Planktonic cells

Although reaction-diffusion limitation and the presence of nutritionally restricted phenotypes are obviously important determinants of biofilm drug resistance, neither, either separately or in combination, provides a complete explanation of the phenomena. Cells on the periphery of the biofilm, subject to nutrient fluxes similar to planktonic organisms would succumb to antibacterial concentrations that are effective against the planktonic cells. Cell-death at the periphery would lead to increased nutrient availability for deeper-lying cells. These would, in turn, grow faster and adopt a more susceptible... 

Redfield (1934), who analyzed the major elemental content of many samples of mixed plankton (phytoplankton and zooplankton) caught in nets towed through the surface ocean. They compared the carbon, nitrogen, and phosphorus composition of these collections to concentration profiles of dissolved inorganic carbon (DIC), NOs, and P04 throughout the water column. This pioneering research demonstrated that these three elements are continually redistributed in the ocean by selective removal into plankton cells and their remains (i.e., fecal pellets), which are then efficiently respired as they sink through the marine water column. 

In the case of plankton, cell lysis that occurs shortly after death causes ATP to be released into seawater. Like most biomolecules, ATP is rapidly degraded in seawater by microbes. Thus, high surfece concentrations in Figure 22.5 reflect a rapid supply supported by the high rates of plankton production characteristic of the photic zone. Below the surface, concentrations decrease with increasing depth beneath the photic zone and, hence, distance from the biosynthetic source of the ATP... 

Considering the micro-environment close to the surface of plankton cells the existence of Fe(II) complexes has been observed, even in an aerobic environment (Morel, this volume). The macro-environment represents evidently not necessarily the same conditions as the micro-environment close to the organisms. 

Filtration. To separate the dissolved from the particulate fraction filtration or centrifugation will be necessary. This causes a severe risk of contamination it is therefore often not carried out with open ocean samples, where the concentrations of suspended material are low. The presence of phytoplankton or a variable concentration of suspended matter affects the total concentration and a comparison of samples can thus become difficult. In speciation Studies the presence of particles may influence the results even more (complexation, adsorption), therefore filtration over acid washed membrane or screen filters in an appropriate filtration apparatus is recommended for all natural samples (Bewers et al., 1985). High pressure during filtration should be avoided ruptured (plankton-) cells will contribute organic matter, nutrients and trace metals to the solution. A pressure < 25 kPa is recommended (Florence and Batley, 1980). 

Many tentative hypotheses have been proposed to understand the dominance, alternation and succession of P. globosa fife forms, i.e., nano-planktonic cells and large gelatinous colonies... 

Bacteria within a biofilm may be less sensitive to antibacterial compounds than planktonic cells (reviewed in [150]). Several possible reasons (Table 4.9) can be put forward to account for this, notably reduced access of drug or biocide to cells within a biofilm, chemical reaction with the glycocalyx and modulation of the micro-environment [147], In addition, the attached cells may produce degradative enzymes although the significance of this... 

Acidithiobacillus ferrooxidans is able to degrade chalcocite (CU2S) by oxidizing the Cu(I) in the mineral to Cu and the sulphide-S to 804 . Because the end-products of this oxidation are soluble, the oxidation results in the mobilization of the copper and sulphur in the chalcocite. Evidence exists for two distinct mechanisms by which At. ferrooxidans can perform the oxidation of chalcocite. One mechanism involves a direct attack of the crystal lattice of chalcocite by cells attached to the surface of chalcocite. The other mechanism involves an indirect attack of the crystal lattice of chalcocite by the chemical oxidant Fe generated from Fe in the bulk phase by planktonic cells (unattached) oi At. ferrooxidans. 

Quilliam, M.A., Aasen, I, Hardstaff, W.R., and Lewis, N. 2003. Analysis of phycotoxins in handpicked plankton cells by micro-column liquid chromatography-tandem mass spectrometry. In HABTech 2003, Cawthron Report No. 906, ed. Holland, P, Rhodes, L., and Brown, L. Nelson, New Zealand Cawthron Institute, 107-112. 

Twining, B. S., Baines, S. B., and Fisher, N. S. (2004). Element stoichiometries of individual plankton cells collected during the Southern Ocean Iron Experiment (sofex). Limnol. Oceanogr. 49, 2115-2128. 

Additional evidence for a bacterial contribution to HMW DOM proteins comes from molecular-level analyses of dissolved amino acids. Hydrolysis of HMW DON releases 11-29% of the nitrogen as amino acids (McCarthy et al., 1996). Specific amino acids include common protein amino acids, as well as /3-alanine and y-aminobutyric acid which are nonprotein amino acid degradation products. The distribution of amino acids is similar to that of fresh plankton cells, suspended particulate matter, and total dissolved amino acids. However, stereochemical analyses show HMW DOM amino acids to be elevated in the D-enantiomer, with d/l ratios for alanine, aspartic acid, glutamic acids, and serine ranging from 0.1 to 0.5 (McCarthy et al., 1998). Racemization of phytoplankton-derived L-amino acids is too slow at ocean temperatures to yield such high D/L ratios, but bacteria can synthesize D-amino acids, and it is likely that the D-amino acids in HMW DOM result from bacterial bioploymers rich in these particular amino acids. The high dA ratios of some amino acids and the abundance of amide nitrogen in HMW DOM N-NMR spectra led McCarthy et al. (1998) to... 

