The ability of bacteria to attach to surfaces and develop into a biofilm has been of considerable interest to many groups in numerous industries, including the medical and food industry. However, little is understood in the critical initial step seen in all biofilm development, the initial bacterial cell attachment to a surface. This initial attachment is critical for the formation of a bacterial biofilm, as all other cells within a biofilm structure rely on the interaction between surface and bacterial cell for their survival. This review examines what are believed to be some of the most important aspects involved in bacterial attachment to a surface.

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Aims: This project aimed to investigate the mechanism of attachment of the vegetative cells and spores of thermophilic bacilli to stainless steel with a view to devising strategies to limit bio®lm development and survival. Methods and Results: Spores and vegetative cells of bacterial isolates were exposed to protein denaturing agents (sodium dodecyl sulphate (SDS) and trypsin) and polysaccharide removing agents (sodium metaperiodate, trichloroacetic acid (TCA) and lysozyme). Treatment with sodium metaperiodate, TCA and lysozyme increased the number of vegetative cells attaching in many of the strains studied, while SDS and trypsin decreased attachment. Spores attached to stainless steel in greater numbers than vegetative cells, and the various treatments had less effect on this attachment than for vegetative cells. Viability of the cells or spores was not an important factor in attachment, as cells and spores rendered non-viable also attached to stainless steel in similar numbers. Coating the stainless steel with skim milk proteins decreased the attachment of both vegetative cells and spores. There was no correlation between the degree of attachment and the amount of extracellular polysaccharide (EPS) produced by each strain, surface hydrophobicity or zeta potential of vegetative cells or spores, though spores were found to be more hydrophobic than vegetative cells. Conclusions:The results suggest that bio®lm formation by these thermophilic bacilli is probably a multifactorial process, and that cell-surface proteins play a very important role in the initial process of attachment during the formation of bio®lms by these bacteria. Signi®cance and Impact of the Study: This information will provide direction for developing improved cleaning systems to control bio®lms of thermophilic bacilli in dairy manufacturing plants.

Fruit DMC can therefore be measured before or at harvest, and be used to predict the sensory potential for the fruit after storage.

Four-year-old apple (Malus x domestica Borkh.) trees cv. 'Braeburn' on M.26 rootstock were thinned at full bloom to establish six crop loads ranging from a heavy crop to a deflowered treatment. At harvest, mean yield per tree varied from 0 to 38 kg and mean fruit weight ranged from 225 g in the heaviest cropping treatment to 385 g in the lightest cropping treatment. Light cropping resulted in a significant advance in fruit maturity as indicated by background color, starch/iodine score and soluble solids. There were small differences in leaf photosynthetic rate among the treatments when shoot growth was active. However, in early January, coincident with cessation of shoot growth and maximum rate of accumulation of fruit weight, leaf assimilation rate was reduced by as much as 65% on the deflowered trees compared to the trees carrying the heaviest crop. Leaf assimilation rate showed a curvilinear response to crop load at this time, with little increase in leaf assimilation when crop load exceeded 12 fruit m(-2) leaf area.

Aims: To determine the potential for Bacillus stearothermophilus cells to form bio®lms of signi®cance in dairy manufacture. Methods and Results: The ability of isolates of B. stearothermophilus from dairy manufacturing plants to attach to stainless steel surfaces was demonstrated by exposing stainless steel samples to suspensions of spores or vegetative cells and determining the numbers attaching using impedance microbiology. Spores attached more readily than vegetative cells. The attachment of cells to stainless steel was increased 10±100-fold by the presence of milk fouling the stainless steel. The growth of B. stearothermophilus as a bio®lm on stainless steel surfaces was determined using a continuously¯owing experimental reactor. Vegetative cells were released in greater numbers than spores from bio®lms of most strains studied. Bio®lms of one strain (B11) were studied in detail. Bio®lms of > 10 6 cells cm À2 formed in the reactor and released approximately 10 6 cells ml À1 into milk passing over the bio®lm. A doubling time of 25 min was calculated for this organism grown as a bio®lm. Conclusions: The formation of bio®lms of thermophilic Bacillus species within the plant appears to be a likely cause of contamination of manufactured dairy products. Methods to control the formation of bio®lms in dairy manufacturing plants are required to reduce the contamination of dairy products with thermophilic bacilli. Signi®cance and Impact of the Study: Bio®lms of B. stearothermophilus growing in dairy manufacturing plants can explain the contamination of dairy products with these bacteria.

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Effect of crop load on tree growth, leaf characteristics, photosynthesis, and fruit quality of 5-year-old `Braeburn' apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] trees on Malling 26 (M.26) rootstock was examined during the 1994-95 growing season. Crop loads ranged from 0 to 57 kg/tree [0 to 1.6 kg fruit/cm2 trunk cross sectional area (TCA) or 0 to 8.7 fruit/cm2 TCA]. Fruit maturity as indicated by background color, starch/iodine score, and soluble solids was advanced significantly on low-cropping trees compared to high-cropping trees. Whole-canopy leaf area and percentage tree light interception increased linearly with a significant trend as crop load decreased. From midseason until fruit harvest, leaf photosynthesis decreased significantly on lighter cropping trees and similarly, a positive linear trend was found between whole-canopy gas exchange per unit area of leaf and crop load. Leaf starch concentration in midseason increased linearly as crop load decreased, providing some explanation for the increased down-regulation of photosynthesis on trees with lower crop loads. After fruit harvest, the previous crop loads had no effect on leaf photosynthesis and preharvest differences in whole-canopy gas exchange per unit area of leaf were less pronounced. At each measurement date, daily whole-canopy net carbon exchange and transpiration closely followed the diurnal pattern of incident photosynthetic photon flux. The photochemical yield and electron transport capacity depended on crop load. This was due mostly to reaction center closure before harvest and an increased nonphotochemical quenching after harvest.