Biological complexity: bacteria have complex organelles (Introduction)

by David Turell , Tuesday, December 25, 2018, 15:29 (2160 days ago) @ David Turell

Recent discoveries in bacteria reveal their so-called simple protoplasm is highly complex with organelles:

https://www.the-scientist.com/features/bacteria-harbor-geometric-organelles-65114

"The investigators eventually realized they weren’t purifying viruses, but tiny, iron-laden nanocompartments native to the bacteria. (They never did figure out why the holes appeared in the cultures.)

"The structures were relatively new to science, having been described for the first time just a year earlier in the bacterium Thermotoga maritima.1 At 25–66 nm across, they are typically too small to notice unless you’re looking for them, Hoiczyk explains. But in recent years, thanks to modern genomics and bioinformatics, scientists have found nanocompartments across a range of bacterial phyla.

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"Decades earlier, scientists had first described larger structures called microcompartments—100–600 nm in diameter—that appeared in micrographs of cyanobacteria, though researchers are only building a detailed understanding of those compartments today. “It’s becoming accepted, a lot, in the last 10 or 20 years that the prokaryotic cytoplasm is highly organized,” says Cheryl Kerfeld, a structural biologist

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"Preliminary studies suggest that nanocompartments assist with stress responses, while microcompartments often have roles in metabolism. And although the details remain murky, it’s becoming clear that these structures create a specialized microenvironment for a specific purpose, says Kerfeld: “I would define them as organelles.” A growing number of researchers are now working to understand what these organelles do. Kerfeld predicts that eventually, the population of people studying bacterial compartments “is going to be as big as any eukaryotic organelle community.”

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"Yeates’s group took advantage of this fact to identify putative microcompartment groupings of shell and inner enzyme genes and extrapolate their potential functions. In 2013, the team delineated seven categories of microcompartments, including known carboxysomes and metabolosomes as well as novel types, such as one apparently involved in the metabolism of amino alcohols.5 Separately, Kerfeld, by now at Michigan State and Berkeley Lab, and her team used a similar approach to identify 23 different types of microcompartments spread across 23 bacterial phyla, as they reported the following year.

"Now, Kerfeld and Markus Sutter in her Berkeley lab are repeating the bioinformatic analysis and incorporating more genomes, including those from uncultivated species. They’ve already found more microcompartments, Kerfeld says. “The proportion of bacteria that seem to make these is rising.” A couple of species possess genes for six different kinds of microcompartments, potentially giving them access to a complex metabolism.
Why house certain reactions in tiny containers? Computer modeling indicates that microcompartments should maximize the turnover of metabolites by keeping reaction intermediates close and interfering chemicals at a distance.

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"Why house certain reactions in tiny containers? Computer modeling indicates that microcompartments should maximize the turnover of metabolites by keeping reaction intermediates close and interfering chemicals at a distance.7 For instance, concentrating the carbon-fixing enzymes RuBisCO and carbonic anhydrase in a carboxysome makes the processing of carbon dioxide more efficient.8 And cordoning off toxic reactions, such as those that produce aldehyde intermediates—a hypothesized, though unproven, job of metabolosomes—would protect the rest of the cell’s interior.

"Not all bacteria can make nano- and microcompartments. In fact, most denizens of mammalian intestines seem to lack microcompartments, although many pathogens possess them. For example, Salmonella’s microcompartments metabolize the organic compounds propanediol and ethanolamine, which are found in processed foods and the human gut. Compartmentalizing the reactions is thought to allow the bacterium to digest nutrients that members of the human intestinal microbiome cannot, allowing the pathogen to outcompete them. Other pathogens, such as Listeria and Clostridium, also contain metabolosomes."

Comment: If the first cells of life were this complex only a designer could have created them. We know that cells in eukaryotes have compartments for different production functions. It is logical to find bacteria are the same and cellular function hasn't really changed since the beginning of life. Overall complexity is simply different functioning cells coming together to make complex organisms.