Hydrodynamic entrapment of bacteria swimming near a solid surface.

The near-surface motility of bacteria is important in the initial formation of biofilms and in many biomedical applications. The swimming motion of Escherichia coli near a solid surface is investigated both numerically and experimentally. A boundary element method is used to predict the hydrodynamic entrapment of E. coli bacteria, their trajectories, and the minimum separation of the cell from the surface. The numerical results show the existence of a stable swimming distance from the boundary that depends only on the shape of the cell body and the flagellum. The experimental validation of the numerical approach allows one to use the numerical method as a predictive tool to estimate with reasonable accuracy the near-wall motility of swimming bacteria of known geometry. The analysis of the numerical database demonstrated the existence of a correlation between the radius of curvature of the near-wall circular trajectory and the separation gap. Such correlation allows an indirect estimation of either of the two quantities by a direct measure of the other without prior knowledge of the cell geometry. This result may prove extremely important in those biomedical and technical applications in which the near-wall behavior of bacteria is of fundamental importance.

Estimation of micro-flora associated with different stages of Macrobrachium rosenbergii (de Man)

The bacterial flora occurring in muscle, haemolymph, hepatopancreas and gill of brood, juveniles, water, eggs, larvae and rearing water were estimated by selective plate count technique for Entrobacteriaceae, Streptococaceae and Vibrionaceae members. The total viable bacterial count was estimated by total plate count technique on nutrient agar. The total viable counts of bacteria were lowest in water from 6.10x10² CFU/mL) and highest in egg (6.06x10super(8) CFU/g). In brood the total counts were varying from 1.62x10² CFU/g in muscle to 2.20x10super(5) CFU/g in gills. In juveniles, the total plate counts were varying from 2.8x10super(4) CFU/g in muscles to 3.67x10 super(8) CFU/g in hepatopancreas. Selective plate counts show that Enterobacteriaceae members dominate in egg and gills of brood and hepatopancreas of juveniles. Vibrios were found to be dominant in water and larvae of rearing tank. Haemolymph of brood was sterile and did not contain any bacteria while muscle of juvenile was having very low count of total viable bacteria.

Studies on immobilization of Bacteria

Cell immnhilizatinn technology in a rapidly expanding arna in the endeavour of microbial fnrmentatiwn.During the lnmt 15 years anveral prnceafinn have been developed and more are in developmental atage of approaching commercial utilizatinn.In the present programme it was planned to develop an optimized process for the innobilization of alpha amylase producing Bacillus polymyxa (CBTB 25) an isolate obtained from Cochin University campus primarily for the production of alpha-amylase.Optimal concentration of support material that attributaa stability and maximal activity to the immobilized cell beads was determined using different concentrations of sodium aliginate as support and estimation of amylase production.An overeall assessment of the data obtained for the various studies conducted denotes that immobilized cells synthesize alpha-amylase at comparable rates with free cells and produce reducing sugara at a higher level than free cells.Results indicated that both phosphate and citrate buffers could be used for disrupting the immobilized beads since they enforced maximal release of cells through leaching from the beads within one hour.On comparative analysis it was observed that immobilized cells could synthesize alpha amylase at similar levels with free cells of B.polymyxa.On Co-immobilization of B.Polymyxa with S.cerevisiae,the co-immobilizate beads could effeciently convert starch directly to ethanol with a yield of 14.8% at 1 : 2 ratio.

Abundance of bacteria, cyanobacteria and nanoflagellates at sime series station DYNAPROC

The variability in microbial communities (abundance and biomass), bacterial production and ectoaminopeptidase activity, particulate and dissolved organic carbon (POC, DOC), and particulate and dissolved lipids was examined in spring 1995 in the northwestern Mediterranean, where a transition from the end of a bloom to pre-oligotrophic conditions was observed. Four time series of 36 h each and 4 h sampling intervals were performed at 5 m and at the chlorophyll maximum (30 m) between 11 and 31 May. Simultaneous measurements of pigments, abundance of hetero- and autotrophic flagellates, bacteria and POC enabled the estimation of living POC (defined as autotrophic-C plus heterotrophic-C biomass), and thus the detrital organic carbon. During the first 2 time series (11 to 15 May), the bacterial-C biomass was higher than the autotrophic-C biomass at 5 m (ratio 1.4 and 1.7), whereas the opposite trend was observed in the chlorophyll peak (ratio 0.7 for the first cycle). However, at the end of May, autotrophic-C biomass was equivalent to bacterial-C biomass at both depths studied. The detrital pool remained a more or less constant fraction of the POC (52, 53 and 47% on 11-12 May, 14-15 May and 30-31 May) at the chlorophyll peak, whereas it decreased significantly with time (62 to 53%) at 5 m. Relationships between bacterial activities and evolution of available resources were not systematically evidenced from our 36 h diel cycle data. Nevertheless, at the monthly scale, comparison of bacterial carbon demand (BCD) to potential carbon resources (detrital POC and DOC) showed that bacteria fed differently on the various pools. From ectoaminopeptidase turnover rates and detrital POC, the potential hydrolysis rate of detritus was calculated. Depending on the choice of conversion factors for bacterial production and estimates of hydrolysis turnover rates, it was shown that bacterial hydrolysis of detritus could be one of the DOC accumulation sources. We observed that the percentage of BCD supplied by detrital POC hydrolysis increased in the surface and decreased in the chlorophyll peak. An index of lipid degradation in POC, the lipolysis index, increased during the month at 5 m, also indicating a higher hydrolysis of POC. The opposite trend was observed in the chlorophyll maximum layer. The selective decrease in dissolved lipids in DOC in the chlorophyll maximum layer, particularly free fatty acids, also suggests that bacteria utilized increased fractions of carbon sources from the DOC. We concluded that partitioning between DOC and detritus as resources for bacteria can change during the rapid transition period from mesotrophy to oligotrophy in the northwestern Mediterranean.

