Abstract
In order to determine if micro-organisms can be found in the stratosphere, balloon-transported cryosamplers have been used to sample the stratosphere at a height of 41 km. The cryosampler cylinders were washed out with phosphate buffer which was then passed through 0·2 µm cellulose nitrate filters to trap any particles, including micro-organisms. The membranes were then gold-coated and examined using scanning electron microscopy. At all stages of the preparation of the cryosampler, balloon flight and subsequent laboratory examination, every effort was made to maintain sterility. Further details of the sampling procedure are reported elsewhere (Harris et al., 2002; Wainwright et al., 2003).
Nanoparticles were occasionally observed on the membranes. The obvious question then arose, could some of these particles be bacteria? The existence of very small bacteria (now referred to as nanobacteria) has long been recognized but largely overlooked (Wainwright, 1999). However, the finding of very small bacteria-like structures in an Allan Hills meteorite (McKay et al., 1996), despite being controversial, has once again focused attention on nanobacteria.
The surface of the membranes on which the stratospheric wash-out was deposited was seen to be covered with a variety of particulates not seen on control filters. Fig. 1(a) shows one of a large variety of such particulate masses. The initial impression is that this mass is a clump of bacteria overlaying inorganic dust. The largest cocci-like particles are of the order of 1 µm in diameter (Fig. 1a, 1), while numerous sub-micron cocci-like structures can also be seen (Fig. 1a, 2). Such masses could act as a protective carrier for stratospheric micro-organisms, as any micro-organism in the centre of the mass would be protected from the damaging effects of UV light. But do such masses contain bacteria, or are they simply a mixture of inorganic particles? One approach to answering this question would be to employ EDAX (Energy Dispersive Analysis of X-rays) analysis.