的溶磷能力;4株菌都几乎不能利用淀粉.(3)Lx81和Jm92在以(NH_4)_2SO_4和NH_4 NO_3为氮源时溶磷活性均较高,(NH_4)_2SO_4 是Lx191的最佳氮源,而NH~+-N存在会导致Dm84溶磷活性降低.(4)供试4株菌均不是专性厌氧菌,但不同菌株对氧的需求量不同.(5)4株溶磷菌对Ca_3-P和Ca_8-P有较大的溶解效率,但它们几乎都不能溶解Ca_(10)-P.图3表4参14     

Spatial variation of phosphorus fractionation in the coral reef sediments of Lakshadweep Archipelago,Indian Ocean

Surface sediments were collected from the shore and lagoons of Kavaratti, Kadamat and Agatti islands of Lakshadweep Archipelago during May 2015 and analysed for the spatial distribution of the micronutrient element, phosphorus. Phosphorus was separated by sequential extraction procedure into five fractions – exchangeable (Ex-P), iron bound, (Fe-P), calcium bound (Ca-P), organic and residual fractions (OP) and total phosphorus (TP). The average relative contribution of each P species to TP was: OP?>?Ca –P?>?Ex – P?>?Fe – P. The high concentration of organic and residual phosphorus (87–96%) compared to inorganic phosphorus is particularly evident at stations characterised by higher total phosphorus concentrations. Among the three forms of IP in the sediments, Ca-P was dominant at all stations. The OC/OP ratio ranged from 3 to 163 in the sediments, suggesting that the organic matter in sediments had been subjected to degradation. Hence, the major contribution towards organic and residual phosphorus form is from the residual fraction comprising biologically resistant or non-available phosphorus form composed of refractory materials. The concentration of phosphorus reported in the present study is higher than that of the earlier studies in Lakshadweep, indicating a terrestrial and anthropogenic in?uence on the sediment.     

丁草胺污染对高产水稻土微生物区系的影响

土壤微生物多样性是表征土壤质量最有潜力的指标,与农田生态系统的稳定性和生产力密切相关。云南永胜涛源乡是保持我国水稻小面积超高产纪录的特殊生态区,常年施用丁草胺作为选择性芽前除草剂,因此,了解丁草胺对其土壤微生物物种多样性的影响意义重大。采用平板菌落计数法,研究了模拟条件下不同丁草胺剂量（有效成分质量分数0.15、0.30和1.5 mg·kg^-1）对高产水稻土中好氧细菌（aerobic bacteria）、放线菌（actinobacteria）和真菌（fungi）,以及功能微生物自生固氮菌（nitrogen fixing bacteria）、磷酸盐溶解菌（phosphate solubilizing bacteria）和硅酸盐细菌（silicate dissolving bacteria）数量的影响。结果表明：施药7 d,中、高质量分数（0.30和1.50 mg·kg^-1）丁草胺处理好氧细菌数量比CK分别高出78.6%和153.8%,而后数量逐渐下降,表现出先刺激生长、后抑制活性的作用,低质量分数（0.15 mg·kg^-1）丁草胺对好氧细菌的生长和增殖影响不明显;施药7 d,高质量分数处理放线菌数量超过CK 75.1%,表现出明显的刺激作用;施药15 d,中等质量分数处理放线菌数量比 CK 高出125.0%,丁草胺浓度越高,刺激作用越迅速,低浓度丁草胺对放线菌则主要表现为抑制作用。低浓度丁草胺对真菌的生长和增殖基本没有影响,中等浓度有先抑制后刺激的作用,施药30 d后其真菌数量超过CK 56.9%,高浓度丁草胺则表现为抑制作用,施药7、30和45 d其真菌数量始终显著低于CK;不同浓度处理丁草胺均能刺激自生固氮菌的数量显著增加,施药7 d,低、中、高质量分数处理自生固氮菌数量分别高出CK 237.1%,179.9%和138.1%,刺激作用显著,但随培养时间延长,高浓度开始表现出抑制作用;不同浓度丁草胺均能抑制磷酸盐溶解菌的生长和增殖,低浓度处理抑制作用微弱,中、高浓度处     

