Reading into strange results

Last entry finished with:

“…We repeated the experiements over a new culture of 3G S. meliloti strain (I remind you the previous was 3I). In which every treatment (0, 15 and 30 seconds of uv) was made twice. Now, Plates are in Paula’s home (and also in the Lab).

Hopefully, these new results allow to determine uv effect more accurately. …”

The experiment performed was plates 1 and 4 no uv treatment; plates 2 and 5, 15’’ uv treatment; and plates 3 and 6, 30’’ uv treatment.

However,  last results did not show the expected numbers (Fig. 1). 

Fig 1: Aspect of all plates incubated at Paula’s home after 6 days at room temperature.  Numbers and dilutions performed are indicated in the last blog entry. 

Analyzing the plates we found that uv treatment was properly made on both groups of plates (those growing on Paula’s home and also the lab one). However, the plates to count the mutants present in every culture give an unexpected  high numbers,  even in the most diluted plates (see figure).

What is the explanation of this strange result? 

Have we got a different mut frequency in this experiment?

If we analyze the differences in the protocol with the previous experiment performed, we can inffer where it could be the problem. Also we can see in the previous blog (¿Dónde mutan los genes?) some clues about what could occur in this last experiments (particularly in the post Consecuencias del brain storming).

I would like we could discuss here in the blog what is happening; how we can avoid it and try to repeat properly the experiment (Next session 2nd of March).

I encourage you to give an answer. Who is the first?? (specially those who came on last experimental session).

Francisco Martínez-Abarca

Estación Experimental del Zaidín. CSIC.

Departamento de Microbiología y Sistemas Simbióticos.

Granada

When the mess is less mess

Last session confirm we are too much closer to the end of our Project. Again, we find out our Project deals with counting bacteria, don’t we?. But examining your faces yesterday  we also realized the meaning to count bacterial colonies in a plate: 

to know the number of bacteria present in a particular tube or treatment. 

All serial dilutions performed aim to obtain that number as accurate as posible. In this regard and analyzing the data obtained in the last experiment Paula’s home we could observe an interesting “tendency” in the data. Remind last experiment (see Figure 1).

Figure 1: This figure summarizes what we did in the previous sesión (18th Jan) and yesterday (16th Feb). A S. meliloti culture was distribuited to three plates and stress under uv treatments (0, 15’’ and 30’’). All further steps where designed in order to get the number of bacteria and mutants present in the different treatments.

As we could observed; some of the plates were a real mess (Lab plates see previos entry in the blog). However, after a detail analysis of Paula’s home bacteria plates we could obtain some numbers (see table 1):

Table 1: Colony counts of the respective dilutions and treatments performed

These numbers reflect an interesting result. If we interpret properly what they mean we can observe a clear effect on bacterial growth by uv treatment (Table 2)

 Table 2: Effect of uv treatment on bacterial counts

And also an astonishing “tendency” of the putative frequency of mutants on the plate’s uv treatments (Table 3)

Table 3: Effect of uv treatment on mutation frequency

All of us (teachers, coordinators, friends,  … included) must know how these data appear (all calculations performed). And, most important, we must be aware about the meaning and importance of this last result.

As expected in Science. Experiments must be reproducible. 

What we are waiting for next session?

We repeated the experiements over a new culture of 3G S. meliloti strain (I remind you the previous was 3I). In which every treatment 0, 15 and 30 seconds of uv) was made twice. Now, Plates are in Paula’s home (and also in the Lab).

Hopefully, these new results allow to determine uv effect more accurately.

Come on as I mention previosly the end of the Project is much closer.

And finally only mention that the PIIISA commission (in Granada) did not allowed to hold our next session of 2nd March in the PARQUE DE LAS CIENCIAS in Granada.

We’ll see in the EEZ next session.

Francisco Martínez-Abarca
Estación Experimental del Zaidín. CSIC.
Granada