Gideon M. Wolfaardt

Function of EPS

The production of extracellular polymeric substances (EPS) involves a significant investment of carbon and energy by microorganisms. Considering the tendency in nature to conserve rather than to waste, this expenditure of energy (in some cases more than 70% — see Harder and Dijkhuizen 1983) is likely to hold benefits to the producers of EPS, as well as those organisms associated with them. Bacteria are very efficient in converting nutrients into EPS; it has been calculated (Underwood et al. 1995) that a single Azotobacter cell can produce enough EPS to coat more than 500 particles with a 0.4 µm diameter per day. The size of a single cell is typically 1–2 µm by 0.5 µm, and often much smaller, and therefore this number is impressive. The importance of EPS has long been recognized and a variety of functions have been attributed to EPS as far as the benefits they provide to cells, either living as single organisms, in binary associations, or in heterogeneous communities. However, Christensen and Characklis (1990) implied that there is a lack of knowledge of the properties of EPS in biofilms, as well as their role in biofilm ecology. The aim of this chapter is to provide an overview of some of the progress that has been made in recent years to elucidate the functional role of EPS.

Microbiology of a biological contactor for winery wastewater treatment

Winery wastewaters are characterised by large seasonal fluctuations in volume and composition and are often discarded with little or no treatment. A rotating biological contactor (RBC) was used to investigate microorganisms associated with the biological treatment of winery wastewater. Extensive biofilms developed on the RBC discs and contained a number of yeast and bacterial species that displayed a dynamic population shift during the evaluation period. This suggested that the naturally occurring microorganisms were able to form a stable biofilm and also reduce the chemical oxygen demand (COD) of winery wastewater (on average 43% with a retention time of 1h). One of the yeast isolates, MEA 5, was able to reduce the COD of synthetic wastewater by 95% and 46% within 24h under aerated and non-aerated conditions, respectively. The yeast isolates could therefore play an important role in the degradation of organic compounds under aerobic conditions, such as those associated with an RBC.

Bioenergy and African transformation

Among the world’s continents, Africa has the highest incidence of food insecurity and poverty and the highest rates of population growth. Yet Africa also has the most arable land, the lowest crop yields, and by far the most plentiful land resources relative to energy demand. It is thus of interest to examine the potential of expanded modern bioenergy production in Africa. Here we consider bioenergy as an enabler for development, and provide an overview of modern bioenergy technologies with a comment on application in an Africa context. Experience with bioenergy in Africa offers evidence of social benefits and also some important lessons. In Brazil, social development, agricultural development and food security, and bioenergy development have been synergistic rather than antagonistic. Realizing similar success in African countries will require clear vision, good governance, and adaptation of technologies, knowledge, and business models to myriad local circumstances. Strategies for integrated production of food crops, livestock, and bioenergy are potentially attractive and offer an alternative to an agricultural model featuring specialized land use. If done thoughtfully, there is considerable evidence that food security and economic development in Africa can be addressed more effectively with modern bioenergy than without it. Modern bioenergy can be an agent of African transformation, with potential social benefits accruing to multiple sectors and extending well beyond energy supply per se. Potential negative impacts also cut across sectors. Thus, institutionally inclusive multi-sector legislative structures will be more effective at maximizing the social benefits of bioenergy compared to institutionally exclusive, single-sector structures.

Live-streaming: Time-lapse video evidence of novel streamer formation mechanism and varying viscosity.

Time-lapse videos of growing biofilms were analyzed using a background subtraction method, which removed camouflaging effects from the heterogeneous field of view to reveal evidence of streamer formation from optically dense biofilm segments. In addition, quantitative measurements of biofilm velocity and optical density, combined with mathematical modeling, demonstrated that streamer formation occurred from mature, high-viscosity biofilms. We propose a streamer formation mechanism by sudden partial detachment, as opposed to continuous elongation as observed in other microfluidic studies. Additionally, streamer formation occurred in straight microchannels, as opposed to serpentine or pseudo-porous channels, as previously reported.

Monitoring the Organization of Microbial Biofilm Communities

Microbial organization within a biofilm community can be thought of as the product of species composition and spatial positioning of individuals within the biofilm matrix. Species composition within a microbial community, also referred to as community structure,8 determines the community’s overall genetic potential for survival and reproductive success under various environmental conditions. Spatial positioning allows individuals to interact physiologically and genetically. It also allows the creation of favorable microbial microenvironments within hostile macroenvironments. When a biofilm community is subjected to an environmental perturbation (e.g., an introduction of a pollutant or antimicrobial compound), continued reproductive success may be facilitated by a process of reorganization consisting of changes in composition and spatial arrangement of individuals within the community. Thus, the structural and spatial organization of a biofilm community, and its functional significance, should be a consideration when attempting to control or enhance the activities of biofilm communities in industrial or environmental settings.