A mixture of inorganic mineral grains comprised mainly of silica with linked SiO4 tetrahedra together with organic grains characterised by the spectrum of an ‘average’ bacterium provides excellent agreement with astronomical data relating to broad 10 and 20μm emission and absorption features. Mineral clay-like particles of radii ∼0.01 μm are most likely to condense in the atmospheres of Mira-type stars and be expelled by radiation pressure into interstellar space. These particles would tend to stick onto the surfaces of bacterial grains in conditions of high density associated with regions of star formation.