Ganyeka,
Fuel contamination is always a serious issue. Microbial contamination in fuel is a problem not only in aircraft, but in storage and transport systems, as well Delivery from both storage and transfer systems (trucks, underground delivery and so forth) have filters to prevent passing on contaminates.
Microbes in aircraft fuel cells thrive where water is found. Algae and bacteria becomes a problem if the fuel sits and has water available in the fuel (jet fuel suspends water better than other fuels such as gasoline). In aircraft that are constantly on the go, constantly burning their fuel supply and receiving new fuel, it's seldom an issue at all.
Where fuel contamination does take place from organic developments, the corrosion issues are localized to the algae, and are usually not a problem. You mentioned in your original post issues with corrosion of wing electrical components, and so forth. These have nothing to do with the formation of algae and other contaminants in fuel.
I'm a career aviator. I'm also a career mechanic (engineer, to some here). I've worked extensively inside fuel cells, installing fuel cells, repairing fuel cells, etc. I've been a director of maintenance twice. I've been an inspector in repair stations, a line inspector, and filled other maintenance line, floor, and supervisory duties over the past few decades. Fuel contamination, while most certainly a serious issue, is rarely a problematic issue in that it seldom is seen and seldom rears it's head. It's just not an issue as I've seen it over the years, especially for aircraft that are properly maintained and frequently flown. For aircraft that will be stored for a time it can be an issue, but there are numerous considerations to make that determination, and more importantly, it's something that can be addressed.
Another poster mentioned biobor, which is a "shock treatment" for an existing problem in a fuel cell or system. It's also available for ongoing treatment. The most commonly used treatment is the inclusion of fuel additives such as "Prist" in fuel. These are primarily used to affect the freezing temperature of fuel, but they also serve other functions. Often these additives have or include chemicals which offer antimicrobial properties. They tend to inhibit the growth of microbes.
This corrosion happens in a number of ways that the article details, such as:
1. reducing the surface tension of the water so that it spreads into small gaps more effectively;
2. acid byproducts reacting with the chromate in primer paint turning it into a passive form so it will no longer sacrifice itself to protect the aluminium;
3. increasing the electrical condictivity of the water allowing electrons to flow more easily, accelerating the oxidation process;
4. directly attacking aluminium.
The article was written by an aeronauical engineer. I would consider this to be "severe".
While I'd agree that from your perspective this sounds like a terrible thing, it's not.
Corrosion in aircraft comes from a number of courses, including within the metal itself. Galvanic, intergranular, fretting, electrolytical, and numerous other forms of corrosion occur, to say nothing of fatigue, and other factors which are prime concerns to maintenance personnel. You appear to be envisioning a problem in which microbes are on the verge of causing a wing to fall off. This isn't the case.
Pitting on surfaces, and spots of corrosion in faying (overlapping) surfaces can certainly occur. What we're not seeing out there are hoardes of microbes gnawing their way through wings and the wholesale need for replacing wings and aircraft structures due to microbial infestation. It's just not happening.
The wrong soap used on the outside of an aircraft can cause or accelerate corrosion on an airframe. Paint sometimes sustains corrosion. Corrosion is an ongoing process which does not end, and which is a constant battle (albeit a relatively minor one, in the grand scope of things), with which maintenance personnel must deal. Sometimes addressing corrosion means light surface removal of the corrosion, other times it involves repairs of varying degrees. Often it's little more than prevention, which is nearly always the case with fuel tank contamination by microbes. One tests the fuel, deterines the problem, makes a visual inspection where necessary, treats the fuel, flushes the tanks if absolutely necessary, changes and inspects filters, and moves on. We're talking about routine maintenance issues here...not drama, and not a "severe problem." A routine problem.