We all know that humans farm plants and animals, and that the agrarian lifestyle is largely what made modern civilization possible. What is somewhat less well known is that many animals also “farm” for their lifestyle. This is not unusual in social insects like ants. For example leafcutter ants use the leaf material to cultivate fungus that is used to feed the colony. Other ants will protect, or “farm”, aphids and collect their honeydew as food for the colony. There are also examples of damselfish maintaining patches of algae for food.

This week in the journal Nature a group described what must be the smallest farmers yet! They reported that certain colonies of the slime mold Dictyostelium discoideum actually maintain “cultures” of bacteria within their slugs when food becomes scarce and these bacteria are packaged up along with the spores in the fruiting body. Not every strain carried such cultures in their fruiting bodies. Additional experiments showed that the farming strains had higher spore production when plated in a food-limited environment, but fared worse than non-farmers when plated on a rich lawn of a preferred bacterial food source. Furthermore, farmer strains performed better when plated onto unsterilized soils as might be encountered in natural settings. The researchers hypothesize that the ability to carry preferred food sources increases fitness.

They also performed a metagenomic analysis of the bacterial strains that were carried by the farmers. They found that about half the strains were preferred food sources for the slime mold, but suprisingly half were not used as food. This brings up and interesting question: why are half the population of bacteria not used for food? Do they produce antibiotics that protect the slime mold? Are they just freeloaders? There is lots of interesting research yet to be done on these interesting little farmers! (Click the link below to peek at the original paper.)

Primitive agriculture in a social amoeba

I have always been a little intrigued by the processes that regulate how and where membranes bud or fuse or invaginate. Some of my research has touched upon this topic because unlike most secreted proteins, the endosperm storage proteins I study never exit the ER in vesicles, but are retained in highly specialized protein bodies. Therefore in my advanced cell biology course I spend a lot of time talking about the sophisticated regulation that cells have evolved to control which membrane-bound compartments go where in the cell. If you look at it as analogous to a train, bus or airplane, each passenger has a ticket that must be verified by an agent and then the carrier takes off for the final destination. A bus, in particular, usually has a visible sign on the front marking where the final destination is. The process is amazingly similar in cells. Proteins (passengers) with a specific structure (ticket) are recognized by receptors (agents), loaded on specific a “bus” called a vesicle and transported on cytoskeletal highways to the correct destination (Lysosome, golgi, endosome, plasma membrane, etc.). In the cell each “station” and “bus” are painted with specific types of phosphoinositide lipids that in association with specific receptor proteins ensure that the transportation system runs smoothly.

Why did I just pop out and describe this complex regulation? Well, other than the fact we will begin to discuss membranes, membrane transport and membrane trafficking soon:  the most recent “Editors Choice” email from Science magazine highlighted a really interesting article that, for the first time, studied the process of endocytosis in vitro! Why is this exciting? Now that these investigators have established a cell-free system they can bit by bit reduce the system to the necessary players. And why is this important? There are many diseases associated with improper transport and processing of proteins in cells and tissues and as we identify the critical players therapies can be developed. In vitro investigations of transport between the ER and Golgi were critical for understanding how the whole bus station and transportation network were regulated and organized.

A great series of lectures on the topic are given by HHMI investigator Randy Scheckman on the iBioseminars site. I think Scheckman is a serious contender for a Nobel Prize in medicine within the next few years.