Name: how scientists identify bacteria and fungi
Uploaded: 2019-01-29T11:04:46.000Z
Duration: 5 min 6 s
Channel: JoVE

K12 Standards

Louisiana Student Standards for Science

High School

Life Sciences

ecosystems-interactions-energy-and-dynamics

Ecosystems: Interactions, Energy And Dynamics

HS-LS2-7

Microbial and Fungal Diversity

I microrganismi sono definiti come forme di vita troppo piccole per essere viste ad occhio nudo. Ma anche se in genere non li vediamo, i microbi sono ovunque, fanno cose buone come aiutare la nostra digestione o fare yogurt e vino, a cose non così buone come causare infezioni o malattie. 
A proposito di infezioni, nel 1928, Alexander Fleming tornò nel suo laboratorio dalle vacanze e notò una strana contaminazione fungina su una delle sue piastre di coltura batterica. È interessante notare che le colonie batteriche immediatamente intorno alla contaminazione erano state distrutte. Questa osservazione ha portato a molte ulteriori ricerche, culminate infine nello sviluppo della penicillina e di altri antibiotici che potrebbero trattare le infezioni batteriche. Eppure, anche se possono vivere fianco a fianco nel mondo microscopico, sappiamo dallo studio delle loro forme e filogenesi che batteri e funghi sono organismi molto diversi e diversificati. Esaminiamo brevemente alcune delle caratteristiche distintive di questi due gruppi principali. 
I batteri sono procarioti unicellulari, il che significa che sono organismi unicellulari senza nucleo. Tutti i batteri hanno una parete cellulare, ma la sua composizione e il suo spessore variano. I batteri Gram positivi hanno una parete cellulare con uno spesso strato di peptidoglicano, che trattiene prontamente le molecole di cristallovioletto nella colorazione di Gram. Tuttavia, i batteri gram negativi hanno una sottile parete cellulare circondata da una membrana lipopolisaccaridica esterna e conservano solo la controcolorazione, la safranina di colore rosso. La colorazione di Gram consente anche l'osservazione delle forme batteriche. I batteri rotondi sono chiamati cocchi. I batteri a forma di bastoncino sono chiamati bacilli. E i batteri a forma di spirale sono chiamati spirilla. Inoltre, le colonie batteriche possono essere caratterizzate anche ad occhio nudo, utilizzando tratti come il colore, la forma e le dimensioni della colonia. 
Ora, diamo un'occhiata ai funghi. A differenza dei batteri, i funghi sono eucarioti e quindi le loro cellule hanno organelli legati alla membrana e un nucleo. Sono comunemente classificati in gruppi in base alle loro strategie riproduttive. Ad esempio, gli Ascomycota, o funghi a sacco, che includono spugnole, penicillium e tartufi, hanno corpi fruttiferi chiamati ascocarpi. Le spugnole sono piene di queste strutture. Se li guardiamo più da vicino, contengono molte strutture più piccole chiamate asci, che a loro volta contengono molte ascospore formate durante la riproduzione sessuale. Tuttavia, gli Ascomycota spesso si riproducono asessualmente per gemmazione. Il secondo grande gruppo fungino che esamineremo è il Basidiomycota, o fungo club. La maggior parte dei funghi commestibili e velenosi nella foresta sono in realtà strutture riproduttive del Basidiomycota. In questo gruppo, quello che chiameremmo il cappello del fungo è tecnicamente noto come basidiocarpo. Nei funghi branchiali, le branchie sotto il basidiocarpo sono rivestite da minuscole strutture note come basidi, e queste producono basidiospore, spore riproduttive microscopiche, durante la riproduzione sessuale. Queste spore vengono tipicamente erogate dal vento, in modo simile a molti semi di piante. Qui, abbiamo esaminato diversi importanti gruppi di batteri e funghi e le caratteristiche che li definiscono in modo molto semplificato. Tuttavia, a causa del vasto numero di specie microbiche, fino a un trilione secondo molte stime, gli scienziati spesso le identificano e le raggruppano utilizzando metodi aggiuntivi, tra cui l'esame del loro DNA. 
In questo laboratorio, identificherai diverse specie di batteri utilizzando la colorazione di Gram ed esaminerai le caratteristiche della colonia. Esaminerai anche le specie di funghi per identificare le loro strutture riproduttive.

