Biochemistry and physiology of nitrogen fixation

Astrovirology, Astrobiology, Artificial Intelligence: Extra-Solar System Investigations

This chapter attempts to encompass and tackle a large problem in Astrovirology and Astrobiology. There is a huge anthropomorphic prejudice that although life is unlikely, the just-right Goldilocks terrestrial conditions mean that the just-right balance of minerals and basic small molecules inevitably result in life as we know it throughout our solar system, galaxy, and the rest of the universe. Moreover, when such conditions on planets such as ours may not be quite right for the origin of life, it is popularly opined that asteroids and comets magically produce life or at the very least, the important, if not crucial components of terrestrial life so that life then blooms, when their fragments cruise the solar system, stars, and galaxies, and plummet onto appropriately bedecked planets and moons.

It is no longer extraordinary to detect extraterrestrial solar systems. Moreover, since extra-solar system space exploration has commenced, this provides the problem of detecting life with enhanced achievability. Small organisms, which replicate outside of a living cell or host, would not be catalogued as viruses. How about viruses that cohabit with life? On the Earth, viruses are a major, if underestimated, condition of life – will that be the case elsewhere? Detection of extra-solar system viruses, if they exist, requires finding life, since viruses necessitate life to replicate. (It should be noted, though, that viruses could be detected through various types of portable ultra-microscopes, including Electron Microscopes (EM) (scanning and transmission) as well as Atomic Force Microscopes (AFM).) However, extra-solar system detection of life does not oblige that viruses exist ubiquitously. Viruses are important potential components of biospheres because of their multiple interactions and influence on evolution, although viruses are small and obligatory parasitic. In addition, nanotechnology – living or replicating nano-synthetic machine organisms might also be present out there, and require consideration as well. An imposing caveat is that, if found, could some extraterrestrial viruses and synthetic nanotechnological microorganisms infect humans?

Possibly, intelligence and cognition may at times be contemporaneous with life. Concomitantly, life and viruses that may be detected, could well be impacted upon by intelligences existing on such exoplanets (and vice versa). Coming to an understanding of the plurality of extraterrestrial intelligence is an optimal objective, in order to avoid causing harm on exoplanets, as well as avoiding conflict and possible human devastation. This is especially the case if we encounter greatly advanced galactic-level civilizations, compared to terrestrial civilizations. Their machine and bionic technologies on the Dyson engineering civilization scale may be prominently superior to ours; their biological expertise may be similarly critically radical. For example, they may use viruses for purposes for which we are barely aware, and which could be utterly deadly for humans.

A series of steps is being taken in space exploration. Scientists hypothesize and claim that types of life may be near the Earth, in the solar system, and outside the solar system, similar to ours in the sense that only such conditions, Goldilocks conditions, are key sine qua non requirements, based on our terrestrial chemistry and biochemistry. If detected within the solar system, will life or its remnants resemble terrestrial life? Outside the solar system a similar chauvinism exists, although the likelihood for life, in any event, remains probably low, according to more cautious approaches to the problem. The study of our solar system includes planets, asteroids, comets, and other planetesimals that have been in overall contiguity during several billion years; anthropomorphisms claims life consequently has been developing along terrestrial-type mechanisms. However, a non-anthropomorphic view would surmise, probably not, especially for extra-solar system locales. The prime warning and admonition in all these deliberations is the contamination and damage, which current and past practice and procedures has caused and continues, due to insufficient biocontainment concepts and technology to date.

Advances in the development of robotics, artificial intelligence (AI), and high capacity ultrafast quantum computers (QC) greatly enhance the sophisticated control and logical development of extra-solar system studies. Consequently, future long-range manned space exploration seems unwarranted. Clearly, reduced dangers to human health and safety, will result from the use of intelligent machine-based investigations and besides, with increased cost-effectiveness. Space exploration comes at great cost to humanity as a whole and utilizes global resources. Consequently, appropriate organizational measures and planning/cooperation need to be in place. Moreover, the bottom line is that despite all the slogans and claims, there have been next to no financial benefits to our planet as a whole. Such financial and heedless difficulties need to be addressed, the sooner the better. In addition, prior to exposure to exoplanetary life, deep understanding of the problems of infectious diseases and immune dysfunction risks are needed. In addition, global efforts should avoid serendipity and stochasticity as this work should be directed with long-term organization, commitment, scientific, and technological methodology. This chapter briefly reviews such questions assuming a new paradigm for oversight of extrasolar system viral investigations including intelligence and life. Finances are included as an essential adjunct.

