一株生长pH较宽的产甲烷菌分离与系统发育分析

采用Hungate厌氧操作技术,从造纸厂阴沟污泥中分离到一株生长pH范围为5.5～9.5的产甲烷菌株SH4.该菌对酸碱具有良好的适应性,培养3d后,在初始pH值6.0～8.0的培养基中甲烷产量相差不大,且基本达到最大产量.SH4革兰氏染色阳性,短杆状,多数单生,不运动;菌落近圆形,微黄;利用H2+CO2或甲酸盐作为唯一碳源生长,不利用乙酸盐,对氯霉素非常敏感.该菌最适生长pH为7.0,最适生长温度为35℃,最适NaCl浓度为0～1.5%.实验表明,与仅添加厌氧污泥作为接种物相比,添加SH4菌液可使产甲烷启动时间缩短1/3,甲烷总产量亦有大幅提高.形态、生理生化特征以及16S rDNA序列分析表明,该菌为嗜树木甲烷短杆菌(Methanobrevibacter arboriphilus).

Effects of Soil pH on Growth and Dry Matter Accumulation of Tobacco Plants

In order to clarify the relationships between soil pH and flue-cured tobacco growth and dry matter accumulation, effects of soil pH on root morphology and vigor, aboveground agronomic traits and dry matter accumulation of flue-cured tobacco were investigated by pot experiment. The results showed that on the whole, the intensity of soil pH on flue-cured tobacco growth and dry matter accumulation ranked as pH=6＇s 〉 pH=7＇s 〉 pH=5＇s 〉 pH=4＇s 〉 pH=8＇s. Acidic soil （pH=4） was not conducive to the early growth of tobacco plants, reduced root vigor and affected dry matter accumulation; and alkaline soil （pH=8） was not conducive to the growth of tobacco roots and shoot, reduced root vigor and affected dry matter accumulation. In conclusion, the suitable pH of soil for growth of flue-cured tobacco in Xiangxi is 5-7, but weakly acidic soil is the best.

Seedling Growth of Cassia tora, Cassia occidentalis and Cassia sophera in Relation to Salinity and pH

The paper aimed to investigate the growth of seedlings of three species of Cassia （C tora, C. sophera and C occidentalis） at different concentrations of salinity （NaC1） and pH treatments. All the species showed the highest seedling length under control condition, and with the increase of salinity, C occidentalis showed the highest sensitivity. The seedling length of C tora at 0.05 M NaCI significantly （P = 0.05） decreased to 5.71 cm, and further increase of salinity to 0.1 M, the seedling length was decreased to less than the value of 0.05 M NaC1 treatment and one-third （2.15 cm） of that of control （6.92 cm）. Seeds of all the species failed to germinate at 0.5 M NaC1. Scarified seeds of C. sophera and C occidentalis increased seedling length. The highest seedling length was in C. sophera, followed by C. tora and C. occidentalis. All the species showed significant decrease （P 〈 0.05） of fresh weight with the increase of salinity; scarification of seeds in C. occidentalis and C. sophera showed higher fresh weight than those of without scarification. Experiments at different pH levels did not show any significant （P = 0.05） change in seedling length, except C. sophera, while at acidic pH, both seedling length and dry weight were significantly （P 〈 0.05） decreased.

A Two-stage pH and Temperature Control with Substrate Feeding Strategy for Production of Gamma-aminobutyric Acid by Lactobacillus brevis CGMCC 1306