玉米/花生间作条件下土壤环境因子的相关性和主成分分析

玉米/花生间作具有明显的间作优势,对作物生长和产量均有促进作用。为了阐明玉米/花生间作效应机制,测定了玉米/花生间作根际土壤养分含量、酶活性和微生物数量的变化规律,并对这些环境因子进行相关性和主成分分析。结果表明,与单作玉米和单作花生相比,玉米/花生间作显著提高了根际土壤的全氮、有效氮、有效磷含量以及脲酶和酸性磷酸酶活性,促进了间作玉米根际土壤细菌和微生物总数量显著增加。相关分析表明,有效磷含量与脲酶和酸性磷酸酶活性呈极显著正相关(P<0.01),脲酶活性和酸性磷酸酶活性显著正相关(P<0.05),真菌和放线菌数量显著正相关(P<0.05)。总钾含量和p H值、蔗糖酶活性呈显著负相关(P<0.05),蛋白酶和过氧化氢酶呈极显著负相关(P<0.01)。主成分分析获得3个主成分,解析贡献率分别为48.981%,43.617%和7.402%。第一主成分主要是放线菌、真菌、有效磷等组成,第二主成分主要为有机质和p H,第三主成分主要是总氮和细菌。经标准化后计算栽培措施得分显示:间作花生得分最高1.937,其次是间作玉米1.008,两者均显著高于单作玉米和单作花生。该研究表明玉米/花生间作系统的生态环境优于单作系统,机制解析为玉米/花生间作可明显促进土壤有效氮磷含量、脲酶和酸性磷酸酶活性及微生物数量的增加,进而改善土壤微生态环境。     

Decomposition of organic and solubilisation of inorganic phosphorus compounds by bacteria isolated from a marine sandy beach

The ability to decompose organic and to solubilise inorganic phosphorus compounds was studied in heterotrophic bacteria isolated from a sandy beach in Sopot, southern Baltic coast. Bacteria able to hydrolyse DNA and phytin were most numerous, while only a small percentage of the studied strains was able to depolymerise glycerophosphate. The ranking of the potential of the studied bacteria to solubilise metallic phosphate salts as follows: calcium hydrogen phosphate>ferric phosphate>magnesium phosphate>calcium phosphate>aluminium phosphate. There were marked differences in the level of depolymerisation of organic compounds of phosphorus and solubilisation of inorganic phosphorus between bacteria inhabiting different parts of the studied beach, while there were generally no differences between the surface and subsurface sand layers. The activity of alkaline phosphatase was higher than that of acid phosphatase.Communicated by O. Kinne, Oldendorf/Luhe     

Phosphorus release potential and pollution characteristics of sediment in downstream Nansi Lake, China

The research aimed to evaluate present and potential phosphorous pollution due to high sedimentary phosphorus load and release from sediment, when external phosphorus was reduced in downstream Nansi Lake. Pollution load of the sediment and overlying water was investigated. Kinetics and isotherms of adsorption/release of sedimentary phosphorus were studied to determine equilibrium phosphate concentration (EPC₀) and release potential. Kinetics of phosphorus adsorption on sediment and release from sediment were well described by both the pseudo-first-order rate equation and the pseudo-second-order rate equation, but more appropriate to the pseudo-second-order rate equation with the adsorption/release capacity more close to the measured values, suggesting that the processes were chemically rate controlled and dependent on adsorption capacity. Soluble reactive phosphorus (SRP) sorption isotherms on sediment were best fitted by the modified Langmuir model indicating a monolayer adsorption. By comparing EPC₀ and SRP of water, the status (adsorption, releasing or in equilibrium) of sediment phosphorus could be determined. The sediments at site S1, S3, S4, S5, and S7 where the EPC₀s were greater than the SRPs, had a potential to release phosphorus into the water column. However, those sediments at S9, S10, and S12, where the EPC₀s were approximately equal to the SRPs, were in impermanent equilibrium with overlying water in status of phosphorus, the sediments can be likely to release phosphorus to the water column once the equilibrium was broken. Therefore, sedimentary phosphorus can be a secondary pollution source in downstream Nansi Lake.     

