Light and electron microscope assessment of the lytic activity of Bacillus on Microcystis aeruginosa

During the screening of lytic bacteria, plaques were obtained on Microcystis lawns. In the plaques, at least five distinct morphotypes of bacteria were found. The plumb rod-shaped bacilli were the most abundant and were found aggregated around unhealthy Microcystis cells and were the probable cause of deflation and lysis. These bacteria may have utilized the cyanobacteria cell contents as their nutrient source. In contrast to the control areas, the cyanobacteria cells were healthy and did not show any visible distortion of cell structure. The presence and possible role of the free-bacteria, that is, bacteria that were not attached or associated with the cyanobacteria in the plaque is not clear. Maybe their function is to scavenge the skeletal remains of Microcystis cells. Bacillus mycoides B16 were found to have a lytic effect on Microcystis cells. Scanning electron micrographs (SEM) images of B. mycoides B16 did not reveal any unique attachments that may have allowed them to adhere to Microcystis cells. The Microcystis cells were exposed to copper, B. mycoides B16 and Triton X-100, in order to ascertain the level of cell membrane damage. The membrane cell damage was most severe with copper stripping the entire Microcystis cell membrane leaving a honeycomb skeletal structure and B. mycoides B16, leaving perforations on the cell membrane. The electron microscopy observations appeared to reveal at least two mechanisms of Microcystis lysis (contact and parasitism). The light and electron microscope (LEM) observations did not reveal any endoparasitism of B. mycoides B16 or Bdellovibrio-like behaviour.Key words: Microcystis, mechanism of lysis, Bacillus mycoides B16, photosynthesis, copper

The effect of sodium chloride and sodium bicarbonate derived anolytes, and anolyte-catholyte combination on biofilms

Microbial biofilms are problematic in industrial environments where large areas of submerged surfaces are exposed to relatively high nutrient fluxes, providing niches for the formation of copious surface-associated growth. Biofilms growing in drinking water distribution pipes cause deterioration in the microbiological quality of water contributing to the occurrence of water-borne diseases. Many bacteria are resistant to moderate levels of biocides, with bacteria in biofilms being the most difficult to control. Electrochemical activation (ECA) technology provides an alternative way of controlling these micro-organisms. The main objective of this study was to evaluate an electrochemically activated solution, anolyte, as an environmentally safe disinfectant for the control of biofilms. Biofilms were grown using the Pederson device and then exposed to different concentrations of the biocide. Light microscopy and scanning electron microscopy were used to view the effect of treatment on the biofilm structure. Re-growth of the biofilm after treatment with anolyte was detected through epifluorescence microscopy after DAPI staining of the coupons. Neat (undiluted) and mildly dilute anolyte removed the biofilm while the more dilute anolyte did not have any effect on the biofilm. Re-growth of the biofilm occurred after 24 h of biofilm treatment with anolyte and anolyte-catholyte combination, showed by the increase in colony forming units. Re-growth of planktonic bacteria however, occurred only after 72 h of treatment. Water SA Vol. 32(2) 2006: pp.237-24

Short communication: The effect of ultrasound at 256 KHz on Microcystis aeruginosa, with and without gas vacuoles

The effect of ultrasound on the growth of M. aeruginosa confirmed to contain gas vacuoles and on a laboratory culture with no gas vacuoles was investigated. Both cultures were treated continuously for 9 d with an ultrasonic flow device. To evaluate the influence of ultrasound during the treatment, the chlorophyll-a concentration was measured daily. Furthermore, changes in culture characteristics, e.g., flotation and gas vesicle formation, were determined. The results showed that, in contrast to the control, both ultrasonic-treated cultures had a lower chlorophyll-a concentration and cell aggregates were disrupted. Transmission electron microscopy confirmed a collapse of gas vacuoles in the environmental culture, while the laboratory culture, which did not contain gas vacuoles, showed many membrane-damaged cells. It was concluded that ultrasonic treatment of M. aeruginosa caused the disruption of gas vacuoles and destruction of cell membranes.Keywords: Ultrasound, cyanobacteria, Microcystis aeruginosa, chlorophyll, gas vacuole

The isolation and identification of predatory bacteria from a Microcystis algal bloom

Water samples were collected from a hypertrophic lake, Hartbeespoort dam, where lytic or predatory bacteria were isolated. The water samples were spread on BG 11 agar plates where upon incubation, plaques were observed on Microcystis lawns. Two isolates were further subjected to screening toevaluate their lytic activities on Microcystis cells and identification. Isolates B2 and B16 had a lytic effect on the Microcystis cells with isolate B16 having a greater effect than isolate B2. Isolate B2 was identified as Pseudomonas stutzeri with 99.9% certainty and B16 as Bacillus mycoides with 99.7%certainty using the API system