Methods to optimize the production of gamma-aminobutyric acid （GABA） by Lactobacillus brevis CGMCC 1306 were investigated. Results indicated that cell growth was maximal at pH 5.0, while pH 4.5 was pref-erable to GABA formation. The optimal temperature for cell growth （35 °C） was lower than that for GABA forma-tion （40 °C）. In a two-stage pH and temperature control fermentation, cultures were maintained at pH 5.0 and 35 °C for 32 h, then adjusted to pH 4.5 and 40 °C, GABA production increased remarkably and reached 474.79 mmol·L-1 at 72 h, while it was 398.63 mmol·L-1 with one stage pH and temperature control process, in which cultivation con-ditions were constantly controlled at pH 5.0 and 35 °C. In order to avoid the inhibition of cell growth at higher L-monosodium glutamate （L-MSG） concentrations, the two-stage control fermentation with substrate feeding strat-egy was applied to GABA production, with 106.87 mmol （20 g） L-MSG supplemented into the shaking-flask at 32 h and 56 h post-inoculation separately. The GABA concentration reached 526.33 mmol·L-1 at 72 h with the fer-mentation volume increased by 38%. These results will provide primary data to realize large-scale production of GABA by L. brevis CGMCC 1306.

Identification and Physiological Properties of Bifidobacterium Strains Isolated from Different Origin

Bifidobacteria play an important role in maintaining human health, and suppress harmful bacteria by controlling the pH of the large intestine. About 14 strains of the Bifidobacteria have been isolated from the faeces of infants nursed exclusively from the maternal milk （their ages less than 5 months） from commercial French yoghurt （active bifidus] and from milk （celia bifidus） on MRS medium （containing 0.05% cysteine-HC1, with nalidixic acid 2 mg rel）. A total of six strain are strict anaerobic and gram-positive Bifidobacteria, identified as, B. longum （60% of the samples） was the most frequently found species, followed by B. bifidum （21.0%）, B. breve （19%）. These strains were evaluated for potential use as probiotics based on their adhesion to intestinal epithelial cells, resistance towards acidic （resistance to low pH） and bile conditions, pH values ranging from 6.5 to 7, however, these strains are sensitive to the pH 8, Bifidobacterium are mesophiles with optimal growth at 36℃ to 41℃. All isolates studied have a fast growth in glucose.

Stimulated Growth of Aerobic Microbes Using Calcium Peroxide

With continuous and slow oxygen-release characteristic, calcium peroxide （CaO2） has been a new source of supplying oxygen for aerobic microbes in bioremediation of contaminated groundwater. Batch experiments were conducted to evaluate the oxygen-release rate of CaO2reacting with water, the regulation of high pH, as well as the growth of mixed aerobic microbes in the medium containing CaO2, The results show that the oxygen-release process of CaO2 comprises three phases. In the first phase, dissolved oxygen levels of water increased sharply, and average oxygen-release rates increased as the adding weight of CaO2 increased, However, the rates almost kept invariable in the latter phases and were approximately 0.48; and 0. 084 mg O2·h^-1, respectively. As the necessary components of medium, potassium dihydrogen phosphate （KH2PO4 ） and amrnoniurn sulphate （（NH4）2SO4） at a certain ratio could regulate pH caused by CaO2 from 12, 1 to the range of 6.5 -8.5, which is helpful for microbial growth, In addition, diauxic growth curve observed in the medium containing CaO2 suggested that the growth of mixed aerobic microbes could be stimulated by the addition of CaO2.

Microbiologically Induced Corrosion of Concrete and Protective Coatings in Gravity Sewers

Microbiologically induced corrosion of concrete （MICC） and its protective coatings has a high eco-nomic impact on sewer maintenance and rehabilitation. A better understanding of the micro-organisms and the bio- genie acids that are generated in the sewer is essential in controlling the corrosion of concrete pipes and protective coatings. The role of succession of micro-organisms growth in the corrosion of concrete and protective coatings was evaluated in this study. Examination of various sewer pipe materials exhibiting various extents of degradation, including concrete, cement based and epoxy based coating revealed the presence of both organic and biogenic sulphuric acids. This reflects the activity of fungi and the thiobacilli strains. Organism growth and metabolism were strongly related to the substrate pH. Fungi were found to grow and metabolise organic acids at pH from 2.0-8.0. Whilst the thiobacilli strains grew and generated sulohuric acids at oH below 3.0. The successive growth of the organisms provides an impgrtant bearing in deyeloping improved strateegies.to better manage sewers.