黄河沉积物对磷的吸附行为

研究了黄河流域9个沉积物对磷的吸附行为,用修改后的Langmuir等温吸附模型对吸附实验数据进行了拟合,得到最大吸附容量PAC、Langmuir吸附平衡常数k.利用所得拟合参数通过公式计算方法得到EPC_0,以此判断沉积物是磷"源"还是磷"汇",分析了沉积物组成及其理化性质与磷吸附特征的关系.结果表明,各沉积物的吸附,解吸平衡磷浓度EPC_0范围在0.0031～0.109 3 mg/L,,其值也较低,与可解吸的内源磷含量正相关,与地理位置没有表现出相关性.在本研究条件下,在壶口张家湾断面,沉积物对磷表现为"汇";而其他沉积物对磷表现为"源",但释放量和吸附量不大.黄河沉积物对磷的最大吸附容量PAC的范围为0.073～0.454 mg/L,吸附能力较弱,沉积物的最大吸附容量与沉积物的有机质有较好的正相关关系.此外,沉积物对磷的吸附存在明显的固体浓度C_S效应,吸附滞后角随着C_S的增加而增大,随着同体浓度的增加,沉积物对P的吸附量逐渐降低,但EPCC_0值却增大,体现了颗粒物在磷循环中的两性作用.     

新疆罗布泊外围地区极端环境嗜碱放线菌生物学特性及活性物质筛选

2006～2007年从新疆罗布泊外嗣地区的泥土样品中分离了117株放线菌,初步筛选后对其中47株嗜碱放线菌进行了形态学鉴定,不同生长条件(pH值,盐NaCl、KCl、MgCl_2,碱性物质Na_2 CO_3、K_2CO_3、Mg_2CO_3、NaOH、KOH,温度)对菌株生长的影响,拮抗性、产酶活性检测及菌株LA4的分子进化鉴定等研究.结果发现,47株放线菌的15%属于诺卡氏菌属,70%属于链霉菌属,10%属于游动放线菌属,其中嗜碱链霉菌属占优势.在pH 7～11范围内,47株嗜碱放线菌均能生长.生长率为92%～95%.NaCl、KCl、MgCl,对嗜碱放线菌均具有抑制作用,NaCl、KCl的抑制作用高于MgCl_2,NaCl、KCl浓度超过10%时而MgCl_2 浓度超过15%时嗜碱放线菌完全停止生长.47株嗜碱放线菌对Na_2CO_3、K_2CO_3、MgCO_3、KOH、NaOH等碱性物质没有选择性,生长良好.47株嗜碱放线菌的最适生长温度为28～30℃.超过55℃后均不能生长.从47株嗜碱放线菌中筛选出了30株具有抗菌活性的菌株,其中对大肠杆菌有抑制作用的有11株,占36.7%,对金黄色葡萄球菌有抑制作用的有20株,占66.7%,对枯草杆菌有抑制作用的有16株,占53.3%;其中4株嗜碱放线菌LA4、LA24、LA33和LA19对3种指示菌均表现出抑制作用.在47株嗜碱放线菌中,74%具有淀粉酶活性,81%具有纤维素酶活性,43%具有蛋白酶活性,49%具有脂肪酶活性.通过分子鉴定,发现LA4为链霉菌中尚未报道的一个新亚种,其16S序列GenBank登录号为FJ182229.本研究结果表明新疆罗布泊外围地区存在大量的产纤维素酶、淀粉酶的嗜碱放线菌,并且潜藏着新的放线菌资源,为该地区嗜碱放线菌的种质资源开发和新药筛选有效菌源提供了参考.图5表4参20     

