What is More Cost Effective, Algae or Bacteria Fuel?

One of the primary costs of deriving fuel from algae is the space required to grow the algae. Productivity of algae is calculated per acre. Algae requires sunlight and the amount of algae that can be grown on an acre is limited. Synthetic Bacteria on the other hand can produce oil without sunlight, so in comparison to algae the productivity per acre can be very high. One could theoretically grow bacteria in giant silos many stories tall. However, in order for synthetic bacteria to produce oil without sunlight they must consume sugar for energy. According to a recent article in Popular Mechanics, current technology still requires sugars to come from an easy to use source of sucrose such as sugar cane or corn.  This means that synthetic bacteria fuel will compete for food stocks much the same way ethanol does,  driving up the price of both.  Technologies to easily derive sugars from nonfood stock cellulosic material, such as corn's remaining stalks, leaves and cobs, do not yet exist. Furthermore, even when they are developed, it estimated that it would take one acre to produce 2,000 gallons of fuel.  Algae by comparison is expected to yield over 30,000 gallons per acre.  On the other hand, cellulosic materials may be cheaper and easier to grow and harvest than algae.

There are, however, fuel producing bacteria that derive their energy from the sun using photosynthesis.  Such bacteria would not have the advantage over algae of growing in the dark but there may be other advantages over algae.  According to Bruce Rittman of the ASU BioDesign Institute,

Algae and bacteria both accumulate a lot of lipids, but they do so for different reasons. When bacteria accumulate a lot of lipids, they do it when they are growing fast. That is ideal. Algae do the opposite, and produce high lipids when under stress, and are not growing very well.

In other words, bacteria can produce lipids (oil) faster. Furthermore, bacteria excrete their oil which floats to the top of their bioreactor whereas algae requires costly extraction methods.   It would be nice to see a method that use both algae and bacteria.  The algae to grow and produce oil along with cellulosic material that can be metabolized by bacteria to release the oil in the algae and create even more oil.