Nitrate is reduced by heterotrophic bacteria but not transferred to Prochlorococcus in non-axenic cultures
Nitrate is reduced by heterotrophic bacteria but not transferred to Prochlorococcus in non-axenic cultures
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DOI：
10.1111/j.1574-6941.2002.tb00976.x
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发表时间：
2002-08-01
影响因子：
4.2
通讯作者：
García-Fernández, JM
中科院分区：
文献类型：
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作者：
López-Lozano, A;Diez, J;García-Fernández, JM
原氯球菌非无菌分离株吸收硝酸盐的能力。在这项工作中涉及到，特别是来自海洋深处的三个低辐射适应菌株，其硝酸盐浓度可测量。所有研究菌株都不能将硝酸盐作为唯一的氮源。然而，所有研究的原氯球菌菌株的粗提液中都检测到了硝酸还原酶(NR；EC 1.6.6.2)的活性。对这一活性的表征明确地证明了它的酶来源。我们观察到，在黑暗条件下，体内的NR活性并没有下降。根据原氯球菌中NARB基因的特殊密码子用法设计的引物，试图用聚合酶链式反应检测NARB基因(在其他蓝藻中编码NR)，但均未成功。然而，当考虑到其他细菌的典型密码子频率来设计引物时，我们可以扩增出不同的Nas基因片段，编码细菌的同化NRS。以原氯球菌培养的污染菌落为模板，获得了类似的扩增产物。此外，在这些污染物的培养物中发现了NR活性，表明该酶来自非蓝藻来源。这些结果有力地表明，所研究的原氯球菌尽管生活在以硝酸盐为主要氮源的环境中，但缺乏NR。此外，他们还表明，异养菌产生的亚硝酸盐没有转移到原氯球菌生长，从而在所研究的培养物中丢弃了异养菌和原氯球菌之间的营养氮链。(C)2002年欧洲微生物学会联合会。爱思唯尔科学公司出版。版权所有。
The ability to assimilate nitrate in non-axenic isolates of Prochlorococcus spp. was addressed in this work, particularly in three low-irradiance adapted strains originating from ocean depths with measurable nitrate concentrations. None of the studied strains was able to use nitrate as the sole nitrogen source. Nitrate reductase (NR; EC 1.6.6.2) activity was, however, detected using the methyl viologen/dithionite assay in crude extracts from all studied Prochlorococcus strains. Characterization of this activity unambiguously demonstrated its enzymatic origin. We observed that NR activity did not decrease in vivo under darkness. Attempts to detect the narB gene (coding for NR in other cyanobacteria) by PCR with primers designed on the basis of the specific codon usage in Prochlorococcus were unsuccessful. However, when primers were designed considering the codon frequencies typical of other bacteria, we could amplify different fragments of nas genes, coding for bacterial assimilatory NRs. Similar amplification products were obtained using colonies of contaminant bacteria from Prochlorococcus cultures as PCR template. Furthermore, NR activity was found in cultures of these contaminants, demonstrating the non-cyanobacterial origin of the enzyme. These results strongly suggest that the studied strains of Prochlorococcus lack NR, in spite of inhabiting environments with nitrate as the main nitrogen source. In addition, they indicate that the nitrite produced by heterotrophic bacteria is not transferred to Prochlorococcus for growth, thus discarding a trophic nitrogen chain between heterotrophic bacteria and Prochlorococcus in the studied cultures. (C) 2002 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.