The contribution of bacteroidal nitrate and nitrite reduction to the formation of nitrosylleghaemoglobin complexes in soybean root nodules

It is becoming recognized that leghaemoglobin constitutes an important buffer for the cytotoxic nitric oxide radical (NO(*)) in root nodules, although the sources of this NO(*) within nodules are unclear. In Bradyrhizobium japonicum bacteroids, NO(*) can be produced through the denitrification process, during which nitrate is reduced to nitrite by the periplasmic nitrate reductase Nap, and nitrite is reduced to NO(*) by the respiratory nitrite reductase NirK. To assess the contribution of bacteroidal denitrification to the NO(*) within nitrate-treated soybean nodules, electron paramagnetic resonance and UV-visible spectroscopy were employed to study the presence of nitrosylleghaemoglobin (LbNO) within nodules from plants inoculated with wild-type, napA or nirK B. japonicum strains. Since it has been found that hypoxia induces NO(*) production in plant root tissue, and that plant roots can be subjected to hypoxic stress during drought and flooding, the effect of hypoxic stress on the formation of LbNO complexes within nodules was also investigated. Maximal levels of LbNO were observed in nodules from plants treated with nitrate and subjected to hypoxic conditions. It is shown that, in the presence of nitrate, all of the LbNO within normoxic nodules arises from nitrate reduction by the bacteroidal periplasmic nitrate reductase, whereas Nap activity is only responsible for half of the LbNO within hypoxic nodules. In contrast to Nap, NirK is not essential for LbNO formation under any condition tested.

The role of Bradyrhizobium japonicum nitric oxide reductase in nitric oxide detoxification in soya bean root nodules

The identification of nitric oxide-bound leghaemoglobin within soya bean nodules has led to the question of how Bradyrhizobium japonicum bacteroids overcome the toxicity of this nitric oxide. It has previously been shown that one candidate for nitric oxide detoxification, the respiratory nitric oxide reductase, is expressed in soya bean nodules from plants supplied with nitrate. In this paper, the role of this enzyme in nitric oxide detoxification is assessed and discussion is provided on other possible B. japonicum nitric oxide detoxification systems.

Evidence that the plant host synthesizes the heme moiety of leghemoglobin in root nodules

Although it is well established that the plant host encodes and synthesizes the apoprotein for leghemoglobin in root nodules, the source of the heme moiety has been uncertain. We recently found that the transcript for coproporphyrinogen III oxidase, one of the later enzymes of heme synthesis, is highly elevated in soybean (Glycine max L.) nodules compared with roots. In this study we measured enzyme activity and carried out western-blot analysis and in situ hybridization of mRNA to investigate the levels during nodulation of the plant-specific coproporphyrinogen oxidase and four other enzymes of the pathway in both soybean and pea (Pisum sativum L.). We compared them with the activity found in leaves and uninfected roots. Our results demonstrate that all of these enzymes are elevated in the infected cells of nodules. Because these are the same cells that express apoleghemoglobin, the data strongly support a role for the plant in the synthesis of the heme moiety of leghemoglobin.

Nitrogen fixation genes involved in the Bradyrhizobium japonicum-soybean symbiosis

The symbiotic nitrogen fixation genes (nif, fix) of Bradyrhizobium japonicum, the root nodule endosymbiont of soybean, are organized in at least two separate chromosomal gene clusters. These genes code for proteins of the nitrogenase complex, for proteins involved in their assembly with cofactors and for putative electron transport functions. One gene, nifA, codes for a transcriptional regulatory protein that plays a central role in the control of expression of the other genes in response to the cellular oxygen status. Only at low partial pressures of O2 will the target promoters be activated by NifA.