)&#'*iei 
aei
*,+!-/"ssscsjkcsn

jkaieiic@eikkkk@ekki)--1)(.

snjeeiii
i

c5

f

jie

C

A B

Ce

f f
j
fcoi
A Bi

- -Cif

1 mLf@ep

3f

A B
ii
f

100i

fi

1ie

feiie

2j

Ai
50i
B B
100ei

CACe

- .

f

- /@eB B
f fifi@e
C Aif fCAe- 0isiiAfeCiicfejfei 1 mL@j

UV i 6c3UVccee3fciCeifAgUVjfAfCiciiACCfAAC

UV i 1Af UV i 6cf
j@geC

. ieUVAeiiAj
CiieCeCeCf fACicxzefw

ifi

Ai
UV i 64Ci

-  (  *)  ,1$%C**w

xz

A
. .
Ccwxz

Acfeii. /C1 mL
5w

w
100Ai

/

f 1 mLUV ic50eiii
UV iAw

fCeCeeAA BeCoejfe
cfe

5iA BjC

Instructions:This examination is aimed at measuring your creativity, your abilities in logical thinking andwriting (including drawing schematics), and your basic knowledge in biology. The setting of thequestion is basically imaginary. You are free to choose experimental settings unless they aredescribed, but please describe your settings clearly in the answer sheet.
When we evaluate the answers, we will take your research background and future researchinterests into consideration.
Even if you cannot answer a given question (or a part of a question), you may be able to answer
subsequent questions (or subsequent parts of a question).

Read the following story and answer Questions 1 to 3.
* Please write and draw your answers within the assigned spaces in the answer sheet. Please
do not change the size of the space. You are free to set the line spacing.
* The answer may be entered directly to the electronic file (Microsoft Word or pdf) and/or in
handwriting on a printed answer sheet. A handwritten answer should be converted to anelectronic file within 20 minutes after the exam.
* You may use schematics and/or tables as appropriate. If you enter your answer directly to theelectronic file, you may prepare schematics and/or tables by any software before pastingthem on the file of your answer sheet. Alternatively, you may scan handwritten schematics
and/or tables and paste them on the file of your answer sheet.
*At the end of the written exam, an electronic file of complete answer sheet should be submitted
by e-mail within 20 minutes (before submission, a handwritten answer should be converted
to an electronic file (e-mail address: info-soken@nig.ac.jp).

1Dr. Mishima is studying microorganisms that inhabit soil. She sampled wet soil from aforest behind her institute and suspended a small piece of the soil in an organic medium
for microbial growth. Five days later, she viewed the medium with a microscope andsaw three distinct morphologies (microorganisms A, B and C) (Fig. 1). The same
medium was used for all the experiments described below.

You can assume that A, B and C are different species of unicellular organisms and that
all three species propagate clonally (i.e., produce genetically identical offspring). Dr.
Mishima isolated single cells of each species and grew them separately to make stockcultures. The studies described below were conducted using these populations.
She diluted stock cultures of A, B, and C separately (single culture) into the fresh
growth medium with starting concentrations of 100 cells/mL. She then allowed thecultures to grow. Fig. 2 shows cell counts over time in these cultures.

2Q1-1 Please briefly describe in words (no need for calculations) the main findings ofthe experiments shown in Fig. 2. Please note the similarities and differences amongspecies.

In order to examine inter-species effects on cellular growth of respective species, Dr.
Mishima conducted co-cultures (growth in the same medium) of each pairs of species:
A/B, B/C, and A/C. In each co-culture, two species were inoculated into the medium togive concentrations of 50 cells/mL for each species (total concentration, 100 cells/mL).
The courses of population growth in these co-cultures are shown in Fig. 3.