diversità microbica e fungina

Batteri e funghi sono due gruppi molto diversi di organismi che possono avere impatti benefici o dannosi significativi sulla salute umana. Per questo motivo, è importante capire e distinguere tra le singole specie di questi gruppi. Come ricorderete, i tassonomisti biologici raggruppano gli organismi in base alla loro parentela filogenetica. I tre domini della vita, batteri, archaea ed eucariota, segregano la vita in tre gruppi distinti. Mentre tutti i batteri rientrano nel dominio dei batteri, i funghi si trovano nel dominio Eukaryota (Kingdom Fungi). Oltre agli Archaea, il dominio Bacteria include esclusivamente procarioti unicellulari, il che significa che le loro cellule mancano sia di una membrana nucleare che di organelli legati alla membrana. Al contrario, i funghi del dominio Eukaryota hanno organelli legati alla membrana e includono sia organismi unicellulari che pluricellulari.
<h4>Batteri</h4>
I batteri si trovano quasi ovunque sulla Terra e sono altamente adattati agli ambienti in cui crescono. Di conseguenza, questo dominio include una quantità sbalorditiva di diversità. L'impatto di questi organismi sulla salute umana è altrettanto vario. Ad esempio, specie come lo Streptococcus thermophilus possono essere utilizzate per produrre cibi fermentati come lo yogurt, mentre le spore del batterio Bacillus anthracis sono responsabili della malattia potenzialmente mortale dell'antrace.
Per aiutare nell'identificazione di tale organismo, i microbiologi hanno sviluppato una miriade di test per caratterizzare sia le singole cellule che intere colonie di batteri. Uno dei metodi più comuni per identificare i batteri è la colorazione di Gram. Questo test utilizza coloranti colorati per determinare la composizione della parete cellulare dei batteri. I batteri Gram-positivi, che portano una spessa parete cellulare costituita da una proteina chiamata peptidoglicano, conservano un colorante chiamato cristallovioletto e quindi appaiono viola. Al contrario, i batteri gram-negativi hanno una parete cellulare più sottile senza peptidoglicano e non trattengono il cristallovioletto. Invece, queste cellule appaiono rosa a causa di una colorazione di contrasto chiamata safranina. L'uso della colorazione di Gram serve spesso come passo preliminare nell'identificazione di una specie batterica. Un'ulteriore classificazione richiede l'identificazione di caratteristiche aggiuntive. Ciò può includere la forma di singoli batteri, che possono essere cocchi (rotondi), spirillum (a spirale) o bacilli (a forma di bastoncino). Inoltre, il colore, la forma, la lucentezza, la consistenza e persino l'odore delle colonie batteriche possono essere utilizzati per distinguere le specie.
<h4>Funghi</h4>
I funghi del dominio Eukaryota sono anche ecologicamente molto diversi e possono variare in dimensioni dal microscopico lievito al più grande organismo sulla terra, il fungo del miele (Armillaria ostoyae). Tutti i funghi sono eterotrofi, il che significa che devono acquisire il loro cibo dall'ambiente. Questi organismi mostrano anche diversità nelle loro attività specifiche, nicchie e potenziali effetti sulla salute umana. Ad esempio, alcuni funghi vengono consumati o utilizzati per produrre cibo dagli esseri umani, mentre altri possono causare infezioni gravi o addirittura mortali2.
All'interno del regno dei funghi, esistono due distinte divisioni tassonomiche basate sulla strategia riproduttiva della specie. Innanzitutto, gli Ascomycota, noti come funghi del sacco, hanno una struttura riproduttiva chiamata ascus. Insieme, molti aschi formano l'ascocarpo, o "corpo fruttifero" dei funghi. Questi funghi possono riprodursi sessualmente o asessualmente per gemmazione. Gli Ascomycota sono costituiti da alcune specie economicamente importanti come il lievito utilizzato nella produzione della birra e nella cottura del pane, e da alcune specie popolari in cucina, come le spugnole e i tartufi. Il secondo gruppo, Basidiomycota, comprende organismi comunemente noti come "funghi club" per la presenza di una grande struttura riproduttiva a forma di clava chiamata basidio. A differenza degli Ascomycota, la maggior parte dei Basidomucota si riproduce esclusivamente per riproduzione sessuale. Ciò si verifica quando due miceli aploidi si uniscono per formare un basidiocarpo. Su un fungo a bottone, questa è la struttura del cappuccio. Sul lato inferiore del basidiocarpo, le strutture riproduttive chiamate branchie rivestite con strutture chiamate basidi producono nuclei aploidi che alla fine formano basidiospore. Le basidiospore vengono poi disperse dal vento. Questa divisione tassonomica include molti funghi champignon comunemente consumati, così come i funghi soffiati selvatici.
<h4>Importanza della microbiologia</h4>
Nel complesso, è chiaro che le diverse funzioni e proprietà dei microrganismi rendono la loro identificazione estremamente importante per la salute e il benessere umano. Mentre un vasto numero di specie di funghi e batteri è stato identificato fino ad oggi, si stima che altri milioni debbano ancora essere identificati e classificati. Inoltre, le discipline umane che esplorano funghi e batteri sono tanto diverse quanto gli organismi stessi e senza dubbio continueranno a crescere. L'importanza dei microrganismi nei campi medici è più diffusa che mai, poiché le specie di batteri infettivi multiresistenti agli antibiotici minacciano la salute umana. La comprensione della struttura e delle caratteristiche biologiche delle specie infettive e non infettive fornisce le informazioni chiave necessarie per la creazione di nuovi trattamenti antibiotici e strategie preventive3-4.
Anche la microbiologia è fondamentale per l'industria alimentare. Numerosi prodotti, tra cui yogurt, formaggio, kombucha, pane e alcol, sono realizzati utilizzando specifiche categorie o specie di microbi. Allo stesso tempo, gli scienziati alimentari si concentrano sull'ingegnerizzazione di composti chimici e conservanti che ridurranno la crescita di microbi indesiderati sul cibo. In tutti questi processi, è necessaria una comprensione di come i microbi sopravvivono, si riproducono e influenzano il loro ambiente.
<h4>Referenze </h4>
<ol class="riferimenti">
	<li>Hiroshi Asakura, Holger Brueggemann, Sou-ichi Makino e Yoshiko Sugita-Konishi, "Approcci molecolari per la classificazione di patogeni microbici di rilevanza per la salute pubblica", BioMed Research International, vol. 2014, ID articolo 725801, 2 pagine, 2014. https://doi.org/10.1155/2014/725801.</li>
	<li>Treseder, K. K. e J. T. Lennon (2015). "Tratti fungini che guidano le dinamiche dell'ecosistema sulla terraferma." Microbiol Mol Biol Rev 79(2): 243-262.</li>
	<li>Arvanitis, M. ed E. Mylonakis (2015). "Interazioni fungine-batteriche e loro rilevanza per la salute". Microbiolo cellulare 17(10): 1442-1446.</li>
	<li>Aarestrup, F. M., et al. (2008). "Resistenza nei batteri della catena alimentare: epidemiologia e strategie di controllo". Esperto Rev Anti Infect Ther 6(5): 733-750.</li>
</ol>