A biofilm is a community of microorganisms that settles on a surface and is covered by an exopol)mier matrix. Cells in biofilms are slow-growing, and exhibif clear phenotypic differences from free-living planktonic cells. Biofilm sfmcfure is bofh complex and dynamic, and... 

Planktonic cells are routinely used for almost all the testing procedures that have been designed to... 

Compared with suspended (planktonic) cells, bacteria on surfaces as biofilms are invariably phe-notypically more resistant to antimicrobial agents. With biofilms, suspension tests can be modified to involve biofilms produced on small pieces of an appropriate glass or metal substrate, or on the bottom of microtitre tray wells. After being immersed in, or exposed to the disinfectant solution for the appropriate time interval, the cells from the biofilm are removed, e.g. by sonication, and resuspended in a suitable neutralizing medium. Viable counts are then performed on the resulting planktonic cells. 

After colonization of the surface, the microorganisms utilize the available nutrients to grow, multiply, and synthesize both intracellular products and extracellular polymeric substances that constitute the substance of the biofilm. Significant amounts of biofilm can be produced under ideal conditions, and even if planktonic cells are no longer present in the flowing water, the sessile cells already on the surface can provide the basis for biofilm development. 

A four-stage model has been used to describe the development of a bacterial biofilm. The stages comprise, first, primary attachment of cells to the underlying biomaterial, second, accumulation in multiple bacterial layers, third, maturation of the biofilm, and fourth, detachment of planktonic cells from the biofilm, which may then initiate a new cycle of biofilm formation elsewhere [11], In the staphylococci clear evidence exists for the attachment and accumulation/maturation stages of the biofilm model [12] (Fig. 1), while active detachment mechanisms are not well... 

The organic carbon of the plankton cell must first be buried to a sediment horizon below the penetration depth of sulfate. Here, the particulate organic material must be degraded by hydrolytic exoenzymes. The breakdown products are then fermented by bacteria in several steps to acetate, hydrogen and CO, which are ultimately converted to methane by methanogenic archaea. 

Blenkinsopp et al [1992] have shown that the efficacy of some biocides against Pseudomonas aeruginosa biofilms grown on stainless steel studs, is increased by the application of a low strength electric field. Biocide concentrations lower than those necessary to kill planktonic cells were bactericidal within 24 h when applied within the electric field. It is possible that this discovery could have implications for industrial biofilm control in the future. 

All trace elements are taken up intracellularly by specialized transport proteins (enzymes) on the outer membrane of plankton cells. Consequently, uptake rates generally follow Michaelis-Menten enzyme kinetics ... 

Fig. 3.73. Horizontal distribution of the chlorophyll a ( lg/L), plankton cell density (xlO cells/L), and zooplankton biomass based on wet weight (mg/m ) in the surface seawater of the SYS (Zhang et al., 2007) (With permission from Elsevier s Copyright Clearance Center)...

H. Mikkelsen, Z. Duck, K.S. LiUey, M. Welch. Interrelationships between colonies, biofilms, and planktonic cells of Pseudomonas aeruginosa. Journal of Bacteriology, Vol. 189, No. 6, pp. 2411-2416, 2007. 

Until very recently, the antibaaerial activity of peptoids had only been evaluated against planktonic cells of BSL-1, BSL-2, and MDR strains of bacteria. To develop peptoids as potential therapeutics, it is important to investigate the efficacy of peptoids against more resilient systems, such as biofilms and Mycobacterium tuberculosis (Mtb). 

Biofllms are complex bacterial commtmities which are encased by a protective exopolysaccharide (EPS) matrix that helps the bacteria thrive in hostile environmental conditions and reduces the efficacy of antibiotics by up to 100-fold relative to planktonic cells/ Briefly, the formation of biofllms can be described as a multistep process. The planktonic bacteria are first attached by strong association of the adherent cells to the surface such as respiratory mucosa and bladder cells in case of lung and urinary tract infections, respectively. Upon attachment, the bacteria multiply to form microcolonies. These microcolonies develop into well-defined mushroom-like three-dimensional structures and eventually produce the EPS coating around them. At times, the biofilm matrix breaks and the bacterial cells disperse, which leads to a spread in infection (Figure 16). ... 

A crystal violet (CV) assay, which stains the total bacterial biomass, was used to study the efficacy of peptoids against biofilms. The absorbance of the CV stain is measured at = 590nm, and a decrease in absorbance (pale purple) compared to imtreated control (dark purple) implies a decrease in biomass. At 12.5 pM, six out of the seven peptoids tested in this study were able to prevent the formation of P. aeruginosa biofilms by 40-70%, with peptoid 1 being the most active (70% redurtion) and comparable in efficacy to ciprofloxacin and tobramycin (Table 3). However, AMPs only caused 10% reduaion. This was probably because the peptoids were able to kill the planktonic cells which in turn reduced the number of bacterial cells that could have led to the formation of biofilms. 

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