Q1-2
The final concentrations for each species in the co-culture (Fig. 3) were lower than theirconcentrations in single cultures (Fig. 2). Please propose an explanation for thisdifference in the final cellular concentrations.
Q1-3 Do the single culture growth patterns in Fig. 2 predict the co-culture growth
patterns in Fig. 3? In other words, are the single culture growth patterns sufficient toexplain the co-culture growth patterns? Please give separate answers for the threegraphs (A/B co-culture, B/C co-culture and A/C co-culture in Fig. 3) and explain yourreasoning in each case.

3

Q1-4 For the case(s) in which you answered no (i.e. single culture growth patterns are
not sufficient to explain co-culture growth patterns) in Q1-3 above, please propose apossible explanation for the observed co-culture growth pattern.

Dr. Mishima found that co-cultured microorganisms A and C form “spores” when theco-culture is exposed to UV light for 6 hours. Spores are dormant cells surrounded by acharacteristic thick casing. Spores consume very little nutrients and do not proliferate.
Cell casing formation occurs gradually during the transition from active cells to spores.
Closer inspection revealed that microorganism C initiates spore formation immediately
upon UV illumination whereas microorganism A started the sporulation process 3 hours
after the onset of UV illumination (Fig. 4).
Dr. Mishima became interested in the mechanism of spore formation in microorganisms
A and C. She performed two experiments described below.
When microorganisms A and C were cultured separately and exposed to UV light for 6hours, microorganism C formed spores whereas no obvious change was observed inmicroorganism A (Fig. 5).
When a co-culture of microorganisms A and C was exposed to UV light for 1 hour andthen kept in the dark for 5 hours, both microorganisms A and C formed spores (Fig. 6).

4

Q2-1 Based on the results shown in Figs. 4, 5 and 6, propose a simple mechanism ofinitiation of spore formation upon UV illumination in microorganisms A and C. Please
explain how your model accounts for the results shown in Figs. 4, 5 and 6.

In order to obtain further insights into the mechanisms of spore formation inmicroorganisms A and C, Dr. Mishima mutagenized microorganism C. She obtained
three kinds of mutants (mutants w, x, z), in which spore formation in organism A and/or
C is impaired in the co-culture.
Each mutant strain has a nucleotide substitution that inactivates a single gene.
Un-mutated strains will be referred to as “wild-type”. Wild-type and mutant strains ofmicroorganism C were co-cultured with wild-type microorganism A and exposed to UV
light for 6 hours. Phenotypes of the resulting organisms are summarized in Table 1.

5Table 1. Phenotypes of microorganisms A and C after exposure of co-cultures to UV
light for 6 hours
Microorganism C
Microorganism AWild type

Mutant w

Mutant x

Mutant z

SporesSporesActive cells

Active cells

SporesActive cells

Active cells

Spores

Q2-2 Based on the results shown in Table 1, please explain which part(s) of themechanism you described above (your answer to Q2-1) are impaired in the co-culturesof microorganism C mutants w, x or z and wild-type microorganism A. If you cannot
explain the effects of mutations based on the mechanism (your answer to Q2-1), please
propose a modification of your model so that it can account for the findings in Table 1
and then describe your answer.
Q2-3 Microorganism A and mutant strain w of microorganism C were inoculated into
the growth medium to give concentrations of 50 cells/mL for each species (total 100cells/mL) and co-cultured. The initial conditions were similar to the experiments in Fig.
3 (iii), but the co-culture was exposed to UV light 5 days after the inoculation. Pleasepredict any growth rate changes for microorganism A and mutant strain w ofmicroorganism C upon exposure to UV light. In addition, predict the final
concentrations of microorganism A and strain w of microorganism C after cultivation inUV light. Please be sure to explain your reasoning.

Q3 You are asked to conduct research related to growth and/or spore formation ofmicroorganisms A, B, and/or C. You can focus on any topic or finding described abovethat interests you. Please construct a proposal that includes the following parts: “title ofresearch”, “research aims”, “outline of experiments/analyses” and “expected results andconclusions”.

