Chemical modification of the surfaces of bacterial cell walls.

The surfaces of the isolated cell walls of four bacterial species were studied by microelectrophoresis following chemical treatments intended to remove specific charged groups. Acid-base titrations of the walls were used to assess specificity and extent of the modifications. Carboxyl groups were specifically and completely modified by activation with a water-soluble carbodiimide and subsequent reaction with a nucleophile, such as glycinamide, to give an uncharged pH-stable product. Aqueous media and mild reaction conditions make the method suitable for modifying carboxyl groups on cell surfaces too labile to withstand the harsh conditions required for conventional esterification reactions. Use of the carbodiimide-mediated reaction for discharging carboxyl groups, along with fluorodinitrobenzene for discharging amino groups and extraction procedures for removing constituents carrying phosphoester groups (teichoic acids), made it possible to obtain information about the spatial arrangement of charged groups on the wall surfaces. Removal of the exterior negative charge dominating wall surfaces allowed underlying amino groups to become electrokinetically effective and, in the case of E. coli, also revealed a lipophilic region with an affinity for a cationic surfactant.     

Ultrastructure of rumen bacterial attachment to forage cell walls.

The degradation of forage cell walls by rumen bacteria was investigated with critical-point drying/scanning electron microscopy and ruthenium red staining/transmission electron microscopy. Differences were observed in the manner of attachment of different morphological types of rumen bacteria to plant cell walls during degradation. Cocci, constituting about 22% of the attached bacteria, appeared to be attached to degraded plant walls via capsule-like substances averaging 58 nm in width (range, 21 to 84 nm). Many bacilli appeared to adhere to forage substrates without distinct capsule-like material, although unattached bacteria with capsules were observed occasionally. Certain bacili appeared to be attached to degraded tissue via small amounts of extracellular material, but others apparently had no extracellular material. Bacilli with a distinct morphology due to an irregularly folded, electron-dense outer layer or layers (about 15 nm thick) and without fibrous extracellular material consituted about 37% of the attached bacteria and were observed to adhere so closely to degraded plant walls that the bacterial shape conformed to the shape of the degraded zone. In the rumen ecosystem, bacteria appeared to adhere to plant substrates during degradation by capsule-like material and by small amounts of extracellular material, as well as by the other means not observable by electron microscopy.