Micro-microbes
Biologists have found impossibly small "nanobacteria" in groundwater
An international group of microbiologists found several strains of bacteria in samples of ordinary groundwater at once, whose size turned out to be several times smaller than the generally accepted minimum limit for life, according to an article published in the journal Nature Communications (Luef et al., Diverse uncultivated ultra-small bacterial cells in groundwater – VM).
"These ultra-small bacteria may be the first example of that subsection of microbial life on a planet about which we know practically nothing. They are very mysterious. We have found traces of their presence in many environments, and these bacteria most likely play an important role in microbial communities and in the work of ecosystems. We don't quite understand what they are doing yet," said Jill Banfield from the University of California at Berkeley (USA).
Banfield and her colleagues found the answer to one of the most discussed questions among biologists and evolutionists – what are the minimum limits and dimensions of life, studying groundwater samples using a powerful electron microscope.
As the authors of the article explain, today most scientists believe that there is a certain size limit for life, below which living organisms simply will not exist. It is usually understood as a certain minimum volume of a cell, which can contain genetic material and several ribosome – protein "assembly machines". This is where the consensus among scientists ends, and discussions begin about how tightly these elements can be "packed".
The Banfield group tried to find the answer to this question not in theory, but in living nature, drawing attention to the fact that in recent years their colleagues have managed to find several hundred microbes with very short and compact DNA. The authors of the article suggested that carriers of such genomes may have extremely small sizes.
To test this hypothesis, scientists have created a special system of filters, the lower "cells" in which pieces of matter smaller than 0.2 microns, which are now used in the medical industry for water sterilization, were not passed through. Having passed samples of ground water through these filters, the authors of the article studied its contents and were surprised to find several types of microbes at once, whose sizes were several times smaller than expected.
According to the calculations of Banfield and her colleagues, the volume of each such bacterium is only 0.009 cubic micrometers – in other words, they are so small that a colony of 150 such microorganisms can fit inside one escherichia coli, and 150 thousand – on the tip of a human hair.
Having discovered the existence of microbes beyond the supposed limits of life, the authors of the article tried to determine their ancestral affiliation by studying the structure of their genome. It turned out that they belong to three relatively little–studied groups of bacteria - OD1, WWE3 and OP11. According to scientists, about half of their genes have an unusual structure, and their purpose remains a mystery to geneticists.
The relatively small length of their genome – only a million genetic "letters"- nucleotides – suggests that they cannot live separately from larger bacteria that supply them with the missing proteins and nutrients. This is supported by the fact that the surface of the "mini-bacteria" is covered with numerous tendrils, which can help them exchange substances with larger counterparts.
Electronic micrographs (scale size – 100 microns) from the Berkeley Lab press release
First Detailed Microscopy Evidence of Bacteria at the Lower Size Limit of Life – VM.
As the researchers note, a few years earlier, their colleagues found almost as small archaea – bacteria-like representatives of the microcosm, more ancient in origin and possessing unique features that bring them closer to eukaryotes. Both of these facts significantly expand the possible limits of life and the potential for searching for its oldest traces on Earth and other planets.
Portal "Eternal youth" http://vechnayamolodost.ru02.03.2015