Hope has a color, and it's green. One German research team is convinced that algae（[植] 藻类） can help solve some of humanity（人性）'s greatest problems. Around the globe, biologists（生物学家） are hunting for microorganisms with extraordinary abilities, like lime-secreting（隐秘） algae（[植] 藻类）, which might one day generate climate-neutral cement. 5% of global atmospheric（大气的） CO2 comes from construction, from concrete production. Now here's a possible concrete substitute（代用品） that's the exact opposite. It doesn't produce CO2.

  It absorbs it. For over a year, we've accompanied researchers from Kaiser's Lauternes University of Applied Sciences to the depths of a Spanish cave, where life on Mars is being simulated（模拟）. Here on Earth or in space, algae could be the key. "Algae can take in waste materials and waste water and extract（提取） nutrients from it, with very little light. They can also produce oxygen. They can bind（捆绑） the CO2 we exhale（呼气）, creating oxygen and food at the same time. Algae are probably amongst the best organisms for producing food."

  An expedition in northern Spain, an hour's drive from Bilbao. These researchers, led by biologist Michael Lakatos, are exploring a cave in hopes of discovering new species of algae and furthering their research on known ones. They're not exactly sure what awaits（等候） them. There are almost 300 caves in this valley alone, and some four thousand in all of Cantabria. One cave in particular is of special interest to the German expedition team. What they discover here is mind-blowing.

  Michael Lakatos finds organisms that bear witness to the very origins of life on Earth. "I've just found this huge patch（片） with one of the oldest cyanobacteria we're aware of. It's incredible. I've never seen anything like it. It's quite incredible. I'm at a loss for words." What's left him speechless is how these bacteria, known colloquially as blue-green algae, can survive with so little light.

  "On one hand, we really want to discover and isolate new cyanobacteria and use them for biotechnological applications. At the same time, though, when we're here in such a marvellous habitat, the first question is naturally, how are they surviving? So that's what we're doing here. We're measuring photosynthesis（光合作用） with this device, but we're also seeing to what extent they've adapted to the light and how they utilize（利用） it." For the algae researchers, this Cantabrian cave is a godsend. A layperson might just see a mossy-looking rock face, but for the biologists, it's a window into a fascinating world. An extraordinary, multi-generational colony.

  "You can see this colourful surface here, these fluffy（绒毛似的） little grey-green pads（垫）. These are cyanobacteria. So are these yellow ones here. These pink, jelly-like blobs are striking. That's the particular cyanobacterium we're after, gloobacter. It's one of the oldest living cyanobacteria, so it's a very basic, primitive cyanobacterium that's living here alongside more modern species that have evolved differently. They're all living here, in the colony."

  Michiel Lakatos and Patrick Young are thrilled with the wealth of research material they've found, and excited about the new questions that arise from it. "We know that they can survive without much light, but we don't know exactly what the lower limit is. There's also the question of how exactly this works（使工作） in the low-light situation we've encountered deeper inside the cave. The cyanobacteria population there is different. We found different species. So certain processes are different here." "So the algae here is quite clever?" "Yes, they can photosynthesise in the dark."

  "We've moved even further into the cave, and despite the total darkness, find species of algae living here too." "Down here, only a hundred thousandth（第一千的） of the light from above can reach them. They're visual artists, in the dark. They've simply structured their physiology（生理学）, their photosynthesis, so they can use not only the visible light spectrum（光）, but and this would be hugely exciting they may also be able to draw from further along the range of light, in the red or in the far red." It was Spanish biologist Antonio Guillén who first drew his German colleagues' attention to the cave and sent them samples. It was the beginning of a great friendship between the Spanish and German algae researchers. "It opens up a new field of research. I find it very interesting in terms of the production and research of useful substances and materials.

  Not just the biological aspect, which is already fascinating, but also the practical applications. In that regard, Patrick and Michael's ideas are in line with ours. In other words, we're happy to continue supporting them here, and we're looking forward to working even more closely with them." The Spanish biologist works for a company that wants to model Mars missions here. They've set up a space station of sorts, deep within the cave. The algae research conducted by the German team could also be interesting for missions into space.

  "It aligns（使结盟） perfectly with our original plan to draw on the potential of these unexplored（[地质] 未勘查过的） microorganisms. They're all apparently capable of producing substances that have not yet been researched. Antibiotics（抗生素）, for instance, these organisms are in fierce（凶猛的） competition with each other, so they produce antibiotics. They produce nutrients that serve as food for other organisms, so they could serve as food for us. It could all be possible." A change of scene. We head to the laboratory at Kaisers Laotens University of Applied Sciences.

  The Parmizans campus is home to the world's largest collection of terrestrial（陆地） cyanobacteria, algae that live on land, not in water. For study purposes, they're being cultivated（培养） in liquid nonetheless（尽管如此）. Over 350 species from all over the world can be found here. "For example, here we've isolated crocoxidiopsis from the Antarctic, a unicellular alga（水藻）. Here we've isolated microcolius, a thread（线）-like alga（水藻） from very hot desert regions, and a completely new alga we've identified, from Svalbard in the Arctic, oculotella." What does that do? "It has a small red tip, quite unusual. We don't know why it's there."