Kleptoplasty

Kleptoplasty is a wonderful term. It is used to describe the behavior of a group of organisms that are able to ingest algal cells and degrade the cells, but not the chloroplasts contained within the cells. The chloroplasts remain functional for some period of time during which the photosynthetic products generated by the sequestered chloroplasts are utilized by the new 'host'.

On the left is a figure from a paper by Gast et al. in the journal Enviornmental Microbiology from earlier this year showing a kleptoplastic dinoflagellate isolated from the Ross Sea in Antartica (the paper is in a free issue of the journal so go read the whole thing).

In addition to being a very interesting behavior from an ecological perspective, kleptoplasty is of evolutionary interest because the capacity to grow autotrophically by photosynthesis arose within dinoflagellates by the retention of chloroplasts from ingested algal cells. This ability appears to have arisen multiple times within dinoflagellates because not all contain chloroplasts from the same type of algal cell.

African deforestation

The rainforest of the Congo Basin in Central Africa is the second largest in the world. It covers millions of square kilometers and spans 6 different countries (including Gabon where I spent 2 years). As with other tropical rain forests this region is home to substantial biodiversity. Here in the US we hear a great deal about deforestation in the Amazon, less is heard about the African rainforests.

The most recent issue of the journal Science contains a brief report documenting the extent of deforestation and increases in commercial logging in the Congo Basin. The information was acquired by analyzing almost 30 years of satellite data for changes in forest cover and the appearance of new logging roads. The objectives of the report were to highlight the lack of good data on the extent of deforestation in the Congo Basin, present the data acquired from the available satellite data and demonstrate the value of the satellite data as a tool to assess changes in land use and document the extent of logging.

*added on edit: Here is some more information about the article and here is the figure from the paper showing the extent of the deforestation. Note how much of the area still has >75% forest cover.

adopt a cheetah

A recent report in Proceeding of the Royal Society describes the genetic relationship among cheetah litter mates. They found that almost half the litters were comprised kittens of mixed paternity. Female cheetah parole a territory of 300-400 km² and this allows them to interact with more than one male during a single reproductive cycle. This is a behavior that they share with the common cat. A summary of the paper can be found here.

One finding that struck me was that within the 47 litters surveyed, they found 3 instances of adoption by mother cheetahs of unrelated kittens. This finding has been described previously and there are several ideas as to the potential selective advantage this behavior. My first question is given the huge territories these cats parole, how on earth do the new mothers find orphaned kittens?

Plant-bacteria communication

In a previous post I mentioned that the nitrogen fixation performed by leguminous plants is the result of a symbiosis between the plants and bacteria. In this relationship, the plants create an environment within their roots (called nodules) where the bacteria take up residence. In exchange for energy provided by the plant, the bacteria fix atmospheric nitrogen that is then made available to the plant. Allowing bacteria access to the interior of the root is a potentially risky act on the part of the plant. So, a mechanism to exclude all bacteria except for the desired nitrogen fixer has developed and the symbiotic relationships are species specific. Each plant has specific bacterial symbionts. In the early stages of the establishment of the root nodule, signals are exchanged between the plant roots and bacteria in the soil. First, the plants release phytochemicals that attract the desired bacteria. The target bacteria are attracted by the phytochemicals and these chemicals induce the bacteria to release their own compounds called nod factors. The nod factors, in turn are sensed by the plant. Detection of the appropriate nod factor will induce the plant to initiate the process of allowing the bacteria access to the interior of the root where the nodule will form.

In the latest PNAS, Fox et al. report that many common pesticides inhibit the formation of root nodules by interfering with communications between the plants and bacteria.

While the significance of this in the environment is not known, it has the potential to be of concern because the use of crop rotations that include plants (such as soy or alfalfa) that are capable of enriching the nitrogen content of the soil is one important way to reduce the use of fertilizer (and energy) in modern agriculture.

In the bay 6 June 2007

One word: SNAILS! They were abundant last time and there are even more of them out there this week.

I know a fair amount about phytoplankton and am pretty good at identifying them. See the list of previous students here. When I came up with the idea of posting microscope images take of samples from the bay here on mixotrophy, I was ( and still am) planning on focusing on phytopankton. Of course this time of year, the zooplankton population is high and all of these little heterotrophs are busy grazing on the phytoplankton. This keeps phytoplankton cell abundance low. As a result, I am not seeing much of what I was planning on photographing. There are plenty of zooplankton to look at of course. The problem is, identifying zooplankton is much harder for me. Getting good live pictures is also a challenge because they move around.

I did get a few nice images though. Here is another larvae viewed in bright field. It is the nauplius stage of some type of crustation (I think).



This is the same view in dark field:

Computing power!

