bestehend aus
consisting of
Describes the composition of something; says which parts something is made of or which elements it contains.
Das Komitee besteht aus fünf Mitgliedern.
The committee consists of five members.

existing / consisting
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consisting of
Describes the composition of something; says which parts something is made of or which elements it contains.
Das Komitee besteht aus fünf Mitgliedern.
The committee consists of five members.

The word 'bestehend' is the present participle of the verb 'bestehen' (to exist / to consist). It is used like an adjective to describe a state or quality.
Die bestehenden Regeln sind für alle verbindlich.
The existing rules are binding for everyone.
In this meaning, 'bestehend' is almost always part of the fixed expression 'bestehend aus' (consisting of). The parts that something is composed of follow in the dative.
Das Team, bestehend aus Experten verschiedener Fachrichtungen, beginnt heute seine Arbeit.
The team, consisting of experts from various disciplines, begins its work today.
When 'bestehend' means 'existierend' (existing), it stands directly before a noun and is declined like a normal adjective.
Der bestehende Vertrag muss verlängert werden.
The existing contract must be extended.
In the meaning 'existierend' (existing), 'bestehend' is often combined with abstract nouns such as 'Gesetze' (laws), 'Regeln' (rules), 'Strukturen' (structures), or 'Probleme' (problems).
Wir müssen die bestehenden Probleme analysieren, bevor wir eine Lösung finden.
We need to analyze the existing problems before we find a solution.
new
'neu' and 'bestehend' can form a contrast when talking about changes. 'neu' then means that something is being added or is different from before. 'bestehend' means that something is already present and continues to apply or be used. This difference is especially typical in work, planning, contracts, or rules. 'Eine neue Regel' (a new rule) is only just being introduced; 'eine bestehende Regel' (an existing rule) already exists.

Zur Planung nutzt das Team zuerst die bestehenden Daten.
For the planning, the team first uses the existing data.
Für mehr Sicherheit gibt es ab Montag eine neue Regel im Gebäude.
For greater safety, there will be a new rule in the building starting Monday.