有机磷细菌的分离鉴定及其对MC-RR的响应(The Isolation and Identification of Organic Phosphorus Bacteria and Its Response to MC-RR)

从云南滇池水样中分离出具有解磷能力的有机磷细菌P-2,并利用现代分子生物学技术进行了初步鉴定.用0.01、5mg·L-1微囊藻毒素(MC-RR)处理有机磷细菌P-2,研究了MC-RR对其生长、细胞内酸碱磷酸酶活性(ACP和AKP)以及培养液中可溶性磷酸盐含量的影响.结果表明,高浓度MC-RR能显著抑制有机磷细菌的生长,延缓其细胞增殖,抑制细胞内酸碱磷酸酶活性以及培养液中可溶性磷酸盐含量的升高,因而可能改变或减缓生态系统中磷循环的进程,这表明微囊藻毒素在一定程度上可能调节水体细菌功能群落.     

庐山植物园11种植物的根际土壤氮磷有效性和酶活性

通过比较不同种源植物的土壤理化性质与生物学活性的差异及根际效应,探讨不同种源植物对庐山酸性山地土壤的环境适应性。在庐山植物园内选择引种多年的11种不同种源的常绿树种,在生长季节中采集根际土和非根际土,测定有机碳含量、碱解氮及有效磷含量、脲酶和酸性磷酸酶活性,并分析各树种根际土壤氮磷养分及酶活性的根际效应。结果表明,（1）不同树种之间的根际土壤酸性磷酸酶（P〈0.01）、有效磷（P〈0.05）和碱解氮（P〈0.01）存在明显差异,而脲酶没有差异。（2）根际与非根际土壤氮磷有效性和酶活性表现出不同的特征,大部分树种根际土壤有效磷及酸性磷酸酶存在一定的根际效应（R/S〉1）,例如红花木莲Manglietia insignis、桂南木莲Manglietia chingii及云南拟单性木兰Parakmeria yunnanensis的根际与非根际土壤有效磷含量存在显著差异（P〈0.05）,红花木莲、桂南木莲、巴东木莲Manglietia patungensis、红茴香Illicium henryi及红皮糙果茶Camellia crapnelliana与乡土树种云锦杜鹃Rhododendron fortunei根际与非根际土壤酸性磷酸酶存在显著差异（P〈0.05）。但是,根际与非根际土壤碱解氮和脲酶差异不明显,有的甚至出现脲酶的根际负效应（R/S〈1）,如巴东木莲和红花木莲等树种根际土壤低于非根际土壤（P〈0.05）。（3）不同种源树种影响下的土壤有效磷和酸性磷酸酶的根际效应（R/S比值）明显,原产西南地区的树种如桂南木莲、云南拟单性木兰和巴东木莲与华南地区的红花木莲、红茴香等土壤有效磷的根际效应（R/S〉1.5）比原产华东亚热带地区的深山含笑Michelia maudiae和云锦杜鹃更明显,相应的酸性磷酸酶的根际效应也较高。土壤脲酶和碱解氮的根际效应却不明显。（4）土壤有机碳与碱解氮、有效磷和酸性磷酸酶存在显著正相关关系（P〈0.01）,土壤碱解氮与有效磷（P〈0.01）和酸性磷酸酶（P〈0.05）具显著正相关关系,酸性磷酸酶与pH值（P〈0.05）显著负相关,说明根际土壤有机物质的积累对根际微区的理化环境及根际土壤养分活性具有重要影响。     

Mobilization of arsenic in groundwater of Bangladesh: evidence from an incubation study