6

解答用紙： 受験番号
以下に各問を簡単に記載してありますが、必ず問題用紙の情報に基づいて解答して下さい。解答スペースのサイズは変更しないでください。解答スペース内の行間は自由に変更して構いません。

問 1-1 図２のグラフに示される結果の主な特徴（種間の類似点と相違点）（計算をする必要はありません。）

問 1-2

最終細胞密度の違いの理由1

解答用紙： 受験番号
問 1-3 各微生物種の単独培養における増殖パターン（図２）の情報のみで、各共培養における各微生物種の増殖パターン（図３）を説明することは可能ですか。微生物 A と B、B と C、A と C の共培養についてそれぞれ答えてください。またその理由も、それぞれの共培養について述べてください。
微生物 A と B の共培養の場合

微生物 B と C の共培養の場合

微生物 A と C の共培養の場合

問 1-4 問 1-3 で、単独培養での増殖パターンで共培養での増殖パターンを説明できないと答えたケースについて、どの様なことを想定すれば、その共培養の増殖パターンを説明できるか述べてください。

2

解答用紙： 受験番号
問 2-1 図 4、５及び６の結果に基づいて、UV 照射によって微生物 A と C が胞子形成を開始する簡潔なメカニズムを提唱してください。あなたの提唱するメカニズムが、どのように図 4、５及び６の結果を説明できるのかも述べてください。

3

解答用紙： 受験番号
問 2-2 表１の結果から、微生物 C の変異体 w、x または z と微生物 A の共培養では、問２−１で提唱したメカニズム（またはその改訂版）のどの部分に異常が起きていると考えますか。

4

解答用紙： 受験番号
問 2-3 UV を当てる前と後で微生物 C の変異体 w と微生物 A の増殖速度はどの様に変化すると予想しますか、また、微生物 C の変異体 w と微生物 A は最終的に何細胞まで増えると予想しますか。理由とともに答えてください。

5

解答用紙： 受験番号問3
研究のタイトル：

目的：

実験・解析の方法：

得られる結果と考察：

6

Answer sheet： Application Number
Note that the exam questions are only briefly summarized in the answer sheet. Please be sure to read theexam for the full information and questions. Please do not change the size of the space. You are free to set
the line spacing in the given spaces.
Q1-1 The main findings of the experiments shown in Fig. 2 (no need for calculations; note thesimilarities and differences among species).

Q1-2

An explanation for the difference in the final cellular concentrations.

1

Answer sheet： Application Number
Q1-3 Do the single culture growth patterns in Fig. 2 predict the co-culture growth patterns in Fig. 3?
Please give separate answers for the three graphs (A/B co-culture, B/C co-culture and A/C co-culture inFig. 3) and explain your reasoning in each case.
A/B co-culture

B/C co-culture

A/C co-culture

Q1-4 For the case(s) in which you answered no (i.e. single culture growth patterns are not sufficient toexplain co-culture growth patterns) in Q1-3 above, please propose a possible explanation for the observed
co-culture growth pattern.

2Answer sheet： Application Number
Q2-1 Based on the results shown in Figs. 4, 5 and 6, propose a simple mechanism of initiation of spore
formation upon UV illumination in microorganisms A and C. Please explain how your model accounts forthe results shown in Figs. 4, 5 and 6.

3Answer sheet： Application Number
Q2-2 Based on the results shown in Table 1, please explain which part(s) of the mechanism you
described above (your answer to Q2-1 or a modified version) are impaired in the co-cultures ofmicroorganism C mutants w, x or z and wild-type microorganism A.

4

Answer sheet： Application Number
Q2-3 Predict any growth rate changes for microorganism A and mutant strain w of microorganism C
upon exposure to UV light. In addition, predict the final concentrations of microorganism A and strain w
after cultivation in UV light. Please be sure to explain your reasoning.

5Answer sheet： Application Number
Q3
Title of research:

Research aims:

Outline of experiments/analyses:

Expected results and conclusions:6