Diversità microbica e fungina

Batteri e funghi sono due gruppi molto diversi di organismi che possono avere impatti benefici o dannosi significativi sulla salute umana. Per questo...

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how scientists identify bacteria and fungi

Bacteria and fungi are highly diverse organisms, and scientists identify them by looking at their structure, growth, and role in health. Some species help people, while others can cause disease, so learning how to tell them apart matters in biology and medicine.

Biological taxonomists group organisms by evolutionary relatedness. Life is divided into three domains: Bacteria, Archaea, and Eukaryota. Bacteria belong to the domain Bacteria, which includes single-celled prokaryotes. Prokaryotic cells lack a nuclear membrane and membrane-bound organelles. Fungi belong to the domain Eukaryota, in Kingdom Fungi. They have membrane-bound organelles and can be either unicellular or multicellular.

Bacteria live almost everywhere on Earth, and their diversity is very large. This group includes helpful species such as Streptococcus thermophilus, which is used to make fermented foods like yogurt. It also includes harmful species such as Bacillus anthracis, whose spores cause anthrax. Microbiologists use several tests to identify bacteria. One common test is Gram staining, which uses colored dyes to show cell wall structure.

Gram-positive bacteria have a thick cell wall made of peptidoglycan, so they retain crystal violet and appear purple. Gram-negative bacteria have a thinner cell wall without peptidoglycan, so they do not keep crystal violet. Instead, they take up safranin and appear pink. Gram staining is often a first step in bacterial identification. Scientists then look at other traits, including cell shape. Cocci are round, spirillum are spiral, and bacilli are rod-shaped. Colony color, shape, sheen, texture, and even smell can also help distinguish species.

Fungi are also diverse and can range from microscopic yeast to the honey fungus, Armillaria ostoyae, which is the largest organism on Earth. Fungi are heterotrophic, which means they must get food from their environment. Some fungi are used in food production or are eaten by people, while others can cause severe or even deadly infections.

Within Kingdom Fungi, two major divisions are based on reproduction. Ascomycota are the sac fungi. They have a reproductive structure called an ascus, and many asci form an ascocarp, or fruiting body. These fungi can reproduce sexually or asexually by budding. This group includes yeast used in brewing beer and baking bread, as well as edible fungi like morels and truffles.

Basidiomycota are commonly called club fungi because they have a club-shaped basidium. Most Basidiomycota reproduce sexually. Two haploid mycelia join to form a basidiocarp, which is the cap of a button mushroom. On the underside, gills lined with basidia produce haploid nuclei that later form basidiospores. Wind spreads these spores. This group includes many button mushrooms and wild puff mushrooms.

Studying microbes is important for human health and for food production. Millions of species may still need to be identified and classified, and microbiology continues to grow as a field. This work is especially important now because multi-antibiotic-resistant bacteria can threaten human health. Knowing microbial structure and biology helps scientists develop new antibiotics and prevention strategies. Microbiology also supports the food industry, where microbes are used to make yogurt, cheese, kombucha, bread, and alcohol, while other compounds and preservatives are designed to limit unwanted microbial growth.

How Scientists Identify Bacteria and Fungi

how-scientists-identify-bacteria-and-fungi

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Bacteria and fungi are highly diverse organisms, and scientists identify them by looking at their structure, growth, and role in health. Some species help people, while others can cause disease, so learning how to tell them apart matters in biology and medicine. Biological taxonomists group organisms by evolutionary relatedness. Life is divided into three domains: Bacteria, Archaea, and Eukaryota. Bacteria belong to the domain Bacteria, which includes single-celled prokaryotes. Prokaryotic...

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HS-LS2-6

How Scientists Identify Bacteria and Fungi

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