Developing an index of dietary estimation of fermentable carbohydrate to allow dietary analysis for epidemiological studies

It has been proposed that long-term consumption of diets rich in non-digestible carbohydrates (NDCs), such as cereals, fruit and vegetables might protect against several chronic diseases, however, it has been difficult to fully establish their impact on health in epidemiology studies. The wide range properties of the different NDCs may dilution their impact when they are combined in one category for statistical comparisons in correlations or multivariate analysis. Several mechanisms have been suggested to explain the protective effects of NDCs, including increased stool bulk, dilution of carcinogens in the colonic lumen, reduced transit time, lowering pH, and bacterial fermentation to short chain fatty acids (SCFA) in the colon. However, it is very difficult to measure SCFA in humans in vivo with any accuracy, so epidemiological studies on the impact of SCFA are not feasible. Most studies use dietary fibre (DF) or Non-Starch Polysaccharides (NSP) intake to estimate the levels, but not all fibres or NSP are equally fermentable. It has been proposed that long-term consumption of diets rich in non-digestible carbohydrates (NDCs), such as cereals, fruit and vegetables might protect against several chronic diseases, however, it has been difficult to fully establish their impact on health in epidemiology studies. The wide range properties of the different NDCs may dilution their impact when they are combined in one category for statistical comparisons in correlations or multivariate analysis. Several mechanisms have been suggested to explain the protective effects of NDCs, including increased stool bulk, dilution of carcinogens in the colonic lumen, reduced transit time, lowering pH, and bacterial fermentation to short chain fatty acids (SCFA) in the colon. However, it is very difficult to measure SCFA in humans in vivo with any accuracy, so epidemiological studies on the impact of SCFA are not feasible. Most studies use dietary fibre (DF) or Non-Starch Polysaccharides (NSP) intake to estimate the levels, but not all fibres or NSP are equally fermentable. The first aim of this thesis was the development of the equations used to estimate the amount of FC that reaches the human colon and is fermented fully to SCFA by the colonic bacteria. Therefore, several studies were examined for evidence to determine the different percentages of each type of NDCs that should be included in the final model, based on how much NDCs entered the colon intact and also to what extent they were fermented to SCFA in vivo. Our model equations are FC-DF or NSP$ 1: 100 % Soluble + 10 % insoluble + 100 % NDOs¥ + 5 % TS** FC-DF or NSP 2: 100 % Soluble + 50 % insoluble + 100 % NDOs + 5 % TS FC-DF* or NSP 3: 100 % Soluble + 10 % insoluble + 100 % NDOs + 10 % TS FC-DF or NSP 4: 100 % Soluble + 50 % insoluble + 100 % NDOs + 10 % TS *DF: Dietary fibre; **TS: Total starch; $NSP: non-starch polysaccharide; ¥NDOs: non-digestible oligosaccharide The second study of this thesis aimed to examine all four predicted FC-DF and FC-NSP equations developed, to estimate FC from dietary records against urinary colonic NDCs fermentation biomarkers. The main finding of a cross-sectional comparison of habitual diet with urinary excretion of SCFA products, showed weak but significant correlation between the 24 h urinary excretion of SCFA and acetate with the estimated FC-DF 4 and FC-NSP 4 when considering all of the study participants (n = 122). Similar correlations were observed with the data for valid participants (n = 78). It was also observed that FC-DF and FC-NSP had positive correlations with 24 h urinary acetate and SCFA compared with DF and NSP alone. Hence, it could be hypothesised that using the developed index to estimate FC in the diet form dietary records, might predict SCFA production in the colon in vivo in humans. The next study in this thesis aimed to validate the FC equations developed using in vitro models of small intestinal digestion and human colon fermentation. The main findings in these in vitro studies were that there were several strong agreements between the amounts of SCFA produced after actual in vitro fermentation of single fibre and different mixtures of NDCs, and those predicted by the estimated FC from our developed equation FC-DF 4. These results which demonstrated a strong relationship between SCFA production in vitro from a range of fermentations of single fibres and mixtures of NDCs and that from the predicted FC equation, support the use of the FC equation for estimation of FC from dietary records. Therefore, we can conclude that the newly developed predicted equations have been deemed a valid and practical tool to assess SCFA productions for in vitro fermentation.