Check out this video on meta-imaging from a recent TED conference. Phil Plait at BA was struck by the reconstruction of Notre Dame and its potential for use within astronomy. The whole presentation is incredible. I wonder how powerful a computer he was using. With image resolution so high the memory needs must also be huge. Here is a link to the photosynth software. Of course I am using a mac so I can't download it.

Nitrogen fixation

Industrial agriculture is highly dependent on a ready supply of labile nitrogen fertilizer for high yields. Roughly half of all the nitrogen used in agriculture is in the form of ammonia (NH₃) synthesized using the Haber-Bosch process. In this process, atmospheric nitrogen in the form of N₂ gas is mixed with hydrogen gas at high temperature (500 ^oC) and pressure (200 atm) in the presence of an iron catalyst. That's 500 ^oC and 200 atm. Very hot and very high pressure.

Bacteria (and archaea) are also capable of converting nitrogen gas to ammonium (often referred to as 'fixing nitrogen') but they do it at normal temperatures and under 1 atmosphere of pressure. In these organisms the process is also energy intensive but the energy is supplied in the form of ATP and the catalyst is an enzyme complex containing 2 proteins, dinitrogenase and dinitrigenase reductase. This capacity is found in both bacteria and archaea in diverse environments including the root nodules of so called nitrogen fixing plants such as clover and soy. Bacteria, not the plants, fix the nitrogen.

There are many blog worthy aspects of microbial nitrogen fixation. I have created a label for this topic and intend to explore some of them here in the future.

Ancient life?

An item in a list of news reports over at Primordial Blog caught my eye this evening. It is a report in CBC News about a paper in the most recent issue of the journal Geology describing what is believed to be ichnofossils in 3.5 billion years pillow basalts from Australia.

Ichnofossils, or trace fossils are not the remains of organisms themselves but tracks left by organisms that become preserved. In this case the traces are tunnels in the volcanic rock presumably left by microorganisms as they degraded the rock to mobilize nutrients contained within. The images on the left are from a 1998 report (Fisk, M. R., Giovannoni, S. J. & Thorseth, I. H. (1998) Alteration of Oceanic Volcanic Glass: Textural Evidence of Microbial Activity. Science, 281, 978-980.) describing these tunnels from oceanic basalts. The scale bars are 50 and 10 microns long in the top and bottom panels respectively.

There is some controversy over whether these tunnels are due to the activity of microbes or are the result of some poorly understood form of abiotic chemical weathering. These images are not easy to get as the rock has to be cut into think slices with a diamond saw and then polished to allow light through. The sections that were used to take the images shown here were 30 microns thick.

MDR mobility

There is much talk in the blogsphere about this idiot who knowingly exposed a huge number of people to a multi drug resistant strain of TB. f you are interested, Tara Smith over at Aetiology has several posts (1,2,3 & 4 so far) on the topic including links to other discussions and information.

Instead of commenting on that situation I thought I'd call attention to a recent paper by Tim Welch and others in Plos One about a plasmid inferring multi drug resistance that has been found to be present quite common in our food supply.

This plasmid is of concern because it was isolated from a strain of the plague bacteria, Yersinia pestis, back in the mid 1990s. Since then it has not turned up in Y. pestis again but this new paper reports finding related plasmids in the fish pathogen Yersinia ruckeri and in a strain of the food born pathogen Salmonella. The picture on the left shows the relationship between the three plasmids.

The inner circle shows the conserved backbone indicating that the plasmids isolated from three different species of bacteria have a recent, common origin. They all have the genes necessary to be self mobilizing but they differ in the number of drug resistance genes they carry, ranging from 9 to 13.

using data from the conserved backbone Welch et al. screened a large number of MDR strains of Salmonella, E. coli and Klebsiella sp. isolated from agricultural products and found that the majority of the resistant strains harbor a relative of this plasmid.

From the paper:

The discovery of these MDR IncA/C plasmids in evolutionarily distinct pathogens attests to recent genetic exchange, either directly between these bacterial species or through bacterial intermediates, and it suggests that overlap in the ecological niches of these organisms is sufficient to permit past or future plasmid transmission.

And

we present evidence that a common plasmid backbone is prevalent among E. coli, Klebsiella sp. and multiple Salmonella serotypes isolated from retail meats in the US, and among some food animal isolates of E. coli. Our data imply that high levels of MDR in the causative agent of plague may rapidly evolve naturally...

In the bay 30 May 2007 II

Snail larvae. The water was loaded with these. Probably the periwinkle Littorina littorea. An invasive species introduced to Canada from Europe in the 1800. It is abundant on rocky shores throughout New England. I am not sure how far south they are found.

Here are 2 pictures:


Side view of the shell. the blurring at the top right of the image is due to the movement of cilia along the edge of their feeding apparatus called a velum.

End on view:

the picture is fuzzy but you can see the extended velum and the cilia along the edge.

And a video: