Sediment particles and their associated bacteria did not disperse within 60 s of sonication
until a threshold value of 75 W was applied. At the 100 W power level bacterial and
sediment dispersion began within 5 s of sonication (Fig. 3). Maximum bacterial numbers
were observed after 30 s treatment. At 125 W maximal numbers of bacterial cells were
observed after 15 s of sonication, thereafter the bacterial counts declined as the time of
sonication increased (Fig. 3). In all cases, small aggregates of bacterial cells and detrital
material remained after sonication. There still appeared to be colloidal material surrounding the bacterial and sediment aggregates after treatment with sonication. Sediment
samples have been previously shown to require extensive treatment before interference
from detrital particles and background fluorescence was eliminated (Montagna, 1982).
Bacterial lysis may occur upon prolonged homogenization (Montagna, 1982).
It is likely that sonication severs some of the bridging polymers, causing large aggregate
disruption (Marshall, 1980 ; Bingle, 1980). The bacteria and sediment material also
accumulated at the edges of the filter adjacent to the glass barrel rather than spreading
evenly over the entire filter. This may be due to the negative charge on the surface of
bacterial cells and sediment particles at pH 7.9 resulting in attraction to the glass surface
of the filter assembly. This may be mediated by cationic bridging mechanisms (Costerton
et al., 1978). Adherence of bacteria to glass can be reduced by coating the surface with
dimethyldichlorosilane (Garvey et ai, 1977).
Treatment of sediment and kelp discs with hydrochloric acid, sodium hydroxide, sodium
carbonate, tetrasodium pyrophosphate and sodium periodate, respectively, followed by
vortex-mixing, under the experimental conditions, did not result in bacterial and sediment disaggregation or bacterial detachment from the kelp discs. In addition, sodium
carbonate caused precipitation of cations from the sediment which interfered with the
observation of bacteria.
Chemical reagents have not been widely used to disperse bacteria from aquatic samples.
Various studies have demonstrated that bacterial isolates are repelled from surfaces such
as soil particles, chitin and plankton, by high pH levels (Santoro and Stotsky, 1968;
Hattori, 1970; Marshall, 1973 ; Kaneko and Colwell, 1975). A decrease in the degree of
aggregation of soil particles and the attachment of bacteria to clay and glass surfaces
occurs when univalent cations rather than di- and tri-valent cations are used (Peele, 1936
cited in Marshall, 1980, Santoro and Stotsky, 1968), or the concentration of monovalent
cations, such as sodium, is increased (Kaneko and Colwell, 1975).
Prevention of bacterial attachment has been shown to occur by the use of tetrasodium
pyrophosphate, a sequestering agent, followed by sodium periodate (Marshall, 1973).
Fletcher (1980) examined the use of sodium periodate, sodium borate, ethylenediamine
tetraacetic acid (EDTA), tetrasodium pyrophosphate, antibodies and bovine serum
albumin in influencing the attachment of a Pseudomonas sp. to glass. Pyrophosphate was
found to be the most effective in preventing attachment and removal of adhered bacterial
cells. However, the results from these in vitro experiments may not apply to the natural
environment. The heterogeneous nature of sediment and kelp surfaces may have more
firmly attached and embedded bacterial cells as a result of their longer attachment periods
in the marine environment. Attachment of pure bacterial isolates to glass surfaces in
laboratory experiments has been examined over relatively shorter time periods, usually
less than 24 h (Marshall and Cruikshank, 1973 ; Corpe, 1974 ; Fletcher, 1980). One of the
effects of the longer time period in the natural environment may be the production of a
greater quantity and/or different quality of bridging polymers by the microorganisms
and macrophytes than that which will occur in 24 h on glass surfaces.
254
until a threshold value of 75 W was applied. At the 100 W power level bacterial and
sediment dispersion began within 5 s of sonication (Fig. 3). Maximum bacterial numbers
were observed after 30 s treatment. At 125 W maximal numbers of bacterial cells were
observed after 15 s of sonication, thereafter the bacterial counts declined as the time of
sonication increased (Fig. 3). In all cases, small aggregates of bacterial cells and detrital
material remained after sonication. There still appeared to be colloidal material surrounding the bacterial and sediment aggregates after treatment with sonication. Sediment
samples have been previously shown to require extensive treatment before interference
from detrital particles and background fluorescence was eliminated (Montagna, 1982).
Bacterial lysis may occur upon prolonged homogenization (Montagna, 1982).
It is likely that sonication severs some of the bridging polymers, causing large aggregate
disruption (Marshall, 1980 ; Bingle, 1980). The bacteria and sediment material also
accumulated at the edges of the filter adjacent to the glass barrel rather than spreading
evenly over the entire filter. This may be due to the negative charge on the surface of
bacterial cells and sediment particles at pH 7.9 resulting in attraction to the glass surface
of the filter assembly. This may be mediated by cationic bridging mechanisms (Costerton
et al., 1978). Adherence of bacteria to glass can be reduced by coating the surface with
dimethyldichlorosilane (Garvey et ai, 1977).
Treatment of sediment and kelp discs with hydrochloric acid, sodium hydroxide, sodium
carbonate, tetrasodium pyrophosphate and sodium periodate, respectively, followed by
vortex-mixing, under the experimental conditions, did not result in bacterial and sediment disaggregation or bacterial detachment from the kelp discs. In addition, sodium
carbonate caused precipitation of cations from the sediment which interfered with the
observation of bacteria.
Chemical reagents have not been widely used to disperse bacteria from aquatic samples.
Various studies have demonstrated that bacterial isolates are repelled from surfaces such
as soil particles, chitin and plankton, by high pH levels (Santoro and Stotsky, 1968;
Hattori, 1970; Marshall, 1973 ; Kaneko and Colwell, 1975). A decrease in the degree of
aggregation of soil particles and the attachment of bacteria to clay and glass surfaces
occurs when univalent cations rather than di- and tri-valent cations are used (Peele, 1936
cited in Marshall, 1980, Santoro and Stotsky, 1968), or the concentration of monovalent
cations, such as sodium, is increased (Kaneko and Colwell, 1975).
Prevention of bacterial attachment has been shown to occur by the use of tetrasodium
pyrophosphate, a sequestering agent, followed by sodium periodate (Marshall, 1973).
Fletcher (1980) examined the use of sodium periodate, sodium borate, ethylenediamine
tetraacetic acid (EDTA), tetrasodium pyrophosphate, antibodies and bovine serum
albumin in influencing the attachment of a Pseudomonas sp. to glass. Pyrophosphate was
found to be the most effective in preventing attachment and removal of adhered bacterial
cells. However, the results from these in vitro experiments may not apply to the natural
environment. The heterogeneous nature of sediment and kelp surfaces may have more
firmly attached and embedded bacterial cells as a result of their longer attachment periods
in the marine environment. Attachment of pure bacterial isolates to glass surfaces in
laboratory experiments has been examined over relatively shorter time periods, usually
less than 24 h (Marshall and Cruikshank, 1973 ; Corpe, 1974 ; Fletcher, 1980). One of the
effects of the longer time period in the natural environment may be the production of a
greater quantity and/or different quality of bridging polymers by the microorganisms
and macrophytes than that which will occur in 24 h on glass surfaces.
254