Quality assessment and primary uses of harvested rainwater in Kleinmond, South Africa

water security, reaching the Millennium Development Goals (MDGs) and sustaining water resources. The microbial and chemical quality of RWH samples collected from tanks in a sustainable housing development in Kleinmond, South Africa, were monitored. Results indicated that the tank water quality was within all the chemical standards (cations and anions) analysed for potable water. However, the counts of the indicator organisms, for example, total coliforms and Escherichia coli, exceeded the guidelines stipulated by the Department of Water Affairs and Forestry (1996). The microbial analysis results thus indicate that the tank water was not fit for potable use without treatment. A social research project was then conducted to describe, amongst others, the condition of the tank and the users’ knowledge of the RWH system. In addition, demographic data, viz., gender, household size and employment status, etc., were gathered in order to provide a socio-economic background description of the study population. Data were gathered by means of face-to-face interviews with 68 respondents. Generally, RWH was used for washing clothes and for cleaning inside and outside the houses. This study noted that without acceptance and necessary training to maintain and use the tank optimally, it is possible that social development projects, such as the one in Kleinmond, will not be sustainable.Keywords: domestic rainwater harvesting; microbial and chemical quality; social perception; acceptanc

Comparative antibacterial potential of selected aldehyde-based biocides and surfactants against planktonic Pseudomonas fluorescens

The antimicrobial efficacy of two aldehydebased biocides (glutaraldehyde, GTA, and orthophthalaldehyde, OPA) and two surfactants (cetyltrimethyl ammonium bromide, CTAB, and sodium dodecyl sulphate, SDS) was tested against planktonic Pseudomonas fluorescens. The antimicrobial effects were evaluated by respiratory activity as a measure of the oxygen uptake rate, adenosine triphosphate (ATP) release, outer membrane proteins (OMP) expression and cellular colour changes. The results were compared with the bacterial characteristics without chemical treatment. Tests in the presence of bovine serum albumin (BSA), in order to mimic a disinfection process in the real situation under dirty conditions, were performed according to the European Standard EN-1276. P. fluorescens was completely inactivated with OPA (minimum bactericidal concentration, MBC = 0.5 mM) and CTAB (MBC = 5 mM) and was resistant to GTA and SDS. Only CTAB promoted cellular disruption and consequent ATP release. The antimicrobial action of the chemicals tested was significantly reduced when BSA was introduced into the bacterial cultures, increasing markedly the MBC values. Additionally, the presence of BSA acted as a disruption protective agent when CTAB was applied and stimulated the bacterial respiratory activity when lower concentrations of SDS were tested. The OMP of the bacterial cells was affected by the application of both surfactants. OMP expression remained unaltered after biocide treatment. Bacterial colour change was noticed after treatment with biocides and surfactants. In summary, P. fluorescens was extremely resistant to GTA and SDS, with antimicrobial action being quenched markedly by the reaction with BSA.Instituto de Biotecnologia e Química Fina (IBQF).Fundação para a Ciência e a Tecnologia (FCT) - (Project CHEMBIO - POCI/BIO/61872/2004

Surfactants and the attachment of Pseudomonas aeruginosa to 3CR12 stainless steel and glass

Five non-ionic and three anionic surfactants were evaluated using 4'6-diamidino-2-phenylidole (DAPI) staining, scanning electron microscopy (SEM) and spectrophotometry for their efficacy in preventing adhesion and removing Ps. Aeruginosa attached to 3CR12 stainless steel coupons and glass. All the surfactants tested gave more than 90% inhibition of adhesion to the surfaces tested with no significant difference between the effectivity of the different anionic surfactants (p > 0.18) nor between the effectivity of the non-ionic surfactants (p > 0.16). The non-ionic and anionic surfactants resulted in more than 80% and 63% removal of attached Ps. Aeruginosa cells, respectively. The non-ionic surfactants were significantly more effective in removing attached bacteria, than the anionic surfactants (p < 0.001). The prevention of attachment of Ps. Aeruginosa cells to a glass surface, using the surfactants, was also monitored spectrophotometrically. There was no significant difference (p = 0.437) when comparing the DAPI - staining technique with spectrophotometric evaluations. WaterSA Vol.27(1) 2001: 21-2

The effect of ultrasound at 256 KHz on <I>Microcystis aeruginosa</I>, with and without gas vacuoles

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Water Services: Stellenbosch municipality water services

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Phylogenetic diversity of dominant bacterial communities during bioremediation of crude oil-polluted soil

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