蓝藻伪空胞的特性及浮力调节机制

伪空胞为蓝藻在水体中提供浮力,使其获得适宜的生长条件,最终导致蓝藻水华暴发,了解伪空胞的特征对控制蓝藻水华暴发有重要意义。文章简要回顾了蓝藻伪空胞自1865年被Klebahn发现到1965年被正式命名的研究历程,目前已发现150多种原核生物中含有伪空胞;伪空胞是两末端呈圆锥状的中空圆柱体,伪空胞半径与临界压强遵循方程:Pc=275(r/nm)-1.67MPa;伪空胞气体含量可根据不同原理,利用Walsby伪空胞测定装置、压力浊度计和细胞流式仪测得。总结了伪空胞组成的化学特性,评述了伪空胞gvp基因丛结构功能和GvpA、GvpC的蛋白空间结构。GvpA是伪空胞合成的主要成分,gvpA在伪空胞内存在多个拷贝,其功能仍不清楚;GvpC由33个氨基酸重复单位组成,重复单位越多,伪空胞越不易破裂;概述了伪空胞3种浮力调节机制:镇重物的改变、伪空胞的合成、伪空胞的破裂;归纳了环境因子(光照、温度、氮、磷、钾)参与伪空胞浮力网络调控的途径。提出了目前伪空胞研究面临的困难和问题,对伪空胞的未来研究方向提出探索性的建议。

The characteristics and buoyancy regulations of cyanobacterial gas vesicles

Gas vesicles are important factor for the occurrence of cyanobacterial water-bloom, which provide varying buoyancy for cyanobacteria to obtain favorable growth conditions. Therefore, it is important to understand the characteristics of gas vesicle for cyanobacteria water-bloom control. In this article, we introduced the research history of gas vesicle, and then conducted a systematic review about gas vesicle morphology, the relationship between the cylinder radius and critical pressure, the measurement approach of gas vesicle volume and its chemical features. Gas vesicle was discovered by Klebahn in 1895 and this name was officially accepted in 1965. So far, gas vesicles have been found in more than 150 prokaryotes. Gas vesicle shape is described as a cylinder with two cones on two ends and its cylinder radius is closely related to critical pressure following the equation: Pc= 275(r / nm)-1.67MPa. Gas vesicle volume could be measured by capillary apparatus, pressure nephelometry and flow cytometry. Furthermore, we reviewed the genetic features of gas vesicle including gvp gene cluster structure, the function and the spatial structure of gvpA and gvpC. Until now, 14 gvp genes (gvpA, gvpC, gvpN, gvpO, gvpD, gvpE, gvpF, gvpG, gvpH, gvpI, gvpJ, gvpK, gvpL, gvpM,) have been identified in gvp gene cluster, but it is still unclear that which one is imperative during the process of gas vesicle synthesis. In this paper, we summarized the function of all the 14 Gvp proteins, especially, gvpA copy number and the 33 amino acid repeat number of GvpC. GvpA is present in the gas vesicles of most cyanobacterium, but its copy number is different in various taxanomic groups. GvpC is mainly composed of 33 amino acid repeat sequences, and the increased number of which could strengthen the structure of cyanobacerial gas vesicles against collapse. The spatial structure of GvpA and GvpC protein were also described in this paper. In addition, three buoyancy regulation mechanisms and the ways of environmental factors involving in buoyancy network regulation were summarized. Gas vesicles could adjust buoyancy through change in cell ballasts, production and dilution of gas vesicles and irreversible collapse of gas vesicles. Environmental factors, such as light and nutrients are important for gas vesicles synthesis. Nitrogen and phosphorus limitation lead to gas vesicle content decrease. Continuous carbon limitation could restrain gas vesicle synthesis due to energy shortage. Additionally, we addressed the current difficulties and problems in gas vesicle researches, such as the uncertainty of whether gas vesicles exclusively determine cyanobacterial buoyancy and the difficulties to answer ecological questions based on the results of molecular biology of gas vesicles. Eventually, we proposed the future research directions in the physiological ecology and molecular biology of gas vesicles, e.g. the relative contribution of gas vesicles to regulate cyanobacterial buoyancy compared with that of gap junction, the influence of environmental factors on gas vesicles, the genetic features of gas vesicles, as well as the function and the spatial structure of individual gvp gene.