Pseudomonas aeruginosa PAO1 Preferentially Grows as Aggregates in Liquid Batch Cultures and Disperses upon Starvation

In both natural and artificial environments, bacteria predominantly grow in biofilms, and bacteria often disperse from biofilms as freely suspended single-cells. In the present study, the formation and dispersal of planktonic cellular aggregates, or ‘suspended biofilms’, by Pseudomonas aeruginosa in liquid batch cultures were closely examined, and compared to biofilm formation on a matrix of polyester (PE) fibers as solid surface in batch cultures. Plankton samples were analyzed by laser-diffraction particle-size scanning (LDA) and microscopy of aggregates. Interestingly, LDA indicated that up to 90% of the total planktonic biomass consisted of cellular aggregates in the size range of 10–400 µm in diameter during the growth phase, as opposed to individual cells. In cultures with PE surfaces, P. aeruginosa preferred to grow in biofilms, as opposed to planktonicly. However, upon carbon, nitrogen or oxygen limitation, the planktonic aggregates and PE-attached biofilms dispersed into single cells, resulting in an increase in optical density (OD) independent of cellular growth. During growth, planktonic aggregates and PE-attached biofilms contained densely packed viable cells and extracellular DNA (eDNA), and starvation resulted in a loss of viable cells, and an increase in dead cells and eDNA. Furthermore, a release of metabolites and infective bacteriophage into the culture supernatant, and a marked decrease in intracellular concentration of the second messenger cyclic di-GMP, was observed in dispersing cultures. Thus, what traditionally has been described as planktonic, individual cell cultures of P. aeruginosa, are in fact suspended biofilms, and such aggregates have behaviors and responses (e.g. dispersal) similar to surface associated biofilms. In addition, we suggest that this planktonic biofilm model system can provide the basis for a detailed analysis of the synchronized biofilm life cycle of P. aeruginosa

Water quality of shallow tube wells as affected by sanitary latrines and groundwater flow

The present study investigated the probable influence of latrines and groundwater flow on the water quality of shallow tube wells in Shinduria village (23?52\u27 N and 90?14\u27 E) of Dhaka district, Bangladesh. A questionnaire survey was made to collect basic information on tube wells and latrines. Four boreholes were drilled to investigate lithostratigraphy. Twenty one water samples were collected and their physico-chemical parameters (Dissolved Oxygen, pH, phosphate, sulphate, nitrate, nitrite and iron) were analyzed using standard method. Total viable bacterial count (TVBC), total coliform count (TCC), total faecal coliform count (TFCC), total salmonella shigella (TSS) and total vibrio count (TVC) were also made using membrane filtration method. Average depth of the tube wells was 120 ft and most of them were less then ten years old. About 85% latrines were ring slab type and about 50% of these were built during the last five years. From borehole data, a shallow aquifer was identified at a depth of hundred feet from where local people extract drinking water. Although most of the physico-chemical parameters of the tested samples were within the Department of Environment (DoE). But almost all of the tested samples failed to ensure the quality of acceptable level for drinking water recommended by World Health Organization (WHO) due to the presence of higher load of TVBC (5.07 &times; 10&sup3; cfu/100 ml), TCC (8.44 &times; 103cfu/10 0ml), TFCC (5.16 &times; 10&sup2; cfu/100 ml) and TSS (1.10 &times; 103cfu/100 ml). Local geological conditions and proximity between tube well and latrine promoted bacterial transport towards tube well while groundwater flow direction from the adjacent Bangshi River influenced the phenomenon. DOI: http://dx.doi.org/10.3329/jbas.v37i2.17565 Journal of Bangladesh Academy of Scinces, Vol. 37, No. 2, 231-243, 2013</jats:p