Microbial community

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A community is an assemblage of species living close enough for potential interactions. Within a community different consortia may be found.

The types of microbes in a community are identified and characterized by several methods. Communities may change over time.

A-I represent organisms, the arrows represent interactions between the organisms, the blue circle represents species that are making up a community. The pink circles represents species that are also part of consortia
A-I represent organisms, the arrows represent interactions between the organisms, the blue circle represents species that are making up a community. The pink circles represents species that are also part of consortia

Bioleaching and wastewater treatment plants are non-sterile environments. Therefore different types of microorganisms will live together in a community. The interactions between the microbes matter much for the outcome of the processes.

Contents

Microbes don't live alone

"Our perception of bacteria as unicellular life forms is deeply rooted in the axenic (‘‘pure’’)-culture paradigm. Since bacteria can, in a strict sense, be diluted to a single cell and studied in liquid culture, this approach has been exploited to study many bacterial activities. Although growing bacteria in liquid or solid media has been the traditional means to study microbial pathogenesis and to uncover some amazing facets of microbial physiology, in nature, bacteria rarely grow as axenic planktonic cultures. Microbial ecology researchers have long recognized that complex bacterial communities drive the biogeochemical cycling that maintains the biosphere. Until recently, the lack of methods for exploring these communities in situ has hampered detailed analyses. Recent advances in microscopy and molecular techniques, however, have made it possible to examine such communities in situ in great detail and without the bias of laboratory cultures. The observation of a wide range of natural habitats has established that bacteria never function as single individuals. Instead, populations of bacteria arise from individual cells, and metabolically similar populations (i.e. teams of several kinds of bacteria that have a similar metabolism), such as sulfate and sulfur-reducing bacteria (SRB), and constitute groupings referred to as guilds."

Image:Conceptual changes in the study of microorganisms by Guerro 2002.jpg

Source: Microbial mats and the search for minimal ecosystems by Guerro, 2002

More effective bioleaching in mixed cultures

Irrespective of concentrate and operating conditions, the same three bacteria dominate bioleaching communities. These are the iron-oxidizing Leptospirillum ferriphilum, the sulfur-oxidizing Acidithiobacillus caldus and the iron- and sulfur-oxidizing Sulfobacillus sp. Still, there is research going on to find the ‘Dream-team consortium

Leaching rate depends on the mixture of microbes in the consortia
Leaching rate depends on the mixture of microbes in the consortia

"Chemolithotrophic iron-oxidizing acidophilic bacteria share mineral leaching environments with a range of other microorganisms, including fungi, algae, protozoans, and rotifers, as well as other bacteria (10, 15). Some data indicate that the presence of heterotrophic acidophilic bacteria may enhance the rate of sulfide mineral oxidation by iron-oxidizing acidophiles (28); one way in which this may occur is by the heterotrophic bacteria metabolizing organic materials which inhibit the iron oxidizers and which accumulate in leachate liquids. Acidophilic bacteria which oxidize reduced sulfur compounds but not ferrous iron, such as the obligate chemolithotroph Thiobacillus thiooxidans and the mixotroph Thiobacillus acidophilus, may also aid leaching by producing sulfuric acid; this may be particularly beneficial when these bacteria are present in mixed cultures with L. ferrooxidans, which does not metabolize sulfur (21)."

Source: Bacelar-Nicolau, P., and D. B. Johnson. 1999. Leaching of pyrite by acidophilic heterotrophic iron-oxidizing bacteria in pure and mixed cultures. Appl. Environ. Microbiol. 65:585-590. [1]

Communities removing toxic compounds or producing essential compounds for bioleaching microbes

"Whilst it is often the case that many extremely acidic waters are oligotrophic (containing < 5 mg dissolved organic carbon/l), numbers of heterotrophic prokaryotes even in these environments frequently exceed those of the primary producers. Organic carbon may originate both from outside of the environment (e.g. wind-blown leaves in AMD streams) and from the primary producers themselves (as cell exudates and lysates). In situations where mineral-oxidising primary producing prokaryotes are present in large numbers (such as stirred-tank mineral leaching operations) concentrations of dissolved organic carbon (DOC) may exceed 100 mg/l. Some of the more important mineral-leaching bacteria (in particular Leptospirillum spp.) are highly sensitive to DOC in general and some organic compounds (e.g. organic acids) in particular, and the removal of these materials by heterotrophic prokaryotes becomes critically important. ... "


" ... Other iron- and sulphur-oxidising prokaryotes either require or may utilize (mixotrophs) organic carbon. ..."

Source: Biotechnological potential of pure cultures and consortia of acidophilic microorganisms by Barrie Johnson. Unpublished material

See also

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