The extensive extraction of arsenic (As)-contaminated groundwaters for drinking, household and agricultural purposes represents a serious health concern in many districts of Bangladesh. This laboratory-based incubation study investigated the sources and mechanisms of As mobilization in these groundwaters. Several incubation studies were carried out using sediments collected from the Bangladesh aquifer that were supplemented, or not, with different nutrients, followed by an analysis of the sediment suspensions for pH, ORP (oxidation-reduction potential), EC (electrical conductivity) and As and Fe(ΙΙ) concentrations. In the substrate-amended sediment suspensions incubated under anaerobic environment, there was a mobilization of As (maximum: 50–67 μg/l) and Fe(ΙΙ) (maximum: 182 μg/l), while the ORP value decreased immediately and drastically (as much as −468 mV to −560 mV) within 5–6 days. In the sediment suspensions incubated under control and aerobic conditions, no significant As mobilization occurred. The simultaneous mobilization of As and Fe(ΙΙ) from sediments is a strong indication that their mobilization resulted from the reduction of Fe oxyhydroxide by the enhanced activity of indigenous bacteria present in the sediments; this phenomenon also provides insights on the mobilization mechanism of As in groundwater. The concentrations of As in the sediments used in the incubation studies were strongly linked to the gradients of redox potential development that was stimulated by the quantity of organic nutrient (glucose) used. The penetration of surface-derived organic matter into the shallow aquifer may stimulate the activity of microbial communities, thereby leading to a reduction of iron oxyhydroxide and As release.     

Phosphatase activity in Eutrophic Tokyo Bay

Alkaline phosphatase activity in seawater samples taken from Tokyo Bay was measured by both spectrophotometric and fluorometric methods. A stratified distribution pattern of the enzyme was observed in August, a vertically mixed pattern in December. The distribution of phosphatase activity in the eutrophic seawater was paralleled by variations in other parameters, such as viable counts of bacteria, chlorophyll a content, inorganic and total phosphorus concentrations, amounts of seston, particulate deoxyribonucleic acids (DNA) and protein. A significant correlation between phosphatase activity and these measurements indicated that the enzyme was a good indicator of the degree of eutrophication. The positive relationship between phosphatase and inorganic phosphorus indicates that enzyme activity was not inhibited at inorganic phosphorus levels present in the bay and that production of phosphatase by microorganisms inhabiting the bay was not repressed at the inorganic phosphorus levels in the bay. Culture experiments revealed that the formation of repressible phosphatase by bacteria isolated from the bay was not affected by the inorganic phosphorus levels in the bay.     

Role of phosphate solubilizing bacteria on rock phosphate solubility and growth of aerobic rice

Use of phosphate-solubilizing bacteria (PSB) as inoculants has concurrently increased phosphorous uptake in plants and improved yields in several crop species. The ability of PSB to improve growth of aerobic rice (Oryza sativa L.) through enhanced phosphorus (P) uptake from Christmas island rock phosphate (RP) was studied in glasshouse experiments. Two isolated PSB strains; Bacillus spp. PSB9 and PSB16, were evaluated with RP treatments at 0, 30 and 60 kg ha(-1). Surface sterilized seeds of aerobic rice were planted in plastic pots containing 3 kg soil and the effect of treatments incorporated at planting were observed over 60 days of growth. The isolated PSB strains (PSB9 and PSB16) solubilized significantly high amounts of P (20.05-24.08 mg kg(-1)) compared to non-inoculated (19-23.10 mg kg(-1)) treatments. Significantly higher P solubilization (24.08 mg kg(-1)) and plant P uptake (5.31 mg plant(-1)) was observed with the PSB16 strain at the highest P level of 60 kg ha(-1). The higher amounts of soluble P in the soil solution increased P uptake in plants and resulted in higher plant biomass (21.48 g plant(-1)). PSB strains also increased plant height (80 cm) and improved root morphology in aerobic rice. The results showed that inoculation of aerobic rice with PSB improved phosphate solubilizing activity of incorporated RP.