Nanobacteria are the smallest cell-walled bacteria, only recently discovered in human and cow blood and in commercial cell culture serum. Nanobacteria do show several extreme properties, such as growth in over 5% sodium chloride, small size, very slow growth rate and ability to survive under unfavorable conditions, including lack of nutrients, boiling temperature, high pressure and 1.5 Mrad dose of gamma irradiation. Environmental changes can cause drastic changes in their unit size: under unfavorable conditions they form very large multicellular units. Yet, they can release elementary particles, some of which are less than 100 nm in size, smaller than many viruses. Although metabolic rates of nanobacteria are very slow, they can produce carbonate apatite on their cell envelop mineralizing rapidly most of the available calcium and phosphate. Nanobacteria belong to, or may be ancestors of, alpha-2 subgroup of Proteobacteria. They may still partially rely on primordial life-strategies, where minerals and metal atoms associated to membranes, played catalytic and structural roles reducing the number of enzymes and structural proteins needed for life. Simple metabolic pathways apparently only compatible with life in very small cells, may support the 10,000-fold slower growth rate of nanobacteria, as compared to the common bacteria. Simplistic life-strategy may also explain the endurability of this life-form in extreme environmental conditions.