Let’s return to Lake’s new hypothesis about the origin of double-membrane bacteria:
Here, by analysing the flows of protein families, I present evidence that the double-membrane, Gram-negative prokaryotes were formed as the result of a symbiosis between an ancient actinobacterium and an ancient clostridium.
Since actinobacteria and clostridia might represent cells very similar to the original cells, let’s have a look at them. First, consider actinobacteria.
We’ll begin with the abstract from an extensive review:
Actinobacteria constitute one of the largest phyla among Bacteria and represent gram-positive bacteria with a high G+C content in their DNA. This bacterial group includes microorganisms exhibiting a wide spectrum of morphologies, from coccoid to fragmenting hyphal forms, as well as possessing highly variable physiological and metabolic properties. Furthermore, Actinobacteria members have adopted different lifestyles, and can be pathogens (e.g., Corynebacterium, Mycobacterium, Nocardia, Tropheryma, and Propionibacterium), soil inhabitants (Streptomyces), plant commensals (Leifsonia), or gastrointestinal commensals (Bifidobacterium). The divergence of Actinobacteria from other bacteria is ancient, making it impossible to identify the phylogenetically closest bacterial group to Actinobacteria.
Okay, so we are dealing with an immensely diverse group of bacteria. And they also appear to be good candidates for terraformers:
They include some of the most common soil life, freshwater and marine life, playing an important role in decomposition of organic materials, such as cellulose and chitin and thereby playing a vital part in organic matter turnover and carbon cycle. This replenishes the supply of nutrients in the soil and is an important part of humus formation. – Here
Even more significant in regards to terraforming is that actinobacteria can fix nitrogen from the atmosphere and engage in symbiosis with pioneer plants:
The Frankia alni ACN14a strain was isolated from a green alder (Alnus crispa) growing in Tadoussac, Canada. This bacterium is able to establish a nitrogen-fixing symbiosis with alder (Alnus spp. ) and myrtle (Myrica spp. ), two pioneer plant genera of temperate regions, found on forest clearings, mine wastes, sand dunes and glacial moraines where nitrogen is the limiting factor. – Here
Actinobacteria also provide yet another remarkable example of convergent evolution:
In addition to these costs or benefits, there is a morphological diversity which beggars belief, from the familiar bacterial shapes of cocci and rods, through to hyphal organisms, with a lifestyle pioneered before the fungi.
The hyphal fragmenting lifestyle almost shows a progression from rods to the next group of morphologically complex actinomycetes which form branching hyphae, and true spores directly on the substrate mycelium. This group includes Micromonospora and Salinospora, both of which are important producers of pharmaceutically useful products. The micromonosporas are extensive producers of aminoglycoside antibiotics, with gentamicin being the most well known.
The Micromonosporaceae exhibit some of the most amazingly complex dispersal strategies found within the actinobacteria. Several species have evolved the formation of sporangialike structures, as in fungi, essentially small sacks for holding spores. –Here
See for yourself. Here are actinobacteria:
And here are fungi:
Next, we’ll look at clostridia.