Explore the vast range of titles available.

为了解农田土壤兽用抗生素污染对粮食作物水稻生长的潜在影响，选择我国养殖业中常用的抗生素之一土霉素作为目标化合物，试验研究了不同土霉素浓度水平对水稻苗期、生长期生长与产量的影响，探讨了水稻各器官中土霉素积累与土壤中土霉素浓度水平的关系。结果表明，土壤土霉素污染对水稻生长的影响主要发生在苗期，对地下部分的影响显著大于地上部分；苗期地下部生物量、根系活力、叶片叶绿素含量和氧化酶活性随浓度水平（30mg·kg^-1以上）的升高而显著降低。苗期受到土霉素污染影响的水稻其影响一直可延续至整个生育期，表现在分蘖数降低、产量减少等。土霉素在水稻各器官中的积累量大小顺序：根系〉叶片〉茎秆〉籽粒。水稻对土壤中的土霉素富集能力较小，土霉素由根部向地上部分叶、茎、籽粒的迁移作用也较弱。考虑到当前农田土壤中土霉素污染水平一般较低（多在10mg·kg^-1以下），且在谷物中土霉素积累水平较低，推断在目前农地土壤中土霉素污染水平下，其对水稻生长的直接危害相对较小。

Increasing the self-resistance levels of Streptomyces is an effective strategy to improve the production of antibiotics.To increase the oxytetracycline（OTC） production in Streptomyces rimosus,we investigated the cooperative effect of three co-overexpressing OTC resistance genes：one gene encodes a ribosomal protection protein（otrA） and the other two express efflux proteins（otrB and otrC）.Results indicated that combinational overexpression of otrA,otrB,and otrC（MKABC） exerted a synergetic effect.OTC production increased by 179%in the recombinant strain compared with that of the wild-type strain M4018.The resistance level to OTC was increased by approximately two-fold relative to the parental strain,thereby indicating that applying the cooperative effect of self-resistance genes is useful to improve OTC production.Furthermore,the previously identified cluster-situated activator OtcR was overexpressed in MKABC in constructing the recombinant strain MKRABC;such strain can produce OTC of approximately7.49 g L~（（-1））,which represents an increase of 19%in comparison with that of the OtcR-overexpressing strain alone.Our work showed that the cooperative overexpression of self-resistance genes is a promising strategy to enhance the antibiotics production in Streptomyces.

Fenneropenaeus chinensis, an economically important shrimp species, currently suffers from epizootic diseases due to high density stocking and bacterial infections. Oxytetracycline （OTC） has been widely used to treat various systemic bacterial infec- tions in shrimp farming. In the present study, the effect of gender on pharmacokinetics of OTC in F. chinensis was investigated. The OTC concentrations in hemolymph of shrimp after single intramuscular administration （75 mg OTC per kg body weight） were ana- lyzed by high performance liquid chromatography and best described with a two-compartment open model which is characterized by a short elimination half-life, low clearance, and a relatively large apparent volume of distribution. The pharmacokinetic equations were Ct= 58.54e-0.38t＋ 11.67e-0.04t for females; and Ct= 27.94e-0.28t＋ 14.87e-0.04t for males. The distribution and elimination half-lives of OTC were 1.82 and 19.58 h, respectively, in females and 2.50 and 16.11 h, respectively, in males at 22 ℃. The areas under the drug concentration curve were 480 mg L-1 h-1 in females and 430 mg L-1 h-1 in males. The total body clearance of the drug was 157.11 mL kg-1 h-l in females and 172.47mLkg-1 h-1 in males. The apparent volume distribution was 4.44 in females and 4.01 Lkg-1 in males. There was no significant difference in pharmacokinetic parameters between female and male shrimps, indicating that there is no need to consider the gender effect in clinical use of OTC in F. chinensis farming.

A two-step zero-length cross-linking procedure using active esters was successfully adopted for conjugating enrofloxacin （EF） to human serum albumin （HSA）. The derived conjugate was characterized by UV spectrum and then used for immunization of BALB/C mice. In enzyme-linked immunosorbent assay （ELISA） and competitive inhibition ELISA experiments, the derived antiserum exhibited high antibody titer （greater than 1 ： 250 000） as well as varied cross-reactivity （from 97.8% to 161.7%） to three analogs of EF belonging to fluoroquinolones family. But over the concentration range studied, no significant cross-reactivity was observed to other group of antibiotics （chloramphenicol, oxytetracycline, sulphamethoxazole and nysfungin）. It was confirmed that the synthesized immunogen was highly antigenic and elicited specific antibody responses in BALB/C mice against EF.