Rhizobium bacteroid development

细菌是简单的单细胞生物，缺乏植物和动物高等细胞中的膜结合结构。然而，尽管细菌可能没有那么复杂的细胞组织，但它们可以进行植物和动物所没有的大量化学反应。细菌负责许多营养物质的循环，如N2 （N2也被称为氮气，由两个氮原子由一个强大的三键结合而成），这是一种非常惰性的大气气体。氮气占大气的78%，但非常不活泼，不能直接用作氨基酸、蛋白质和DNA合成所需的氮的来源。然而，少数细菌可以将N2还原（加入氢）并将其转化为氨（NH3），氨很容易被包括细菌和植物在内的各种生物合成为氨基酸和所有其他构成生命的物质。在世界上许多地方，限制植物生长的是作为氨或相关化合物的氮的供应，而植物反过来又支持动物的生命。由于高达65%的可用氮（如氨）来自细菌，这使得它们对地球上的生命至关重要。在细菌内部，大部分的氮实际上是由一个叫做根瘤菌的家族产生的。这种显著的细菌群与豆科植物形成共生关系（双方都受益），导致根瘤的形成（在豌豆植物上，根瘤是2-3毫米的鳞茎，通过拔起植物并检查其根很容易看到）。根瘤菌被控制在根瘤内，植物为它们提供了一个理想的环境（低氧和大量的能量），在这个环境中，它们可以将N2还原成氨。氨作为氮源提供给植物，这就是为什么这被称为共生相互作用。这意味着植物不需要向土壤中添加任何氮，从而使其能够快速生长。本研究的目的是了解豆科植物根瘤内的细菌是如何发育的。在这项研究中，我们使用豌豆作为我们的模型豆类。问题包括细菌是如何在植物体内生长的，是什么因素控制了这一过程？细菌如何知道何时开启N2固定？

Bacteria are simple single celled organisms that lack the membrane bound structures found in higher cells of plants and animals. However, while bacteria may have a less complex cellular organisation they carry out a huge range of chemical reactions not found in plants and animals. Bacteria are responsible for the cycling of many nutrients such as N2 (N2 is also known as nitrogen gas and consists of two nitrogen atoms bound by a strong triple bond), which is a very inert atmospheric gas. N2 makes up 78% of the atmosphere but is very unreactive and cannot be used directly as a source of nitrogen, which is needed for amino acid, protein and DNA synthesis. However, a small number of bacteria can reduce (add hydrogen) to N2 and convert it into ammonia (NH3), which is readily incorporated into amino acids and then all the other building blocks of life, by a wide range of organisms including bacteria and plants. In many parts of the world the limitation to growth of plants, which in turn support animal life, is the supply of nitrogen as ammonia or related compounds. Since up to 65% of available nitrogen (eg ammonia) comes from bacteria this makes them essential for life on earth. Within the bacteria, most of the nitrogen is actually produced by one family known as the Rhizobiacea. This remarkable group of bacteria form a symbiotic association (both partners benefit) with plants of the legume family, that results in the formation of root nodules (on pea plants these are 2-3 mm bulbs that can easily be seen by pulling up a plant and inspecting its roots). The rhizobia are held inside the nodules where the plant provides them with an ideal environment (low O2 and lots of energy) in which they can reduce N2 to ammonia. The ammonia is supplied to the plant as its nitrogen source so this is why this is known as a symbiotic interaction. It means that the plant does need any nitrogen added to the the soil and enables rapid growth. The purpose of this research is to understand how the bacteria develop inside legume root nodules. In this reserach we use peas as our model legume. Questions include how do the bacteria grow inside plants and what factors control this process? How do the bacteria know when to switch on N2 fixation?