Cadmium accumulation by a Citrobacter sp. growing in the presence of the metal occurred as a sharp peak during the mid-exponential phase of growth, but cultures showed considerable inhibition of growth compared to cadmium-free controls. This problem was overcome by pregrowing the cells in cadmium-free medium and subsequently exposing them to the metal in the resting state, under which conditions higher concentrations of cadmium were tolerated and metal uptake was enhanced. This ability was retained when the cells were immobilized and then challenged with a flow containing Cd2+; 65% of the metal presented was removed from solution. The influence on uptake of the composition of the exposure buffer and of various cell treatments were investigated and the results are discussed with respect to the anticipated speciation of the cadmium presented to the cells and also with respect to the probable mechanism of metal uptake. This is thought to occur through the activity of a cell-bound phosphatase, induced during pre-growth by the provision of glycerol 2-phosphate as sole phosphorus source. Continued enzyme function in resting cells would then precipitate the metal as cell-bound cadmium phosphate.

Cleft lip and palate is the most common of the congenital conditions affecting the face and cranial bones and is associated with a raised risk of difficulties in infant-caregiver interaction; the reasons for such difficulties are not fully understood. Here, we report two experiments designed to explore how adults respond to infant faces with and without cleft lip, using behavioural measures of attractiveness appraisal (‘liking’) and willingness to work to view or remove the images (‘wanting’). We found that infants with cleft lip were rated as less attractive and were viewed for shorter durations than healthy infants, an effect that was particularly apparent where the cleft lip was severe. Women rated the infant faces as more attractive than men did, but there were no differences in men and women's viewing times of these faces. In a second experiment, we found that the presence of a cleft lip in domestic animals affected adults' ‘liking’ and ‘wanting’ responses in a comparable way to that seen for human infants. Adults' responses were also remarkably similar for images of infants and animals with cleft lip, although no gender difference in attractiveness ratings or viewing times emerged for animals. We suggest that the presence of a cleft lip can substantially change the way in which adults respond to human and animal faces. Furthermore, women may respond in different ways to men when asked to appraise infant attractiveness, despite the fact that men and women ‘want’ to view images of infants for similar durations.

Cells of a strain of a Citrobacter sp., pre-grown in cadmium-free continuous culture, accumulated cadmium extensively when resuspended in a buffer that contained Cd'+ and glycerol 2-phosphate. The accumulated compound was identified by X-ray microanalysis and magic angle spinning NMR analysis as cell-bound cadmium phosphate, probably CdHPOS. Its accumulation is consistent with the activity of a phosphatase, induced during pre-growth, that continues to function in the resuspended cells to liberate HPO$-from glycerol 2-phosphate. This anion then combines with Cd'+ to form insoluble cell-bound CdHPOj. (Michel et al., 1986) present in the perfusing cadmium-containing solution, suggested an enzymically mediated metal uptake mechanism, possibly involving an acid-phosphatasetype enzyme cleaving the organic phosphate to yield HPOS- (Kawabe et al., 1981); indeed, quantitative conversion of glycerol 2-phosphate to inorganic phosphate by Citrobacter cells that have not been exposed to metals has been observed (Macaskie et al., 1987). The inorganic phosphate released would then precipitate with Cd2+ to form insoluble cadmium phosphate; a kinetic interpretation of the release of inorganic phosphate and the accumulation of cadmium by immobilized cells supports a reaction mechanism of this type in this Citrobacter sp. (Macaskie et al., 1987), while previous studies on the uptake of lead by a different strain of Citrobacter (see below) suggested that the lead was accumulated as PbHPOS (Aickin et al., 1979).In contrast to the evidence for the role of phosphatase in metal accumulation, direct evidence for the production of cell-bound cadmium phosphate has been hitherto lacking; information on t Present address : Microbiology Unit, Department of Biochemistry, University of Oxford, South Parks Road, Abbreviation : MASN MR, magic angle spinning nuclear magnetic resonance.Oxford OX1 3QU, UK. 0001-3593 0 1987 SGM

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